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College  of  ^Ijpgiciansf  mh  burgeons; 
^ibrarp 


Digitized  by  the  Internet  Archive 

in  2010with  funding  from 

Open  Knowledge  Commons  (for  the  Medical  Heritage  Library  project) 


http://www.archive.org/details/kirkeshandbookof1902kirk 


HAND-BOOK 


PHYSIOLOGY. 


BLDDD-5PECTRA  COMPARED  WITH  SPECTRUM  DP  ARBAND- LAMP 


1  Spectrum  dT  Argand-lamp  with  FraunhaFerfe  lines  inpnsitmn. 

2  BpEctrum  dP  DxyhEmndlnbin  in  diluted  blnod. 
•3  Spectrum  aP  Reduced  HsmDj^iubin. 

4  Spectrum  dP  Carbonic  oxide  Hsmo^lobin. 

5  Spectrum  cP  AcidHsmatm  m  etherial  SDJutinn. 

6  Spectrum  ui^  AlkBline  HEmatin. 

7  Spectrum  dT  ChlarnForm  extract  dF  acidulated  Dx-Bile. 

8  Spectrum  dF  Melhsmaqiahin. 
y  Spectrum  dF  hiffimQchrnma^En. 

10  Spectrum  oF  Hamatoparphyrin. 

Moul ofllip  (ihovp  Spccfm  haw  bpcii  drcmn  /ivm  obseivrrfrons  by  MTWlepmrk  F.C.S. 

Sdctoll  H  V/ilholnm  bUio  Co.  Hew  York 


KIRKES'    HANDBOOK    OF    PHYkSIOLOGY 


KIKKES'    HANDBOUK    OF    PHYtJlOLUGY 

HvVNDBOOK 

OF 

Pll  Y8I0L0GY 


REVISED  BY 


WILLIAM   H.  ROCKWELL,  JR.,  M.D. 


CHARLES  L.  DANA,  A.M.,  M.D. 

Professor  of  Diseases  of  the  Nervous  System,  (J.a-nell  University  Medical  College,  N'ew 
York  ;  Physician  to  Bellevue  Hospital ;  Neurologist  to  the  Monteflore  Home. 


Seventecntb  Hmerican  leMtion 


WITH    UPWARDS  OF  FIVE  HUNDRED  ILLUSTRATIONS 

INCLUDING  MANY  IN  COLORS 


NEW    YORK 
WILLIAM  WOOD  AND  COMPANY 

MDCCCCII 


COPYRIGHT,   1902, 
By   WILLIAM    WOOD    AND   COMPANY. 


THE    PUBLISHERS'  PRINTING  COMPANY 

32-34   LAFAYETTE    PLACE 

NEW    YORK 


PREFATOEY   J^OTE. 


In  this  edition  the  chief  changes  will  be  found  in  the  articles  relat- 
ing to  physiological  chemistry,  the  revision  having  been  deemed 
necessary  because  of  recent  advances  in  this  branch  of  physiology. 
( Uiupters  IV. ,  IX. ,  and  XI.  are  those  most  affected,  while  minor  alter- 
ations have  been  made  elsewhere  as  required. 

A  few  changes  have  also  been  made  in  the  chapter  on  the  Blood, 
in  conformance  with  the  more  prominent  of  the  present  views  on  the 
subject. 

In  many  instances  cuts  have  been  replaced  by  others  which  illus- 
trate the  text  more  clearly. 

W.  H.  Rockwell,  Jr. 


CONTENTS. 


CHAPTER   I. 


The  Phenomena  of  Life. 
Properties  of  Protoplasm, 
Structure  of  Protoplasmic  Cells, 
The  Cell  Nucleus,  . 
Attraction  Sphere, 
Cell  Division, 
Plants  Compared  with  Animals. 


IVOK 

1 
3 
!» 
11 
Vd 
18 
17 


CHAPTER  II. 

The  Functions  of  Okoamzkd  ('ells. 


22 


(CHAPTER   HI. 

The  Stri?cture  of  the  Elementary  Tissues, 
Epithelial  Tissues, 
Connective  Tissues, 
The  Teeth,       .... 
Development  of  the  Teeth.     . 
Muscular  Tissues.    . 
Nervous  Tissues, 


26 

28 
40 
69 
76 
81 
91 


CHAPTER  IV. 

The  Chemical  Composition  of  the  Body, 

Organic  Substances, 

Inorganic  Substances 

CHAPTER    V. 

The  Bi-ood, 

Coagulation 

The  Corpuscles 

Chemical  Composition.    ..... 

Gases  of  the  Blood, 

Develo]iinent  of  the  Corpuscles, 


110 
111 
12.-) 


12i) 
181 
UO 
loO 
155 
167 


CHAPTER   VI. 


The  Circulation  of  the  Bi.oon. 

The  Heart 

The  Arteries 

The  Capillaries, 


171 
172 

180 
183 


Vlll  CONTENTS. 

PAGE 

The  Circulation  of  The  Blood  ( Continued). 

TheYeius, 186 

The  Action  of  tlie  Heart, 189 

The  Sounds  of  the  Heart .         .         .194 

The  Impulse  of  the  Heart, 196 

Endocardiac  Pressure, 198 

Frequency  of  Heart's  Action, 303 

Blood  Pressure, 205 

The  Arterial  Flow, •  .         .213 

The  Pulse 215 

The  Capillary  Flow, 222 

The  Venous  Flow, .224 

The  Velocity  of  the  Flow,      .         . 225 

Local  Peculiarities  of  the  Circulation, 228 

Regulation  of  the  Flow, 231 

Proofs  of  the  Circulation  of  the  Blood, 249 

CHAPTER  VII. 

Respikation, 251 

The  Respiratory  Ai)paratus 252 

The  Respiratory  Mechanism, 261 

Respiratory  Changes, 271 

Special  Respiratory  Acts, 278 

Nervous  Mechanism, 281 

Effect  on  Circulation, 287 

Asphyxia, 292 

CHAPTER  VIII. 

Secretion, 297 

Organs  and  Tissues  of  Secretion, 298 

Secreting  Glands, 302 

The  Mammary  Glands, 306 

Milk,        .       * .309 

The  Ductless  Glands  and  Internal  Secretions,        .         .         ...         .         .  312 

CHAPTER  IX. 

Food  and  Digestion, 326 

Organic  Nitrogenous  Foods, 326 

Organic  Non-Nitrogenous  Foods, .  329 

Mineral  Foods, 329 

Liquid  Foods, 330 

Enzymes, 331 

The  Mouth  and  Mastication, 332 

The  Salivary  Glands .         .333 

Saliva, 337 

The  Tongue, 346 

The  Pharynx, 349 

The  CEsophagus 351 

Deglutition, 352 


CONTENTS. 


IX 


Pood  .vnd  Digkstion  (OnttiiLnrd). 
The  Stoinacli. 
The  Gastric  Juice, 
Voniitiiii;-,         .... 
The  Intestines. 
Tlie  Paucreas, 

The  Liver,        .... 
The  Intestiiiiii  Scci-etioii, 
Digestion  in  the  Small  Intestine, 
Digestion  in  the  Large  Intestine, 
Micro- organisms  in  tiie  Intestine, 
Movements  of  the  Intestines, 
The  Faeces,      .... 
Gases  of  the  Ah'mentarv  C'anal. 


PAGK 

.  354 
.  3oS 
.  369 
.  370 
.  379 
.  385 
.  398 
.  398 
.  400 
.  401 
.  4U3 
.  405 
.  406 


CHAPTEl?  X. 


AnsoKi'Trox,  .... 

Methods 

The  Lynii)hatic  iSjstem. 

The  Lymph  Flow. 

The  Lympli  and  Chyle, 

Channels  of  Absorption, 

Where  Ahsorplion  "Shxy  Take  Place, 


408 
408 
413 
416 
421 
422 
424 


CHAPTER    XI. 


Metauolism,  Xutuition,  AM)  Diet, 
Reciuisites  of  Normal  Diet.     . 
Variations  in  Diet  Tables. 
Income  and  Ontpnt  of  Energy, 


427 

441 
444 
444 


CHAPTER   XIT. 


Animal  Hk.\'I' 

Production  of  Heat, 

Hegnlation  of  Body  Temperature, 


449 
451 
453 


(JHAPTEH    XIII. 


XCRKTION.      . 

.  4(;() 

The  Kidneys. 

.  460 

The  Urine, 

.   4(i9 

Method  of  K.xci'etion  i 

pf  the  Urine. 

.  482 

The  Passage  nl'  rrine 

into  the  Bladder. 

.  488 

The  Skin. 

.  489 

Functions  of  I  lie  Skin, 

.  496 

CHAPTER   XIV. 


Mubci.k-Nkkvk   Piiysi()1,()(;y, 

Chemical  Composition  of  ;\Iu.scle, 
Muscle  at  Rest, 


500 
500 
502 


CONTENTS. 


Muscle-Nerve  Piri'sioLOGY  (^Contimied). 
Muscle  in  Activity,  .... 

Accompaniments  of  Muscular  Contraction, 
Muscle  in  Rigor  Mortis, 
Action  of  Voluntary  Muscles, 
Action  of  Involuntary  Muscles, 
Electrical  Currents  in  Nerves, 
Battery  Currents  and  Human  Nerves, 
Muscular  and  Nervous  Metabolism, 


PAGE 

505 
514 
521 
522 
527 
527 
531 
533 


CHAPTER   XY. 

The  Pkoduction  of  the  Voice, .  586 

The  Larynx, 536 

Movements  of  the  Vocal  Cords, .         .         .  544 

Tlie  Voice  in  Singing  and  Speaking, 545 


CEIAPTER  XVI. 


The  Nekvous  System, 

Functions  of  Nerve  Fibres,     . 

Functions  of  Nerve-Centres    . 

The  Spinal  Cord  and  its  Nerves,     . 

Functions  of  the  Spinal  Nerve-Root 

Functions  of  the  Spinal  Cord, 

Relations  of  the  Different  Parts  of  the  Brain 

The  Bulb, 

Functions  of  the  Bulb, 

The  Cranial  Nerves, 

The  Pons  Varolii,  . 

The  Crura  Cerebri, 

Corpora  Striata, 

Optic  Thalami, 

Corpora  Quadrigemina, 

The  Cerebrum 

Motor  Areas  of  the  Cerebral  Cortex 
Functions  of  the  Cerebrum,     . 
Sensory  Centres,      .... 
The  Cerebellum,      .•        .         .         . 
Functions  of  the  Cerebellum, 
The  Sympathetic  System, 


552 

552 

555 

560 

571 

572 

581 

587- 

593 

596 

612 

613 

615 

616 

616 

617 

626 

633 

639 

643 

647 

650 


CHAPTER   XVII. 


Tf[e  Senses, 

The  Sense  of  Touch, 
The  Sense  of  Taste, 
Tlie  Sense  of  Smell, 
The  Sense  of  Hearing, 
The  Sense  of  Sight, 


657 
660 
667 
670 
676 
693 


CONTENTS.  XI 

PAGK 

OHAPTKH    XVIll. 

TiiK  Kkproductivk  ()1!(;a.\s 744 

Of  the  Female 744 

Of  the  Male 7-W 

j^iiysiolotiy  <>!'  the  Sexual  Organs,  .  .  .  .         .         .  .         .   T-" 

CHAPTER    XIX 

Dkvki.opmknt 766 

The  Changes  in  the  Ovum, 766 

The  Fa^tal  Membranes 779 

The  Devel()|)M)ent  of  the  Organs,    .........   78K 

APPENDIX «2r, 

INDEX «3y 


FAHEENHEIT 

and 

CENTIGEADE 

SCALES. 


F. 

500° 

401 

39a 

383 

374 

356 

347 

338 

329 

320 

311 

302 

284 

275 

266 

348 

239 

230 

212 

2a3 

194 

176 

167 

140 

122 

113 

105 

101 

100 


C. 
260° 
205 
200 
195 
190 
180 
175 
170 
365 
160 
155 
150 
140 
135 
130 
120 
115 
110 
100 

95 

90 

80 

75 

60 

50 

45 

40.54 

40 

37.8 


98.5 

95 

86 

77 

68 

50 

41 

32 

23 

14 
+  5 
-  4 
-13 
-22 
-40 
-76 


36.9 

35 

30 

25 

20 

10 

5 

0 

-  5 

-  10 

-  15 
-20 
-25 
-30 
-40 

-eo 


1    cleg.F.  =  .W°C. 
1.8      "    -    1°C. 
3.6       "    =    2°0. 
4.5       "     ^    2.5°C 
5.4       "     =    3°C. 


To  convert  de- 
grees F.  into  de- 
grees C,  subtract 
32,  and  multiply 


To  convert  de- 
grees C.  into  de- 
grees F.,  multiply 
by  ?,  and  add  32°. 


MEASUREMENTS 

FKENCH  INTO  ENGLISH. 


LENGTH. 

1  m^tre  1 

10  dficimt'tres'  I    :=  39.37  English 
100  centimetres  f  inches. 

1,000  millimetres  J  (or  1  jd.  andSJ^in.) 


1  d6clm6tre      ) 

10  centimetres  V  =  3.9.37  inches 
100  millimetres  )  (or  nearly  4  inches.) 


1  centimetre 
10  millimetres 
1  millimetre 


=  .3937  or  about 

(nearly  i  inch.) 
=  nearly  j'j  inch. 


Or, 

One  Metre  —  39.37079  inches. 
(It  is  the  ten-millionth  part  of  a  quarter 

of  the  meridian  of  the  earth.) 

1  Decimetre    =  4  in. 

1  Centimetre  =  1*5  in. 

1  Millimetre    =  V.,  in- 

Decametre      =  S2.80  feet. 

Hectometre    -  109.36  yds. 

Kilometre        =  0.62  miles. 
One  incli  =  2.539  Centimetres. 
One  foot  =  3.047  Decimetres. 
One  yard  =  0.91  of  a  Bietre. 
One  mile  =  1.60  Kilometre. 
The  cubic  centimetre  (15.432  grains — 1 
gramme)  is  a  standard  at  4°  C,  the 
grain  at  16". 60  C. 


WEIGHT. 

(One  gramme  is  the  weight  of  a  cubic 
centimetre  of  water  at  4°  C.  at  Paris). 
1  gramme  ] 

10  decigrammes    I  =  15.432349  grs. 
100  centigrammes  f      (or  nearlj- 1514). 
1,000  milligrammes  J 


1  decigramme      ) 
10  centigrammes   -  =  rather  more 
100  milligrammes  )     than  IJ^  grain. 


1  centigramme 
10  decigrammes 


=  i-ather  more 
than  j^j  grain. 


1  milligramme 


=  rather  more 
than  ^  grain. 


Or 

1  Decigramme  =  2  dr.  34  gr. 

1  Hectogrm.      =  314  oz.  (Avoir.) 

1  Kilogrm.  =  2  lb.  3 oz.  2  dr.  (Avoir.) 


A  grain  equals  about  1.16  gram., 

a  Troy  oz.  about  31  gram., 

a  lb.  Avoirdupois  about  ^  Kilogrm. 

and  1  cwt.  about  50  Kilogrms. 


CAPACITY. 

1,000  cubic  decimetres  1  —  1  cubic 
1 .000.000  cubic  centimetres  C      metre. 


■  =  1  litre. 


1  cubic  decimetre 

or 

1,000  cubic  centimetres    \ 

Or 
One  Litre  =  1  pt.  15  oz.  1  dr.  40. 
(For  simplicity.  Litre  is  used  to  signify 
1  cubic  decimetre,  a  little  less  than  1 
English  quart.) 


Decilitre  (100  c.c.) 

=  314  oz. 

CVntilitre  (10  c.c.) 

=  n  dr. 

Millilitre  (1  c.c.) 

=  17  m. 

Decalitre 

=  2J  ^al. 

Hectolitre 

=  22  gals. 

Kilolitre  (cubic  metre)  —  3714  bushels. 
A  cubic  inch  =  16..38  c.c.  :  a  cubic  foot 
=  28.315  cubic  dec.  and  a  gallon  = 
4.54  litres. 


CONVERSION  SCALE. 

To  convert  (iRAMMES  to  OrxcES  avoir- 
dupois, multiply  by  20  and  divide  by  567. 

To  convert  Kilogrammes  to  Pof^'Ds, 
multiply  by  1 ,000  and  divide  by  454. 

To  convert  Litres  to  Gallons,  mul- 
tiplj'  by  22  and  divide  by  100. 

To  convert  Litres  to  Pints,  multiply 
by  88  and  divide  by  50. 

To  convert  BIillimetres  to  Ls'ches. 
multiply  by  10  and  divide  by  254. 

To  convert  Metres  to  Yards,  multi- 
ply by  70  aud  divide  by  64. 


SURFACE   MEASURE. 

1  square  metre  =  about  1550  sq.  inches. 
Or  10.000  sq.  centimetres,  or  10.75  sq.  ft. 
1  sq.  inch  =  about  G  4  sq.  centimetres. 


1  sq.  foot 


930 


ENERGY  MEASURE. 
1  kilogrammetre=about7.24ft.  pounds. 
1  foot  pound        =    "      .1381  kg:m. 

1  foot  ton  =     '•      310  kgni. 


HEAT  EQUIVALENT. 

1  kiloealorie  =  424  kilogrammetres. 


ENGLISH    MEASURES 
Apothecaries  Weight.  Avoirdupois  Weight 


7000  grains  =  1  lb. 

Or 
437.5  grains  =  1  oz. 


16  drams      =  1  oz. 
16  oz.  =  1  lb. 

28  lbs.  =  1  quarter. 

4  quarters  =  1  cwt. 
20  cwt.  =  1  ton. 


Measure  of  1  deciiii<-'ti-e,  or  10  centiiiiBtres,  or  100  iiiilliuif!tres. 


—  Cranium 

--7  Cervical  Vertebr» 

—  Clavicle. 

—  Scapula. 

12  Dorsal  Vertebrae. 
Humerus. 

5  Lumbar  Vertebrae, 


nium. 

Ulna. 

Radius. 

Pelvis. 


—  Bones  of  the  Carpus. 
Bones  of    the    Meta- 
carpus. 
Phalanges  of  Fingers, 


Femur. 


Patella^ 


.Tibia. 
.Fibula. 


_  Bones  of  the  Tarsus. 
_  Bones   of    the    Meta 

-   Phalanges  of  Toes. 


THE    SKELETON  (after  Houjkn;. 


SjinpTiysia  Pubis. 


DIAGRAM    OF    THORACIC    AND    ABDOMINAL    REGIONS. 


A.  Aortic  Valve. 
M.  Mitral  Valve. 


P.  Pulmonary  Valve. 
T.  Tricuspid  Valve. 


Handbook  of  Physiology. 


CHAPTER  I. 

THE  PHENOMENA  OF  LIFE. 


Human"  Physiology  is  the  science  which  treats  of  the  various  pro- 
cesses or  changes  which  take  place  during  life  in  the  organs  and  tissues 
of  the  body  of  man.  These  processes,  however,  must  not  be  considered 
as  by  any  means  peculiar  to  the  human  organism  since,  putting  aside 
the  properties  which  serve  to  distinguish  man  from  other  animals,  as 
well  as  those  which  mark  out  one  animal  from  another,  the  changes 
which  go  on  in  the  tissues  of  man  go  on  much  in  the  same  way  in  the 
tissues  of  all  other  animals  as  long  as  they  live.  Furthermore  it  is 
found  that  similar  changes  proceed  in  all  living  vegetable  tissues;  they 
indeed  constitute  what  are  called  vital  phenomena,  ^iiiiX  are  those  proper- 
ties which  mark  out  living  from  non-living  material. 

Tlie  lowest  types  of  life,  whether  animal  or  vegetable,  are  found  to 
consist  of  minute  masses  of  a  jelly-like  substance,  which  is  now  gener- 
ally known  under  the  name  of  ])rotoj)hmn.  Each  such  minute  mass  is 
called  a  cell,  so  that  these  minute  elementary  organisms  are  designated 
unicellular.  Not  only  is  it  true  that  the  lowest  types  of  life  are  made 
up  of  protoplasm,  but  it  has  also  been  shown  that  the  tissues  of  which 
the  most  complex  organisms  are  composed  consist  of  protoplasmic  cells. 

Thus,  for  example,  the  human  body  can  be  shown  by  dissection  to 
be  constructed  of  various  dissimilar  parts,  bones,  muscles,  brain,  heart, 
lungs,  intestines,  etc.,  and  these  on  more  minute  examination  with  the 
aid  of  the  microscope,  are  found  to  be  composed  of  different  tissues, 
such  as  epithelial,  connective,  nervous,  muscular,  and  the  like.  Each  of 
these  tissues  is  made  up  of  cells  or  of  their  altered  equivalents.  Again, 
we  are  taught  by  Embryology,  the  science  which  treats  of  the  growth 
and  structure  of  organisms  from  their  first  coming  into  being,  that  the 
human  body,  made  up  of  all  these  dissimilar  structures,  commenced  its 
life  as  a  minute  cell  or  ovum  (fig.  2)  about  ^l-^ih  of  an  inch  in  diame- 
ter, consisting  of  a  spherical  mass  of  protoplasm  in  the  midst  of  which 
was  contained  a  smaller  spherical  body,  the  nuclcua  or  fjenninal  vesicle. 

1 


2 


HANDBOOK    OF    PHYSIOLOGY. 


The  plienomeua  of  life  then  are  exhibited  in  cells,  whether  existing 
alone  or  developed  into  the  organs  and  tissues  of  animals  and  plants. 
It  must  be  at  once  evident  that  a  correct  knowledge  of  the  nature  and 
activities  of  the  cell  forms  the  very  foundation  of  physiology;  cells 
being,  in  fact,  physiological  no  less  than  morphological  units. 

The  prime  importance  of  the  cell  as  an  element  of  structure  was  first 
established  by  the  researches  of  the  botanist  Schleiden,  and  his  conclu- 
sions, drawn  from  the  study  of  vegetable  histology,  were  at  once  ex- 
tended by  Theodor  Schwann  to  the  animal 
kingdom.  The  earlier  observers  defined  a  cell 
Space cou-     '^^  ^  morc  or  less  spherical  body  limited  by  a 

tainiug 
■    liquid. 


membrane,   and    containing    a    smaller   body 


Protoplasm. 


.Nucleus. 


Cell-wall. 


Nucleus  or  germinal 
,    vesicle. 

Nucleolus  or  germi- 
nal spot. 

Space  left  by  retrac- 
tion of  yelk. 

.Yelk  or  vitellus. 


■Vitelline  membrane. 


Fig.  1.— Vegetable  cells. 


Fig.  S. — Semidiagrammatic  representation  of  a  hiunan 
ovum,  showing  the  parts  of  an  animal  cell.    (Cadiat.) 


termed  a  nucleus,  which  in  its  turn  incloses  one  or  more  still  smaller 
bodies  or  nucleoli.  Such  a  definition  applied  admirably  to  most  vege- 
table cells,  but  the  more  extended  investigation  of  animal  tissues  soon 
showed  that  in  many  cases  no  limiting  membrane  or  cell-wall  could  be 
demonstrated. 

The  presence  or  absence  of  a  cell-wall,  therefore,  was  now  regarded 
as  quite  a  secondary  matter,  while  at  the  same  time  the  cell-substance 
came  gradually  to  be  recognized  as  of  primary  importance.  Many  of 
the  lower  forms  of  animal  life,  e.g.,  the  Ehizopoda,  were  found  to  con- 
sist almost  entirely  of  matter  very  similar  in  appearance  and  chemical 
composition  to  the  cell-substance  of  higher  forms;  and  this  from  its 
chemical  resemblance  to  flesh  was  termed  Sarcode  by  Dujardin.  When 
recognized  in  vegetable  cells  it  was  called  Protoplasm  by  Mulder,  while 
Eemak  applied  the  same  name  to  the  substance  of  animal  cells.  As  the 
presumed  formative  matter  in  animal  tissues  it  was  termed  Blastema, 
and  in  the  belief  that,  wherever  found,  it  alone  of  all  substances  has  to 
do  with  generation  and  nutrition,  Beale  has  named  it  Germinal  matter 
or  Bioplasm.  Of  these  terms  the  one  most  in  vogue  at  the  present  day, 
as  we  have  already  said,  is  Protoplasm,  and  inasmuch  as  all  life,  both  in 
the  animal  and  vegetable  kingdoms,  is  associated  with  protoplasm,  we 


THE    PHENOMENA    OF   LIFE.  3 

are  justified  in  describing  it,  with  Huxley,  :is  the  "physical  basis  of 
life,"  or  simply  "  living  nuitter/' 

A  cell  may  now  be  defined  as  a  nucleated  mass  of  protoplasm,  of 
microscopic  size,  varying  in  the  human  body  from  the  red  blood-cell 
which  is  about  3-13^10-  of  an  incli  in  diameter  to  the  ganglion  cell,  3/,-,,-  of 
an  inch,  which  ^iossesses  sufficient  individuality  to  have  a  life-history  of 
its  own.  Each  cell  originates  from  a  pre-existing  cell,  grows,  produces 
other  cells,  and  dies,  going  through  the  same,  though  briefer,  cycle  as  the 
whole  organism.  8ome  of  the  lower  forms  of  life  seem  to  consist  of  non- 
nucleated  protoplasm,  but  the  above  definition  holds  good  for  all  the 
higher  plants  and  animals,  though  some  few  cells  lose  their  nuclei  in 
the  course  of  develoj^mentj  e.g.,  the  red  blood-cells  of  all  mammals. 

Properties  of  Protoplasm. 

Protoplasm  is  a  semi-fluid  substance,  which  swells  up  but  does  not 
mix  with  water.  It  is  transparent  and  generally  colorless,  with  refrac- 
tive index  higher  than  that  of  water  but  lower  than  that  of  oil.  It  is 
neutral  or  weakly  alkaline  in  reaction,  but  may  under  special  circum- 
stances be  acid,  as,  for  example,  after  activity.  It  undergoes  stiffening 
or  coagulation  at  a  temperature  of  about  54.5°  0.  (130°  F.),  and  hence 
no  organism  can  live  when  its  own  temperature  is  raised  above  that 
point;  it  is  also  coagulated  and  therefore  killed  by  alcohol,  by  solutions 
of  many  of  the  metallic  salts,  by  strong  acids  and  alkalies,  and  by  many 
other  substances. 

Under  the  microscope  it  is  seen  almost  universally  to  be  granular,  the 
granules  consisting  of  different  substances,  either  albuminous,  or  fatty,  or 
glycogenous  matters,  or  more  rarely  of  inorganic  salts.  The  granules  are 
not  equally  distributed  throughout  the  whole  cell-mass,  as  they  are  some- 
times absent  from  the  outer  part  or  layer,  and  very  numerous  in  the 
interior.  The  granules  may  exhibit  an  irregular  shaking,  dancing  move- 
ment, which  is  not  vital  and  is  knowai  as  the  Brownian  movement.  In 
addition  to  granules,  protoplasm  generally  exhibits  spaces  or  vacuoles, 
generally  globular  in  shape,  excepting  during  movement  when  they  may 
be  irregular,  filled  with  a  watery  fluid.  These  vacuoles  are  more  numer- 
ous and  pronounced  in  vegetable  than  in  animal  cells.  Gas  bubbles  also 
sometimes  exist  in  cells. 

It  is  impossible  to  make  any  definite  statement  as  to  the  exact  chem- 
ical composition  of  living  protoplasm,  since  the  methods  of  chemical 
analysis  necessarily  imply  the  death  of  the  cell;  it  is,  however,  stated 
tliat  protoplasm  contains  75  to  85  per  cent  of  water,  and  of  the  15  to  25 
per  cent  of  solids,  the  most  important  part  belongs  to  the  classes  of  sub- 
stances called  jyro^t^/rfo  or  «/^?</»?>i6'.  Proteids  contain  the  chemical  ele- 
ments carbon,  hydrogen,  nitrogen,  oxygen,  sulphur,  and  phosphorus,  the 


4:  HANDBOOK    OF    PHYSIOLOGY. 

last  two  In  small  quantities  o'n]y.  A  proteid-like  substance,  nuclein, 
found  in  the  nuclei  of  cells,  contains  pliosphorns  in  greater  abundance. 
In  cell  protoplasm  ti  compound  of  nuclein  with  proteid,  called  nucleo- 
proteid,  forms  the  most  abundant  proteid  substance.  Other  bodies  are 
frequently  found  associated  with  the  proteids,  such  as  glycogen,  f<tarcli, 
cellulose,  which  contain  the  elements  carbon,  hydrogen,  and  oxygen,  the 
last  two  in  the  proportion  to  form  water,  and  hence  are  termed  carlo- 
hydrates  ^  fatty  iodies,  containing  carbon,  hydrogen,  and  oxygen,  but 
not  in  proportion  to  form  water;  lecitliin,  a  complicated  fatty  body  con- 
taining phosphorus;  cliolesterin,  a  monatomic  alcohol;  cliloropliyll,  the 
coloring  matter  of  plants;  inorganic  salts,  particularly  the  chlorides  and 
phosphates  of  calcium,  sodium,  and  potassium;  ferments,  and  other  sub- 
stances. 

The  vital  or  physiological  characteristics  of  protoplasm  may  be 
well  stndied  in  the  microscopic  animal  called  the  amoeba,  a  unicellular 
organism  found  chiefly  in  fresh  water,  but  also  in  the  sea  and  in  damp 


Fig.  3. — Phases  of  amoeb  id  movement. 

earth.  These  properties  may  be  conveniently  studied  under  the  follow- 
ing heads: — 

1.  The  Power  of  SjJontaneous  Movement. — When  an  amoeba  is  ob- 
served with  a  high  power  of  the  microscope,  it  is  found  to  consist  of  an 
irregular  mass  of  protoplasm  probably  containing  one  or  more  nuclei, 
the  protoj)lasm  itself  being  more  or  less  granular  and  vacuolated.  If 
watched  for  a  minute  or  two,  an  irregular  projection  is  seen  to  be  grad- 
ually thrust  out  from  the  main  body  and  retracted;  a  second  mass  is 
then  protruded  in  another  direction,  and  gradually  the  whole  proto- 
plasmic substance  is,  as  it  were,  drawn  into  it.  The  amoeba  thus  comes 
to  occupy  a  new  position,  and  when  this  is  re^^eated  several  times  we 
have  locomotion  in  a  definite  direction,  together  with  a  continual  change 
of  form.  These  movements,  when  observed  in  other  cells,  such  as  the 
colorless  blood-corpuscles  of  higher  animals  (fig.  3),  in  the  branched 
cornea  cells  of  the  frog  and  elsewhere,  are  hence  termed  amoehoid. 

The  remarkable  movement  of  pigment  granules  observed  in  the 
branched  pigment  cells  of  the  frog's  skin  by  Lister  are  also  probably 
due  to  amoeboid  movement.  These  granules  are  seen  at  one  time  distrib- 
uted imiformly  through  the  body  and  branched  processes  of  the  cell, 
while  at  another  time  they  collect  in  the  central  mass  leaving  the 
branches  quite  colorless. 


THE    PHKNOMEXA    01'    LIFE.  5 

This  movement  within  the  pigment  cells  might  also  be  considered 
an  example  of  the  so-called  streamhuj  movement  not  infrequently  seen 
in  certain  of  the  i^rotozoa,  in  which  the  mass  of  protoplasm  extends 
long  and  fine  processes,  themselves  very  little  movable,  but  upon  the 
surface  of  which  freely  moving  or  streaming  granules  are  seen.  A  glid- 
ing movement  nas  also  been  noticed  in  certain  animal  cells;  the  motile 

/i         ^.         (^^         y~C 

Fig.  4.— Changes  of  form  of  a  white  corpuscle  of  newfs  V)Ioocl.  sketched  at  brief  intervals 
^The  figures  sliow  also  the  intussusception  of  two  small  granules.     (Schafer.) 

part  of  the  cell  being  composed  of  protoplasm  bounding  a  central  and 
more  compact  mass.  By  means  of  the  free  movement  of  this  layer, 
the  cell  may  be  observed  to  move  along. 

In  vegetable  cells  the  protoj^lasmic  movement  can  be  well  seen  in 
the  hairs  of  the  stinging-nettle  and  Tradescantia  and  the  cells  of  Vallis- 
neria  and  Chara;  it  is  marked  by  the  movement  of  the  granules  nearly 
always  imbedded  in  it.  For  example,  if  j^art  of  a  hair  of  Tradescantia 
(fig.  5)  be  viewed  under  a  high  magnifying  power,  streams  of  proto- 
plasm containing  crowds  of  granules  hurrying  along,  like  the  foot- 
passengers  in  a  busy  street,  are  seen  flowing  steadily  in  definite  direc- 
tions, some  coursing  round  the  film  which  lines  the  interior  of  the  cell- 
Avall,  and  others  flowing  toward  or  away  from  the  irregular  mass  in  the 
centre  of  the  cell-cavit}^     Many  of  these  streams  of  protoplasm  run 


Fig.  .5.— Cell  of  Tradescantia  drawn  at  successive  intervals  of  two  minutes.— The  cell-conte  rta 
consist  of  a  central  mass  connected  by  many  irregular  processes  to  a  peripheral  film,  the  w)  olo 
forming  a  vacuolated  mass  of  protoplasm,  which  is  continually  changing  its  shape.    ^Schofield.) 


together  into  larger  ones  and  are  lost  in  the  central  mass,  and  thut 
ceaseless  variations  of  form  are  produced.  The  movement  of  the  pro- 
toplasmic granules  to  or  from  the  periphery  is  sometimes  called  vegeta- 
ble  circulatiun,  whereas  the  movement  of  the  protoplasm  round  the  in- 
terior of  the  cell  is  called  rotation. 

The  first  account  of  the  movement  of  protoplasm  was  given  by 
Rose]  in  1755,  as  occurring  in  a  small  Proteus,  probably  a  large  fresh- 
water amoeba.     His   description  was   followed   twenty   years   later   by 


6  HANDBOOK    OV    PHYSIOLOGY. 

Corti's  demonstration  of  the  rotation  of  the  cell  sap  in  characeae,  and  in 
the  earlier  part  of  the  century  by  Meyer  in  Vallisneria,  1827;  Kobert 
Brown,  1831,  in  "  Staminal  Hairs  of  Tradescantia."  Then  came  Dujar- 
diu's  description  of  the  granular  streaming  in  the  pseudopodia  of  Ehizo- 
pods  and  movement  in  other  cells  of  animal  protoplasm  (Planarian  eggs, 
V.  Siebold,  1841;  colorless  blood-corpuscles,  Wharton  Jones,  1846). 

2.  The  Power  of  Eesponse  to  Stimuli,  or  Irritability. — Although  the 
movements  of  the  amoeba  have  been  described  above  as  spontaneous,  yet 
they  may  be  increased  under  the  action  of  external  agencies  which 
excite  them  and  are  therefore  called  stimuli,  and  if  the  movement  has 
ceased  for  the  time,  as  is  the  case  if  the  temperature  is  lowered  beyond 
a  certain  point,  movement  may  be  set  up  by  raising  the  temperature. 
Again,  contact  with  foreign  bodies,  gentle  pressure,  certain  salts,  and 
electricit}'',  produce  or  increase  the  movement  in  the  amoeba.  The  pro- 
toplasm is,  therefore,  sensitive  or  irritable  to  stimuli,  and  shows  its  irri- 
tability by  movement  or  contraction  of  its  mass. 

The  effects  of  some  of  these  stimuli  may  be  thus  further  detailed : — 

a.  Changes  of  Temperature. — Moderate  heat  acts  as  a  stimulant;  the 
movement  stops  below  0°  C.  (32°  F.),  and  above  40°  C.  (104°  F.) ;  be- 
tween these  two  points  the  movements  increase  in  activity;  the  optimum 
temperature  is  about  37°  to  38°  C.  Exposure  to  a  temperature  even 
below  0°  C.  stops  the  movement  of  j)rotoplasm,  but  does  not  prevent  its 
reappearance  if  the  temperature  is  raised;  on  the  other  hand,  prolonged 
exposure  to  a  temperature  of  over  40°  C.  altogether  kills  the  protoplasm 
and  causes  it  to  enter  into  a  condition  of  coagulation  or  heat  rigor. 

h.  Mechanical  Stimuli. — When  gently  squeezed  between  a  cover  and 
object-glass  under  proper  conditions,  a  colorless  blood-corpuscle  is  stim- 
ulated to  active  amoeboid  movement. 

c.  Nerve  Influence. — By  stimulation  of  the  nerves  of  the  frog's  cornea, 
contraction  of  certain  of  its  branched  cells  has  been  produced. 

d.  Chemical  Stimuli. — Water  generally  stops  amoeboid  movement, 
and  by  imbibition  causes  great  swelling  and  finally  bursting  of  the  cells. 
In  some  cases,  however  (myxomycetes),  protoplasm  can  be  almost  en- 
tirely dried  up,  but  remains  capable  of  renewing  its  movements  when 
again  moistened.  Dilute  salt-solution  and  many  dilute  acids  and  alka- 
lies stimulate  the  movements  temporarily.  Strong  acids  or  alkalies 
permanently  stop  the  movements;  ether,  chloroform,  veratria,  and  qui- 
nine also  stop  it  for  a  time. 

Movement  is  suspended  in  an  atmosphere  of  hydrogen  or  carbonic 
acid  and  resumed  on  the  admission  of  air  or  oxygen,  but  complete  with- 
drawal of  oxygen  will  after  a  time  kill  the  protoplasm. 

e.  Electrical. — Weak  currents  stimulate  the  movement,  while  strong 
currents  cause  the  cells  to  assume  a  spherical  form  and  to  become 
motionless. 


THE    PHENOMENA    OK    LIP?:. 


3.  The  Power  of  Digestion,  Respiration,  and  Nutrition. — This  con- 
sists in  the  power  which  is  possessed  by  the  amoeba  and  similar  animal 
cells  of  taking  in  food,  modifying  it,  building  up  tissue  by  assimilating 
it,  and  rejecting  what  is  not  assimilated.  These  various  processes  are 
effected  by  the  protoplasm  simply  flowing  round  and  inclosing  within 
itself  minute  organisms  such  as  diatoms  and  the  like,  from  which  it 
extracts  what  it  requires,  and  then  rejects  or  excretes  the  remainder, 
which  has  never  formed  part  of  the  body.  This  latter  proceeding  is 
done  by  the  cell  withdrawing  itself  from  the  material  to  be  excreted. 
The  assimilation  constantly  taking  place  in  the  body  of  the  amoeba,  is 
for  the  purpose  of  replacing  waste  of  its  tissue  consequent  upon  mani- 
festation of  energy.  The  respiratory  process 
of  absorbing  oxygen  goes  on  at  the  same  time. 

The  processes  which  take  place  in  cells, 
both  animal  and  vegetable,  are  summed  up 
under  the  term  metabolism  (from  ij.z-a.^iukr^, 
change).  The  changes  which  go  on  are  of 
two  kinds,  viz.,  assimilation,  or  building  up, 
and  disassimilaf ion, or  breaking  down;  they 
may  be  also  called  composition  or  decom- 
position, or,  using  the  nomenclature  of  Gas- 
kell,  anahoUsm  or  constructive  metabolism, 
and  Tcataholism  or  destructive  metabolism. 
In  the  direction  of  anabolism  two  processes 
occur,  viz.,  the  building  up  of  materials  which 
it  takes  in,  and  secondly,  the  building  up  of 
its  own  substance  by  those  or  other  mate- 
rials. As  we  sliall  see  in  a  subsequent  para- 
graph, the  process  of  anabolism  differs  to 
some  extent  in  vegetable  and  animal  cells. 
The  katabolism  of  the  cell  consists  in  chem- 
ical changes  which  occur  in  the  cell-substance  itself,  or  in  substances 
in  contact  with  it. 

The  destructive  metabolism  of  a  cell  is  increased  by  its  activity,  but 
goes  on  also  during  quiescence.  It  is  probably  of  the  nature  of  oxida- 
tion, and  results  in  the  evolution  of  carbonic  anhydride  and  water  on 
the  one  hand,  and  in  the  f^i-mation  of  various  substances  on  the  other, 
some  of  which  may  be  stored  up  in  the  cell  for  future  use,  and  are 
called  secretions,  and  others,  like  the  carbonic  anhydride  and  certain 
bodies  containing  nitrogen,  are  eliminated  as  excretions. 

4.  The  Power  of  Growth. — In  protoplasm  then,  it  is  seen  that  the 
two  processes  of  waste  and  repair  go  on  side  by  side,  and  as  long  as  they 
are  equal  the  size  of  the  animal  remains  stationary.  If,  however,  the 
building  up  exceed  the  w^aste,  then  the  animal  grows  ;  if  the  waste  ex- 


Fig.  6.— Cells  from  the  staminal 
hairs  of  Tradescantia.  A,  Fresh  in 
water;  B,  the  same  cell  after  slight 
electrical  stimulation;  a,  b.  region 
stimulation ;  c,  cl,  clumps  and  knobs 
ofcontractedprotoplasm.  (Kiihne.) 


8  nAXDBOOK    OF    PHYSIOLOGY. 

ceed  the  repair,  the  animal  decays;  and  if  decay  go  on  be3'ond  a  certain 
point,  life  becomes  impossible,  and  the  animal  dies. 

Growth,  or  the  inherent  power  of  increasing  in  size,  although  essen- 
tial to  our  idea  of  life,  is  not,  it  must  be  recollected,  confined  to  living 
beings.  A  crystal  of  common  salt,  for  examj)le,  if  placed  under  appro- 
priate conditions  for  obtaining  fresh  material,  will  grow  in  a  fashion  as 
definitely  characteristic  and  as  easily  to  be  foretold  as  that  of  a  living- 
creature;  but  the  growth  of  a  crystal  takes  jolace  merely  by  additions 
to  its  outside;  the  new  matter  is  laid  on  particle  by  pai'ticle,  and  layer 
by  layer,  and,  when  once  laid  on,  it  remains  unchanged.  In  a  living 
structure,  where  growth  occurs,  it  is  by  addition  of  new  matter,  not  to 
the  surface  only,  but  throughout  every  part  of  the  mass. 

Again,  all  living  structures  are  subject  to  constant  decay.  Thus,  a 
man's  body  is  not  composed  of  exactly  the  same  jaarticles  day  after  day, 
although  to  all  intents  he  remains  the  same  individual.  Almost  every 
part  is  changed  by  degrees;  but  the  change  is  so  gradual,  and  the  re- 
newal of  that  which  is  lost  so  exact,  that  no  difference  may  be  noticed, 
except  at  long  intervals  of  time.  A  lifeless  structure,  as  a  crystal,  is 
subject  to  no  such  laws;  neither  decay  nor  repair  is  a  necessary  condi- 
tion of  its  existence.  That  which  is  true  of  structures  which  never  had 
to  do  with  life  is  true  also  with  respect  to  those  which,  although  they 
are  formed  by  living  parts,  are  not  themselves  alive.  Thus,  an  oyster- 
shell  is  formed  by  the  living  animal  which  it  incloses,  but  it  is  as  lifeless 
as  any  other  mass  of  inorganic  matter;  and  in  accordance  with  this 
circumstance  its  growth  takes  place  layer  by  layer,  and  it  is  not  subject 
to  constant  decay  and  reconstruction.  The  hair  and  nails  are  examples 
of  the  same  fact. 

In  connection,  too,  with  the  growth  of  lifeless  masses  there  is  no 
alteration  in  the  chemical  composition  of  the  material  which  is  taken 
uj)  and  added  to  the  previously  existing  mass.  For  example,  when  a 
crystal  of  common  salt  grows  on  being  placed  in  a  fluid  which  contains 
the  same  material,  the  pro]3erties  of  the  salt  are  not  changed  by  being 
taken  out  of  the  liquid  by  the  crystal  and  added  to  its  surface  in  a  solid 
form.  But  the  case  is  essentially  different  in  living  beings,  both  animal 
and  vegetable,  as  the  materials  which  serve  ultimately  to  build  them 
up  are  much  altered  before  they  are  finally  assimilated  by  the  structures 
they  are  destined  to  nourish. 

The  growth  of  all  living  things  has  a  definite  limit,  and  the  law 
which  governs  this  limitation  of  increase  in  size  is  so  invariable  that  we 
should  be  as  much  astonished  to  find  an  individual  plant  or  animal 
without  limit  as  to  growth  as  without  limit  to  life. 

5.  Tlie  Power  of  Be])rodnciion. — The  amoeba,  to  return  to  our  former 
illustration,  when  the  growth  of  its  protoplasm  has  reached  a  certain 
point,  manifests  the  power  of  reproduction,  by  splitting  up  into  (or  in 


THK    fllKXOMKNA    Ol"    LTFE.  \) 

some  other  way  producing)  two  or  more  parts,  eacli  of  which  is  capable 
of  independent  existence.  The  new  amcsbae  manifest  the  same  proper- 
ties as  their  parent,  perform  the  same  functions,  grow  and  reproduce  in 
their  turn.     This  cycle  of  life  is  being  continually  passed  through. 

In  more  com^jlicated  structures  than  the  amoeba,  the  life  of  indi- 
vidual protoplasmic  cells  is  probably  very  short  in  comparison  with  that 
of  the  organism  they  compose;  and  their  constant  decay  and  death 
necessitate  constant  reproduction. 

The  mode  in  which  this  takes  place  has  long  been  the  subject  of 
great  controversy. 

It  is  now  very  generally  believed  that  every  cell  is  descended  from 
some  pre-existing  (mother-)   cell.     This  derivation  of  cells  from  cells 


Fig.  7. — Diagram  of  an  ovum  (a)  undergoing  segmentation— In  (h}  it  has  divided  into  two,  in 
(c)  into  four;  and  in  (d)  thie  process  has  ended  in  the  production  of  tlie  so  called  "mulberry  mass." 
(Frey.) 

takbs  place  by  (1)  gemmation,  which  essentially  consists  in  the  budding 
ofi  and  separation  of  a  portion  of  the  parent  cell;  or  (2)  fissio)i  or  divi- 
sion. 

The  exact  manner  of  the  division  of  cells  is  a  matter  of  some  diffi- 
culty, and  will  not  be  described  until  the  subject  of  the  structure  of 
protoplasmic  cells  has  been  considered. 

Structure  of  Protoplasmic  Cells. 

Protoplasm  was  formerly  thought  to  be  homogeneous:  though  this 
may  be  true  in  some  cases,  it  is  now  generally  found  to  consist  of  two 
substances,  spongioplasni  and  hyaloplasm.  The  .y)o>iiji(i/)I(is)n  or  reticu- 
lum forms  a  fine  network,  increases  in  relative  amount  as  tlie  cell  grows 
older,  and  has  an  aftinity  for  staining  reagents.  The  liyaloplaam  is  less 
refraetile,  elastic,  or  extensile,  and  has  no  aftinity  for  stains;  it  pre- 
dominates in  young  cells,  is  thought  to  be  tiuid,  and  tills  the  interspaces 
of  the  reticulum.  The  nodal  points  of  the  reticulum,  witli  the  granules 
(niicrosomrsi)  found  in  the  protoplasm,  cause  the  granular  appearance. 
Butschli  has  recently  asserted  that  protoplasm  is  an  emulsion  made  up 
of  numerous  microscopic  vacuoles  whose  walls  are  in  close  apposition  and 
are  seen  under  the  microscope  in  optical  section  only,  thus  causing  the 
reticular  appearance.     This  idea  is  accepted  by  few. 

The  arrangement  of  the  reticulum  varies  considerably  in  different 
cells,  and  even  in  different  parts  of  the  same  cell.  Sometimes,  for  ex- 
ample (fig.  8),  the  meshwork  has  an  elongated  radial  arrangement  from 


10 


HAISTDBOOK    OF    PHYSIOLOGY. 


the  nnciens;  at  others,  the  mesh  work  is  more  evenly  disposed,  as  in 
fig.  9.  At  the  jimctious  of  the  fihrils  there  are  usually  slight  enlarge- 
ments or  nodes. 

In  some  cells,  particularly  in  plants,  but  also  in  some  animal  cells, 
there  is  a  tendency  toward  a  formation  of  a  firmer  external  envelope, 


Membrane  of  cell 


Reticulum  of  cell  — . 


Membrane  of  nucleus. 


Achromatic  substance  of 

nucleus. 
Chromatic  substance  of 

nucleus. 


Fig.  8. — Cell  with  its  reticulum  disposed  radially ;  from  the  intestinal  epithelium  of  a  worm. 

(Carnoy.) 


constituting  in  vegetable  cells  a  membrane  distinct  from  the  more 
central  and  more  fluid  part  of  the  protoplasm.  In  such  cases  the  reticu- 
lum at  the  periphery  of  the  cell  is  made  up  of  very  fine  meshes.  The 
membrane  when  formed  is  usually  pierced  with  pores  by  which  fluid  may 
pass  in,  or  through  which  protrusion  of  the  protoplasmic  filaments  form- 
ing the  cell's  connection  with  other  cells  surrounding  it  may  take  place. 
It  is  an  exceedingly  interesting  qiiestion  whether  in  cells  the  one 


Fig.  9. — (a.)  The  colorless  blood-corpuscle  showing  the  intra-cellular  network,  and  two  nuclei 
with  intra-nuclear  network,  (b.)  Colored  blood-corpuscle  of  newt  showing  the  intra-cellular  net- 
work of  fibrils.  Also  oval  nucleus  composed  of  liniiting  membrane  and  fine  intra-nuclear  network 
of  fibrils.     X  800.     (Klein  and  Noble  Smith.) 


part  of  the  protoplasm  can  exist  without  the  other.  Schafer  summar- 
izes the  matter  thus: — "There  are  cells,  and  unicellular  organisms  both 
animal  and  vegetable,  in  which  no  reticular  structure  can  be  made  out, 
and  these  may  be  formed  of  hyaloplasm  alone.  In  that  case,  this  must 
be  looked  upon  as  the  essential  part  of  protoplasm.  So  far  as  amoeboid 
phenomena  are  concerned  it  is  certainly  so;  but  whether  the  chemical 


THE   PHENOMEJTA   OP   LIFE.  11 

changes  which  occur  in  many  cells  are  effected  by  this  or  by  spongio- 
plasm  is  another  matter." 

Another  question  about  which  there  is  some  difference  of  opinion  is, 
which  part  of  the  protoplasm  is  chiefly  contractile.  It  is  usually  con- 
cluded that  this  property  rests  iu  the  mesh  work,  but  there  seems  a 
considerable  amount  of  evidence  in  favor  of  the  view  that  part  if  not 
all  of  the  contractility  resides  in  the  hyaloplasm;  for  example,  in  amoe- 
boid cells  the  pseudopodial  protoplasm  are  certainly  made  of  this  and 
not  of  spongioplasm,  and  when  the  corpuscle  is  stimulated  the  hyalo- 
plasm flows  back  into  the  reticular  network.  If  the  view  that  the  hyalo- 
plasm is  chiefly  contractile  be  a  correct  one,  the  special  condition  of  an 
amoeboid  cell  must  be  considered  to  be  condition  of  contraction,  and 
the  flowing  out  of  the  process  to  be  relaxation. 

The  Cell  Nucleus. 

All  cells  at  some  period  of  their  existence  possess  luiclei.  As 
has  been  incidentally  suggested  the  origin  of  a  nucleus  in  a  cell  is  the 
first  trace  of  the  differentiation  of  protoplasm.  The  existence  of  nuclei 
was  first  pointed  out  in  the  year  1833  by  Robert  Brown,  who  observed 
them  in  vegetable  cells.  They  are  either  small  transparent  vesicular 
bodies  containing  one  or  more  smaller  particles  (nucleoli),  or  they  are 
semi-solid  masses  of  proto23lasm  always  in  the  resting  condition  bounded 
by  a  well-defined  envelope.  In  their  relation  to  the  life  of  the  cell  they 
are  certainly  hardly  second  in  importance  to  the  protoplasm  itself,  and 
thus  Beale  is  fully  justified  in  comprising  both  under  the  term  "ger- 
minal matter."  They  control  the  nutrition  of  the  cell,  and  probably- 
initiate  the  process  of  subdivision.  If  a  cell  be  mechanically  divided, 
that  2)ortion  not  containing  the  nucleus  dies. 

Histologists  have  long  recognised  nuclei  by  two  important  char- 
acters : — 

(1.)  Their  power  of  resisting  the  action  of  various  acids  and  alkalies, 
particularly  acetic  acid,  by  which  their  outline  is  more  clearly  dclined, 
and  they  are  rendered  more  easily  visible.  This  indicates  some  chemi- 
cal difference  between  the  protoplasm  of  the  cells  and  nuclei,  as  the 
former  is  destroyed  by  these  reagents. 

(2.)  Their  quality  of  staining  in  solutions  of  carmine,  hannatoxylin. 
etc.  Nuclei  are  most  commonly  oval  or  round,  and  do  not  generally 
conform  to  the  diverse  shapes  of  the  cells;  they  are  altogether  less  vari- 
able elements  than  cells,  even  in  regard  to  size,  of  which  fact  one  may 
see  a  good  example  in  the  uniformity  of  the  nuclei  in  cells  so  multiform 
as  those  of  epithelium.  But  sometimes  nuclei  occupy  almost  the  whole 
of  the  cell,  as  in  the  lymph  corpuscles  of  lymphatic  glands,  and  iu  some 
small  nerve  cells,  and  may  even  jn-ojoot  alxive  the  surface. 


13 


HANDBOOK    OF    PHTSIOLOGY. 


Their  position  in  the  cell  is  verj-  variable.     In  many  cells,  especially 
where  active  growth  is  progressing,  two  or  more  nuclei  are  present. 


Structure  of  Nuclei. 

The  nucleus  when  in  a  condition  of  rest  is  bounded  by  a  distinct 
membrane,  the  nuclear  membrane,  possibly  derived  from  the  spongio- 
plasm  of  the  cell,  which  encloses  the  nuclear  contents  or  haryoplasm. 
The  membrane  consists  of  an  inner,  or  chromatic,  and  an  of  outer,  or 


Xode  of  meshwork  - 


Node  of  meshwork 


— »-Nuclear  membrane. 
Nucleolus. 

Nuclear  matrix. 

Nuclear  meshwork. 


Fig.  10. — The  resting  nucleus — diagrammatic.     (Wakleyer. 


achromatic  layer,  so  called  from  their  reaction  to  stains.  The  karyo- 
plasm  is  made  up  of  a  reticular  network,  or  chroinoplasni,  whose  in- 
ters2Daces  are  filled  by  the  karyolymph,  or  midear  matrix,  a  homogeneous 
substance  which  is  rich  iu  proteids,  has  but  slight  affinity  for  stains, 
and  is  supposed  to  be  fluid. 

The  network  is  composed   of  linin,   or    achromatin,   a   transparent 
unstainable  framework;  and  of  cliromatin,  which  stains  deeply,  is  sup- 

A  B 


p.cj 


Fig.  11. — Diagram  of  nucleus  showing  the  arrangement  of  chief  chromatic  filaments,  a.  Viewed 
from  the  side,  the  polar  end  being  uppermost,  p.c.f..  Primary  chromatic  filaments;  n.,  nucleolus; 
n.o.m.,  node  of  meshwork.  b.  Viewed  at  the  polar  end.  i.c.f.,  Looped  chromatic  filament;  /./.,  ir- 
regular filament.    (Rabl.> 


ported  by  the  linin,  and  occurs  sometimes  in  the  form  of  granules,  but 
usually  as  irregular  anastomosing  threads,  both  thicker  primary  fibres 
and  thinner  connecting  branches.  The  threads  often  form  thickened 
nodes,  karyosemes  or  false  nucleoli,  at  their  points  of  intersection.     It 


THE    PHENOMENA    OF    LIFE.  13 

is  now  quite  geDerally  believed  that  tlie  chromatin  occurs  as  short,  rod- 
like and  highly  refractive  masses,  which  are  embedded  in  the  linin  in  a 
regular  series. 

The  nucleoli,  or  plasmosomes,  are  spherical  bodies  of  unknown  func- 
tion. They  stain  deeply,  and  may  either  lie  free  in  the  nuclear  matrix 
or  be  attached  to  the  threads  of  the  network. 


Attraction  Sphere. 

In  addition  to  the  nucleus,  a  minute  spherical  body  called  the  coitro- 
so/iie  is  believed  to  be  constantly  present  in  animal  cells,  though  some- 
times too  small  to  be  demonstrated.  The  centrosome  is  smaller  than 
the  nucleus,  close  to  which  it  lies,  and  exerts  a  peculiar  attraction  for 


Fig.  11a.— Leucocyte  of  Salamander  Larva,  sliowin^  attraction  sphere.     (After  Klemming.) 

the  protoplasmic  tilanients  and  granules  in  its  vicinity,  so  that  it  is  sur- 
rounded by  a  zone  of  fine  radiating  fibrils,  forming  the  atiraction  sphere 
or  archoplasm.  Some  authorities  assert  that  the  centrosome  lies  within 
the  nucleus  in  the  resting  state,  and  only  passes  into  the  cell  proper  in 
the  earlier  stages  of  cell  division.  The  attraction  sphere  is  most  dis- 
tinctly seen  in  cells  about  to  divide.  It  plays  an  important  role  in 
nuclear  division,  but  it  is  doubted  if  it  gives  the  initial  impulse  to  the 
process. 

Cell  Division. 

The  division  of  a  cell  is  jireceded  by  division  of  its  nucleus,  which 
may  be  either  direct  or  indirect.  Direct  or  simple  division,  amitosis  or 
akinesis  (zivr^rvis-,  movement),  occurs  witliout  any  change  in  the  arrange- 
ment of  the  intranuclear  network;  it  is  probalily  lin\ited  to  the  anurbas. 


14 


HANDBOOK    OF    PHYSIOLOGY. 


A  constriction  develops  at  the  centre  of  the  nucleus,  possibly  preceded 
by  division  of  the  nucleoli,  and  gradually  divides  it  into  two  equal 
daughter  nuclei.  A  similar  constriction  of  the  protoplasm  of  the  cell 
occurs  between  the  daughter  nuclei  and  divides  it  in  two  parts. 


FJg.  13. — Akinesis,  amitosis,  or  direct  cell  division.  A,  Constriction  of  nucleus;  B,  division 
of  nucleus  and  constriction  of  cell  body;  G,  daughter  nuclei  still  connected  by  a  thread,  division 
being  delayed  ;  jD,  division  of  cell  body  nearly  complete.     (After  Arnold.) 

Indirect  division,   mitosis  (//iro?,  a  thread),  or  karyokinesis   (xapuv^, 
a  kernel),  is  the  almost  universal  method,   and  consists  of  a  series  of 


Fig.  12a.— Karyokinesis,  mitosis,  or  indirect  cell  divisioq  (diagrammatic).  .4,  Cell  with  rest- 
ing nucleus;  B,  wreath,  daughter  centrosomes  and  early  stage  of  acliromatic  spindle;  C,  chromo- 
somes; D,  monaster  stage,  achromatic  spindle  in  long  axis  of  nucleus,  cliromosomes  dividing: 
E,  chromosomes  moving  toward  centrosomes ;  F,  diaster  stage,  cliromosomes  at  poles  of  nucleus, 
commencing  constriction  of  cell  body ;  G,  daughter  nuclei  beginning  return  to  resting  state;  H, 
daughter  nuclei  .showing  monaster  and  wreath;  i,  complete  division  of  cell  body  into  daugliter 
cells  whose  nuclei  have  returned  to  the  resting  state.     (After  Bohm  and  von  Davidoff. ) 


changes  in   the  arrangement  of  the  intranuclear  network,  resulting  in 
the  exact  division  of  the  chromatic  fibres  into  two  parts,  which  form  the 


THE    PHENOMENA    OF    LIFE. 


15 


chromoplasm  of  the  daughter  nuclei.  The  changes  follow  a  closely 
similar  course  in  both  plant  and  animal  cells.  The  process  has  been 
divided  by  different  authorities  into  a  varying  number  of  stages,  with 
varying  names,  but  for  the  sake  of  simplicity  it  seems  best  to  accept  the 


Achromatic  spiral 


Fig  13.— Early  stages  of  karyokinesis.  a.  The  thicker  primary  fibres  remain  and  the  achro- 
matic spindle  appears,  b.  The  thick  fibres  split  into  two  and  the  achromatic  spindle  becomes  longi- 
tudinal.    (Waldeyer.) 

authority  of  Yerworn  and  recognize  two  stages  only — a  progressive  one  in 
which  the  changes  in  the  nucleus  advance  to  a  maximum,  and  a  retro- 
gressive one  in  which  the  resulting  nuclear  halves  revert  to  the  resting 
state. 

Progressive  stage.     The  resting  nucleus  becomes  somewhat  enlarged, 
and  the  centrosome  (according  to  those  who  regard  it  as  lying  normally 


centred. 


(CyLctsier) 
ckrcintci.(<n> 


'"I'l'Jj    loruft' 


clear  area 
of  nucleus'" 


Fig.  1-1.— Monaster  stage  of  karyokinesis.    (Rabl. ) 


within  the  nucleus)  migrates  into  the  cell  protoplasm.  The  centrosome 
then  divides  into  two  daughter  centrosomes  which  lie  near  the  nucleus 
but  are  separated  by  a  considerable  interval.  Each  is  surrounded  by  the 
radiating  fibrils  of  the  attraction  sphere,  and  some  of  these  fibrils  pass 
continuously  from  one  centrosome  to  the  other,  forming  the  achromatic 
spindle.  At  the  same  time  (prophases)  the  intranuclear  network  be- 
comes converted  into  a  fine  convoluted  coil  (spircm  or  skein)  which  may 
be  either  continuous  or  else  broken  up  into  several  threads.     Tlie  thread 


16 


HANDBOOK    OF    PHYSIOLOGY. 


or  threads  then  shorten  and  become  thicker,  while  the  convolutions, 
which  haye  become  less  numerous,  arrange  themselves  in  a  series  of  con- 
necting loops,  forming  the  ■wreath.  The  nuclear  membrane  and  the 
nucleolus  disappear,  the  latter  passing  at  times  into  the  cell  protoplasm 
and  disintegrating.     The  wreath  then  breaks  up  into  V-shaped  segments, 


iVt       Fine  uniting 
•  '  • "       filaments. 


Fig.  15.— Stages  of  karyokinesis.  (Rabl.)  A.  Commencing  separation  of  the  spUt  chromosomes. 
B.  The  separation  fuither  advanced.  C.  The  separated  chromosomes  passing  along  the  fibres  of  the 
achromatic  spindle. 


the  chrumosoines,  of  which  each  species  of  animal  has  a  constant  and 
characteristic  number.  This  varies  from  two  to  thirty-six  in  the  differ- 
ent animals,  but  is  sixteen  in  man. 

The  two  centrosomes  migrate  to  the  poles  of  the  nucleus,  while  the 
achromatic  spindle  which  connects  them  occujDies  the  long  axis  of  the 


Remains  of  spindle. 


Line  of  separation 
of  the  two  cells. 

Antipole  of  daugh- 
ter nucleus. 


Lighter    substance 
of  the  nucleus. 


Cell  protoplasm. 

Hilus. 


Fig.  16.— Final  stages  of  karyokinesis.    In  the  lower  figure  the  changes  are  still  more  advanced  than 

in  the  upper.     (Waldeyer.) 


nucleus.  The  chromosomes,  becoming  much  shorter  and  thicker,  gather 
around  the  spindle  in  its  equatorial  plane,  with  their  angles  directed 
toward  the  centre,  forming  the  aster  or  monaster. 

The  actual  division  of  the  nucleus  is  begun  at  this  time  (vietaphases) 
by  the  splitting  of  each  chromosome  longitudinally  into  halves  which  lie 
at  first  close  together  so  that  each  seems  doubled.  Soon  afterward  the 
fibrils  of  tho  achromatic  spindle  begin  to  contract,  and  thus  separate  the 


THE    PHENOMEXA    OF    LIFE,  l7 

halves  of  the  chromosomes  iu  such  a  way  that  one-half  of  each  is  turned 
toward  one  pole,  and  the  other  half  toward  the  other.  As  this  con- 
tinues, the  two  groups,  which  are  equal  in  size,  draw  away  from  each 
other  and  from  the  equator,  each  group  being  formed  of  daughter 
chromosomes. 

Ivetrogressive  stage  {(inaphases  and  telo^jhases) .  The  two  groups 
(daughter  chromosomes)  now  gradually  aj^proach  their  respective  poles, 
or  centrosomes,  and  the  equator  becomes  free.  On  reaching  the  jiole, 
each  group  gathers  iu  a  form  which  is  similar  iu  arrangement  to  the 
monaster  and  is  known  as  the  diaster.  During  this  time  the  cell  bodv 
becomes  slightly  constricted  by  a  circular  groove  at  its  equatorial  j^lane. 
Soon  afterward  the  fibrils  of  the  achromatic  spindle  which  connect  the 
two  groups  begin  to  grow  dim  and  finally  disappear.  The  daughter 
chromosomes  assume  the  form  of  threads  twisted  in  a  coil  and  develop 
each  a  nuclear  membrane  and  a  nucleolus,  forming  a  daughter  nucleus. 
The  nuclei  enlarge  and  the  nuclear  threads  assume  the  appearance  of  the 
resting  state  of  the  nucleus.  Meanwhile,  the  constriction  about  the 
body  of  the  cell  has  become  deeper  and  deeper  until  the  protojilasm  is 
divided  into  two  equal  parts,  or  daughter  cells,  each  with  its  daughter 
nucleus,  and  the  process  of  karyokinesis  is  completed. 

Differences  between  Animals  and  Plants. 

Having  considered  at  some  length  the  vital  j^roperties  of  protoplasm, 
as  shown  in  cells  of  vegetable  as  well  as  of  animal  organisms,  we  are  now 
in  a  position  to  discuss  the  question  of  the  differences  betwee7i  jjlanta  and 
animals.  It  might  at  the  outset  of  our  inquiry  have  seemed  an  unnec- 
essary thing  to  recount  the  distinctions  which  exist  between  an  animal 
and  a  vegetable  as  they  are  in  many  cases  so  obvious,  but,  however  great 
the  differences  may  be  between  the  higher  animals  and  plants,  in  the 
lowest  of  them  the  distinctions  are  much  less  plain. 

In  the  first  j^lace,  it  is  important  to  lay  stress  upon  the  differences 
between  vegetable  and  animal  cells,  first  as  regards  their  structure  and 
next  as  regards  their  functions. 

(].)  It  has  been  already  mentioned  that  in  animal  cells  an  envelope 
or  cell-wall  is  by  no  means  always  present.  In  adult  vegetable  cells,  on 
the  other  hand,  a  well-defined  cellulose  wall  is  highly  characteristic; 
this,  it  should  be  remembered,  is  non-nitrogenous,  and  thus  differs 
chemically  as  well  as  structurally  from  the  contained  protoplasmic 
mass. 

]\Ioreover,  in  vegetable  cells  (hg.  17,  b),  the  jirotoplasmic  contents 
of  the  cell  fall  into  two  subdivisions:  (1)  a  continuous  film  which  lines 
the  interior  of  the  cellulose  Avail;  aud    (2)   a  reticulate  mass  contain- 


18 


HANDBOOK    OF    PHYSIOLOGY, 


ing  the  nucleus  and  occupying  the  cell  cavity;  its  interstices  are  filled 
with  fluid.  In  young  vegetable  cells  such  a  distinction  does  not 
exist;  a  finely  granular  protojDlasm  occupies  the  whole  cell-cavity 
(fig.  17,  A). 

Another  striking  difference  is  the  frequent  presence  of  a  large  quan- 
tity of  intercellular  substance  in  animal  tissues,  while  in  vegetables  it  is 
comparatively  rare,  the  requisite  consistency  being  given  to  their  tissues 
by  the  tough  cellulose  walls,  often  thickened  by  deposits  of  lignin. 
As  an  example  of  the  manner  in  which  this  end  is  attained  in  animal 
tissues,  may  be  mentioned  the  deposition  of  lime  salts  in  a  matrix  of 
intercellular  substance  which  occurs  in  the  formation  of  bone. 

(2.)  As  regards  the  respective  functions  of  animal  and  vegetable  cells, 
one  of  the- most  important  differences  consists  in  the  power  which  vege- 
table cells  possess  of  being  able  to  build  up  new  complicated  nitrogenous 


Fig.  17.— (a.)  Young  vegetable  cells,  showing  cell-cavity  entirely  filled  tvith  granular  protoplasm 
inclosing  a  large  oval  nucleus,  with  one  or  more  nucleoli,  (b.)  Older  cells  from  same  plant,  show- 
ing distinct  cellulose-wall  and  vacuolation  of  protoplasm. 

and  lion -nitrogenous  bodies  out  of  very  simple  chemical  substances  ob- 
tained from  the  air  and  from  the  soil.  They  obtain  from  the  air,  oxy- 
geUj  carbonic  anhydride,  and  water,  as  well  as  traces  of  ammonia  gas; 
and  from  the  soil  they  obtain  water,  ammonium  salts,  nitrates,  sulphates^, 
and  phosphates,  and  such  bases  as  potassium,  calcium,  magnesium,  so- 
dium, iron,  and  others.  The  majority  of  plants  are  able  to  work  up 
these  elementary  compounds  into  other  and  more  complicated  bodies. 
This  they  are  able  to  do  in  consequence  of  their  containing  a  certain 
coloring  matter  called  cMorojjliyll,  the  presence  of  which  is  the  cause  of 
the  green  hue  of  plants.  In  all  plants  which  contain  chlorophyll  two 
processes  are  constantly  going  on  when  they  are  exposed  to  light :  one, 
which  is  called  true  respiration  and  is  a  process  common  to  animal  and 
vegetable  cells  alike,  consists  in  the  taking  of  the  oxygen  from  the  at- 
mosphere and  the  giving  out  of  carbon  dioxide;  the  other,  which  is 
peculiar  apparently  to  bodies  containing  chlorophyll,  consists  in  the 
taking  in  of  carbon  dioxide  and  the  giving  out  of  oxygen.  It  seems  that 
the  chlorophyll  is  capable  of  decomposing  the  carbon  dioxide  gas  and 
of  fixing  the  carbon  in  the  structures  in  the  form  of  some  new  com- 


THE    PHENOMENA    OF    LIFE,  111 

pound,  one  of  the  most  rapidly  formed  of  which  is  starrJi.  'J'lie  tiri^t 
step  in  the  formation  of  starch  is  the  union  of  carbon  dioxide  and  water 
to  form  formic  aldehyde,  COaH-H20  =  CH20  +  02,  oxygen  being  evolved; 
then  by  polymerization  the  formation  of  sugar  thus,  G  CIl20  =  C6Hi206; 
and  by  dehydration,  CbHi^Oo— H20  =  C6Hio05,  the  production  of  starch. 
In  this  way  is  starch  synthesized  or  built  up.  Vegetable  protoplasm  by 
the  aid  of  its  chlorophyll  is  able  to  build  up  a  large  number  of  bodies 
besides  starch,  the  most  interesting  and  important  being  proteid  or 
albumin.  It  appears  to  be  a  fact  that  the  power  which  bodies  possess 
of  being  able  to  synthesize  is  to  a  large  extent  dependent  upon  the  chlo- 
rophyll they  contain.  Thus  the  j)0wer  is  only  present  to  any  marked 
extent  in  the  plants  in  which  chlorophyll  isfoiind  and  is  absent  in  those 
which  do  not  possess  it;  while  on  the  other  hand  it  is  present  in  the 
extremely  few  aninuils  which  contain  it  and  is  absent  except  in  certain 
rare  instances  as  one  of  the  properties  of  animal  protoplasm. 

It  must  be  recollected,  however,  that  chlorophyll  without  the  aid  of 
the  light  of  the  sun  can  do  nothing  in  the  way  of  building  up  substances, 
and  a  plant  containing  chloroph3dl  when  placed  in  the  dark,  as  long  as 
it  lives,  and  that  is  not  as  a  rule  long,  acts  as  though  it  did  not  contain 
any  of  that  substance.  It  is  an  interesting  fact  that  certain  of  the  bac- 
teria have  the  chlorophyll  rejjlaced  by  a  similar  pigment  which  is  able 
to  decompose  carbon  dioxide  gas. 

Animal  cells,  except  in  the  very  rare  cases  above  alluded  to,  do  not 
possess  the  power  of  building  up  from  simple  materials;  their  activity 
is  chiefly  exercised  in  the  opposite  direction,  viz.,  they  have  brought  to 
them  as  food  the  complicated  compounds  produced  by  the  vegetable 
kingdom,  and  with  them  they  are  able  to  perform  their  functions,  set- 
ting free  energy  in  the  direction  of  heat,  motion,  and  electricity,  and  at 
the  same  time  eliminating  such  bodies  as  carbon  dioxide  and  water,  and 
producing  other  bodies,  many  of  which  contain  nitrogen,  but  which  are 
derived  from  decomposition,  and  only  in  very  rare  cases  from  building 
up. 

It  must  be  distinctly  understood,  however,  that  there  are  instances 
of  animal  cells  performing  synthetic  functions  and  of  combining  two 
simpler  compounds  to  produce  one  more  complex,  and  it  is  quite  possi- 
ble that  many  of  the  processes  performed  by  the  cells  of  certain  organs 
are  instances  of  synthesis,  and  not  as  they  have  been  described  of  break- 
ing down;  and  the  reverse  is  undoubtedly  the  case  with  vegetable  cells, 
so  that  it  is  impossible  to  generalize  to  a  greater  extent  than  to  say  that 
the  tendency  of  the  activity  of  the  vegetable  cell  is  chiefly  toward  syn- 
thesis, and  of  the  animal  cell  toward  analysis. 

With  reference  to  the  substance  chlorophyll  it  is  necessary  to  say  a 
few  words.     It  has  been  noted  that  the  synthetical  operations  of  vege- 


20  HANDBOOK    OF    PHYSIOLOGY. 

table  cells  are  peculiarly  associated  with  the  possession  of  chlorophyll 
and  that  these  operations  are  dependent  npon  the  light  of  the  sun.  It 
has  been  further  shown  that  a  solution  of  chlorophyll  has  a  definite 
absorption  spectrum  when  examined  with  the  spectroscope,  and  that  it 
is  particularly  those  parts  of  the  solar  spectrum  corresponding  to  these 
absorption  bands  which  are  chiefly  active  in  the  decomposition  of  car- 
bonic anhydride,  and  that,  moreover,  the  position  of  the  maximum  absorp- 
tion corresponds  with  the  maximum  of  energy  of  light.  In  the  synthet- 
ical processes  of  the  plant  then,  by  aid  of  its  chlorophyll,  the  radiant 
energy  of  the  sun's  rays  becomes  stored  up  or  rendered  potential  in  the 
products  formed.  The  potential  energy  is  set  free,  or  is  again  made 
kinetic,  when  these  products  simply  by  combustion  produce  heat,  or 
when  they  are  taken  into  the  animal  organism  and  used  as  food  and  to 
produce  heat  and  motion. 

The  influence  of  light  is  not  an  absolute  essential  to  animal  life;  in- 
deed, it  is  said  not  to  increase  the  metabolism  of  animal  tissue  to  any 
extent,  and  the  animal  cell  does  not  receive  its  energy  directly  from  the 
sun's  light,  nor  yet  to  any  extent  from  the  sun's  heat,  but  from  the 
products  formed  by  vegetable  metabolism  supplied  as  food,  either  di- 
rectly, as  in  the  case  of  herbivora,  or  indirectly  in  the  case  of  carnivora.. 
The  potential  energy  of  these  food  stufEs  is  set  free  in  the  destructive 
metabolism  of  the  animal  cell  already  alluded  to.  But  it  must  be  always 
recollected  that  anabolism  is  not  peculiar  to  vegetable,  or  katabolism  to 
animal  cells ;  both  processes  go  on  in  each,  but  the  cliief  function,  as 
far  as  we  know  at  present  of  the  former,  is  to  transform  kinetic  into  po- 
tential energy,  and  of  the  latter  to  render  potential  energy  kinetic,  as 
in  heat,  motion,  and  electricity. 

With  reference  to  the  food  of  plants,  it  should  not  be  forgotten  that 
some  of  the  lowest  forms  of  vegetable  life,  e.g.,  the  bacteria,  will  live 
only  in  a  highly  albuminous  medium,  and  in  fact  seem  to  require  for 
their  growth  elements  of  food  stuffs  which  we  shall  see  later  on  are  es- 
seutial  to  animal  life.  In  their  metabolism,  too,  they  very  closely  ap- 
proximate to  animal  cells,  not  only  requiring  an  atmosphere  of  oxygen, 
but  giving  out  carbonic  anhydride  freely,  and  secreting  and  excreting 
many  very  complicated  nitrogenous  bodies,  as  well  as  forming  proteid, 
carbohydrates,  and  fat,  requiring  heat  but  not  light  for  the  due  perform- 
ance of  their  functions.  It  must  be  added,  however,  that  certain  bac- 
teria grow  only  in  the  absence  of  oxygen. 

(3.)  There  is,  commonly,  a  difference  in  general  chemical  composition 
between  vegetables  and  animals,  even  in  their  lowest  forms;  for  associated 
with  the  protoplasm  of  the  former  is  a  considerable  amount  of  cellulose, 
a  substance  closely  allied  to  starch  and  containing  carbon,  hydrogen,  and 
oxygen  only.     The  presence  of  cellulose  in  animals  is  much  more  rare 


THE    PHENOMKNA    OF    JJFE.  21 

than  in  vegetables,  but  there  are  many  aninials  in  wliich  traces  of  it  may 
be  discovered,  and  some,  the  Ascidians,  in  which  it  is  found  in  consider- 
able quantity.  The  presence  of  starch  in  vegetable  cells  is  very  charac- 
teristic, though,  as  we  have  seen  above,  it  is  not  distinctive,  and  a  sub- 
stance, glycogen,  similar  in  composition  to  starch,  is  very  common  in  the 
organs  and  tissues  of  animals. 

(4.)  Inherent  power  of  movement  is  a  quality  which  we  so  commonly 
consider  an  essential  indication  of  animal  nature,  that  it  is  difficult  at 
first  to  conceive  it  existing  in  any  other.  The  capability  of  simj^le  mo- 
tion is  now  known,  however,  to  exist  in  so  many  vegetable  forms,  that 
it  can  no  longer  be  held  as  an  essential  distinction  between  them  and 
animals,  and  ceases  to  bo  a  mark  by  which  the  one  can  be  distinguished 
from  the  other.  Thus  the  zoospores  of  many  of  the  Cryptogamia  ex- 
hibit ciliary  or  amoeboid  movements  of  a  like  kind  to  those  seen  in 
amoebae;  and  even  among  the  higher  orders  of  plants,  many, e.^., i)io?ifea 
Muscijnda  (Venus's  fly-trai)),and  Mimosa  sensitlva  (Sensitive  plant),  ex- 
hibit such  motion,  either  at  regular  times,  or  on  the  application  of 
external  irritation,  as  might  lead  one,  were  this  fact  taken  by  itself,  to 
regard  them  as  sentient  beings.  Inherent  poAver  of  movement,  then, 
although  especially  characteristic  of  animal  nature,  is,  when  taken  by 
itself,  no  proof  of  it. 


CHAPTER   II. 

THE  FUNCTIONS  OF  ORGANIZED   CELLS. 

As  we  proceed  upward  in  the  scale  of  life  from  unicellular  orgauisms, 
we  find  that  another  phenomenon  is  exhibited  in  the  life  history  of  the 
higher  forms,  namely,  that  of  Develojjment.  An  amoeba  comes  into  be- 
ing derived  from  a  previous  amoeba;  it  manifests  the  properties  a,nd 
performs  the  functions  of  its  life  which  have  been  already  enumerated; 
it  grows,  it  reproduces  itself,  whereby  several  amoebae  result  in  place  of 
one,  and  it  dies.  It  cannot  be  said  to  develop,  however,  unless  the  for- 
mation of  a  nucleus  can  be  considered  as  an  indication  of  such  a  process. 
In  the  higher  organisms  it  is  different;  they,  indeed,  begin  as  a  single 
cell,  but  this  cell  on  division  and  subdivision  does  not  form  so  many 


Fi^.  18.— Transverse  section  through  embryo  chick  (26  hours),  a,  Epiblast;  6,  mesoblast;  c, 
hypoblast;  d,  central  portion  of  mesoblast,  which  is  here  fused  with  epiblast;  e,  primitive  groove; 
/,  dorsal  ridge.    (Klein.) 

independent  organisms,  but  produces  the  material  from  which,  by  devel- 
opment, the  complete  and  perfect  whole  is  to  be  derived.  Thus,  from 
the  spherical  ovum,  or  germ,  which  forms  the  starting-point  of  animal 
life  and  which  consists  of  a  protoplasmic  cell  with  a  nucleus  and  nucle- 
olus, in  a  comparatively  short  time,  by  the  process  of  segmentation  which 
has  been  already  mentioned,  a  complete  membrane  of  cells,  polyhedral 
in  shape  from  mutual  pressure,  called  the  Blastoderm,  is  formed,  and 
this  speedily  divides  into  two  and  then  into  three  layers,  chiefly  from 
the  rapid  proliferation  of  the  cells  of  the  first  single  layer.  These  layers 
are  called  the  Epiblast,  the  Mesoblast,  and  the  Hypoblast  (fig.  18). 
It  is  found  in  the  further  development  of  the  animal  that  from  each 
of  these  layers  is  produced  a  very  definite  part  of  its  completed  body. 
For  example,  from  the  cells  of  the  epiblast  are  derived,  among  other 

22 


THE    FUNCTIONS    OF    ORGANIZED    CELLS.  23 

structures,  the  skin  and  the  central  nervous  system;  from  themesoblast 
is  derived  the  flesh  or  muscles  of  the  body,  and  from  the  h3'iDoblast  the 
epithelium  of  the  alimentary  canal  and  some  of  the  chief  glands,  and  so  on. 

It  is  obvious  that  the  tissues  and  organs  so  derived  exhibit  in  a  vary- 
ing degree  the  primary  properties  of  protoplasm.  The  muscles,  for 
example,  derived  from  certain  cells  of  the  mesoblast  are  particularly  con- 
tractile and  respond  to  stimuli  readily,  while  the  cells  of  the  liver, 
although  possibly  contractile  to  a  certain  extent,  have  to  do  chiefly  with 
the  processes  of  nutrition. 

Thus,  in  development,  we  see  that  as  the  cells  of  the  embryo  in- 
crease in  number  it  speedily  becomes  necessary  for  the  organism  to 
depute  to  different  groups  of  cells,  or  to  their  equivalents  {i.e.,  to  the 
tissues  or  organs  to  which  they  give  rise),  special  functions,  so  that  the 
various  functions  which  the  original  cell  may  be  supposed  to  discharge, 
and  the  various  properties  it  may  be  supposed  to  possess,  become  divided 
up  among  various  groups  of  resulting  cells.  The  work  of  each  grouj) 
is  specialized.  As  a  result  of  this  division  of  labor,  as  it  may  be  called, 
these  functions  and  properties  are,  as  might  be  expected,  developed  and 
made  more  perfect,  while  the  tissues  and  organs  arising  from  each 
group  of  cells  are  developed  also,  with  a  view  to  the  more  convenient 
and  effective  exercise  of  their  functions  and  employment  of  their  prop- 
erties. 

In  studying  the  functions  of  the  human  body  it  is  necessary  flrst  of 
all  to  know  of  what  it  is  composed,  of  what  tissues  and  organs  it  is  made 
up;  this  can  of  course  only  be  ascertained  by  the  dissection  of  the  dead 
body,  and  thus  it  comes  that  Anatomy  {ijyariijyw,  to  cut  up)  the  science 
which  treats  of  the  structure  of  organized  bodies,  is  closely  associated 
with  physiology;  so  closely,  indeed,  that  Histology  {1<t-uz.,  a  web),  which 
is  especially  concerned  with  the  minute  or  microscopic  structure  of  the 
tissues  and  organs  of  the  body,  and  which  is  strictly  speaking  a  depart- 
ment of  anatomy,  is  usually  included  in  Avorks  on  physiology.  There  is 
much  to  be  said  in  favor  of  such  an  arrangement,  since  it  is  impossible 
to  consider  the  changes  which  take  place  in  any  tissue  during  life, 
apart  from  the  knowledge  of  the  structure  of  the  tissues  themselves. 
To  understand  the  structure  of  the  human  body  in  an  intelligent  way, 
much  help  is  obtained  from  the  study  of  the  structure  of  other  animals, 
from  the  lowest  to  the  highest,  which  is  the  province  of  Comparative 
Anatomy  ;  wliile  Embryology,  which  is  concerned  with  the  mode  of 
origin  of  the  various  tissues  in  the  embryo  of  each  animal,  and  which  is 
usually  studied  at  the  end  of  physiology,  should  from  some  points  of 
view  be  considered  as  an  introduction  to  the  subject. 

A  second  important  essential  to  the  right  comprehension  of  the 
changes  which  take  place  in  the  living  organism  is  a  knowledge  of  the 
chemical  composition  of  the  body.     Here,  however,  we  can  only  deal 


24:  HANDBOOK    OF   PHYSIOLOOT. 

with  the  chemical  comjiosition  of  tlie  dead  body,  and  it  is  as  well  at 
once  to  admit  that  there  may  be  many  chemical  differences  between 
living  and  not  living  tissnes;  but  as  it  is  impossible  to  ascertain  the 
exact  chemical  composition  of  the  living  tissues,  the  next  best  thing 
which  can  be  done  is  to  find  out  as  mi^ch  as  possible  about  tbe  com- 
position of  the  same  tissues  after  they  are  dead.  This  is  the  assistance 
which  the  science  of  Chemistry  can  afford  to  the  physiologist,  and  the 
same  science  is  concerned  with  the  composition  of  the  ingesta  and  egesta, 
as  well  as  with  that  of  the  fluids  of  the  body. 

Having  mastered  the  structure  and  composition  of  the  body,  we  are 
brought  face  to  face  with  physiology  proper,  and  have  to  investigate  the 
vital  changes  which  go  on  in  the  tissues,  the  various  actions  taking  place 
as  long  as  the  organism  is  at  work.  The  subject  includes  not  only  the 
observation  of  the  manifest  processes  which  are  continually  taking- 
place  in  the  healthy  body,  but  the  conditions  under  which  these  are 
brought  about,  the  laws  which  govern  them  and  their  effects. 

We  know  from  our  study  of  biology  that  the  cells  of  which  the  tis- 
sues are  composed  cannot  live  without  food,  both  solid  and  liquid.  In 
a  complicated  organism  like  the  body  of  man,  the  tissues  cannot  supply 
themselves  with  food  directly  like  the  amoeba,  and  so  it  comes  that  the 
various  tissues  are  furnished  Avitli  what  they  require  by  means  of  a 
fluid,  the  blood,  which  is  carried  to  them  in  tubes  or  canals,  the  blood- 
vessels, which  are  distributed  to  every  region  of  the  body.  In  order  that 
the  blood  shall  reach  all  parts,  the  system  of  vessels  in  which  it  is  con- 
tained is  suj^plied  with  a  central  pumping  organ,  the  Jtearf.  Then  we 
find  that  as  the  ox3^gen,  Avhich  is  one  of  the  requisites  of  the  life  of  the 
tissues,  and  which  is  carried  to  the  tissues  by  the  blood,  is  used  up,  a 
special  means  is  provided  by  resjnratio)),  or  breathing,  by  means  of 
which  the  blood  is  exposed  to  a  new  supply  of  oxygen  of  the  air,  which 
is  taken  into  special  organs,  the  lungs,  for  the  purpose,  and  which  at 
the  same  time  allows  of  the  elimination  of  the  carboiiic  anhydride  the 
blood  conveys  from  the  tissues.  Then  again,  as  the  solid  food  for  the 
tissues  cannot  be  conveyed  in  the  blood  in  the  exact  form  in  which  it  is 
introduced  into  the  body,  a  special  and  complicated  apparatus  is  pro- 
vided, that  of  digestion,  by  means  of  which  the  necessary  changes  are 
brought  about  in  the  food.  The  digested  food  is  then  absorbed  and 
carried  to  the  blood,  either  directly  with  little  further  change  by  means 
of  another  system  of  vessels  in  connection  with  the  blood-vessels,  the 
lympludic  vessels,  or  after  passing  through  a  special  organ  or  gland,  the 
liver,  by  means  of  which  some  further  changes  take  place.  In  the 
digestive  apparatus  we  have  the  organs,  the  stomach  and  intestines,  into 
which  the  food  is  received  for  the  purpose  of  being  acted  upon  by  cer- 
tain chemical  agents,  of  which  ferments,  bodies  which  are  capable  of 
setting  up  profound  changes  in  other  bodies  without  themselves  under- 


TllK    ITNCTTONS    OK    OKUAXTZEl)    CELLS.  35 

ffoing  change,  are  the  most  important;  there  is  added  tlic  apparatus  by 
means  of  which  the  altered  food  staffs  are  absorbed  or  reach  the  two 
systems  of  blood-vessels  already  mentioned,  and  a  muscular  apparatus 
contained  in  the  walls  of  the  intestinal  tube  by  means  of  which  that 
part  of  the  food  which  is  not  fit  for  absorption  is  removed  from  the 
body.  In  addition  to  this  excretory  apparatus  we  have  another,  the 
kidneys,  which  are  concerned  with  the  removal  of  certain  substances 
from  the  blood  which  have  served  their  purpose  in  the  economy. 

Then  we  have  the  muscular  system,  which  by  its  special  power  of 
contraction  is  capable  of  bringing  about  all  the  movements  of_  the  body 
— those  of  the  frame,  the  head,  arms,  legs,  etc.,  as  well  as  those  of  the 
lieart,  the  vessels,  the  alimentary  canal,  and  the  like.  The  nervous  sys- 
tem, by  the  aid  of  which  the  processes  of  the  living  body  may  be  regu- 
lated and  controlled.  Lastly,  we  have  a  special  system— that  of  the 
generative  system,  by  means  of  which  the  reproduction  of  the  species 
may  take  place. 

To  these  subjects,  the  merest  outline  of  which  has  been  here 
sketched,  our  attention  has  to  be  given  in  the  succeeding  chapters,  but 
it  may  be  well  to  mention  as  a  preliminary  that  the  information  about 
them  which  we  have  at  our  disi)osal  has  been  derived  from  many  sources, 
the  chief  of  which  are  as  follows : — 

(1.)  From  actual  observation  of  the  various  phenomena  occurring  in 
the  human  body  from  day  to  day,  and  from  hour  to  hour,  as,  for  exam- 
ple, the  estimation  of  the  amount  and  composition  of  the  ingesta  and 
egesta,  the  respiration,  the  beat  of  the  heart,  and  the  like; 

(2.)  From  observations  upon  other  animals,  the  bodies  of  which  we 
are  taught  by  comparative  anatomy  approximate  to  tlu^  human  body 
in  structure; 

(3.)  From  observations  of  the  changes  produced  by  experiment  upon 
the  various  processes  in  such  animals; 

(4.)  From  observations  of  the  changes  in  tlie  working  of  the  liuman 
body  produced  by  disease ; 

(5.)  From  observations  upon  the  gradual  changes  which  take  })lace 
in  the  functions  of  organs  when  watched  in  the  embryo  from  their 
earliest  beginnings  to  tlieir  comi)leted  development. 

In  accordance  with  the  plan  sketched  out  above,  the  next  chapter 
will  be  devoted  to  a  consideration  of  the  minute  structure  of  the  ele- 
mentary tissues,  and  the  one  after  that  to  a  preliminary  account  of  the 
chemical  composition  of  the  body.  These  two  chapters  will  serve  as  an 
introduction  to  the  study  of  the  problems  of  physiology  proper,  which 
will  be  commenced  in  Chapter  V. 


CHAPTER   III. 

THE   STRUCTURE   OF  THE  ELEMENTARY  TISSUES. 

The  careful  examination  of  the  minute  anatomy  of  the  body  has 
shown  that  there  are  certain  elementary  structures,  of  which,  alone  or 
when  combined  in  varying  proportions,  the  whole  of  the  organs  and 
tissues  of  the  body  are  made  up.  These  Elementary  Tissues  are  four 
in  number,  called:  (1.)  The  Epithelial;  (2.)  Tlie  Connective;  (3.)  The 
Muscular,  Skud  (4.)  The  Nervous.  To  these  four,  some  would  add  a  fifth, 
looking  upon  the  Blood  and  Lymph,  containing,  as  they  do,  formed 
elements  in  a  fluid  menstruum,  as  a  distinct  tissue. 

All  of  these  elementary  tissues  consist  of  cells  and  of  their  altered 
equivalents.  It  will  be  as  well  therefore  to  indicate  some  of  the  differ- 
ences between  the  cells  of  the  body.  They  are  named  in  various  ways, 
according  to  their  shape,  situation,  contents,  origin,  and  functions. 

{a.)  From  their  shape,  cells  are  called  spherical  or  spheroidal,  which 
is  the  typical  shape  of  the  free  cell;  this  maybe  altered  to  polyhedral 
when  the  pressure  on  the  cells  in  all  directions  is  nearly  the  same;  of 
this  the  primitive  segmentation  cells  afford  an  example.  The  discoid 
form  is  seen  in  blood-corpuscles,  and  the  scale-Wee  form  in  superficial 
epithelial  cells.  Some  cells  have  a  jagged  outline  and  are  then  called 
prichle  cells.  Cells  of  cylindrical,  conical,  or  p)rismatic  form  occur  in 
various  places  in  the  body.  Such  cells  may  taper  off  at  one  or  both 
ends  into  fine  processes,  in  the  former  case  being  caudate,  in  the  latter 
fusiform.  They  may  be  greatly  elongated  so  as  to  become  fibres.  Cells 
with  hair-like  processes,  or  cilia,  projecting  from  their  free  surfaces,  are 
a  special  variety.  The  cilia  vary  greatly  in  size,  and  may  even  exceed 
in  length  the  cell  itself.  Finally,  cells  may  be  branched  or  stellate  with 
long  outstanding  processes. 

(J.)  From  their  situation  cells  may  be  called /ree,  as  in  the  blood, 
or  combined,  when  connected  together  or  with  other  elements  to  form 
organs  and  tissues. 

(c.)  From  their  contents  cells  are  called,  when  containing  fat  for 
example, /a^  cells  ;  when  containing  Tpigment,  pigment  cells,  etc. 

(d.)  From  their  function  cells  are  called  secreting,  protective,  sensi- 
tive, contractile,  and  the  like. 

(e.)  From  their  origin  cells  are  called  epiblastic  and  mesoblastic  and 
hypoUastic. 

26 


THE    STKUCtURE    OF   THE    ELEMENTARY   TISSUES.  »» 

Modes  of  Connection. — Cells  are  conuected  together  to  form 
tissues  in  various  ways. 

(1.)  By  mean  of  a  cementing  intercellular  substance.  This  is  prob- 
ably always  present  as  a  transparent,  colorless,  viscid,  albuminous  sub- 
stance, even  between  the  closely  apposed  cells  of  epithelium,  while  in 
the  case  of  cartilage  it  forms  the  main  bulk  of  the  tissue,  and  the  cells 
only  appear  as  imbedded  in,  not  as  cemented  together  by,  the  intercel- 
lular substance.  This  intercellular  substance  may  be  either  homogene- 
ous or  fibrillated.  In  many  cases  {e.g.,  the  cornea)  it  can  be  shown  to 
contain  a  number  of  irregular  branched  cavities,  Avhich  communicate 
with  each  other,  and  in  which  branched  cells  lie:  through  these  branch- 
ing spaces  nutritive  fluids  can  find  their  way  into  the  very  remotest 
parts  of  a  non-vascular  tissue. 

As  a  special  variety  of  intercellular  substance  must  be  mentioned  the 
basement  membrane  {meinbrana  propria)  which  is  found  at  the  base  of 
the  epithelial  cells  in  most  mucous  membranes,  and  especially  as  an 
investing  tunic  of  gland  follicles  whicli  determines  their  shape,  and 
which  may  persist  as  a  hyaline  saccule  after  the  gland  cells  have  all 
been  discharged. 

(2.)  By  anastomosis  of  their  processes.  This  is  the  usual  Avay  in 
which  stellate  cells,  e.g.  of  the  cornea,  are  united :  the  individuality  of 
each  cell  is  thus  to  a  great  extent  lost  by  its  connection  with  its  neigh- 
bors to  form  a  reticulum  :  as  an  example  of  a  network  so  produced  we 
may  cite  the  stroma  of  lymphatic  glands. 

Sometimes  the  branched  processes  breaking  up  into  a  maze  of 
minute  fibrils,  adjoining  cells  are  connected  by  an  intermediate  reticu- 
lum :  this  is  the  case  in  the  nerve  cells  of  the  sjDinal  cord. 

Derived  Tissue-elements. — Besides  the  Cell,  which  may  be  termed 
the  primary  tissue-element,  there  are  materials  which  may  be  termed 
secondary  or  derived  tissue-elements.  Such  are  Intercellular  substance. 
Fibres,  and  Tubules. 

a.  Intercellulnr  substance  is  jjrobably  in  all  cases  directly  derived 
from  the  cells  themselves.  In  some  cases  {e.g.  cartilage),  by  the  use  of 
reagents  the  cementing  intercellular  substance  is,  as  it  were,  analyzed 
into  various  masses,  each  arranged  in  concentric  layers  around  a  cell  or 
group  of  cells,  from  which  it  was  probably  derived. 

/5.  Fibres.  In  the  case  of  the  crystalline  lens,  and  of  muscle  both 
striated  and  non-striated,  each  fibre  is  simply  a  metamorphosed  cell:  in 
the  case  of  a  striped  fibre,  the  elongation  being  accompanied  by  a  mul- 
tiplication of  the  nuclei.  The  various  fibres  and  fibrillae  of  connective 
tissue  result  from  a  gradual  transformation  of  an  originally  homogene- 
ous intercellular  substance.  Fibres  thus  formed  may  undergo  great 
chemical  as  well  as  physical  transformation :  this  is  notably  the  case 
with  yellow  elastic  tissue,  in  which   the  sliarply  defined  elastic  fibres, 


28  HANDBOOK    OF    PHYSIOLOGY. 

possessing  great  power  of  resistance  to  reagents,  contrast  strikingly 
with  the  homogeneous  matter  from  which  they  are  derived. 

y.  TuhuJes,  sucli  as  the  capillary  hlood-vessels,  which  were  originally 
supposed  to  consist  of  a  structureless  membrane,  have  now  been  proved 
to  be  composed  of  flat,  thin  cells,  cohering  along  their  edges. 

Decay  and  Death  of  Cells. — There  are  two  6'AtV/waysin  which  the 
comparatively  brief  existence  of  cells  is  brought  to  an  end,  (1)  Mechan- 
ical abrasion,  (2)  Chemical  transformation. 

1,  The  various  epithelia  furnish  abundant  examples  of  mechanical 
abrasion.  As  it  approaches  the  free  surface,  the  cell  becomes  more  and 
more  flattened  and  scaly  in  form  and  more  horny  in  consistency,  till  at 
length  it  is  simjjly  rubbed  off  as  in  the  epidermis.  Hence  we  find  epi- 
thelial cells  in  the  mucus  of  the  mouth,  intestine,  and  genito-urinary 
tract. 

2.  In  the  case  of  chemical  transformation  the  cell-contents  undergo 
a  degeneration  which,  though  it  may  be  pathological,  is  very  often  a 
normal  process. 

Thus  we  have  (a)  fatty  metamorphosis  producing  oil-globules  in  the 
secretion  of  milk,  fatty  degeneration  of  the  muscular  fibres  of  the  uterus 
after  the  birth  of  the  fcetus,  and  of  the  cells  of  the  Graafian  follicle 
giving  rise  to  the  "  corpus  luteum."  (b)  Pigmentary  degeneration  from 
deposit  of  pigment,  e.g.  in  the  ejDithelium  of  the  air  vesicles  of  the  lungs, 
(c)  Calcareous  degeneration,  which  is  common  in  the  cells  of  many 
cartilages. 

I.  The  Epithelial  Tissues. 

The  term  epithelium  is  applied  to  the  cells  covering  the  skin,  the 
mucous  and  serous  membranes,  and  to  those  forming  a  lining  to  other 
parts  of  the  body  as  well  as  entering  into  the  formation  of  glands.  For 
example : — 

Epithelium  clothes  (1)  the  whole  exterior  surface  of  the  body,  form- 
ing the  epidermis  with  its  ajjjDendages— nails  and  hairs;  becoming  con- 
tinuous at  the  chief  orifices  of  the  body — nose,  mouth,  anus,  and  urethra 
— with  the  (2)  ejjithelium  which  lines  the  Avhole  length  of  the  (3)  respi- 
ratory, alimentary,  and  genito-urinary  tracts,  together  with  the  ducts  of 
their  various  glands.  Epithelium  also  lines  the  cavities  of  (4)  the  brain 
and  the  central  canal  of  the  spinal  cord,  (5)  the  serous  and  synovial 
membranes,  and  (6)  the  interior  of  all  blood-vessels  and  lymphatics. 

Epithelial  cells  possess  an  intracellular  and  an  intranuclear  network 
(p.  9  and  10).  When  combined  together  to  form  a  tissue,  they  are  held 
together  by  a  clear,  albuminous,  cement-substance,  scanty  in  amount. 
The  viscid  semi-fluid  consistency  both  of  cells  and  intercellular  sub- 
stance permits  such  changes  of  sliape  and  arrangement  in  the  individual 


THE    STKUCTUKE    OF   TUB    ELEMENTARY    TISSUES.  20 

cells  as  are  necessary  if  the  epithelium  is  to  maintain  its  integrity  in 
organs  tlie  area  of  whose  free  surface  is  so  constantly  changing,  as  the 
stomach,  lungs,  etc.  Thus,  if  there  be  but  a  single  layer  of  cells,  as  in 
the  epithelium  lining  the  air  vesicles  of  the  lungs,  the  stretching  of  this 
membrane  causes  such  a  thinning  out  of  the  cells  that  they  change 
their  shape  from  siiheroidal  or  short  columnar,  to  squamous,  and  vice 
verm,  when  the  membrane  shrinks. 

Epithelial  tissues  are  non-vasculur,  ihat  is  tu  say,  do  not  contain 
blood-vessels,  but  in  some  varieties  minute  channels  exist  between  the 
cells  of  certain  layers  through  which  they  may  be  su2)plied  witli  nour- 
ishment from  the  subjacent  blood-vessels.  jS'crve  fibres  are  sujiplied  to 
the  cells  of  many  epithelia. 

Epithelial  tissue  is  classified  according  as  the  cells  composing  it  are 
arranged  in  a  single  layer  when  it  is  .simjile,  or  in  several  layers  when  it 
is  called  stratified  or  Jamiitdted,  or  in  two  or  three  layers  occupying  a 
position  between  the  other  two  forms,  wlien.  it  is  termed  trcoisitiinifil. 
Of  each  form,  when  there  are  several  varieties,  they  are  named  accord- 
ing to  the  shape  of  the  cells  composing  it. 

Classification  of  Epithelium, 

(a)  Simple.— (I.)  Squamous,  scnily,  pavement,  or  tessellated;  (3.) 
Spheroidal  or  glandular:  (15.)  Columnar,  cyliudi-ical,  conical  or  goblet- 
shaped;  (4.)   Ciliated. 

(b)  Transitional. 

(c)  Stratified. 

(a)  Simple  Epithelium. 

Squamous  Epithelium. — This  form  of  epithelium  is  found  arranged 
as  a  single  layer  of  flattened  cells,  as  {a)  the  pigmentary  layer  of  the 
retina,  and  forms  the  lining  of  (J))  tbe  interior  of  the  serous  and  syno- 
vial sacs,  (c)  the  alveoli  of  the  lungs,  and  [d)  of  the  heart,  blood-  and 
lymph-vessels.  It  consists  of  cells,  which  arc  flattened  and  scaly,  with 
\i  more  or  less  irregular  outline. 

In  the  pigment  cells  of  the  retina  there  is  a  deposit  of  pigment  in 
the  cell-substance.  This  pigment  consists  of  minute  molecules  of  a 
colored  substance,  melanin,  imbedded  in  the  cell-substance  and  almost 
concealing  the  nucleus,  which  is  itself  transparent. 

In  white  rabbits  and  other  albino  animals,  in  which  the  pigment  of 
the  eye  is  absent,  this  layer  is  found  to  consist  of  colorless  pavement 
epithelial  cells. 

The  squamous  ej)ithelinm  which  is  found  as  a  single  layer  lining  the 
serous  membranes,  and  the  interior  of  blood-  and  lymphatic-vessels,  is 
generally  called  bv  a,  distinct  name— Endothelium. 


30 


HANDBOOK    OF    PHYSIOLOGY. 


The  presence  of  endothelium  in  any  locality  may  be  demonstrated  by 
staining  the  part  lined  by  it  with  silver  nitrate,  which  brings  into  view 

the  intercellular  cement  sub- 
stance. 

It  is  found  that  when  a 
small  portion  of  a  perfectly 
fresh  serous  membrane  for 
example  (fig.  20),  is  im- 
mersed for  a  few  minutes  in 
a  solution  of  silver  nitrate, 
and  exposed  to  the  action  of 
light,  the  silver  is  precipi- 
tated in  some  form  iti  the 
intercellular  cement  sub- 
stance, and  the  endothelial 
cells  are  thus  mapped  out 
by  fine,  dark,  and  generally 
sinuous  lines  of  extreme  delicacy.  The  cells  vary  in  size  and  shape,  and 
are  as  a  rule  irregular  in  outline;  those  lining  the  interior  of  blood- 


Fig.  19.— Pigmented  epithelial  cells  from  the  retina. 


Fig.  20. — A  piece  of  the  omentum  of  a  cat,  stained  in  silver  nitrate,  x  100.  The  tissue  forms  a 
"fenestrated  »je?n6?-a7ie,"  that  is  to  say,  one  which  is  studded  with  lioles  or  windows.  In  tlie 
figure  these  are  of  various  shapes  and  sizes,  leaving  trabeculse,  the  basis  of  which  is  fibrous  tissue. 
The  trabeculae  are  of  various  sizes  and  are  covered  with  endothelial  cells,  the  nuclei  of  which  have 
been  made  evident  by  staining  with  hsematoxylin  after  the  silver  nitrate  lias  outlined  the  cells  by 
.staining  the  intercellular  substance.    (V.  D.  Harris.) 


vessels  and  lymphatics  being  spindle-shaped  Avith  a  very  wavy  outline. 
They  inclose  a  clear,  oval  nucleus,  which,  when  the  cell  is  viewed  in 
profile,  is  seen  to  project  from  its  surface.  The  nuclei  are  not  however 
evident  unless  the  tissue  which  has  been  already  stained  in  silver  nitrate. 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


31 


is  placed  in  another  dye,  such  as  haematoxylin,  which  has  the  property 
of  selecting  and  staining  its  nuclei. 

Endothelial  cells  in  certain  situations  may  be  ciliated,  e.g.,  those  of 
the  mesentery  of  the  frog,  especially  during  the  breeding  season. 


Fig.  21. — Abdominal  surface  of  central  tendon  of  the  diaphragm  of  rabbit,  showing  the  general 
polygonal  shape  of  the  endothelial  cells:  each  cell  is  nucleated.     (Klein.)     x  300. 

Besides  the  ordinary  endothelial  cells  above  described,  there  are 
found  on  the  omentum  and  parts  of  the  pleura  of  many  animals,  little 
bud-like  processes  or  nodules,  consisting  of  small  polyhedral  granular 
cells,  rounded  on  their  free  surface,  which  have  multiplied  very  rapidly 
by  division  (figs.  23  and  23).  These  constitute  what  is  known  as  ger- 
minating endotlieJium.  The  process  of  germination  doubtless  goes  on 
in  health,  and  the  small  cells  which  are  thrown  off  in  succession  are 


Fig.  33.— Peritoneal  surface  of  a  portion  of  the  septum  of  tlie  great  lymph-sacs  of  frog.  The 
stomata,  some  of  which  are  open,  some  collapsed,  are  surrounded  by  eridotheUal  cells.  (Xlein.) 
X  160. 

carried  into  the  lymphatics  and  contribute  to  the  number  of  the  lymph 
corpuscles.  The  buds  may  be  enormously  increased  both  in  number 
and  size  in  certain  diseased  conditions. 

On  those  portions  of  the  peritoneum  and  other  serous  membranes  in 
whicli  lymphatics  abound  apertures  (fig.  22)  are  found  surrounded  by 
small,  more  or  less  cubical,  cells.  These  apertures  are  called  stomata. 
They  are  particularly  well  seen  in  the  anterior  wall  of  the  great  lymph 


32 


HANDBOOK    OF    PHYSIOLOGY. 


sac  of  the  frog  (fig.  32),  and  in  the  omentum  of  the  rabbit.     These  are 
really  the  open  mouths  of  lymphatic  vessels  or  spaces,  and  through 


Fig.  -JS.— A  portion  of  the  great  omentum  of  dog,  which  shows,  among  the  flat  endothelium  of 
the  surface,  small  and  large  groups  of  germinating  endothelium  between  which  are  many  stomata. 
(Kleino     x  300.  ^    (-       t-         &  b 

them  lymph-corpuscles  and  the  serous  fluid  from  the  serous  cavity  pass 
into  the  lymphatic  system.  They  should  be  distinguished  from  smaller 
and  more  numerous  apertures  between  the  cells  which  are  not  lined  by 


Fig.  24. 


Fig.  25. 


Fig.  24. — A  small  piece  of  the  liver  nf  the  horse.     (Cadiat. ) 

Fig.  25.— Glandular  epithelium.    Small  lobule  of  a  mucous  glaud  of  the  tongue,  showing  nu- 
cleated glandular  cells.    X  200.    (V.D.Harris.) 

small  cells,  although  the  surrounding  cells  seem  to  radiate  from  them, 
filled  up  by  intercellular  substance  or  by  processes  of  the  cells  under- 
neath.    These  are  called  pseudo-slonuifa  (fig.  23). 


THE    STRUCTURE    OF   THE    ELEMEXTARY   TISSUES. 


33 


In  the  neigliborliood  of  the  stomata  the  cells  olteii  manifest  indica- 
tions of  germinating.  They  may  be  either  large  with  two  or  more 
nuclei,  or  about  half  the  size  of  the  generality  of  cells.  Germinating 
cells  of  this  kind  or  of  the  kind  above  described,  are  generally  very 
granular. 

Spheroidal  or  glandular  epilheliam  forms  the  active  secreting  agent 
in  the  glands,  the  cells  are  usually  spheroidal,  but  may  be  polyhedral 
from  mutual  pressure,  or  even  columnar;  their  protoplasm  is  generally 
occupied  by  the  materials  whicli  the  gland  secretes. 

Examples  of  glandular  epithelium  are  to  be  found  in  the  liver  (fig. 
24),  in  the  secreting  tubes  of  the  kidney,  and  in  the  salivary  (fig.  25) 
and  gastric  glands. 

Columnar  epithelmm  (fig.  28,  a  and  b)  as  a  single  layer  lines  (a.)  the 
mucous   membrane  of  the   stomach  and   intestines,   from  the   cardiac 


d         c 


a       & 


..J 


V 


Fip 


Fig.  3G. — Columnar  cpitlielial  cells  froiii  the  intestinal  mucous  membrane  of  a  cat.    n  and  6, 
Small  cells  of  the  lowest  layer;  c,  suiierlicial  layer;  d,  goblet  cells.     (C'adiat.J 
Fig.  a?.— Goblet  cells.     (Klein.; 

orifice  of  the  stomach  to  the  anus,  and  (1).)  wholly  or  in  part  the  duets 
of  tlie  glands  opening  on  its  free  surface;  also  (c.)  many  gland-ducts  in 
other  regions  of  the  body,  e.g.,  mammary,  salivar}^  etc. 

Columnar  epithelium  consists  of  cells  which  are  cylindrical  or  pris- 
matic in  form  containing 'a  large  oval  nucleus.  They  vary  in  size  and 
also  to  a  certain  extent  in  shape;  the  outline  is  often  jagged  and  irreg- 
ular from  pressure  of  neighboring  cells,  but  one  end  of  the  cell  is  always 
narrower  than  the  other,  and  by  this  :iarrower  end  the  cell  is  as  a  rule 
attached  to  the  membrane  beneath.  The  intracellular  and  intranuclear 
networks  are  well  developed,  and  in  some  cases  the  spongioplasm  is 
arranged  in  rods  or  longitudinal  stria)  at  one  part  of  the  cell,  generally 
the  attached  border,  as  in  some  of  the  cells  of  the  duets  of  salivary 
glands. 

This  may  also  be  the  case  with  the  columnar  epithelial  cells  of  the 
alimentary  canal  which  possess  an  apparently  structureless  layer  on 
their  free  surface:  such  a  layer,  appearing  striated  when  viewed  in  sec- 
tion, is  termed  the  "striated  btisilar  border"  (fig.  28,  a). 

The  protoplasm  of  columnar  cells  may  be  vacuolated  and  may  also 


34 


HANDBOOK    OF    PHYSIOLOGY. 


eoiitaiii  f;it  or  other  substances,  of  which  the  most  likely  is  mucin  or 
its  iiutecedent  mucigen,  to  be  seen  in  the  form  of  granules.  It  is  to  the 
presence  of  mucin  that  a  curious  transformation  which  columnar  cells 
may  undergo  is  due,  and  from  which  the  alteration  in  their  shape 
whereby  "goblet-cells"  are  produced  (fig.  27)  arises.  These  altered  cells 
are  hardly  ever  evident  in  a  perfectly  fresh  specimen;  but  if  such  a 
specimen  be  watched  for  some  time^  little  knobs  are  seen  gradually  to 
appear  on  the  free  surface  of  the  epithelium  and  are  finally  detached; 
these  consist  of  the  cell-contents  which  are  discharged  by  the  open 
mouth  of  the  goblet,  leaving  the  nucleus  surrounded  by  the  remains  of 
the  protoplasm  in  its  narrow  stem. 

This  transformation  is  a  normal  process  which  is  continually  going 
on  during  life,  the  discharged  cell-contents  contributing  to  form  tmtcus, 


Fig  28.— Cross  pectinn  of  a  villus  of  the  inteati'>e.  (\  ColuTimar  epithelium  with  striated 
border;  g.  goblec  cell,  with  its  mucus  partly  ^xrruded:  I,  lyinph-L-orpusoies  between  the  epi- 
thelial cells;  b.  basement  membrane;  e,  sections  of  blood  capillaries;  //i,  section  of  plain  muscle 
fibres;  c.  /,  central  lacteal.     (Schafer.) 


the  cells  themselves  being  supposed  in  many  cases  after  discharge  to 
recover  their  original  shape. 

Ciliated  epithelium  consists  of  cells  which  are  generally  cylindrical 
in  form  (figs.  29,  30),  but  may  be  spheroidal  or  even  almost  squamous. 

This  form  of  epithelium  lines — (a.)  the  mucous  membrane  of  the 
respiratory  tract  beginning  just  beyond  the  nasal  aperture  and  com- 
pletely covering  the  nasal  passages,  except  the  upper  part  to  which  the 
olfactory  nerve  is  distributed,  and  also  the  sinuses  and  ducts  in  connec- 
tion with  it  and  the  lachrymal  sac;  the  upper  surface  of  the  soft  palate 
and  the  naso-pharynx,  the  Eustachian  tube  and  tympanum,  the  larynx, 
except  over  the  vocal  cords,  to  the  finest  subdivisions  of  the  bronchi. 
In  part  of  this  tract,  however,  the  epithelium  is  in  several  layers,  of 
which  only  the  most  superficial  is  ciliated,  so  that  it  should  more  accu- 
rately be  termed  transitional  (p.  37)  or  stratified,  (b.)  Some  portions 
of  the  generative  apparatus  in  the  male,  viz.,  lining  the  "  vasa  efferentia" 
of  the  testicle,  and  their  prolongations  as  far  as  the  lower  end  of  the 


THE   STRUCTURE    OF   THE    ELKMKXTARY"    TISSUES. 


35 


epididymis;  in  the  fem.ile  (c.)  commencing  about  the  middle  of  the 
neck  of  the  uterus,  and  extending  tliroughout  the  uterus  and  Fallopian 
tubes  to  their  fimbriated  extremities,  and  even  for  a  short  distance  on 
the  peritoneal  surface  of  the  latter,  (d.)  The  ventricles  of  the  brain 
and  the  central  canal  of  the  spinal  cord  are  clothed  with  ciliated  epithe- 
lium in  the  child,  but  in  the  adult  this  epithelium  is  limited  to  the 
central  canal  of  the  cord.  In  the  embryo  the  pharynx,  oesophagus,  and 
part  of  the  stomach  may  also  be  lined  with  ciliated  cells,  (e.)  The  ex- 
cretory ducts  of  certain  small  glands  in  different  localities,  (f.)  In 
certain  animals,  especially  the  lower  vertebrates,  ciliated  cells  line  the 
beginning  of  the  tubes  of  the  kidneys. 

The  Cilia  are  fine  hair-like  processes  Avhich  give  the  name  to  this 
variety  of  epithelium;  they  vary  a  good  deal  in  size  in  different  classes 


Fig.  20. 


Fig.  30. 


Fig.  29.— Spheroidal  ciliated  cells  from  the  mouth  of  the  frog.     X  200  diameters.    (Sharpey.) 
Fig.  30.— Ciliated  epiclieliuiu  from  the  liuniau  trachea.  «,  Large,  fully  formed  cell,   (j,  Shorter 
cell;  c,  developiu;^'  cells  wuh  more  than  one  nucleus.    (Cadiat. ) 


of  animals,  being  very  much  smaller  in  the  higher  than  among  the 
lower  orders,  in  which  they  sometimes  exceed  in  length  the  cell  itself. 

The  number  of  cilia  on  any  one  cell  ranges  from  ten  to  thirty,  and 
those  attached  to  the  same  cell  are  often  of  different  lengths,  in  the 
human  trachea  measuring  jy-J-rj-  to  u-gVir  of  '^^i  inch,  but  nearly  ten  times 
tlie  length  in  the  cells  of  the  epididymis. 

The  cilia  themselves  are  fine  rounded  or  fiattened  processes,  appar- 
ently homogeneous,  pointed  toward  their  free  extremities.  According 
to  some  observers  these  processes  are  connected  through  intervening 
knob-like  junctions  with  longitudinal  fibres  which  pass  to  the  other 
end  of  the  cell,  but  which  arc  not  connected  with  the  nucleus. 

When  living  ciliated  epithelium,  e.ij.,  from  the  gill  of  a  mussel,  or 
oyster,  or  from  the  mouth  of  the  frog,  or  from  a  scraping  from  a  polypus 
from  the  human  nose,  is  examined  under  the  microscope  in  a  drop  of 
0.6  per  cent  solution  of  common  salt  {normal  saline  solution),  the  cilia 
are  seen  to  be  in  constant  rapid  motion,  each  cilium  being  fixed  at  one 
end,  and  swinging  or  lashing  to  and  fro.     The  general  impression  given 


36  HANDBOOK    OF    PHYSIOLOGY. 

to  the  eye  of  tlie  observer  is  very  similar  to  tliat  produced  by  waves  in  a 
field  of  corn,  or  swiftly  rnuniug  and  rippling  water,  and  the  result  of 
their  movement  is  to  produce  a  continuous  current  in  a  definite  direc- 
tion, and  this  direction  is  invariably  the  same  on  the  same  surface^ 
being  always,  in  the  case  of  a  cavity,  toward  its  external  orifice. 

Ciliary  Motion. — Ciliary,  which  is  closely  allied  to  amoeboid  and 
muscular  motion,    is    alike    independent   of    the  will,   of   the   direct 
influence  of  the  nervous  system,  and  of  muscular  contraction.     It  may 
contiune  for  several  hours  after  death  or  removal  from  the  body,  pro- 
vided the  portion  of  tissue  under  examination  be  kept  moist.     Its  inde- 
pendence of   the   nervous    system  is  shown  also  in  its  occurrence  in 
the  lowest  invertebrate  animals  apparently  unprovided  with  anything 
analogous  to  a  nervous  system,  in  its  i^ersistence  in  animals  killed  by 
prussic  acid,  by  narcotic  or  other  poisons,  and  after  the  direct  applica- 
tion of  narcotics,    such  as    morphia,   opium,   and    belladonna,   to   the 
ciliary  surface,  or  of  electricity  through  it.     The  vapor  of  chloroform 
arrests  the   motion;  but  it  is  renewed   on    the   discontinuance  of  the 
application.     The   movement  ceases   when  the  cilia   are    deprived   of 
oxygen,   although   it  may  continue  for  a  time  in  the  absence  of  free 
oxygen,  but  is  revived  on  the  admission  of  this  gas.     Carbonic  acid 
stops  the  movement.     The  contact  of  various  substances,  e.g.,  bile,  strong 
acids,  and  alkalies,  will  stop  the  motion  altogether;  but  this  seems  to 
depend  chiefly  on  destruction  of  the  delicate  substance  of  which  the 
cilia  are  composed.     Temperatures  above  45°  C.  and  below  0°  C.  stop 
the  movement,  whereas  moderate  heat  and  dilute  alkalies  are  favorable 
to  the  action  and  revive  the  movement  after  temporary  cessation.     The 
exact  explanation  of  ciliary  movement  is  not  known;  whatever  may  be 
the  exact  cause,  however,  at  any  rate  the  movement  must  depend  upon 
some  changes  going  on  in  the  cell  to  which  the  cilia  are  attached,  as 
when  the  latter  are  cut  ofl  from  the  cell  the  movement  ceases,  and  when 
severed  so  that  a  j^ortion  of  the  cilia  are  left  attached  to  the  cell,  the 
attached  and  not  the  severed  portions  continue  the  movement.     Some 
authorities  consider  it  due  to  actual  contraction  of  the  cilia  themselves; 
others  assert  that  it  is  caused  by  movements  in  the  cell  protoplasm  acting 
upon  the  rootlets  of  the   cilia.     Schiifer  suggests  a  very  plausible  ex- 
jjlanation,  viz.,  that  a  cilium  is  either  a  curved  hollow  extension  of  the 
cell,  which  is  filled  by  hyalo2:)lasm  and  invested  by  a  delicate  membrane, 
or  else  a  straight  one  whose  investing  membrane  is  thicker  (or  otherwise 
Jess  extensible)  along  one  side  than  along  the  other.     In  either  case  a 
rhythmic  flowing  of  the  hyaloplasm  into  and  out  of  the  cilium  would 
cause  its  alternate  flexion  and  extension. 

As  a  special  subdivision  of  ciliary  action  may  be  mentioned  the  motion 
of  spermatozoa,  which  may  be  regarded  as  cells  with  a  single  cilium. 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


37 


(b)  Transitional  Epithelium. 

This  term  has  been  applied  to  cells,  which  are  neither  arranged  in  a 
single  layer,  as  is  the  case  with  simple  epithelium,  nor  yet  in  many 
superimposed  strata  as  in  laminated;  in  other  words,  it  is  employed 
when  epithelial  cells  are  found  in  two,  three,  or  four  superimposed 
layers. 

The  upper  layer  may  be  either  single  columnar,  columnar  ciliated, 
or  squamous.  AVhen  the  upper  layer  is  columnar  or  ciliated  the  second 
layer  co2isists  of  smaller  cells  fitted  into  the  inequalities  of  the  cells 
above  them,  as  in  the  trachea  (fig.  30). 

The  epithelium  which  is  met  with  lining  the  urinary  bladder  and 
ureters  is,  however,  the  transitional  par  excelle)ice.     In  this  variety  there 


3  "'-<:^-''Q^4^y 


Fig.  31. 


Fig.  32. 


Fig.  31.— Epithelium  of  the  bladder,  a.  One  of  the  cells  of  the  first  row;  h,  a  cell  of  the  second 
row;  c,  cells  in  situ,  of  first,  second,  and  deepest  layers.    ( Obersteiner. ) 

Fig.  3x!.— Transitional  epithelial  cells  from  the  mucous  membrane  of  the  bladder  of  a  rabbit. 
Highly  magnified.  «,  Large  flattened  cell  of  superficial  layer;  a',  similar  cell  in  profile;  6,  pear- 
shaped  cell  of  second  layer.     cKleiu.) 

are  two  or  three  layers  of  cells,  the  upper  being  more  or  less  flattened 
according  to  the  full  or  collapsed  condition  of  the  organ,  their  under 
surface  being  marked  with  one  or  more  depressions,  into  which  the 
heads  of  the  next  layer  of  club-shaped  cells  fit.  Between  the  lower  and 
narrower  parts  of  the  second  row  of  cells  are  fixed  the  irregular  cells 
which  constitute  the  third  row,  and  in  like  manner  sometimes  a  fourth 
row  (fig.  31).  It  can  be  easily  understood,  therefore,  that  if  a  scrajiing 
of  the  mucous  membrane  of  the  bladder  be  teased,  and  examined  under 
the  microscope,  cells  of  a  great  variety  of  forms  may  be  made  out  (fig. 
32).  Each  cell  contains  a  large  nucleus  and  the  larger  and  superficial 
cells  often  possess  two. 

(c)  Stratified  Epithelium. 

The  term  stratified  epithelium  is  employed  when  the  cells  forming 
the  epithelium  are  arranged  in  a  considerable  number  of  superimposed 
layers.  The  shape  and  size  of  the  cells  of  the  different  layers,  as  well 
as  the  number  of  the  layers,  vary  in  different  situations.     Thus  th^ 


38 


HANDBOOK    OF    PHYSIOLOGY. 


superficial  cells  are  as  a  rule  of  the  squamous,  or  scaly  variet}',  and  the 
deepest  of  the  columnar  form. 

The  cells  of  the  intermediate  layers  are  of  different  shapes,  but  those 
of  the  middle  layers  are  more  or  less  rounded.  The  superficial  cells  are 
broad  and  overlap  by  their  edges  (figs.  33  and  34).     Their  chemical  com- 


Fig.  33.— Squamous  epithelium  scales  from  the  inside  of  the  mouth.    X  260.    (Henle.) 

position  is  different  from  that  of  the  underlying  cells,  as  they  contain 
keratin,  and  are  therefore  horny  in  character. 

The  nucleus  is  often  not  apparent.  The  really  cellular  nature  of 
even  the  dry  and  shrivelled  scales  cast  off  from  the  surface  of  the  epi- 
dermis can  be  proved  by  the  application  of  caustic  potash,  which  causes 
them  rapidly  to  swell  and  assume  their  original  form. 

The  squamous  cells  exist  in  the  greatest  number  of  layers  in  the  epi- 
dermis or  superficial  part  of  the  skin;  the  most  superficial  of  these  are 
being  continually  removed  by  friction,  and  new  cells  from  below  supply 
the  place  of  those  cast  off. 

The  intermediate  cells  approach  more  to  the  flat  variety  the  nearer 
ihey  are  to  the  surface,  and  to  the  columnar  as  they  approach  the  lowest 


Fig.  34.— Vertical  section  of  the  stratified  epithelium  covering  the  front  of  the  cornea. 
Highly  magnified.  (Schafer.)  c,  Lowermost  columuar  cells;  js,  polygonal  cells  above  these; 
/?,  flattened  ceils  near  tue  suj  facj.  The  intercellular  channels,  bridged  by  minute  cell  processes, 
are  well  seen. 

layer.  There  may  be  considerable  intercellular  intervals;  and  in  many 
of  the  deeper  layers  of  epithelium  in  the  mouth  and  skin,  the  outline  of 
the  cells  is  very  irregular,  in  consequence  of  processes  passing  from  cell 
to  cell  across  these  intervals. 

Such  cells  (fig.  35)  are  termed  "ridge  and  furrow,^' " cogged  "  or 
"  prickle  "  cells.  These  "  prickles  "  are  prolongations  of  the  intracellular 
network  which  run  across  from  cell  to  cell,  thus  joining  them  together, 


THE    STRUCTURE    OF    THE    ELEMENT  A  KY    TISSUES. 


39 


the  interstices  being  filled  by  the  transpurent  intercclluhir  cement-sub- 
stance. When  this  increases  in  quantity  in  inflaniination  the  cells  are 
pushed  further  apart,  and  the  connecting  fibrils  or  '"  ])rickles"  elongated 
and  therefore  more  clearly  visible. 

The  columnar  cells  of  the  deepest  layer  are  distinctly  nucleated;  they 
multiply  rapidly  by  division;  and  as  new  cells  are  formed  beneath,  they 
press  the  older  cells  forAvard  to  be  in  turn  pressed  forward  themselves 
toward  the  surface,  gradually  altering  in  shape  and  chemical  composition 
until  they  are  cast  off  from  the  surface. 

Stratified  epithelium  is  found  in  the  following  situations:  (1.)  Form- 
ing the  epidermis,  covering  the  whole  of  the  external  surface  of  the  body; 
(3.)  Covering  the  mucous  membrane  of  thenose,  tongue,  mouth,  pharynx, 
and  oesophagus;  (3.)  As  the  conjunctival  epithelium,  covering  the  cor- 
nea; (4.)  Lining  the  vagina  and  the  vaginal  part  of  the  cervix  uteri. 


Fig.  35.— Jagged  cells  from  the  middle  layers  of  pavement  epithelium,  from  a  vertical  section  of  the 
gum  of  a  new-born  infant.     (Klein.) 

Functions  of  Epithelium. — According  to  function,  epithelial  cells 
may  be  classified  as:  (1.)  Protective,  e.g.,  in  the  skin,  mouth,  blood- 
vessels, etc.  (2.)  Protective  and  moving — ciliated  epithelium.  (3.) 
Spxreting — glandular  epithelium;  or.  Secreting  formed  elements — epi- 
thelium of  testicle  secreting  spermatozoa.  (4.)  Protective  and  secreting, 
e.g.,  epithelium  of  intestine.  (5)  Sensorial,  e.g.,  olfactory  cells,  rods  and 
cones  of  retina,  organ  of  Corti. 

Epithelium  forms  a  continuous  smooth  investment  over  the  whole 
body,  being  thickened  into  a  hard,  horny  tissue  at  the  points  most  ex- 
posed to  pressure,  and  developing  various  appendages,  such  as  hairs  and 
nails,  whose  structure  and  functions  will  be  considered  in  a  future  chapter. 
Epithelium  lines  also  ihe  sensorial  surfaces  of  the  eye,  ear,  nose,  and 
mouth,  and  thus  serves  as  the  medium  through  which  all  impressions 
from  the  external  world — touch,  smell,  taste,  sight,  hearing — reach  the 
delicate  nerve  endings,  whence  they  are  conveyed  to  the  brain. 

The  ciliated  epithelium  which  lines  the  air-passages  serves  not  only 
as  a  protective  investment,  but  also  by  the  movements  of  its  cilia  pro- 
motes currents  of  the  air  in  the  bronchi  and  bronchia,  and  is  enabled  to 
liropcl  fluids  and  minute  particles  of  solid  matter  so  as  to  aid  th(/ir  ex- 


40  HANDBOOK    OF    PHYSIOLOGY. 

pulsion  from  the  body.  In  the  case  of  the  Fallopian  tube,  chis  agency 
assists  the  progress  of  the  ovum  toward  the  cavity  of  the  uterus.  Of  the 
purposes  served  by  cilia  in  the  ventricles  of  the  brain  nothing  is  known. 

The  epithelium  of  the  various  glands,  and  of  the  whole  intestinal 
tract,  has  the  power  of  secretion,  i.e.,  of  chemically  transforming  certain 
materials  of  the  blood ;  in  the  case  of  mucus  and  saliva  this  has  been 
proved  to  involve  the  transformation  of  the  epithelial  cells  themselves; 
the  cell-substance  of  the  epithelial  cells  of  the  intestine  being  discharged 
by  the  rupture  of  their  envelopes,  as  mucus. 

Epithelium  is  likewise  concerned  in  the  processes  of  transudation, 
diffusion,  and  absorption. 

It  is  constantly  being  shed  at  the  free  surface  and  reproduced  in  the 
deeper  layers.  The  various  stages  of  its  growth  and  development  can 
be  well  seen  in  a  section  of  any  laminated  epithelium  such  as  the  epidermis. 

II,  The  Connective  Tissues. 

This  group  of  tissues  forms  the  Skeleton  with  its  various  connections 
— bones,  cartilages,  and  ligaments— and  also  affords  a  supporting  frame- 
work and  investment  to  the  various  organs  composed  of  nervous,  mus- 
cular, and  glandular  tissue.  Its  chief  function  is  the  mechanical  one  of 
support,  and  for  this  purpose  it  is  so  intimately  interwoven  with  nearly 
all  the  textures  of  the  body  that  if  all  other  tissues  could  be  removed, 
and  the  connective  tissues  left,  we  should  have  a  wonderfully  exact  model 
of  almost  every  organ  and  tissue  in  the  body,  correct  even  to  the  small- 
est minutiae  of  structure. 

Structure  of  Connective  Tissues  in  General. 

Connective  tissue  is  made  up  of  two  chief  elements,  namely,  cells 
and  intercellular  substance. 

(A.)  Cells. — ^The  cells  are  of  two  kinds: 

{a.)  Fixed  Cells. — ^Theae  are  of  a  flattened  shape,  with  branched  pro- 
cesses, which  are  often  united  together  to  form  a  network:  they  can  be 
most  readily  observed  in  the  cornea,  in  which  they  are  arranged,  layer 
above  layer,  parallel  to  the  free  surface.  They  lie  in  spaces  in  the  inter- 
cellular or  ground  substance,  which  are  of  the  same  shape  as  the  cells 
they  contain,  but  rather  larger,  and  which  form  by  anastomosis  a  sj'stem 
of  branching  canals  freely  communicating  (fig.  36). 

To  this  class  of  cells  belong  the  flattened  tendon  corpuscles  which 
are  arranged  in  long  lines  or  rows  parallel  to  the  fibres  (fig.  42). 

These  branched  cells,  in  certain  situations,  contain  a  number  of  pig- 
ment granules,  giving  them  a  dark  aj)pearance;  they  form  one  variety 
of  pigment  cell.  Branched  pigment  cells  of  this  kind  are  found  in  the 
outer  layers  of  the  choroid  (fig.  37).     In  many  of  the  lower  animals. 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


41 


such  as  the  frog,  they  are  found  widely  distributed,  not  only  in  the 
skin,  but  also  in  internal  parts,  e.g.,  the  mesentery  and  sheaths  of  blood- 
vessels. In  the  web  of  the  frog's  foot  such  cells  may  be  seen  with  pig- 
ment granules  evenly  distributed  throughout  the  body  of  the  cell  and 
its  processes;  but  under  the  action  of  light,  electricity,  and  other  stim- 
uli, the  pigment  granules  become  massed  in  the  body  of  the  cell,  leaving 
the  processes  quite  hyaline;  if  the  stimulus  be  removed,  they  will  grad- 
ually be  distributed  again  throughout  the  processes.  Thus  the  skin  in 
the  frog  is  sometimes  nniform.ly  dusky,  and  sometimes  quite  light-colored, 
with  isolated  dark  spots.  In  the  choroid  and  retina  the  pigment  cells 
absorb  light. 

{b.)  Amcehoid  Cells,  of  an  approximately  spherical  shape;  they  have 
a  threat  general  resemblance  to  colorless  blood-corpuscles,  with  which 


FiR.  3(1.— Horizontal  preparation  of  the  cornea  of  frog:,  stained  in  gold  chloride;  showing  the 
network  of  branched  cornea  corpuscles.  The  ground  substance  is  completely  colorless.  X  400. 
(Klein.) 


some  of  them  are  probably  identical.  They  consist  of  finely  granular 
nucleated  protoplasm,  and  have  the  property,  not  only  of  changing  their 
form  but  also  of  moving  about,  hence  they  are  termed  migratory.  They 
are  readily  distinguished  from  the  branched  connective-tissue  corpuscles 
by  their  free  condition,  and  the  absence  of  processes.  Some  are  much 
larger  than  others,  and  are  found  especially  in  the  sublingual  gland  of 
the  dog  and  guinea-pig,  and  in  the  mucous  membrane  of  the  intestine. 
A  second  variety  of  these  cells  called  plasma  cells  are  larger  tban  the 
amoeboid  cells,  apparently  granular,  less  active  in  their  movements.  They 
are  chiefly  to  be  found  in  the  inter-muscular  septa,  in  the  mucous  and 
sub-mucous  coats  of  the  intestine,  in  lymphatic  glands,  and  in  the  omen- 
tum. 

(B.)  Intercellular  Substance. — This  may  be  fibrillar,  as  in  the 
fibrous  tissues,  and  in  certain  varieties  of  cartilage;  or  homogeneous,  as 
in  hyaline  cartilage. 


42 


HANDBOOK    OF    PHYSIOLOGY, 


The  fibres  conijDosiiig  the  former  are  of  two  kinds — (a.)  White  fibrea 
(b.)  Yellow  elastic  fibres. 

{a.)  White  Fibres. — These  are  arranged  parallel  to  each  other  in  wavy 
bundles  of  various  sizes:  sach  bundles  may  either  have  a  parallel  ar- 


Fig.  37.  Fig.  38.  Fig.  39. 

Fig.  37.— Ramified  pigment  cells  from  the  tissue  of  the  choroid  coat  of  the  eye.  X  350.  a,  Cell 
with  pigment;  6,  colorless  fusiform  cells.     (Kolliker.) 

Fig.  38. — Flat,  pigmented,  branched  connective-tissue  cells  from  the  sheath  of  a  large  blood- 
vessel of  the  frog's  mesentery:  the  pigment  is  not  distributed  uniformly  throughout  the  substance 
of  the  larger  cell,  consequently  some  parts  of  it  look  blacker  than  others  (uncontracted  state).  In 
the  two  smaller  cells  most  of  the  pigment  is  withdrawn  into  the  cell-body,  so  that  they  appear 
smaller,  blacker,  and  less  branched.     X  350.    (Klein  and  Noble  Smith.) 

Fig.  39. — Fibrous  tissue  of  cornea,  showing  bundles  of  fibres  with  a  few  scattered  fusiform  cells 
(a)  lying  in  the  inter-fascicular  spaces.     X  400.    (Klein  and  Noble  Smith.) 


fine,  varying  from  -^^^ 


rangement  (fig.  39),  or  may  produce  quite  a  felted  texture  by  their  inter- 
lacement.   The  individual  fibres  composing  these  fasciculi  are  exceedingly 

to  ^^W  inch,  i.e.,  -^-^  to  -^^  mm.,*  or  0.5  to 
1//,  homogeneous,  unbranched,  and  of  the 
same  diameter  throughout.  They  can  readily 
be  isolated  by  macerating  a  portion  of  white 
fibrous  tissue  {e.g.,  a  small  piece  of  tendon) 
for  a  short  time  in  lime,  or  baryta-water,  or 
in  a  solution  of  common  salt,  or  of  potassium 
permanganate:  these  reagents  possess  the 
power  of  dissolving  the  cementing  inter- 
fibrillar  substance  and  of  thus  separating  the 
fibres  from  each  other.  By  prolonged  boil- 
ing the  fibres  yield  gelatin. 

(b.)  Yellow  Elastic  Fibres  (fig.  40)  are  of 
all  sizes,  from  excessively  fine  fibrils,  -jj-^o 
inch,  up  to  fibres  of  considerable  thickness, 
■^-^j^  inch  (i.e.,  from  about  1/j.  to  6/^) :  they 
are  distinguished  from  white  fibres  by  the 
following  characters:  (1.)  Their  great  power 
of  resistance  even  to  the  prolonged  action  of  chemical  reagents,  e.g., 
caustic  soda,  acetic  acid,  etc.     (2.)  Their  well-defined   outlines.     (3.) 

*     1     millimetre  =  1  micron,  which  is  represented  by  the  Greek  //. 


Fig.  40.— Elastic  fibres  from 
the  ligamenta  subflava.  x  200 
(Sharpey.) 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES.  43 

Their  great  tendency  to  branch  and  to  form  networks  by  anastomosis. 
(4.)  Their  twisted  corkscrew-like  appearance,  and  that  their  free  ends 
usually  curl  up,  (o.)  Their  yellowish  tint  and  considerable  elasticity. 
(6.)  Their  resistance  to  hfematoxylin  and  similar  reagents,  and  their 
affinity  for  magenta  and  other  aniline  staining  colors. 

These  fibres  yield  on  boiling  not  gelatin,  but  a  gelatinous  substance 
called  elastin. 

The  chief  varieties  of  connective  tissues  may  be  thus  classified : 

I.  The  Fibrous  Connective  Tissues. 

A. — Chief  Forms. 

a.  White  fibrous. 

b.  Elastic. 

c.  Areolar. 

B. — Special  Varieties. 

a.  Gelatinous. 

b.  Adenoid  or  Eetiform. 

c.  Adipose. 

II.  Cartilage. 

III.  Bone  a)id  dentine. 

I.  Fibrous  Connective  Tissues. 

A. — Chief  Forms. — (rr.)  White  Fibrous  Tissue. 

Distrihuti'ni. — It  is  found  typically  in  tendon;  also  in  ligaments,  in 
the  periosteum  and  perichondrium,  the  dura  mater,  the  pericardium, 
the  sclerotic  coat  of  the  eye,  the  fibrous  sheath  of  the  testicle;  in  the 
fasciae  and  aponeuroses  of  muscles,  and  in  the  sheaths  of  lymphatic 
glands. 

Structure. — To  tlie  naked  eye  tendons  and  many  of  the  filirous 
membranes,  when  in  a  fresh  state,  present  an  appearance  as  of  watered 
silk.  This  is  due  to  the  arrangement  of  the  fibres  in  wavy  parallel  bun- 
dles. Under  the  microscope  the  tissue  appears  to  consist  of  long,  often 
parallel,  bundles  of  fibres  of  different  sizes.  The  fibres  of  the  same  bun- 
dle now  and  then  intersect  each  other.  The  cells  in  tendons  (fig.  42) 
are  arranged  in  long  chains  in  the  ground  substance  separating  the  bun- 
dles of  fibres,  and  are  more  or  less  regularly  quadrilateral  with  large 
round  nuclei  containing  nucleoli,  which  are  generally  placed  so  as  to  be 
contiguous  in  two  cells.  Each  of  these  cells  consist  of  a  thick  body, 
from  which  processes  pass  in  various  directions  into,  and  partially  fill 
up  the  spaces  between,  the  bundles  of  fibres.  The  rows  of  cells  are 
separated  from  one  another  by  lines  of  cement  substance.  The  cell 
spaces  can  be  brought  into  view  by  silver  nitrate.     The  cells  are  gener- 


44 


HA]<rDBOOK    OF   PHYSIOLOGY. 


ally  marked  by  one  or  more  lines  or  stripes  when  viewed  longitudinally. 
This  appearance  is  really  produced  by  the  wing-like  processes  of  the 
cell  which  project  away  from  the  chief  part  of  the  cell  in  different  di- 
rections. These  processes  not  being  in  the  same  plane  as  the  body  of 
the  cell  are  out  of  focus  and  give  rise  to  these  bright  stripes  are  looked 
at  from  above  and  are  in  focus. 

The  branched  character  of  the  cells  is  seen  in  transverse  section  in 
fig.  43. 

(b)  Yellow  Elastic  Tissue. 

Distrihution. — In  the  ligamentum  nuchfe  of  the  ox,  horse,  and  many 
other  animals;  in  the  ligamenta  subflava  of  man;  in  the  arteries,  con- 
stituting the  fenestrated  coat  of  Henle;  in  veins;  in  the  lungs  and  tra- 


Fig.  41. 


Fig.  42. 


Fig.  41.— Mature  white  fibrous  tissue  of  tendon,  consisting  mainly  of  fibres  with  a  few  scattered 
fusiform  cells.    (Strieker.) 

Fig.  42.— Caudal  tendon  of  young  rat,  showing  the  arrangement,  form,  and  structure  of  the 
tendon  cells.    X  300.    (Klein.) 


chea;  in  the  stylo-hyoid,  thyro-hyoid,  and  crico-thyroid  ligaments;  in 
the  true  vocal  chords;  and  in  areolar  tissue. 

Structure. — Elastic  tissue  occurs  in  various  forms,  from  a  structure- 
less, elastic  membrane  to  a  tissue  whose  chief  constituents  are  bundles 
of  fibres  crossing  each  other  at  different  angles;  when  seen  in  bundles 
elastic  fibres  are  yellowish  in  color,  but  individual  fibres  are  not  so  dis- 
tinctly colored.     The  varieties  of  the  tissue  may  be  classified  as  follows : 

{a.)  Fine  elastic  fibrils,  which  branch  and  anastomose  to  form  a  net- 
work :  this  variety  of  elastic  tissue  occurs  chiefly  in  the  skin  and  mucous 
membranes,  in  subcutaneous  and  submucous  tissue,  in  the  lungs  and 
true  vocal  cords. 

(h.)  Thick  fibres,  sometimes  cylindrical,  sometimes  flattened  like 
tape,  which  branch,  anastomose  and  form  a  network:  these  are  seen 
most  typically  in  the  ligamenta  subflava  and  also  in  the  ligamentum 


THE    STRUCTURE    OF   THE    ELEMEXTARV   TISSUES.  45 

nucliEe  of  such  tmimals  as  the  ox  and  horse,  in  wliich  tluit  ligament  is 
largely  developed  (fig.  40). 

(c.)  Elastic  membranes  with  perforations,  e.g.,  Ilenle's  fenestrated 
membrane :  this  variety  is  found  chiefly  in  tlie  arteries  and  veins. 

[d.)  Continuous,  homogenous  elastic  membranes,  e.g.,  Bowman's  an- 
terior elastic  lamina  and  Descemet's  posterior  elastic  lamina,  both  in  the 
cornea. 

A  certain  number  of  flattened  connective-tissue  cells  ate  found  in 
the  ground  substance  between  the  elastic  fibres  which  make  up  this 
variety  of  connective  tissue. 

(c.)  Areolar  Tissue. 

Diatrihuiioii. — This  variety  of  fibrous  tissue  has  a  very  wide  distribu- 


wm 


Fig.  43.  Fig.  +f. 

Fig.  4.'i.— Transverse  section  of  tendon  from  a  cross  section  of  the  tail  of  a  rabbit,  showing 
sheatli,  libruiis  sepia,  ami  branched  ciiniieetive-tissiie  corpuscles.  The  spaces  left  white  in  the 
drawing  represent  tlie  tendinous  fibres  in  transver.se  section.     X  ~;"J0.     (Klein. ) 

St. 


Fig.  44.— Transverse  section  of  a  portion  of  lig.  nuclue,  showing  tlie  outline  of  the  fibres.    (After 
iJhr.) 


tion  and  constitutes  the  subcutaneous,  subserous,  and  submucous  tissue. 
It  is  found  in  the  mucous  membranes,  in  the  true  skin, and  in  the  outer 
sheaths  of  the  blood-vessels.  It  forms  sheaths  for  muscles,  nerves,  glands, 
and  the  internal  organs,  and  penetrating  into  their  interior,  supports 
and  connects  the  finest  parts. 

Structure. — To  the  naked  eye  it  appears,  when  stretched  out,  as  a 
fleecy,  white,  and  soft  meshwork  of  fine  fibrils,  with  here  and  there  wider 
films  joining  in  it,  the  whole  tissue  being  evidently  elastic.  The  open- 
ness of  the  meshwork  varies  with  the  locality  from  which  the  specimen 
is  taken.  Under  the  microscope  it  is  found  to  be  made  up  of  fine  white 
fibres,  Avhich  interlace  in  a  most  irreguUir  manner,  together  with  a  vari- 
able number  of  elastic  fibres.  On  the  addition  of  acetic  acid,  the  white 
fibres  swell  up,  and  become  gelatinous  in  appearance;  but  as  the  elastic 
fibres  resist  the  action  of  the  acid,  thev  may  still  be  seen  arranged  in 


46 


HANDBOOK    OF    PHYSIOLOGY. 


various  directions,  sometimes  appearing  to  pass  in  a  more  or  less  circular 
or  spiral  manner  round  a  small  gelatinous  mass  of  changed  white  fibre. 
The  cells  of  areolar  tissues  are  connective-tissue  corpuscles.  They  con- 
sist of  several  varieties:  branched,  flattened  cells  which  connect  with 
each  other;  flattened  cells  which  do  not  branch;  plasma  cells;  wander- 
ing cells  from  the  blood ;  and  sometimes  pigment  cells,  as  in  the  choroid 
of  the  eye.  The  various  elements  are  held  together  by  cement  substance, 
penetrated  by  irregular  canals  carrying  lymph. 

B.—Sjjecial  Forms  (a.)  Gelatinous  Tissue. 

Distribution.— GeUtinous  connective  tissue  forms  the  chief  part  of 
the  bodies  of  jelly-fish ;  it  is  found  in  many  parts  of  the  human  embryo, 


Fig    45. 


Fig.  46. 


Fig.  45.— Mucous  connective  tissue  from  th^  umbilical  cord.     n.  Cells;  b.  fibrils. 
Fig.  46.— Part  of  a  section  of  a  lympliatic  jiland,  from  which  the  corpuscles  have  been  for  the 
most  part  removed,  showing  the  adenoid  reticulum.    (Klein  and  Noble  Smith.) 

but  remains  in  the  adult  only  in  the  vitreous  humor  of  the  eye.  It  may 
be  best  seen  in  the  last-named  situation,  in  the  ''  Whartonian  jelly  "  of 
the  umbilical  cord,  and  in  the  enamel  organ  of  developing  teeth. 

Structure. — It  consists  of  cells,  which  in  the  vitreous  humor  are 
rounded,  and  in  the  jelly  of  the  enamel  organ  are  stellate,  imbedded  in 
a  soft  jelly-like  inter-cellular  substance  which  forms  the  bulk  of  the 
tissue,  and  which  contains  a  considerable  quantity  of  mucin.  In  the 
umbilical  cord,  that  part  of  the  jelly  immediately  surrounding  the  stel- 
late cells  shows  marks  of  obscure  fibrillation  (fig.  45). 

(b.)  Adenoid,  this  is  also  called  retiform,  lymplioid  or  lymphatic  tissue. 

Distribution. — This  variety  of  tissue  makes  up  the  stroma  of  the  spleen 
and  lymphatic  glands,  and  is  found  also  in  the  thymus,  in  the  tonsils, 
in  the  follicular  glands  of  the  tongue,  in  Peyer's  patches,  and  in  the  sol- 
itary glands  of  the  intestines,  and  in  the  mucous  membranes  generally. 


THK    STUrr-TrRK    OF    TH  R    ELEMEXtARY    TISSt'ES. 


4? 


Structure. — Adenoid  or  rctifonn  tissue  consists  of  a  very  delicate 
network  of  minute  fibrils,  foi'nied  origiiuilly  by  the  union  of  processes 
of  branched  connective-tissue  corpuscles,  the  nuclei  of  which,  however, 
are  visible  only  during  the  early  periods  of  development  of  the  tissue 
(fig.  4G).  The  network  of  fibrils  is  concealed  Ijy  being  covered  with 
flattened  connective-tissue  corpuscles,  whicli  may  be  readily  dissolved 
in  caustic  potash,  leaving  the  network  bare.  The  network  consists  of 
white  fibres,  the  interstices  of  which  are  filled  with  lymph  corpuscles. 
The  cement  substance  of  adenoid  tissue  is  very  fluid. 

Some  authors  make  a  distinction  between  retiform  and  adenoid  tis- 
sues, the  former  being  tlie  meshwork,  and  tlie  latter  the  meshwork  with 
its  contained  lymph  cells. 

Development  of  Fibrous  Tissues. — In  the  embryo  the  place  of 
the  fibrous  tissues  is  at  first  oeeupied  by  a  mass  of  roundish  cells,  de- 
rived from  the  "  mesoblast." 


Fi;;.  -IT. —Portion  of  sub  iiiicous  tissue  of  gravid  uterus  of  sow.    a,  Branched  cells,  more  or  less 
spindle-shaped;  6,  bundles  of  couuective  tissue.     cKlein.) 

These  develop  either  into  a  network  of  branched  cells  or  into  groups 
of  fusiform  cells  (fig.  47). 

The  cells  are  imbedded  in  a  semi-fluid  albuminous  substance  derived 
either  from  the  cells  themselves  or  from  the  neighboring  blood-vessels; 
this  afterward  forms  the  cement  substance.  In  it  fibres  are  developed, 
cither  by  some  of  the  cells  becoming  fibrils,  the  others  remaining  as  con- 
nective-tissue corpuscles,  or  by  the  fibrils  being  developed  from  the  out- 
side layers  of  the  protoplasm  of  the  cells,  which  grow  up  again  to  their 
original  size  and  remain  imbedded  among  the  fibres.  Tlie  process  gives 
rise  to  fibres  arranged  in  the  one  case  in  interlacing  networks  (areolar 
tissue),  in  the  other  in  parallel  ImuuHcs  (white  iibrous  tissue).  In  the 
mature  forms  of  })urely  fibrous  tissue  not  only  the  remnants  of  the  cell- 
substance,  but  even  the  nuclei,  may  disappear.  Tlie  embryonic  tissue, 
from  which  elastic  fibres  are  developed,  is  coniposed  of  fusiform  ceils, 
and  a  structureless  intereelluLii'  substance  by  the  gradual  fibrillation  of 
which  elastic  fibres  are  formed.  The  fusiform  cells  dwindle  in  size  and 
eventually  disappear  so  eom])lere]y  1 1ll  in  mature  elastic  tissue  hardly 
a  trace  of  them  is  to  be  found:  meaiiwliile  the  elastic  fibres  steadily  in- 
crease iu  size. 


48  HANDBOOK    OF    PHYSIOLOGY. 

Another  theory  of  the  development  of  the  connective-tissue  fibrils 
supposes  that  they  arise  from  deposits  in  the  intercellular  substance  and 
not  from  the  cells  themselves;  these  deposits,  in  the  case  of  elastic  fibres, 
appearing  first  of  all  in  the  form  of  rows  of  granules,  which,  joining  to- 
gether, form  long  fibrils.  It  seems  probable  that  even  if  this  view  be 
correct,  the  cells  themselves  have  a  considerable  influence  in  the  pro- 
duction of  the  dej)Osits  outside  them. 

Functions  of  Areolar  and  Fibrous  Tissue. — The  main  function 
of  connective  tissue  is  mechanical  rather  than  vital:  it  fulfils  the  subsid- 
iary but  important  use  of  supporting  and  connecting  the  various  tissues 
and  organs  of  the  body. 

In  o-lands  the  trabeculse  of  connective  tissue   form   an    interstitial 

O 

framework  in  which  the  parenchyma  or  secreting  gland-tissue  is  lodged: 
in  muscles  and  nerves  the  septa  of  connective  tissue  support  the  bundles 
of  fibres  which  form  the  essential  part  of  the  structure. 

Elastic  tissue,  by  virtue  of  its  elasticity,  has  other  imj)ortant  uses: 


Pig.  48.— Ordinary  fat  cells  of  a  fat  ti-act  in  the  omentum  of  a  rat.    (Klein.) 

these,  again,  are  mechanical  rather  than  vital.  Thus  the  ligamentum 
nuchte  of  the  horse  or  ox  acts  very  much  as  an  India-rubber  band  in  the 
same  position  would;  being  stretched  when  the  head  is  lowered  for 
feeding  or  other  purposes  and  aiding  the  muscles  materially  afterward 
by  its  contraction,  in  raising  the  head  to  its  normal  position  and  keeping 
it  there. 

(c.)  Adipose  Tissue. 

Distribution. — In  almost  all  regions  of  the  human  body  a  larger  or 
smaller  quantity  of  adipose  or  fatty  tissue  is  present;  the  chief  excep- 
tions being  the  subcutaneous  tissue  of  the  eyelids,  penis,  and  scrotum, 
the  nymphse,  and  the  cavity  of  the  cranium.  Adipose  tissue  is  also  absent 
from  the  substance  of  many  organs,  as  the  lungs,  liver,  and  others. 

Fatty  matter,  but  not  in  the  form  of  a  distinct  tissue,  is  also  widely 
present  in  the  body,  e.g.,  in  the  liver  and  brain,  and  in  the  blood  and 
chyle. 

Adipose  tissue  is  almost  always  found  seated  in  areolar  tissue,  and 
forms  in  its  meshes  little  masses  of  unequal  size  and  irregular  shape,  to 
which  the  term  lobules  is  commonly  applied. 


THE    STRUCTURE    OF   THE   ELEMENTARY   TISSUES.  49 

Structure. — Under  the  microscope  adipose  tissue  is  found  to  consist 
essentially  of  little  vesicles  or  cells  which  present  dark,  sharply-defined 
edges  when  viewed  with  transmitted  light:  they  are  about  ^^  or  -^l~^  of 
an  inch  in  diameter,  each  consisting  of  a  structureless  and  colorless 
membrane  or  bag  formed  of  the  remains  of  the  original  protoplasm  of 
the  cell,  filled  with  fatty  matter,  which  is  liquid  during  life,  but  in  part 
solidified  after  death  (fig.  48).  A  nucleus  is  always  present  in  some  part 
or  other  of  the  cell-protoplasm,  but  in  the  ordinary  condition  of  the  cell 
it  is  not  easily  or  always  visible  (fig.  49). 

This  membrane  and  the  nucleus  can  generally  be  brought  into  view 
by  staining  the  tissue :  it  can  be  still  more  satisfactorily  demonstrated 
by  extracting  the  contents  of  the  fat-cells  with  ether,  when  the  shrunken, 
shrivelled   membranes   remain   beliind.     By  mutual  pressure,  fat-cells 


Fig.  49.— Group  of  fat  cells  (f  c)  with  capillary  vessels  (c).     (Noble  Smith.") 


come  to  assume  a  polyhedral  figure  (fig.  49).  When  stained  with  osmic 
acid  fat-cells  appear  black. 

The  ultimate  cells  are  held  together  by  capillary  blood-vessels  (fig. 
50);  while  the  little  clusters  thus  formed  are  grouped  into  small  masses, 
and  held  so,  in  most  cases,  by  areolar  tissue. 

The  oily  matter  contained  in  the  cells  is  composed  chiefly  of  the 
compounds  of  fatty  acids  with  glycerin,  which  are  named  olcin,  siearin, 
And  palinitin. 

Development  of  Adipose  Tissue. — Fat  cells  are  developed  from 
connective-tissue  corpuscles:  in  the  infra-orbital  connective-tissue  cells 
may  be  found  exhibiting  every  intermediate  gradation  between  an  ordi- 
nary branched  connective-tissue  corpuscle  and  mature  fat-cell.  The 
process  of  development  is  as  follows :  a  few  small  drops  of  oil  make  their 
appearance  in  the  protoplasm  and  by  their  confluence  a  larger  drop  is 
produced  (fig.  51):  this  gradually  increases  in  size  at  the  expense  of  the 
original  protoplasm  of  the  cell,  which  becomes  correspondingly  dimin- 
ished in  quantity  till  in  the  mature  cell  it  only  forms  a  thin  crescentic 


50 


HANDBOOK    OF    PHYSIOLOGY. 


film,  closely  pressed  against  the  cell-wall,  and  with  a  nucleus  imbedded 
in  its  substance  (figs.  48  and  49). 

Under  certain  circumstances  this  process  may  be  reversed  and  fat- 
cells  may  be  changed  back  into  connective-tissue  corpuscles. 

Vessels  and  Nerves. 
— A  large  number  of  blood- 
vessels are  found  in  adipose 
tissue,  which  subdivide  un- 
til each  lobule  of  fat  con- 
tains a  fine  meshwork  of 
capillaries  ensheathing  each 
individual  fat-globule  (fig. 
50).  Although  nerve  fibres 
pass  through  the  tissue,  no 
nerves  have  been  demon- 
strated to  terminate  in  it. 

The  Uses  of  Adipose 
Tissue. — Among  the  uses 
of  adipose  tissue  these  are 
the  chief: — 

a.  It  serves  as  a  store  of 
combustible  matter  which 
may  be  reabsorbed  into  the 
blood  when  occasion  requires,  and,  being  used  up  in  the  metabolism  of 
the  tissues,  may  help  to  preserve  the  heat  of  the  body. 


Y\ct.  50.— Blood-vessels  of  adipose  tissue,  a.  Minute  flat- 
tened fat-lobule,  in  which  the  vessels  only  are  represented. 
a,  The  terminal  artery ;  r,  the  primitive  vein ;  h,  the  fat- 
vesicles  of  one  border  of  the  lobule  separately  represented. 
X  lf»0.  B.  Plan  of  the  arranseuient  of  the  capillaries  (c)  on 
the  exterior  of  the  vesicles  ;  mure  highly  magnified.  (Todd 
and  Bowman.) 


Fig.  51. 


Fig.  52. 


Fie  51.-A  lobule  of  developing  adipose  tissue  from  an  eight  months  foetus  «>  Spherical  or, 
from  pressure,  polyhedral  cells  with  large  central  nucleus,  surrounded  by  a  finely  reticulated  bui)- 
8ta™e  staining  uniformly  with  haematoxylin.  b.  Similar  cells  with  spaces  from  which  the  fat  hab 
been  removed  by  oil  of  cloves,  c.  Similar  cells  showing  how  the  nucleus  with  inclosing  protoplasni 
Lsbeing^r^sed  toward  peripherj^.  d.  Nucleus  of  endotlieUum  of  investing  capillaries.  (McCarthy.) 
Drawn  by^Tr^v^s^^^^^^  connective-tissue  corpuscles,  developing  into  fat-ceUs.    (Klein.) 


THE    STKUCTURE    OF   THE    ELEMENTARY   TISSUES.  51 

h.  That  part  of  the  fat  which  is  situate  beneath  the  skin  must,  by 
its  want  of  conducting  power,  assist  in  preventing  undue  w-aste  of  the 
heat  of  the  body  by  escape  from  the  surface. 

c.  As  a  packing  material,  fat  serves  very  admirably  to  fill  up  spaces, 
to  form  a  soft  and  yielding  yet  elastic  material  wherewith  to  wrap  ten- 
der and  delicate  structures,  or  form  a  bed  with  like  qualities  on  which 
such  structures  may  lie,  not  endangered  by  pressure.  As  examples  of 
situations  in  which  fat  serves  such  purposes  may  be  mentioned  the  palms 
of  the  hands  and  soles  of  the  feet  and  the  orbits. 

d.  In  the  long  bones  fatty  tissue,  in  the  form  known  as  yellow  mar- 
row, fills  the  medullary  canal,  and  supports  the  small  blood-vessels  which 
are  distributed  from  it  to  the  inner  part  of  the  substance  of  the  bone. 

Basemext  Membranes. 

Basement  membranes  are  a  special  structure  upon  which  the  epi- 
thelium of  mucous  membranes  rests.  They  are  of  homogeneous  appear- 
ance, and  are  developed  from  flattened  connective-tissue  corpuscles, 
joined  at  their  edges,  or  from  a  concentrated  cement  substance.  Some 
basement  membranes  possess  elasticity,  e.g.,  in  the  cornea. 

II.  Cartilage. 

General  Structure  of  Cartilage. — All  kinds  of  cartilage  are  composed 
of  cells  imbedded  in  a  substance  called  the  matrix :  the  apparent  differ- 
ences of  structure  met  with  in  the  various  kinds  of  cartilage  are  more 
due  to  differences  in  the  character  of  the  matrix  than  of  the  cells. 
Among  the  latter,  however,  there  is  also  considerable  diversity  of  form 
and  size. 

With  the  exception  of  the  articular  variety,  cartilage  is  invested  by  a 
thin  but  tough  firm  fibrous  membrane  called  the  pericJiondrium.  On 
the  surface  of  the  articular  cartilage  of  the  foetus,  the  perichondrium  is 
represented  by  a  film  of  epithelium;  but  this  is  gradually  worn  away 
up  to  the  margin  of  the  articular  surfaces  when  by  use  the  parts  begin 
to  suli'er  friction. 

Nerves  are  probably  not  supplied  to  any  variety  of  cartilage. 

Cartilage  exists  in  three  different  forms  in  the  human  body,  viz.,  1, 
Hyaline  cartilage,  2,  Yellow  elastic-cartilage,  and  3,  White  fibro-cartilage. 

1.  Hyaline  Cartilage. 

Distribution. — This  variety  of  cartilage  is  met  with  largely  in  the 
human  body — investing  the  articular  ends  of  bones,  and  forming 
the  costal  cartilages,  the  nasal  cartilages,  and  those  of  the  larynx  wath  the 
exception  of  the  epiglottis  and  cornicula  laryugis,  as  well  as  those  of 
the  trachea  and  bronchi. 

Structure. — Like  other  cartilages  it  is  composed  of  cells  imbedded  in 


52 


HANDBOOK    OP   PHYSIOLOGY. 


a  matrix.  The  cells,  which  contain  a  nucleus  with  nucleoli,  are  irregular 
in  shape,  and  generally  grouped  together  in  patches  (fig.  53).  The 
patches  are  of  various  shapes  and  sizes  and  placed  at  unequal  distances 
apart.  They  generally  appear  flattened  near  the  free  surface  of  the 
mass  of  cartilage  in  which  they  are  placed  and  more  or  less  perpendicular 
to  the  surface  in  the  more-deeply  seated  portions. 

The  matrix  of  hyaline  cartilage  has  a  dimly  granular  appearance  like 
that  of  ground  glass,  and  in  man  and  the  higher  animals  has  no  appar- 
ent structure.  In  some  cartilages  of  the  frog,  however,  even  when  ex- 
amined in  the  fresh  state,  it  is  seen  to  be  mapped  out  into  polygonal 
blocks  or  cell-territories,  each  containing  a  cell  in  the  centre,  and  repre- 


^K, 


Fig.  53. 


Fig.  54. 


Fig.  53.— Hyaline  articular  cartilage  (human).    The  cell  bodies  entirely  All  the  spaces  in  the 
matrix.     X  340  diams.     (Schafer.) 

Fig.  54.— Fresh  cartilage  from  the  Triton.    (A.  Rollett.) 

senting  what  is  generally  called  the  capsule  of  the  cartilage  cells  (fig. 
54).  Hyaline  cartilage  in  man  has  really  the  same  structure,  which  can 
be  demonstrated  by  the  use  of  certain  reagents.  If  a  piece  of  human 
hyaline  cartilage  be  macerated  for  a  long  time  in  diluted  acid  or  in  hot 
water  35°-45°  C.  (95°-113°  F.),  the  matrix,  which  previously  appeared 
quite  homogeneous,  is  found  to  be  resolved  into  a  number  of  concentric 
lamellae,  like  the  coats  of  an  onion,  arranged  round  each  cell  or  group 
of  cells.  It  is  thus  shown  to  consist  of  nothing  but  a  number  of  large 
systems  of  capsules  which  have  become  fused  with  one  another. 

The  cavities  in  the  matrix  in  which  the  cells  lie  are  connected  to- 
gether by  a  series  of  branching  canals,  very  much  resembling  those  in 
the  cornea:  through  these  canals  fluids  may  make  their  way  into  the 
depths  of  the  tissue. 

In  the  hyaline  cartilage  of  the  ribs  the  cells  are  mostly  larger  than 
in  the  articular  variety  and  there  is  a  tendency  to  the  development  of 
fibres  in  the  matrix  (fig.  55).     The  costal  cartilages  also  frequently  be- 


THE    STKUCTURE    OF   THE    ELEMENTARY   TISSUES. 


53 


come  calcified  in  old  age,  as  also  do  some  of  those  of  the  larynx.  Fat- 
globules  may  also  be  seen  in  many  cartilages  (fig.  55). 

In  articular  cartilage  the  cells  are  smaller  and  arranged  vertically  in 
narrow  lines  like  strings  of  beads. 

In  the  foetus  cartilage  is  the  material  of  which  the  bones  are  first 
constructed;  the  '"model"  of  each  bone  being  laid  down,  so  to  speak, 
in  this  substance.  In  such  cases  the  cartilage  is  termed  temporary.  It 
closely  resembles  the  ordinary  hyaline  kind;  the  cells,  however,  are  not 
grouped  together  after  the  fashion  just  described,  but  are  more  uniformly 
distributed  throughout  the  matrix. 

A  variety  of  temporary  hyaline  cartilage  which  has  scarcely  any  ma- 


Fig.  55, 


Fig.  56. 


Fig.  55.— Costal  cartilage  from  an  adult  dog,  showing  the  fat  globules  in  the  cartilage  cells. 
(Cadiat.) 

Fig.  56.— Yellow  elastic  cartilage  of  the  ear.     Highly  magnified.     (Hertwig.) 


trix  is  found  in  the  human  subject  and  in  the  higher  animals  generally, 
in  early  fo3tal  life,  when  it  constitutes  the  chorda  dorsalis. 

Nutrition. — Hyaline  cartilage  is  reckoned  among  the  so-called  non- 
vascular structures,  no  blood-vessels  being  supplied  directly  to  its  own 
substance;  it  is  nourished  by  those  of  the  bone  beneath.  When  hyaline 
cartilage  is  in  thicker  masses,  as  in  the  case  of  the  cartilages  of  the  ribs, 
a  few  blood-vessels  traverse  its  substance.  The  distinction,  however, 
between  all  so-called  vascular  and  non-vascular  parts  is  at  the  best  a 
very  artificial  one. 

2.  Yellow  Elastic  Cartilage. 

Distribution. — In  the  external  ear,  in  the  epiglottis  and  cornicula 
laryngis,  and  in  tlie  Eustachian  tube. 

Structure. — The  cells  in  this  variety  of  cartilage  are  rounded  or  oval, 
with  well-marked  nuclei  and  nucleoli  (fig.  56).  The  matrix  in  which 
they  are  seated  is  composed  almost  entirely  of  fine  elastic  fibres,  which 


54 


HANDBOOK    OF    PHYSIOLOGY. 


form  an  intricate  interlacement  about  the  cells,  and  in  their  general 
characters  are  allied  to  the  yellow  variety  of  fibrous  tissue :  a  small  and 
variable  quantity  of  hyaline  intercellular  substance  is  also  usually  present. 

A  variety  of  elastic  cartilage,  sometimes  called  cellular,  is  found  to 
form  the  framework  of  the  external  ears  of  rats,  mice,  or  other  small 
mammals.  It  is  composed,  as  its  name  implies,  almost  entirely  of  cells 
which  are  packed  very  closely  with  little  or  no  matrix.  When  present 
the  matrix  consists  of  very  fine  fibres  which  twine  about  the  cells  in 
various  directions  and  inclose  them  in  a  kind  of  network.  Elastic  car- 
tilage seldom  or  never  ossifies. 

3.  White  Fibro-Cartilage. 

Distribution. — White  fibro-cartilage  is  found  to  occur: — 

1.  As  inter-articular  fibro-cartilage,  e.g.,  the  semilunar  cartilages  of 
the  knee-joint. 

2.  As  circumferential  or  marginal  cartilage,  as  on  the  edges  of  the 
acetabulum  and  glenoid  cavity. 

3.  As  connecting  cartilage,  e.g.,  the  inter-vertebral  fibro-cartilages. 

4.  In  the  sheaths  of  tendons  and  some- 
^-j;  M'i'iWillii       times  in  their  substance.     In  the  latter  situ- 

ation the  nodule  of  fibro-cartilage  is  called  a 
sesamoid  fibro-cartilage,  of  which  a  specimen 


Cells  of 
cartilage. 


Very  fibrous 
matrix. 


Fig.  57.      ' 


U*Jliy||liili!aHll!'.ir:til!»l 

Fig.  58. 


Fig.  .W.— White  fibro-cartilage.    (Cadiat.) 

Fig.  58. — White  fibro-cartilage  from  an  inter-vertebral  ligament.    (Klein  and  Noble  Smith.) 


may  be  found  in  the  tendon  of  the  tibialis  posticus  in  the  sole  of  the  foot, 
and  usually  in  the  neighboring  tendon  of  the  peroneus  longus. 

Structure. — White  fibro-cartilage  (fig.  58),  which  is  much  more  widely 
distributed  throughout  the  body  than  the  foregoing  kind,  is  composed, 
like  it,  of  cells  and  a  matrix;  the  latter,  however,  being  made  up  almost 
entirely  of  fibres  closely  resembling  those  of  white  fibrous  tissue. 

In  this  kind  of  fibro-cartilage  it  is  not  unusual  to  find  a  great  part 
of  its  mass  composed  almost  exclusively  of  fibres,  and  deriving  the  name 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES.  55 

of  cartilage  only  from  the  fact  that  in  another  portion,  continuous  with 
it,  cartilage  cells  may  be  pretty  freely  distributed. 

By  prolonged  boiling,  cartilage  yields  a  substance  called  cliondriti — 
which  gelatinizes  on  cooling.  The  cells  of  white  fibro-cartilage  are  as  a 
rule  rounded  or  somewhat  flattened  but  in  some  places  are  distinctly 
branched. 

Functions  of  Cartilage.— Cartilage  not  only  represents  in  the 
fcetus  the  bones  which  are  to  be  formed  {temporary  cartilage)  but  also 
offers  a  firm,  yet  more  or  less  yielding,  framework  for  certain  parts  in 
the  developed  body,  possessing  at  the  same  time  strength  and  elasticity. 
It  maintains  the  shape  of  tubes  as  in  the  larynx  and  trachea.  It  affords 
attachment  to  muscles  and  ligaments;  it  binds  bones  together,  yet  allows 
a  certain  degree  of  movement,  as  between  the  vertebrae;  it  forms  a  firm 
framework  and  protection,  yet  without  undue  stiffness  or  weight,  as  in 
the  pinna,  larynx,  and  chest  walls;  it  deepens  joint  cavities,  as  in  the 
acetabulum,  without  unduly  restricting  the  movements  of  the  bones. 

Development  of  Cartilage. — Cartilage  is  developed  out  of  an  em- 
bryonal tissue,  consisting  of  cells  with  a  very  small  quantity  of  intercel- 
lular substance:  the  cells  multiply  by  fission  within  the  cell- capsules, 
while  the  capsule  of  the  parent  cell  becomes  gradually  fused  with  the 
surrounding  intercellular  substance.  A  repetition  of  this  process  in  the 
young  cells  causes  a  rapid  growth  of  the  cartilage  by  the  multiplication 
of  its  cellular  elements  and  corresponding  increase  in  its  matrix.  Thus 
we  see  that  the  matrix  of  cartilage  is  chiefly  derived  from  the  cartilage 
cells. 

III.  Bone. 

Chemical  Composition. — Bone  is  composed  of  earthi/  and  animal  mat- 
ter in  the  proportion  of  about  67  per  cent  of  the  former  to  33  per  cent 
of  the  latter.  The  earthy  matter  is  composed  chiefly  of  calcium  phos- 
phate, but  besides  there  is  a  small  quantity  (about  11  of  the  67  per  cent) 
of  calcium  carbonate  and  calcium  fluoride,  and  ma g nesi urn  phosphate. 

The  animal  matter  called  collagen  is  resolved  into  gelatin  by  boiling. 

The  earthy  and  animal  constituents  of  bone  are  so  intimately  blended 
and  incorporated  the  one  with  the  other  that  it  is  only  by  cliemical 
action,  as  for  instance  by  heat  in  one  case  and  by  the  action  of  acids  in 
another,  that  they  can  be  separated.  Their  close  union  too  is  further 
sliown  by  the  fact  that  when  by  acids  the  earthy  matter  is  dissolved  out, 
or  on  the  other  hand  when  the  animal  part  is  burnt  out,  the  shape  of 
the  bone  is  alike  preserved. 

The  proportion  between  these  two  constituents  of  bone  varies  in 
different  bones  in  the  same  individual  and  in  the  same  bone  at  different 
ages. 

Structure. — To  tlie  naked  eye  there  appear  two  kinds  of  structure 


56 


HANDBOOK    OF   PHYSIOLOGY. 


in  different  bones,  and  in  different  parts  of  the  same  bone,  namely,  the 
dense  or  comiMct,  and  the  s-pongy  or  cancellous  tissue. 

Thus,  in  making  a  longitudinal  section  of  a  long  bone,  as  the 
humerus  or  femur,  the  articular  extremities  are  found  capped  on  their 
surface  by  a  thin  shell  of  compact  bone,  while  their  interior  is  made  up 
of  the  spongy  or  cancellous  tissue.  The  shaft,  on  the  other  hand,  is 
formed  almost  entirely  of  a  thick  layer  of  the  compact  bone,  and  this 
surrounds  a  central  canal,  the  medullary  cavity — so  called  from  its  con- 
taining the  medulla  or  marrow. 

In  the  flat  bones,  as  the  parietal  bone  or  the  scapula,  one  layer  of  the 
cancellous  structure  lies  between  two  layers  of  the  compact  tissue,  and 
in  the  short  and  irregular  bones,  as  those  of  the  caijms  and  tarsus,  the 
cancellous  tissue  alone  fills  the  interior,  while  a  thin  shell  of  comj^act 
bone  forms  the  outside. 

Marrow. — There  are  two  distinct  varieties  of  marrow — the  red  and 
yelloiv. 


Fig.  59. — Cells  of  the  red  marrow  of  the  guinea-pig,  highly  maguified.  a,  A  large  cell,  the  nu- 
cleus of  which  appears  to  be  partly  dividedinto  three  by  constrictioiis;  b.  a  cell,  the  nucleus  of  which 
shows  an  appearance  of  being  constricted  into  a  numVier  of  smaller  nuclei;  c,  a  so-called  giant  cell, 
or  myeloplaxe,  with  many  nuclei;  d,  a  smaller  myelo-plaxe,  with  three  nuclei;  e-i,  proper  cells  of 
the  marrow.    (E.  A.  Schafer.) 


Red  marrow  is  that  variety  which  occupies  the  spaces  in  the  cancel- 
lous tissue;  it  is  highly  vascular,  and  thus  maintains  the  nutrition  of 
the  spongy  bone,  the  interstices  of  which  it  fills.  It  contains  a  few 
fat-cells  and  a  large  number  of  marrow-cells,  many  of  which  are  undis- 
tinguishable  from  lymphoid  corpuscles,  and  has  for  a  basis  a  small 
amount  of  fibrous  tissue.  Among  the  cells  are  some  nucleated  cells  of 
very  much  the  same  tint  as  colored  blood-corpuscles.  There  are  also 
a  few  large  cells  with  many  nuclei,  termed  giant-cells  or  myelopla'xes, 
which  are  derived  from  over-growth  of  the  ordinary  marrow-cells 
(fig.  59). 

Yellow  marrow  fills  the  medullary  cavity  of  long  bones,  and  consists 
chiefly  of  fat-cells  with  numerous  blood-vessels;  many  of  its  cells  also 
are  in  every  respect  similar  to  lymphoid  corpuscles. 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


57 


From  these  marrow-cells,  especially  those  of  the  red  marrow,  are  de- 
rived, as  we  shall  presently  show,  large  quantities  of  red  blood-corpuscles. 

Periosteum  and  Nutrient  Blood-vessels. — The  surfaces  of  bones, 
except  the  part  covered  with  articular  cartilage,  are  clothed  by  a  tough, 
fibrous  membrane,  the  periosfeuin ;  and  it  is  from  the  blood-vessels 
which  are  distributed  in  this  membrane,  that  the  bones,  especially  their 
more  compact  tissue,  are  in  great  part  suf)plied  with  nourishment, — 
minute  branches  from  the  periosteal  vessels  entering  the  little  foramina 
on  the  surface  of  the  bone,  and  finding  their  way  to  the  Haversian 
canals  to  be  immediately  described.  The  long  bones  are  supplied  also 
Ijy  a  proper  nutrient  artery  which,  entering  at  some  part  of  the  shaft  so 


Fig.  60.— Transverse  section  of  compact  bony  tissue  (of  humerus^  Three  of  the  Haversian 
canals  are  seen,  with  their  concentric  rings;  also  the  lacuna?,  with  the  canaliculi  extending  from 
them  across  the  direction  of  the  lamella.  The  Haversian  apertures  were  filled  with  debris  in  grind- 
ing down  the  section,  and  therefore  appear  black  in  the  figure,  which  represents  the  object. as  viewed 
with  transmitted  light.  The  Haversian  systems  are  so  closely  packed  in  this  section,  that  scarcely 
any  interstitial  lamellee  are  visible.    X  150.    (Sharpey.) 

as  to  reach  the  medullary  canal,  breaks  up  into  branches  for  the  supply 
of  the  marrow,  from  which  again  small  vessels  are  distributed  to  the 
interior  of  the  bone.  Other  small  blood-vessels  pierce  the  articular 
extremities  for  the  supply  of  the  cancellous  tissue. 

Microscopic  Strucfnve  of  Bone. — TS"ot«'ithstanding  the  differences  of 
arrangement  Just  mentioned,  the  structure  of  all  bone  is  found  under 
the  microscope  to  be  essentially  the  same. 

Examined  with  a  rather  high  power  its  substance  is  found  to  contain 
a  multitude  of  small  irregular  spaces,  approximately  fusiform  in  shape, 
called  lacunoe,  with  very  minute  canals  or  canaliculi,  as  they  are  termed, 
leading  from  them,  and  anastomosing  with  similar  little  prolongations 
from  other  lacunar  (fig.  GO).  In  very  thin  layers  of  bone,  no  other 
canals  than  these  may  be  visible;  but  on  making  a  transverse  section  of 


58 


HANDBOOK   OF    PHYSIOLOGY. 


the  compact  tissue  as  of  a  long  bone,  e.g.,  the  humerus  or  ulna,  the 
arrangement  shown  in  fig.  60  can  be  seen. 

The  bone  seems  mapped  out  into  small  circular  districts,  at  or  about 
the  centre  of  each  of  which  is  a  hole,  around  which  is  an  appearance  as 
of  concentric  layers — the  lacunm  and  canaliculi  following  the  same  con- 
centric plan  of  distribution  around  the  small  hole  in  the  centre,  with 
which  indeed  they  communicate. 

On  making  a  longitudinal  section,  the  central  holes  are  found  to  be 
simply  the  cut  extremities  of  small  canals  which  run  lengthwise  through 
the  bone,  anastomosing  with  each  other  by  lateral  branches  (fig.  61), 


Fig.  61. — Longitudinal  section  from  the  human  ulna,  showing  Haversian  canal,  lacunjB,  and 

canaliculi.     (RoUett.) 

and  are  called  Haversian  canals,  after  the  name  of  the  physician,  Clopton 
Havers,  who  first  accurately  described  them. 

The  Haversian  canals,  the  average  diameter  of  which  is  -^^^^  of  an 
inch,  contain  blood-vessels,  and  by  means  of  them  blood  is  conveyed  to 
all,  even  the  densest  parts  of  the  bone;  the  minute  canaliculi  and  lacunae- 
absorbing  nutrient  matter  from  the  Haversian  blood-vessels  and  con- 
veying it  still  more  intimately  to  the  very  substance  of  the  bone  which 
they  traverse. 

The  blood-vessels  enter  the  Haversian  canals  both  from  without,  by 
traversing  the  small  holes  which  exist  on  the  surface  of  all  bones  be- 
neath the  periosteum,  and  from  within  by  means  of  small  channels 
which  extend  from  the  medullary  cavity,  or  from  the  cancellous  tissue. 
The  arteries  and  veins  usually  occupy  separate  canals,  and  the  veins,, 
which  are  the  larger,  often  present,  at  irregular  intervals,  small  pouch- 
like dilatations. 


THE    STBUCTURE    OF    THE    ELEMENTAKY   TISSUES. 


59 


The  lacunae  are  occupied  by  branched  cells,  which  are  called  hone- 
cells,  or  hone-corpuscles  (fig.  62),  which  very  closely  resemble  the  ordi- 
nary branched  connective-tissue  corpuscles;  each  of  these  little  masses 
of  protoplasm  ministering  to  the  nutrition  of  the  bone  immediately  sur- 
rounding it,  and  one  lacunar  corpuscle  communicating  with  another, 
and  with  its  surrounding  district,  and  with  the  blood-vessels  of  the 
Haversian  canals,  by  means  of  the  minute  streams  of  fluent  nutrient 
matter  which  occupy  the  canaliculi. 

It  will  be  seen  from  the  above  description  that  bone  is  essentially 
connective-tissue  impregnated  with  lime  salts :  it  bears  a  very  close  re- 
semblance to  what  may  be  termed 
typical  connective-tissue  such  as 
the  substance  of  the  cornea.  The 
bone-corpuscles    with    their    pro- 


Fig.  62. 


Fig.  63. 


Fig.  62.— Bone-corpuscles  with  their  processes  as  seen  in  a  thin  section  of  human  bone.   (Rollett.) 
Fig.  63.— Thin  layer  peeled  off  from  a  softened  bone.    This  figure,  which  is  intended  to  represent 

the  reticular  structure  of  a  lamella,  gives  a  better  idea  of  the  object  when  held  rather  farther  off 

than  usual  from  the  eye.     X  400.     (Sharpey.) 


cesses  occupying  the  lacunaj  and  canaliculi  correspond  exactly  to  the 
cornea-corpuscles  lying  in  branched  spaces. 

Lamellae  of  Compact  Bone. — In  the  shaft  of  a  long  bone  three 
distinct  sets  of  lamella?  can  be  clearly  recognized. 

(1.)  General  or  fundamental  lamellae  ;  which  are  most  easily  tracea- 
ble just  beneath  the  periosteum,  and  around  the  medullary  cavity,  form- 
ing around  the  latter  a  series  of  concentric  rings.  Ac  a  little  distance 
from  the  medullary  and  periosteal  surfaces  (in  the  deeper  portions  of 
the  bone)  they  are  more  or  less  interrupted  by 

(2.)  Special  or  Haversian  lamellae,  which  are  concentrically  arranged 
around  the  Haversian  canals  to  the  number  of  six  to  eighteen  around 
each. 

(3.)  Interstitial  lamellae,  which  connect  the  system  of  Haversian 
lamellae,  filling  the  spaces  between  them,  and  consequently  attaining 


60 


HANDBOOK    OF   PHYSIOLOGY. 


their  greatest  development  where  the  Haversian  systems  are  few,  and 
vice  versa. 

The  ultimate  structure  of  the  lamellae  appears  to  be  reticular.  If  a 
thin  film  be  peeled  ofE  the  surface  of  a  bone,  from  which  the  earthy 
matter  has  been  removed  by  acid,  and  examined  with  a  high  power  of 
the  mici'oscope,  it  will  be  found  composed  of  a  finely  reticular  struc- 
ture, formed  apparently  of  very  slender  fibres  decussating  obliquely,  but 
coalescing  at  the  points  of  intersection,  as  if  here  the  fibres  were  fused 
rather  than  woven  together  (fig.  63). 

In  many  places  these  reticular  lamellge  are  perforated  by  tajDcring 
fibres  called  the  Claviculi  of  Gagliardi,  or  the  perforating  fibres  of 
Sharpey,  resembling  in  character  the  ordinary  white  or  rarely  the  elastic 


Fig.  64. — Lamellae  torn  off  from  a  decalcified  human  parietal  bone  at  some  depth  from  the  sur- 
face, o,  a,  Lamellae,  showing  reticular  fibres;  h,  b,  darker  part,  where  several  lamellae  are  super- 
posed; c,  perforating  fibres.  Apertures  through  which  perforating  fibres  had  passed,  are  seen  es- 
pecially in  the  lower  part,  a,  a,  of  the  figm'e.    (Allen  Thomson.) 


fibrous  tissue,  which  bolt  the  neighboring  lamellse  together,  and  may  be 
drawn  out  when  the  latter  are  torn  asunder  (fig.  64).  These  perforating 
fibres  originate  from  ingrowing  processes  of  the  periosteum,  and  in  the 
adult  still  retain  their  connection  with  it. 

Development  of  Bone. — From  the  point  of  view  of  their  develop- 
ment, all  bones  may  be  subdivided  into  two  classes. 

{a.)  Those  which  are  ossified  directly  or  from  the  first  in  membrane 
or  fibrous  tissue,  e.g.,  the  bones  forming  the  vault  of  the  skull,  parietal, 
frontal,  and  a  certain  portion  of  the  occipital  bones. 

(b.)  Those  whose  form,  previous  to  ossification,  is  laid  down  in  7ii/a- 
line  cartilage,  e.g.,  humerus,  femur. 

The  process  of  development,  pure  and  simple,  may  be  best  studied  in 
bones  which  are  not  preceded  by  cartilage,  i.e.,  membrane- formed  {e.g., 


THE    STEUCTURE    OF   THE    ELEMENTARY   TISSUES.  61 

parietal)  ;  and  without  a  knowledge  of  this  process  (ossification  in  mem- 
brane), it  is  impossible  to  understand  the  much  more  complex  series  of 
changes  through  which  such  a  structure  as  the  cartilaginous  femur  of 
the  foetus  passes  in  its  transformation  into  the  bony  femur  of  the  adult 
(ossification  in  cartilage). 

Ossification  in  Membrane. — The  membrane,  afterward  forming 
the  periosteum,  from  which  such  a  bone  as  the  parietal  is  developed, 
consists  of  two  layers — an  extemdl  fibrous,  and  an  internal  cellular  or 
osteo-genetic. 

The  external  layer  is  made  up  of  ordinary  connective-tissue,  being 
composed  of  layers  of  fibrous  tissue  with  branched  connective-tissue 
corpuscles  here  and  there  between  the  bundles  of  fibres.  The  internal 
layer  consists  of  a  network  of  fine  fibrils  with  a  large  number  of  nucle- 
ated cells  with  a  certain  addition  of  albuminous  ground  or  cement  sub- 
stance between  the  fibrous  bundles,  some  of  which  are  oval,  others 
drawn  out  into  long  branched  processes:  it  is  more  richly  supplied 
with  capillaries  than  the  outer  layer.  The  relatively  large  number  of 
its  cellular  elements,  which  vary  in  size  and  shape,  together  with  the 
abundance  of  its  blood-vessels,  clearly  mark  it  out  as  the  portion  of  the 
periosteum  which  is  immediately  concerned  in  the  formation  of  bone. 

In  such  a  bone  as  the  parietal,  which  is  represented  then  when  ossi- 
fication commences  by  the  species  of  fibrous  connective  tissue  with  many 
cells  above  indicated,  the  deposition  of  bony  matter,  which  is  preceded 
by  increased  vascularity,  takes  place  in  radiating  spiculfe,  starting  from 
a  centre  of  ossification,  and  shooting  out  in  all  directions  toward  the 
periphery.  These  primary  bony  spiculae  consist  of  the  fibres  of  the  tis- 
sue which  are  termed  osteogenetic  fibres,  composed  of  a  soft  transparent 
substance  called  osteogen,  in  which  calcareous  granules  are  deposited. 
The  fibres  are  said  to  exhibit  in  their  precalcified  state  indications  of  a 
fibrillar  structure,  and  are  likened  to  bundles  of  white  fibrous  tissue,  to 
which  they  are  similar  in  chemical  composition,  but  from  which  they 
differ  in  being  stiffer  and  less  wavy.  The  deposited  granules  after  a 
time  become  so  numerous  as  to  fill  up  the  substance  of  the  fibres  and 
bon^  opiculfe  result.  Calcareous  granules  are  deposited  also  in  the  in- 
terfibrillar  matrix.  By  the  junction  of  the  osteogenetic  fibres  and  their 
resulting  bony  spiculse  a  meshwork  of  bone  is  formed.  The  osteo- 
genetic fibres,  which  become  indistinct  as  calcification  proceeds,  are 
believed  to  persist  in  the  lamellas  of  adult  bone.  The  osteoblasts,  being 
in  part  retained  within  the  bone  trabeculte  thus  produced,  form  bone 
corpuscles.  On  the  bony  trabecul®  first  formed,  layers  of  osteoblastic 
cells  from  the  osteo-genetic  layer  of  the  periosteum  are  developed  side  by 
side,  lining  the  irregular  spaces  like  an  epithelium  (fig.  65,  b).  Lime- 
salts  are  deposited  in  the  circumferential  part  of  each  osteoblast,  and 
thus  a  ring  of  osteoblasts  gives  rise  to  a  ring  of  bone  with  the  remaining. 


62 


HANDBOOK    OF    PHYSIOLOrxY. 


uncalcified  portions  of  the  osteoblasts  imbedded  in  it  as  bone  corpuscles, 
as  in  the  first  formation;  then  the  central  portion  of  the  bony  plate 
becomes  harder  and  less  cancellous.  At  the  same  time,  the  plate  in- 
creases at  the  iDerijihery  not  only  by  the  extension  of  the  bony  spiculae, 
but  also  by  deposits  taking  place  from  the  osteogenetic  layer  of  the 
periosteum. 

The  primitive  spongy  bone  is  formed,  and  its  irregular  branching 
spaces  are  occupied  by  processes  from  the  osteogenetic  layer  of  the  peri- 
osteum consisting  of  numerous  blood-vessels  and  osteoblasts.  Portions 
of  this  primitive  spongy  bone  are  re-absorbed.  The  osteoblasts  are 
arranged  in  concentric  successive  layers  and  give  rise  to  concentric 
Haversian  lamellae  of  bone,  while  the  irregular  space  in  the  centre  is 
reduced  to  a  well-formed  Haversian  canal,  containing  the  usual  blood- 
vessels, the  portions  of  the  primitive  spongy  bone  between  the  Haversian 


Fig.  65.— Osteoblasts  from  the  parietal  bone  of  a  human  embiyo,  thirteen  weeks  old.  a,  Bony 
septa  with  the  cells  of  the  lacunae;  b,  layers  of  osteoblasts;  c,  the  latter  in  transition  to  bone  cor- 
puscles.   Highly  magnified.     (Gegenbaur.) 


systems  remaining  as  interstitial  or  ground-lamellge  (p.  59).  The  bulk 
of  the  j)rimitive  spongy  bone  is  thus  gradually  converted  into  compact 
bony-tissue  of  Haversian  systems.  Those  portions  of  the  ingrowths 
from  the  deeper  layer  of  the  periosteum  which  are  not  converted  into 
bone  remain  in  the  spaces  of  the  cancellous  tissue  as  the  red  marrow. 

Ossification  in  Cartilage. — Under  this  heading,  taking  the  femur 
as  a  typical  example,  we  may  consider  the  process  by  which  the  solid 
cartilaginous  rod  which  represents  the  bone  in  the  foetus  is  converted 
into  the  hollow  cylinder  of  compact  bone  with  expanded  ends  formed 
of  cancellous  tissue  of  which  the  adult  femur  is  made  up.  We  must 
bear  in  mind  the  fact  that  this  foital  cartilaginous  femur  is  many  times 
smaller  than  the  medullary  cavity  even  of  the  shaft  of  the  mature  bone, 
and,  therefore,  that  not  a  trace  of  the  original  cartilage  can  be  present 
in  the  femur  of  the  adult.  Its  j^urpose  is  indeed  purely  temporary;  and, 
after  its  calcification,  it  is  gradually  and  entirely  absorbed  as  will  be 
presently  explained. 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


63 


The  cartilaginous  rod  which  forms  the  foetal  femur  is  sheathed  in  a 
membrane  termed  the  perichondrium,  which,  so  far  resembles  the  peri- 
osteum described  above,  as  to  consist  of  two  layers,  in  the  deeper  one  of 
which  spheroidal  cells  jDredominate  and  blood-vessels  abound,  while  the 
outer  layer  consists  mainh'  of  fusiform  cells  which  are  in  the  mature 
tissue  gradually  transformed  into  fibres.  Thus,  the  differences  betweeu 
the  foetal  perichondrium  and  the  periosteum  of  the  adult  are  such  as 
^i':l-^i  r-j-'-v.,   usually  exist   between  the  embry- 

f^"  tI:  =-  '  "    onic  and  mature  forms  of  conuec- 

%^  ^  ^-  ^  ';  tive  tissue. 

%\  .ts  Between  the   hyaline    cartilage 

ll'v  -:    '-  _    of  v.liich  the  foetal  femur  consists 

^  §m  and  the  bony  tissue   forming  the 

i%|   :.  '       adult  femur,  there    are    tv:o    cliief 

ac/fif:^  intermediate    stages  —  viz.    (1)    of 


■!=.<^  <=r 


=*-^        <C3 


Fig.  66. 


Fig.  67. 


Fig.  66.— Ossifying  cartilage  showing  loops  of  blood-vessels. 

Fig.  67.— Longitudinal  section  of  ossifying  cartilage  from  the  humerus  of  a  foetal  sheep.  Cal- 
cified trabeculce  are  seen  extending  between  the  columns  of  cartilage  cells,  c,  Cartilage  cells. 
X  140.    (Sharpey.) 

calcified  cartilage,  and  (2)  of  embryonic  spongy  bone.     These  ma- 
terials, which  successively  occupy  the  place  of  the  foetal  cartilage,  are 
in  succession  entirely  absorbed,  and  their  place  is  taken  by  true  bone. 
The  process  by   which  the  cartilaginous  is  transformed    into    the 


64 


HANDBOOK    OF    PHYSIOLOGY. 


bony  femnr  may  however  be  divided  for  the  sake  of  clearness  into  the 
following  six  stages : — 

Stage  1. — Proliferation  and  Calcification. — As  ossification  is 
commencing  the  cartilage  cells  in  and  near  the  centre  of  ossification  he- 
come  enlarged  and  proliferate,  arranging  themselves  in  rows  correspond- 
ing to  the  long  axis  of  the  bone  (fig.  67).  Lime  salts  are  next  deposited 
in  the  form  of  fine  grannies  in  the  hyaline  matrix  of  the  cartilage,  and 
this  gradually  becomes  transformed  into  a  number  of  calcified  trabecular. 


Fig.  68.— Transverse  section  of  a  portion  of  a  metacarpal  bone  of  a  fcetus.  showing— 1,  flbfous 
layer  of  periosteum ;  2,  osteogenetic  layer  of  ditto  ;  3,  periosteal  bone ;  4,  cartilage,  with  matrix 
gradually  becoming  calcified,  as  at  5.  with  cells  in  primary  areolee;  beyond  5  the  calcified  matrix  is 
being  entirely  replaced  by  spongy  bone,     x  300.     (V.  D.  Harris.) 

(fig.  68,  5),  inclosing  alveolar  spaces,  which  are  the pi'imary  areolw,  and 
which  contain  cartilage  cells.  The  cartilage  cells,  gradually  enlarging, 
become  more  transparent,  and  finally  undergo  disintegration.  During 
this  stage  the  perichondrium  has  become  the  periosteum,  and  is  be- 
ginning to  deposit  bone  on  the  outside  of  the  cartilage. 

Stage  2. — Vascularization  of  the  Cartilage. — Processes  from 
the  osteogenetic  or  cellular  layer  of  the  periosteum  containing  blood- 
vessels break  into  the  substance  of  the  cartilage  and  grow  much  as  ivy 
insinuates  itself  into  the  cracks  and  crevices  of  a  wall.  This  begins  aii 
the  "centres  of  ossification,"  from  which  the  blood-vessels  spread  chiefly 


THE    STRUCTURE   OF   THE    ELEMENTARY   TISSUES.  05 

up  and  down  the  shaft,  etc.  Thus  the  substance  of  the  cartihige,  which 
previous]}'  contained  no  vessels,  is  traversed  by  a  number  of  branched  anas- 
tomosing channels  formed  by  the  enlargement  and  coalescence  of  the 
spaces  in  which  the  cartilage-cells  lie,  and  containing  loops  of  blood- 
vessels (fig.  GG)  and  spheroidal  cells  whicli  will  become  osteoblasts.  By 
further  absorption  of  some  of  the  trabeculiB  larger  spaces  are  devel- 
oped, which  contain  cartilage-cells  for  a  very  short  time  only,  their 
places  being  taken  by  the  so-called  osteogenetic  layer  of  the  periosteum 
which  constitutes  the  primary  marrow. 

Stage  3. — Substitution  of  Embryonic  Spongy  Bone  for  Carti' 
lage. — The  cells  of  the  primary  marrow  arrange  themselves  as  a  contin- 
uous layer  like  epithelium  ou  the  calcified  trabecul£e  and  deposit  a  layer 


«  'P  ^  ®  9 


"Fig.  69.-— a  small  isolated  mass  of  bone  nex*-  the  periosteum  of  the  lower  jaw  of  human 
fCEtus.  (I.  Osteogenetic  layer  <if  periosteum,  gr,  multinnclear  giant  cells,  the  one  on  the  left  acting 
here  i)robably  like  an  osteocltist.  .-\bove  c,  the  osteoblasts  are  seen  to  become  surrounded  by  an 
osseous  matrix.     (Klei.j  and  Noble  Smith.) 

of  bone,  and  enslieath  them :  tl:e  calcified  trabecula?,  encased  in  the 
sheaths  of  joung  bone,  become  gradually  absorbed,  so  that  finally  we 
have  trabeculas  composed  entirely  of  spongy  bone,  ail  trace  of  the  orig- 
inal calcified  cartilage  having  disappeared.  It  is  probable  that  the  large 
multiuucleated  giant-cells  termed  osfeocJasfs  by  Kolliker,  which  are  de- 
rived from  the  osteoblasts  by  the  multiplication  of  their  nuclei,  are  the 
agents  by  which  the  absorption  of  calcified  cartilage,  and  subsequently 
of  embryonic  spongy  bone,  is  carried  on  (fig.  69,  g).  At  any  rate,  they 
are  almost  always  found  wherever  absorption  is  in  progress. 

These  stages  are  precisely  similar  to  what  goes  on  in  the  growing 
shaft  of  a  bone  which  is  increasing  in  length  by  the  advance  of  the 
process  of  ossification  into  the  intermediary  cartilage  between  the  dia- 
physis  and  epiphysis.  In  this  case  the  cartilage-cells  become  flattened 
and,  multiplying  by  division,  are  grouped  into  regular  columns  at  right 


66 


HANDBOOK    OF    PHYSIOLOGY. 


angles  to  the  plane    of  calcification,  while   che  process  of  calcification 
extends  into  the  hyaline  matrix  between  them  (figs.  67  and  68). 

Stage  4. — Substitution  of  Periosteal  Bone  for  the  Primary 
Embryonic  Spongy  Bone. — The  embryonic  spongy  bone,  formed  as 
above  described,  is  simply  a  temporary  tissue  occupying  the  place  of  the 
fcetal  rod  of  cartilage,  once  representing  the  femur;  and  the  stages  1, 


Fig.  70. — Transverse  section  through  the  tibia  of  a  foetal  kitten,  semi-diagrammatic.  X  60. 
P,  Periosteum.  O,  Osteogenetic  layer  of  the  periost-  um  showing  the  osteoblasts  arranged  side  by 
side,  represented  as  pear-shaped  black  dots  on  the  surface  of  the  newly-formed  bone.  B,  The  peri- 
osteai  bone  deposited  iu  successive  layers  beneath  the  periosteum  and  ensheathing  E,  the  spongy 
endochondral  bone;  represented  as  more  deeply  shaded.  Within  the  trabeculse  of  endochondral 
spongy  bone  are  seen  the  remains  of  the  calcified  cartilage  trabeciilse  represented  as  dark  wavy 
lines.  C,  The  medulla,  with  V,  V,  veins.  In  the  lower  half  of  the  figure  the  endochondral  spongy 
bone  has  been  completely  absorbed.     (Klaiu  and  Noble  Smith. J 


2,  and  3  show  the  successive  changes  which  occur  at  the  centre  of  the 
shaft.  Periosteal  bone  is  at  the  same  time  deposited  in  successive  layers 
beneath  the  periosteum,  f  e. ,  at  tlie  circumference  of  the  shaft,  exactly  as 
described  in  the  section  on  ossification  in  membrane,  and  thus  a  casing 
of  periosteal  bone  is  formed  around  the  embryonic  endochondral  spongy 
bone:  this  casing  is  thickest  at  tiie  centre,  where  it  is  first  formed,  and 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


67 


thins  out  toward  each  end  of  tlie  sliaft.  Tlie  embryonic  spongy  bone  is 
absorbed,  through  the  agency  of  osteoclasis,  its  trabecule  becoming 
gradually  thiuned  and  its  meshes  enlarging,  and  finally  coalescing  into 
one  great  cavity — the  medullary  cavity  of  the  shaft. 

Stage  5. — Absorption  of  the  Inner  Layers  of  the  Periosteal 
Bone. — The  absorption  of  the  endochondral  spongy  bone  is  now  com- 
plete, and  the  medullary  cavity  is  bounded  by  periosteal  bone:  the  inner 
layers  of  this  periosteal  bone  are  next  absorbed,  and  the  medullary  cavity 
is  thereby  enlarged,  while  the  deposition  of  bone  beneath  the  periosteum 


Fig.  71.— Tranverse  section  of  femur  of  a  human  embryo  about  eleven  weeks  old.  a.  Rudimen- 
tary Haversian  canal  in  cross-section;  b,  in  longitudinal  section;  c,  osteoblasts;  d,  newly  formed 
osseous  subscance  of  a  lighter  color;  e,  that  of  greater  age;  /,  lacuuse  with  their  cells;  gr,  a  cell  still 
united  to  an  osteoblasi.    i^Frey.) 


continues  as  before.     The  first-formed   periosteal   bone   is   spongy   in 
character. 

Stage  G.— Formation  of  Compact  Bone.— The  transformation  of 
spongy  periosteal  bone  into  compact  bone  is  effected  in  a  manner  exactly 
similar  to  that  which  has  been  described  in  connection  with  ossification 
in  membrane  (p.  61).  The  irregularities  in  the  walls  of  the  areolte  in 
the  spongy  bone  are  absorbed,  while  the  osteoblasts  which  line  them  are 
developed  in  concentric  layers,  each  layer  in  turn  becoming  ossified  till 
the  comparatively  large  space  in  the  centre  is  reduced  to  a  well-formed 
Haversian  canal  (fig.  Tl).  When  once  formed,  bony  tissue  growls  to 
some  extent  interstitially,  as  is  evidenced  by  the  fact  that  the  lacuuiK  are 
rather  further  apart  in  full-formed  than  in  young  bone. 


68  HAIfDBOOK    OF   PHYSIOLOGY. 

From  the  foregoing  descrijation  of  the  development  of  bone,  it  will  be 
seen  that  the  common  terms  ossification  in  cartilage  and  ossification  in 
membrane  &.ve  a.j)t  to  mislead,  since  they  seem  to  imply  two  processes 
radically  distinct.  The  process  of  ossification,  however,  is  in  all  cases 
one  and  the  same,  all  true  bony  tissue  being  formed  from  membrane 
(perichondrinm  or  periosteum);  but  in  the  development  of  such  a  bone 
as  the  femur,  which  may  be  taken  as  the  type  of  so-called  ossification  in 
cartilage,  lime-salts  are  first  of  all  deposited  in  the  cartilage;  this  calci- 
fied cartilage,  however,  is  gradually  and  entirely  re-absorbed,  being  ulti- 
mately replaced  by  bone  formed  from  the  periosteum,  till  in  the  adult- 
structure  nothing  but  true  bone  is  left.  Thus,  in  the  process  of  "  ossi- 
fication in  cartilage,"  calcification  of  the  cartilaginous  matrix  jDrecedes 
the  real  formation  of  bone.  We  must,  therefore,  clearly  distinguish 
between  calcification  and  ossification.  The  former  is  simply  the  infil- 
tration of  an  animal  tissue  with  lime-salts,  and  is,  therefore,  a  change  of 
chemical  composition  rather  than  of  structure;  while  ossification  is  the 
formation  of  true  bone — a  tissue  more  complex  and  more  highly  organ- 
ized than  that  from  Avhich  it  is  derived. 

Centres  of  Ossification. — In  all  bones  ossification  commences  at 
one  or  more  points,  termed  centres  of  ossifi-cation.  The  long  bones,  e.g., 
femur,  humerus,  etc.,  have  at  least  three  such  points — one  for  the  ossifi- 
cation of  the  shaft  or  diapliysis,  and  one  for  each  articular  extremity 
or  epipliysis.  Besides  these  three  primary  centres  which  are  always 
present  in  long  bones,  various  secondary  centres  may  be  superadded  for 
the  ossification  of  different  ^^rocgs-se^. 

Growth  of  Bone. — Bones  increase  in  length  by  the  advance  of  the 
process  of  ossification  into  the  cartilage  intermediate  between  the  dia- 
physis  and  epiphysis.  The  increase  in  length  indeed  is  due  entirely  to 
growth  at  the  two  ends  of  the  slicft.  This  is  proved  by  inserting  two 
pins  into  the  shaft  of  a  growing  bone:  after  some  time  their  distance 
apart  will  be  found  to  be  unaltered  though  the  bone  has  gradually  in- 
creased in  length,  the  growth  having  taken  place  beyond  and  not  be- 
tween them.  If  now  one  pin  be  placed  in  the  shaft,  and  the  other  in 
the  epiphysis  of  a  growing  bone,  their  distance  apart  will  increase  as  the 
bone  grows  in  length. 

Thus  it  is  that  if  the  epiphyses  with  the  intermediate  cartilage  be 
removed  from  a  young  bone,  growth  in  length  is  no  longer  possible; 
while  the  natural  termination  of  growth  of  a  bone  in  length  takes  place 
when  the  epiphyses  become  united  in  bony  continuity  with  the  shaft. 

Increase  in  thichness  in  the  shaft  of  a  long  bone  occurs  by  the  depo- 
sition of  successive  layers  beneath  the  periosteum. 

If  a  thin  metal  plate  be  inserted  beneath  the  periosteum  of  a  grow- 
ing bone  it  will  soon  be  covered  by  osseous  deposit,  but  if  it  be  put  be- 


THE    STEUCTURE    OF    THE    ELEMENTARY    TISSUES. 


69 


tween  the  fibrous  and  osteogenetic  layers  it  will  never  become  enveloped 
in  bone,  for  all  the  bone  is  formed  beneath  the  latter. 

Other  varieties  of  connective  tissue  may  become  ossified,  e.g.,  the 
tendons  in  some  birds. 

Functions  of  Bones. — Bones  form  the  framework  of  the  body;  for  • 
this  they  are  fitted  by  their  hardness  and  solidity  together  with  their 
comparative  lightness;  they  serve  both  to  protect  internal  organs  in  the 
trunk  and  skull,  and  as  levers  worked  by  muscles  in  the  limbs;  not- 
withstanding their  hardness  they  possess  a  considerable  degree  of  elas- 
ticity, which  often  saves  them  from  fracture. 

The  material  of  which  the  chief  iDortion  of  the  teeth  is  made  up, 
called  Dentine,  is  frequently  classed  with  bone  and  as  one  of  the  con- 
nective tissues.  The  other  constituents  of  the  teeth  also  resemble  bone 
in  structure  to  a  considerable  degree;  it  will  be  as  well  therefore  to  give 
in  this  jilace  some  account  of  the  teeth. 

The  Teeth. 

During  the  course  of  his  life,  man,  in  common  with  most  other 
mammals,  is  provided  with  two  sets  of  teeth;  the  first  set,  called  the 


Fig.  79.-  Normal  well-formed  jaws,  from  which  the  alveolar  plate  has  been  in  great  part  removed, 
so  as  to  expose  the  developing  permanent   teeth  in  their  crypts  in  tlie  jaws.     (Tomes.) 


temporary  or  milh  teeth,  makes  its  appearance  in  infancy,  and  is  in  the 
course  of  a  few  years  shed  and  replaced  by  the  second  or  permanent  set. 

The  temporary  or  milk  teeth  have  only  a  very  limited  term  of 
existence. 

They  are  ten  in  number  in  each  jaw,  namely,  on  either  side  from  the 
middle  line  two  incisors,  one  canine,  and  two  deciduous  molars,  and  are 
replaced  by  ten  permanent  teeth.     'J'he  number  of  permanent  teeth  in 


70 


HANDBOOK    OF    PHYSIOLOGY. 


each  jaw  is,  however,  increased  to  sixteen  by  the  development  of  three 
molars  on  each  side  of  the  jaw,  which  are  called  the  permanent  or  true 
molars. 

The  following  formula  shows,  at  a  glance,  the  comparative  arrange- 
ment and  number  of  the  temporary  and  permanent  teeth : — 


MOLARS.  CANINE. 

2  1 


Temporary  Teeth. 

Middle  Line  of  Jaw. 

incisors.  incisors. 

2 


2 


CANUTE. 
1 


MOLARS. 

2=10 


2=10 


BICUSPIDS 
TRUE  OR  PRE- 

MOLARS.     MOLARS. 

3  2 


CANINE. 
1 


Permanent  Teeth. 

3IIDDLE  Line  op  Jaw. 

INCISORS. 

2 


CANINE. 
1 


BICUSPIDS 

OR  PRE-  TRUE 

MOLARS.  MOLARS. 

2  3 


From  this  formula  it  will  be  seen  that  the  two  bicuspid  or  pre-molar 
teeth  in  the  adult  are  the  successors  of  the  two  deciduous  molars  in  the 
child.  They  differ  from  them,  however,  in  some  respects,  the  temporary 
molars  having  a  stronger  likeness  to  the  permanent  than  to  their  imme- 
diate descendants  the  so-called  bicuspids,  besides  occupying  more  space 
in  the  jaws. 

The  temporary  incisors  and  canines  differ  from  their  successors  but 
little  except  in  their  smaller  size  and  the  abrupt  manner  in  which  their 
enamel  terminates  at  the  necks  of  the  teeth,  forming  a  ridge  or  thick 
edge.     Their  color  is  more  of  a  bluish-white  than  of  a  yellowish  shade. 

The  following  tables  show  the  average  times  of  eruption  of  the 
Temporary  and  Permanent  teeth.  In  both  cases  the  eruption  of  any 
given  tooth  of  the  lower  precedes,  as  a  rule,  that  of  the  corresponding 
tooth  of  the  upper  jaw. 

Temporary  or  Milk  Teeth. 

The  fisrures  indicate  in  months  the  age  at  which  each  tooth  appears. 


LOWER   CENTRAL 
INCISORS. 

UPPER  INCISORS. 

FIRST   MOLARS   AND  LOWER 
LATERAL  INCISORS. 

CANINES. 

SECOND  MOLARS. 

6  to  0 

8  to  12 

12  to  15 

18  to  24 

24  to  30. 

THE    STKUCTURE    OF   THE    ELEMENTARY    TISSUES. 


71 


Permanent  Teeth. 

The  age  at  which  each  tooth  is  cut  is  indicated  in  this  table  in  years. 


FIRST 
MOLARS. 


CENTRALS. 


LATERALS. 


BICUSPIDS    OR   PRE- 
MOLARS. 
FIRST.         i      SECOND. 


10 


12  to  14 


SECOND 
MOLARS. 


12  to  15 


THIRD 
MOLARS  OR 
WISDOMS. 


17  to  25 


The  times  of  eruption  given  in  the  above  tables  are  only  approxi- 
mate: the  limits  of  variation  being  tolerably  wide.  Some  children  may 
cut  their  first  teeth  before  the  age  of  six  months,  and  others  not  till 
nearly  the  twelfth  month.  In  nearly  all  cases  the  two  central  incisors 
of  the  lower  jaw  are  cut  first,  these  being  succeeded  after  a  short  inter- 
val by  the  four  incisors  of  the  ujjper  jaw;  next  follow  the  lateral  in- 
cisors of  the  lower  jaw,  and  so  on  as  indicated  in  the  table  till  the  com- 
pletion of  the  milk  dentition  at  about  the  age  of  two  years.  Certain 
diseases  affecting  the  bony  skeleton,  e.g.,  Rickets,  retard  the  eruptive 
period  considerably. 

The  milk-teeth  usually  come  through  in  batches,  each  period  of 
eruption  being  succeeded  by  one  of  quiescence  lasting  sometimes  several 
months.  The  milk-teeth  should  be  in  use  from  the  age  of  two  up  to 
within  a  few  months  of  the  time  for  their  successors  to  appear.  Their 
retention  serves  the  purpose  of  preserving  the  necessary  space  sufficient 
for  the  succeeding  permanent  teeth  to  occupy. 

It  is  important  to  notice  that  it  is  a  molar  which  is  the  first  tooth  to 
be  cut  in  the  permanent  dentition,  not  an  incisor  as  in  the  case  of  the 
temporary  set,  and  also  that  it  appears  behind  the  last  deciduous  molar 
on  each  side. 

The  third  molars,  often  called  Wisdoms,  are  sometimes  unerupted 
through  life  from  want  of  sufficient  jaw  space  and  the  presence  of  the 
other  teeth:  and  in  highly  civilized  races  there  are  evidences  to  show 
that  they  are  in  process  of  suppression  from  the  dental  series;  cases  of 
whole  families  in  which  their  absence  is  a  characteristic  feature  being 
occasionally  met  with. 

When  the  teeth  are  fully  erupted  it  will  be  observed  that  the  upper 
incisors  and  canines  project  obliquely  over  the  lower  front  teeth  and  the 
external  cusps  of  the  upper  bicuspids  and  molars  lie  outside  those  of 
the  corresponding  teeth  in  the  lower  jaw.  This  arrangement  allows  to 
some  extent  of  a  scissor-like  action  in  dividing  and  biting  food  in  the 
case  of  incisors;  and  a  grinding  motion  in  that  of  the  bicuspids  and 
molars  when  the  side  to  side  movements  of  the  lower  jaw  bring  the  ex- 
ternal cusps  of  the  lower  teeth  into  direct  articulation  with  those  of  the 


72  HANDBOOK    OF    PHYSIOLOGY. 

upper,  and  then  cause  them  to  glide  down  the  inclined  surfaces  of  the 
external  and  up  the  internal  cusps  of  these  same  upper  teeth  during 
the  act  of  mastication. 

The  work  of  the  canine  teeth  in  man  is  similar  to  that  of  his  incisors. 
Besides  being  a  firmly  implanted  tooth  and  one  of  stronger  substance 
than  the  others,  the  canine  tooth  is  important  in  preserving  the  shape 
of  the  angle  of  the  mouth,  and  by  its  shape,  whether  pointed  or  blunt, 
long  or  short,  becomes  a  character  tooth  of  the  dentition  as  a  whole  in 
both  males  and  females. 

Another  feature  in  the  fully  developed  and  properly  articulated  set 
of  teeth  is  that  no  two  teeth  oppose  each  other  only,  but  that  each  tooth 
antagonizes  with  two,  except  the  upper  Wisdom,  usually  a  small  tooth. 
This  is  the  result  of  the  greater  width  of  the  upper  incisors,  which  so 
arranges  the  "  bite  "  of  the  other  teeth  that  the  lower  canine  closes  in 
front  of  the  upper  one. 

Should  a  tooth  be  lost,  therefors,  it  does  not  follow  that  its  former 
opponent  remaining  in  the  mouth  is  rendered  useless  and  thereby  liable 
to  be  removed  from  the  jaw  by  a  gradual  process  of  extrusion  commonly 
seen  in  teeth  that  have  no  work  to  perform  by  reason  of  absence  of  an- 
tagonists. 

It  is  worthy  of  note  that  from  the  age  of  four  years  to  the  shedding 
of  the  first  milk-tooth  the  child  has  no  fewer  than  forty-eight  teeth, 
twenty  milk-teeth  and  twenty-eight  calcified  germs  of  permanent  teeth 
(all  in  fact  except  the  four  wisdom  teeth,  which  show  no  signs  of  devel- 
opment until  the  third  year). 

Structure  of  a  Tooth. 

A  tooth  is  generally  described  as  possessing  a  crown,  neck,  and  root 
or  roots. 

The  crown  is  the  portion  which  projects  beyond  the  level  of  the 
gum.  The  nech  is  that  constricted  portion  just  below  the  crown  which 
is  embraced  by  the  free  edges  of  the  gum,  and  the  root  includes  all  be- 
low this. 

On  making  longitudinal  and  transverse  sections  through  its  centre 
(fig.  73,  A,  b),  a  tooth  is  found  to  be  principally  composed  of  a  hard 
material,  dentine  or  ivory,  which  is  hollowed  out  into  a  central  cavity 
which  resembles  in  general  shape  the  outline  of  the  tooth,  and  is  called 
the  pulp  cavity  from  its  containing  the  very  vascular  and  sensitive  pulp. 

The  tooth  pulj)  is  composed  of  fibrous  connective  tissue,  blood-vessels, 
nerves,  and  large  numbers  of  cells  of  varying  shapes,  e.(/.,  fusiform,  stel- 
late, and  on  the  surface  in  close  connection  with  the  dentine  a  specialized 
layer  of  cells  called  odontoblasts,  which  are  elongated  columnar-looking 
cells  with  a  large  nucleus  at  the  tapering  ends  or  those  farthest  from 


THE   STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


73 


the  denti7ie  (the  hiyer  is  sometimes  mentioned  as  the  memhrona  ehoris, 
from  the  tenacity  with  which  it  clings  to  the  dentine),  all  are  imbedded 
in  a  mucoid  gelatinous  matrix. 

The  blood-vessels  and  nerves  enter  the  pulp  through  a  small  opening 
at  the  apical  extremity  of  each  root.  The  exact  terminations  of  the 
nerves  are  not  definitely  known.  They  have  never  been  observed  to 
enter  the  dentinal  tubes,  but  they  are  probably  connected  with  the  fibrils 
in  those  tubes  through  the  intervention  of  the  odontoblasts  and  deei)er 
layer  of  cells.     No  lymphatics  have  been  traced  to  the  pulp. 

A  layer  of  very  hard  calcareous  matter,  the  enamel,  caps  that  part 
of  the  dentine  which  projects  beyond  the  level  of  the  gum;  while  sheath- 


Fig.  73.— A.  Longitudinal  section  of  a  human  molar  tooth;  c,  cement;  d,  dentine:  e,  enamel;  v, 
pulp  cavity  (Owen),    b.  Trausverse  section.    The  letters  indicate  the  same  as  in  a. 

ing  the  portion  of  dentine  which  is  beneath  the  level  of  the  gum,  is  a 
layer  of  true  bone,  called  the  remenf  or  crii.sta  pefrosa. 

The  enamel  and  cement  are  very  thin  at  the  neck  of  the  tooth  where 
they  come  in  contact,  the  cement  overlapping  the  enamel.  A  thin  epi- 
thelial and  horny  nienibiane  (enamel  cuticle,  or  yas)ni/i/t\s  membrane) 
covers  the  outer  surface  of  the  enamel  on  unworn  teeth.  It  is  formed  of 
aliort  fiattened  pri.'^nis  which  are  the  remains  of  the  uncaleitied  last- 
formed  portions  of  the  enamel  prisms.  The  enamel  becomes  thicker 
toward  the  crown,  and  the  cement  toward  the  lower  end  or  apex  of  the 
root. 

I. — Den/ine  or  Ivory. 

Cheniiral  Composition. — Dentine  closely  resembles  bone  in  chemical 
comi)osition.  It  contains,  however,  rather  less  animal  matter;  the  pro- 
portion in  a  hundred  parts  being  al)out  twenty-eight  animal  to  seventy- 
two  of  earthy.  The  former,  like  the  animal  matter  of  bone,  may  be 
resolved  into  gelatin  by  boiling.  It  also  contains  a  trace  of  fat.  The 
earthy  matter  is  made  up  chiefly  of  calcium  jjJwsphate,  with  a  small  per- 


74 


HANDBOOK    OF    PHYSIOLOGY. 


tion  of  the  carbonate,  and  traces  of  calcium  fluoride  and  magnesium 
pliospJiate. 

Structure. — Under  the  microscope  dentine  is  seen  to  be  finely  chan- 
nelled by  a  multitude  of  delicate  tubes,  which,  by  their  inner  ends  com- 


Enamel 


Dentine. 


Periosteum 
of  alveolus. 


-—  Cement. 


Fig.  74. — Premolar  tooth  of  cat  in  situ. 


municate  with  the  pulp-cavity,  and  by  their  outer  extremities  come  into 
contact  with  the  under  part  of  the  enamel  and  cement,  and  sometimes 


go  a. 

Fig.  75.— Section  of  a  portion  of  the  dentine  and  cement  from  the  middle  of  the  root  of  an  incisor 
tooth,  a,  Dental  tubuli  ramifying  and  terminating,  some  of  them  in  the  interglobular  spaces  b  and 
c,  which  somewhat  resemble  bone  lacunae;  d,  inner  layer  of  the  cement  with  numerous  closely  set 
canalicuh;  e,  outer  layer  of  cement;  /,  lacunae;  g,  canahculi.     X  350.    (Kolliker.J) 

even  penetrate  them  for  a  greater  or  less  distance  (figs.  75,  77).  The 
matrix  in  which  these  tubes  lie  is  composed  of  "a  reticulum  of  fine 
fibres  of  connective  tissue  modified  by  calcification,  and  where  that  pro- 


THE    STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  75 

cess  is  complete,  entirely  hidden  by  the  densely  deposited  lime  salts'* 
(Mummery). 

In  their  course  from  the  pulp-cavity  to  the  surface  the  minute  tubes 
form  gentle  and  nearly  parallel  curves  and  divide  and  subdivide  dicho- 
tomously,  but  without  much  lessening  of  their  calibre  until  they  are 
approaching  their  jDeripheral  termination. 

From  their  sides  proceed  other  exceedingly  minute  secondary  canals, 
which  extend  into  the  dentine  between  the  tubules  and  anastomose  with 
each  other.  The  tubules  of  the  dentine,  the  average  diameter  of  which 
at  their  inner  and  larger  extremity  is  j^Vo  of  an  inch,  contain  fine  pro- 
longations from  the  tooth-pulj),  which  give  the  dentine  a  certain  faint 
sensitiveness  under  ordinary  circumstances  and,  without  doubt,  have  to 
do  also  Avith  its  nutrition.  These  prolongations  from  the  tooth-pulp 
are  probably  processes  of  the  dentine-cells  or  odontohlasts  which  are 
branched  cells  lining  the  pulp-cavity;  the  relation  of  these  processes  to 
the  tubules  in  which  they  lie  being  precisely  similar  to  that  of  the  pro- 
cesses of  the  bone-corpuscles  to  the  canaliculi  of  bone.  The  outer  portion 
of  the  dentine,  underlying  the  cement,  and  the  enamel  to  a  much  lesser 
degree,  forms  a  more  or  less  distinct  layer  termed  the  granular  or  in- 
terglohular  layer.  It  is  characterized  by  the  presence  of  a  number  of 
irregular  minute  cell-like  cavities,  much  more  closely  packed  than  the 
lacuna3  in  the  cement,  and  communicating  with  one  another  and  with  the 
ends  of  the  dentine-tubes  (fig.  75,  b,  c),  and  containing  cells  like  bone- 
corpuscles. 

II, — Enamel. 

Chemical  Composition. — The  enamel,  which  is  by  far  the  hardest  por- 
tion of  a  tooth,  is  composed,  chemically,  of  the  same  elements  that  enter 
into  the  composition  of  dentine  and  bone.  Its  animal  matter,  how- 
ever, amounts  only  to  about  2  or  3  per  cent.  It  contains  a  larger  pro- 
portion of  inorganic  matter  and  is  harder  than  any  other  tissue  in  the 
body. 

Structure. — Examined  under  the  microscope,  enamel  is  found  com- 
posed of  fiine  hexagonal  fibres  (figs.  76,  77)  -g-yVo"  ^^  ^^  inch  in  diameter, 
which  are  set  on  end  on  the  surface  of  the  dentine,  and  fit  into  corre- 
sponding depressions  in  the  same. 

They  radiate  in  such  a  manner  from  the  dentine  that  at  the  top  of 
the  tooth  they  are  more  or  less  vertical,  while  toward  the  sides  they  tend 
to  the  horizontal  direction.  Like  the  dentine  tubules,  they  are  not 
straight,  but  disposed  in  wavy  and  parallel  curves.  The  fibres  are 
marked  by  transverse  lines,  and  are  mostly  solid,  but  some  of  them  may 
contain  a  very  minute  canal. 

The  enamel-prisms  are  connected  together  by  a  very  minute  quantity 
of  hyaline  cement-substance.     In  the  deeper  part  of  badly  formed  en- 


76 


HANDBOOK    OF    PHYSIOLOGY. 


amels,  between  the  prisms,  are  small  lacunm,  or  "interglobular  spaces" 
■which  have  the  processes  or  fibrils  of  the  dentine  tubes  in  connection  with 
them  (fig.  77,  c). 

A 


Fig.  76.— Enamel  fibres.  A,  Fragments  and  single  fibres  of  the  transversely-striated  enamel, 
isolated  by  the  action  of  hydrochloric  acid.  B,  Surface  of  a  small  fragment  of  enamel,  showing  the 
hexagonal  ends  of  the  fibres  with  dariser  centres,  or  not  so  higlily  calcified.     X  350.    (Kolliker.) 


III. — Crusta  Petrosa. 

The  crusta  petrosa,  or  cement  (fig.  75,  e,  cl),  is  composed  of  true  bone, 
and  in  it- are  lacunae  (/)  and  canaliculi  {g),  which  sometimes  communi- 
cate with  the  outer  finely  branched  ends  of  the  dentine  tubules,  and 
generally  with  the  interglobular  spaces.  Its  lamina3  are  as  it  were  bolted 
together  by  perforating  fibres  like  those  of  ordinary  bone  (Sharjoey's 
fibres).  Cement  differs  from  ordinary  bone  in  possessing  no  Haversian 
canals,  or,  if  at  all,  only  in  the  thickest  part.  Such  canals  are  more 
often  met  with  in  teeth  with  the  cement  hypertrophied  than  in  the 
normal  tooth. 

Development  of  the  Teeth. 

Development  of  the  Teetli. — The  first  step  in  the  development  of  the 
teeth  consists  in  a  downward  growth  (fig.  78,  a,  1)  from  the  Rete  Mal- 
pighi  or  the  deeper  layer  of  stratified  epithelium  of  the  mucous  mem- 
brane of  the  mouth,  which  first  becomes  thickened  in  the  neighborhood 
of  the  maxillae  or  jaws  now  in  the  course  of  formation.  This  process 
passes  downward  into  a  recess  of  the  imi^erfectly  developed  tissue  of  the 
embryonic  Jaw.  The  downward  epithelial  growth  forms  the  primary 
enamel  organ  or  enamel  germ,  and  its  position  is  indicated  by  a  slight 
groove  in  the  mucous  membrane  of  the  jaw.  The  next  step  in  the  pro- 
cess consists  in  the  elongation  downward  of  the  enamel  groove  and  of 


THE    STRUCTURE    OF   THE    ELEMEXTARY    TISSUES. 


77 


the  enamel  germ  and  tlie  inclination  outward  of  tlie  deeper  part  (fig. 
78,  B,  f),  which  is  now  inclined  at  an  angle  with  the  upper  portion  or 
neck  ( f),  and  has  become  bulbous.  After  this  there  is  aji  increased  de- 
velopment at  certain  points  corresj)onding  to  the  situations  of  the  future 
milk-teeth.  The  enamel  germ,  or  common  enamel  germ,  as  it  may  be 
called,  becomes  divided  at  its  deeper  portion,  or  extended  by  further 


1 


Fig. 


Fig.  78 


Fig.  77.— Thin  section  of  the  enamel  and  a  part  of  the  dentine,  a.  Ciiticular  pellicle  of  the 
enamel  (Xasmyth's  membrane);  b.  enamel  fibres,  or  columns  with  Assures  between  them  and 
cross  stria-:  c-,  larger  cavities  in  the  enamel,  communicating  with  the  extremities  of  some  of 
the  dentinal  tubuli  (//).     X  'ihO.     (KiJlliker.^ 

Fig.  78.— bection  of  the.upper  iaw  of  a  fcetal  sheep.  A.— 1,  Common  enamel  germ  dipping  down 
into  the  mucous  membrane:  'i,  palatine  process  of  jaw;  H,  rete  Malpighi.  B. — Section  similar  to  A, 
but  passing  through  one  of  the  special  enamel  germs  here  becoming  tlask -shaped;  c,  c',  epithelium 
of  mouth;  /.  neck;  /',  body  of  special  enamel  germ.  C.~A  later  stage;  c,  outline  of  epithelium  of 
gum;  /,  neck  of  enamel  germ:  /',  enamel  organ;  p,  pajiilla;  .s,  dental  sac  foniiing;  f  p.  the  enamel 
germ  of  permanent  tooth;  »!,  bone  of  jaw;  r,  vessels  cut  across.  (Waldeyer  and  Kolliker.)  Copied 
from  Quain's  Anatomy. 


growth,  into  a  number  of  special  enamel  germs  corresponding  to  each 
of  the  above-mentioned  milk-teeth,  and  connected  to  the  common  germ 
by  a  narrow  neck.  Each  tooth  is  thus  placed  in  its  own  special  recess  in 
the  embryonic  jaw  (lig.  78,  b,  //')• 


78 


HANDBOOK    OF    PHYSIOLOGY. 


As  these  changes  proceed,  there  grows  up  from  the  underlying  tissue 
into  each  enamel  germ  (fig.  78,  c,  j'j),  a  distinct  vascular  papilla  (dental 
papilla),  and  upon  it  the  enamel  germ  becomes  moulded,  and  presents 
the  appearance  of  a  cap  of  two  layers  of  epithelium  separated  by  an  in- 
terval (fig.  78,  c, /').  While  part  of  the  sub-epithelial  tissue  is  elevated 
to  form  the  dental  papillas,  the  part  which  bounds  the  embryonic  teeth 
forms  the  dental  sacs  (fig.  78,  c,  s) ;  and  the  rudiment  of  the  jaw,  at  first 
a.  bony  gutter  in  which  the  teeth  germs  lie,  sends  up  processes  forming 
partitions  between  the  teeth.  In  this  way  small  chambers  are  produced 
in  which  the  dental  sacs  are  contained,  and  thus  the  sockets  of  the  teeth 
are  formed.  The  papilla,  which  is  really  part  of  the  dental  sac  (if  one 
thinks  of  this  as  the  whole  of  the  sub-epithelial  tissue  surrounding  the 
enamel  organ  and  interposed  between  the  enamel  germ  and  the  develop- 
ing bony  jaw),  is  composed  of  nucleated  cells  arranged  in  a  meshwork. 


Fig  79. — Part  of  section  of  developing  tooth  of  a  young  rat,  showing  the  mode  of  deposition  of 
the  dentine.  Highly  magnified,  a,  Outer  layer  of  fully  formed  denline;  6,  uncalcifled  matrix  with 
one  or  two  nodules  of  calcareous  matter  near  the  calcified  parts;  c,  odontoblasrs  sending  processes 
into  the  dentine:  d,  pulp;  e,  fusiform  or  wedge-shape  cells  found  between  odontoblasts;  /,  stellate 
•cells  of  pulp  in  fibrous  connective  tissue.  The  section  is  stained  in  carmine,  which  colors  the  un- 
calcifled matrix  but  not  the  calcified  part.     (E.  A.  Schafer.) 

the  outer  or  peripheral  part  being  covered  with  a  layer  of  columnar  nu- 
cleated cells  called  odontoblasts.  The  odontoblasts  possibly  form  the 
dentine,  while  the  remainder  of  the  papilla  forms  the  tooth-pulp.  The 
method  of  the  formation  of  the  dentine  from  the  odontoblasts  is  said  to 
"be  as  follows :  The  cells  elongate  at  their  outer  part,  and  these  processes 
are  directly  converted  into  the  tubules  of  dentine  (fig.  79,  6'),  and,  ac- 
cording to  some,  into  the  contained  fibrils  as  well.  The  continued  for- 
mation of  dentine  proceeds  by  the  elongation  of  the  odontoblasts,  and 
their  subsequent  conversion  by  a  process  of  calcification  into  dentine  tu- 
bules. The  most  recently  formed  tubules  are  not  immediately  calcified. 
The  deatine  fibrils  contained  in  the  tubules  are  said,  by  others,  to  be 
formed  from  processes  of  the  deeper  layer  of  odontoblasts,  which  are 
wedged  in  between  the  cells  of  the  superficial  layer  (fig.  79,  e)  which  form 
the  tubules  only.  There  are  several  theories  upon  these  points.  The 
matrix,  according  to  more  recent  views,  is  formed  by  a  calcification  of 
the  fibrous  connective  tissue  developed  in  the  papilla. 

Since  the  papillae  are  to  form  the  main  portion  of  each  tooth,  i.e.,  the 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


79 


dentine,  each  of  them  early  takes  the  shape  of  the  crown  of  the  tooth 
to  which  it  corresponds.  As  the  dentine  increases  in  thickness  the 
p.ipillae  diminish,  and  at  last  when  the  tooth  is  cut  only  a  small  amount 
of  the  papilla  remains  as  the  dental  pulp,  and  is  supplied  by  vessels  and 
nerves  which  enter  at  the  end  of  the  root.  The  shape  of  the  crown  of 
the  tooth  is  taken  by  the  corresponding  papilla,  and  that  of  the  single 
or  double  root  by  the  subsequent  constriction  below  the  crown,  or  by 
division  of  the  lower  part  of  the  papilla.  The  number  of  roots  being 
foreshadowed  by  the  number  of  arteries  going  to  the  papilla.     The  roots 


Fig.  80.— Vertical  transverse  section  of  tiie  dental  sac,  pulp,  etc.,  of  a  kitten,  a.  Dental  papilla 
or  pulp:  6,  the  cap  of  dentine  formed  upini  the  summit;  c,  its  covering  of  enamel;  rf,  iuuer  ayer  of 
epitlieliuni  of  the  eiianiel  organ;  e.  Kelatiuous  tissue;  /,  outer  epithehal  layer  of  the  enamel  organ; 
(;,  inner  layer,  and  h,  outer  layer  of  dental  sac.     X  1-1.     CThiersch.) 

are  not  completely  formed  at  the  time  of  the  eruption  of  the  teeth,  but 
subsequently. 

The  enamel  cap  is  found  later  on  to  consist  (fig.  80,  d,  c,  f)  of  four 
jiarts:  (1)  an  inner  membrane,  composed  of  a  layer  of  columnar  epithe- 
lium in  contact  with  the  dentine,  called  enamel  cells;  (2)  outside  of 
these  one  or  more  layers  of  small  polyhedral  nucleated  cells  (sfrafum  in- 
icnnedium  of  Hannover) ;  (3)  an  outer  membrane  of  several  layers  of 
epithelium;  (4)  a  middle  membrane  formed  of  a  matrix  of  non-vascular 
gelatinous  tissue,  containing  stellate  cells.  The  enamel  is  formed  by  the 
enamel  cells  of  the  inner  membrane,  by  the  deposit  of  a  keratin-like 
substance,  which  subsequently  undergoes  calcification  and  forms  the  first 
layer.     Other  layers  are  formed   in   the  sam»  manner,  the  cells  retiring 


80  HANDBOOK    OF    PHTST'^LOGY. 

meanwhile,  until  -when  the  tooth  breaks  through  the  gum  it  is  covered 
by  an  iincalcified  layer  of  the  keratin-like  substance  which  is  called 
Nasmyth's  membrane.  At  this  time  the  other  layers  of  the  enamel  cap 
have  disappeared. 

The  cement  or  crusta  petrosa  is  formed  from  the  internal  tissue  of 
the  tooth  sac,  the  structure  and  function  of  which  are  identical  with 
those  of  the  osteogenetic  layer  of  the  periosteum,  or,  in  other  words,  os- 
sification in  membrane  occurs  in  it. 

The  outer  layer  or  portion  of  the  membrane  of  the  tooth  sac  forms 
the  fibrous  dental periodeum. 

This  periosteum,  w^hen  the  tooth  is  fully  formed,  is  not  only  a  means 
of  attachment  of  the  tooth  to  its  socket,  but  also  in  conjunction  with 
the  pulp  a  source  of  nourishment  to  it.  Additional  laminae  of  cement 
are  added  to  the  root  from  time  to  time  during  the  life  of  the  tooth,  us 
especially  well  seen  in  the  abnormal  condition  called  exostosis,  by  the 
process  of  calcification  taking  place  in  the  periosteum.  On  the  other 
hand  absorption  of  the  root  may  equally  occur  through  the  same  mem- 
brane. 

In  this  manner  the  first  set  of  teeth,  or  the  milk-teeth,  are  formed; 
and' each  tooth,  by  degrees  developing,  presses  at  length  on  the  Wiill  of 
the  sac  inclosing  it,  and,  causing  its  absorption,  is  cut,  to  use  a  familiar 
phrase. 

The  temporary  or  milk-teetli  are  speedily  replaced  by  the  growth  of 
the  permanent  teeth,  wdiich  push  their  way  up  from  beneath  them. 

Each  temporary  tooth  is  replaced  by  a  tooth  of  the  permanent  set 
which  is  developed  from  a  small  sac  set  by,  so  to  speak,  from  the  sac  of 
the  temporary  tooth  which  precedes  it,  and  called  the  cavity  of  reserve 
(fig.  78,  c,  fpj).  Thus  the  temporary  incisors  and  canines  are  succeeded 
by  the  corresponding  permanent  ones,  the  temporary  first  molar  by  the 
first  bicuspid,  the  temporary  second  molar  develops  two  offshoots,  one 
for  the  second  bicuspid,  the  other  for  the  permanent  first  molar.  The 
permanent  second  molar  is  budded  off  from  the  first  permanent  molar 
and  the  wisdom  from  the  permanent  second  molar. 

The  development  of  the  temporary  teeth  is  said  to  commence  about 
the  sixth  week  of  intra-uterine  life,  after  the  laying  down  of  the  bony 
structure  of  the  jaws.  Their  permanent  successors  begin  to  form  about 
the  sixteenth  w^eek  of  intra-uterine  life. 

The  second  permanent  molars  are  believed  to  originate  about  the 
third  month  after  birth,  and  the  wisdom  teeth  about  the  third  year. 


THE   STRUCTURE   OP   THE    ELEMENTARY    TISSUES. 


81 


III.  Muscular  Tissue. 

There  are  two  chief  kinds  of  muscular  tissue,  differing  both  in  mi- 
nute structure  as  well  as  in  mode  of  action,  viz.,  (1.)  the  jjlaiit,  or  non- 
driated,  and  (3.)  the  striated. 

Unstriped  or  Plain  Muscle. 

Distrilmtion. — Unstriped  muscle  forms  the  proper  muscular  coats 
(1.)  of  the  digestive  canal  from  the  middle  of  the  cesophagus  to  the  in- 
ternal sphincter  ani;  (2.)  of  the  ureters  and  urinary  bladder;  (3.)  of  the 
trachea  and  bronchi;  (-i.)  of  the  ducts  of  glands;  (5.)  of  the  gall-blad- 
der; (G.)  of  the  vosicula?  seminales;  (7.)  of  the  pregnant  uterus;  (8.)  of 
blood-vessels  and  lymphatics;  (9.)  of  the  iris,  and  some  other  parts  of 


Fiff.  81. — A.  Unstriped  muscle  cells  from  tlie  mesentery  of  a  newt.  The  sheath  exhibits  trans- 
ver.sc  niarkiiiKs.  x  IHO.  B,  From  a  similar  preparation,  sliowinfc  that  each  muscle  ivll  consists  of 
a  central  Ijumile  of  lil)nls,  i''  (.cona-acLile  part),  connrcteil  with  the  iutra-nuck-ar  uecwork,  N,  and  a 
sheatli  with  annular  thickenings,  St.  The  cells  show  varicosities  due  to  local  contraction,  and  on 
tliese  the  annular  thickenings  are  most  marked.     X  450.    (.Klein  and  Noble  Smith.) 

the  eye.  This  form  of  tissue  also  enters  largely  into  the  composition 
(10.)  of  the  tunica  dartos,  the  contraction  of  which  is  the  principal  cause 
of  the  wrinkling  and  contraction  of  the  scrotum  on  exposure  to  cold. 
Unstriped  muscular  tissue  occurs  largely  also  in  the  true  skin  generally, 
being  especially  abundant  in  the  interspaces  between  the  bases  of  the 
papilloe.  Jlence  when  it  contracts  under  the  influence  of  cold,  fear, 
electricity,  or  any  other  stimulus,  the  papilla?  are  made  unusually  prom- 
inent, and  give  rise  to  the  peculiar  roughness  of  the  skin  termed  cutis 
anserina,  or  goose  skin.  It  occurs  also  in  the  superficial  portion  of  the 
cutis,  in  all  parts  where  hairs  occur,  in  the  form  of  flattened  roundish 
bundles,  which  lie  alongside  the  hair-follicles  and  sebaceous  glands. 
They  pass  obliquely  from  without  inward,  embrace  the  sebaceous  glands, 
and  are  attached  to  the  hair-follicles  near  their  base. 

Strucfure. — Unstriated  muscles  are  made  up  of  elongated,  spindle- 
shaped,  nucleated  cells  (fig.  81),  which  in  their  perfect  form  are  flat, 
from  about  j-gVo  to  ^-g^p^^  of  an  inch  broad  (7  to  8,"),  and  -g-i-^  to^J,-^  of  an 
inch  (^  to  -^mm)  in  length—very  clear,  granular,  and  brittle,  so  that 


82 


HANDBOOK    OF    PHYSIOLOGY. 


when  tliey  break  tlie}'  often  have  abruptly  rounded  or  square  extremities. 
Each  cell  of  these  consists  of  a  fine  sheath,  probably  elastic;  of  a  centra] 
bundle  of  fibrils  representing  the  contractile  substance;  and  of  an  ob- 
long nucleus,  which  includes  within  a  menibrane  a  fine  network  anasto- 
mosing at  the  poles  of  the  nucleus  with  the  contractile  fibrils.  The 
ends  of  fibres  are  usually  single,  sometimes  divided.  Between  the  fibres 
is  an  albuminous  cementing  material  or  endomysium  in  which  are  found 


Fig.  82. — Plexus  of  bundles  of  unstriped  muscle  cells  from  the  pulmonary  pleura  of  the  Guiuea-pig. 
X  ISO.     (Klein  and  Noble  Smith.)    A,  Branching  fibres;  B,  their  long  central  nuclei. 

connective-tissue  corjniscles,  and  a  few  fibres.  The  lyerimysium  is  con- 
tinuous with  the  endomysium  in  the  fibrous  connective  tissue  surround- 
ing and  separating  the  bundles  of  muscle  cells. 


Striated  Muscle. 

Distribution. — Striated  or  striped  muscle  is  found  in  the  following 
situations.  It  constitutes  the  whole  of  the  muscular  apparatus  of  the 
skeleton,  of  the  walls  of  the  abdomen,  etc.,  the  whole  of  those  muscles 
which  are  under  the  control  of  the  will  and  hence  termed  voluntary,  as 
well  as  certain  other  muscles,  e.g.,  of  the  internal  ear  and  i^harynx  not 
directly  under  the  control  of  the  will,  and  the  heart. 

Structure. — For  the  sake  of  description,  striated  muscular  tissue  may 
be  divided  into  two  classes,  (a.)  slteletal,  Avhich  comprises  the  whole  of 
the  striated  muscles  of  the  body  except  (b.)  the  heart : — 

(a.)  Skeletal  Muscle. — In  the  majority  of  cases  a  skeletal  muscle 
is  inclosed  in  a  sheath  of  areolar  tissue  called  the  epiniysium,  which  in 
some  cases  is  a  very  thick  and  distinct  investment,  while  in  other  cases 
it  is  much  thinner.  The  sheath  sends  in  partitions  which  serve  to  sup- 
port the  fasciculi  or  bundles  of  fibres,  of  which  the  muscle  is  made  up, 
forming  more  or  less  distinct  sheaths  for  them,  called  perimysium.     The 


THE    STHLCTUKE    UK    TlIK    KEK.MENTAIiY    TISSUES. 


§3 


fibres  themselves  are  supported  in  their  fasciculus  by  a  scanty  amount 
of  areolar  tissue  containing  plasma  cells  and  termed  e?idomi/siiim. 
Within  the  areolar  tissue  sujjporting  the  fasciculi  and  between  the  fibres 
are  contained  the  blood-vessels  and  nerves  of  the  tissue. 

The  muscular  fibres  of  each  fasciculus  are  parallel  to  one  another, 
and  generally  speaking  so  are  the  fasciculi  themselves,  except  that  toward 

their  terminations  they  may  converge  to 
their  insertion  into  the  tendon  of  the 
muscle.  The  fasciculi  extend  throughout 
the  whole  length  of  the  muscle,  but  they 
vary  in  size  and  in  the  number  of  their  con- 


Fig.  83. 


FiK.  84. 


Fig.  83. — Transverse  section  through  muscular  fibres  of  human  tongue.  The  muscle-corpuscles 
are  indicated  by  tlieir  deeply-stained  nuclei  situated  at  the  inside  of  the  sarcolenmia.  Each  muscle- 
fibre  s^lo^vs  "Cohnheim's  fields,"  that  is,  the  sarcous  elements  in  transverse  section  separated  by 
clear  (apparently  linear)  interstitial  substance.     X  4.'50.     (Klein  and  Noble  Smith.) 

Fig.  84. — Muscular  fibre  torn  across;  the  sarcolenmia  still  connecting  the  two  parts  of  the  fibre. 
(Todd  and  Bowman.) 

tained  fibres,  both  in  different  muscles  and  also  in  the  same  muscle,  some 
muscles  having  coarse,  others  fine  fasciculi.  In  some  cases  it  would  seem 
that  the  perimysium  is  altogether  independent  of  the  external  sheath 
of  the  muscle.  As  to  the  fibres  of  which  the  bundles  are  made  up,  they 
liave  a  distinct  elastic  sheath,  the  sarcolemma;  their  size  varies  consid- 
erably, tlieir  cross-section  being  from  100/^  to  10,u,  and  as  regards  their 


Fig.  8.).— Part  of  a  striped  muscle-fihre  of  a  water  beetle  prepared  with  absolute  alcohol.  A 
Sarcoleinma:  B.  Krause's  membrane.  The  sarcolemuia  shows  regular  hnlgings.  .-xbove  and  below 
Krause's  membrane  are  seen  the  transparent  "lateral  dises."  The  chief  mass  of  a  muscular  coiii- 
jpartment  IS  occupied  by  tlie  contractile  disc  composed  of  sarcous  elements.  The  substance  of  the 
I  idividual  sarcous  elements  lias  collected  more  at  the  extremity  than  in  the  centre:  hence  this 
1  itier  i.s  more  transparent.  The  optical  effect  of  this  is  that  the  contrac-tile  disc  appears  to  pos.sess 
a  median  disc  (Disc  of  Hensen).  Several  nuclei  of  muscle  corpuscles,  C  and  1).  are  shown,  and 
in  thein  a  minute  network,     x  3(X).     (Klein  and  Noble  Smith. ) 


shape,  it  is  cylindrical  or  is  triangular,  quadrilateral,  or  pentangular  with 
rounded  angles.    In  length  the  fibres  seldom  exceed  an  inch  and  a  half 


84 


HANDBOOK    OF    PHYSIOLOGY. 


(3.75  cm).  It  is  tlins  evident  that  the  same  fibre  does  not  extend  from 
one  end  of  a  muscle  to  the  other,  and  indeed  it  is  known  that  in  a  fas- 
ciculus fibrils  are  joined  together  by  rounded  or  angular  extremities  in- 
vested with  their  proper  sheath  the  sarcolemma. 

Each  muscular  fibre  then  is  thus  constructed : — Externally  is  a  fine, 
transparent,  structureless  membrane,  the  sa rcolomn a,  M^hich  in  the  form 
of  a  tubular  investing  sheath  forms  the  outer  wall  of  the  fibre  and  which 
contains  the  contractile  material  of  which  the  fibre  is  chiefly  made  up. 
Sometimes,  from  its  comparative  toughness,  the  sarcolemma  will  remain 
untorn,  when  by  extension  the  contained  part  can  be  broken  (fig.  84), 
and  its  presence  is  in  this  way  best  demonstrated.  The  fibres  are  of  a 
pale  yellow  color,  and  apparently  marked  by  fine  strijB  which  pass  trans- 
versely round  them,  in  slightly  curved  or  wholly  parallel  lines.     The 


1& 


EiSi     Sf   ESS;  V 

^  Sb     iSii 


180 


Fig.  86.— A.  Portion  of  a  medium-sized  human  musciilar  fibre.  X  800.  B.  Separated  bundles  of 
fibrils  equally  magnified;  a,  «,  larger,  and  h,  b,  smaller  collections;  c,  still  smaller;  d,  <l,  the  smallest 
whicli  could  be  detached,  jjossibly  representing  a  single  series  of  sarcous  element.    c^Sliarpey.;) 


sarcolemma  is  a  transj)arent  structureless  elastic  sheath  of  great  resist- 
ance which  surrounds  each  fibre  (fig.  84).  There  is  still  some  doubt  re- 
garding the  nature  of  the  fibrils. 

A  striated  muscle  fibre,  when  examined  with  a  sufficiently  high 
power  of  the  microscope,  presents  the  following  appearances,  longitu- 
dinally :— 

.{a..}  Alternate  darlc  avd  liglit  parallel  transverse  stripes,  to  whicli 
this  variety  of  muscle  owes  its  name,  the  depth  of  the  stripes  not 
always  being  tlie  same. 

(b.)  With  still  higher  powers  of  the  microscope,  the  bright  stripes 


THE    STRUCTURE    OF   THE   ELEMEIfTARY   TISSUES. 


85 


may  be  seen  to  be  divided  iu  the  middle  line  by  other  very  fine  trans- 
yerse  dark  lines,  sometimes  called  Dobie's  line. 

(c.)  Each  dark  stripe  may  also  sometimes  be  seen  to  be  divided  by  a 
clear  line,  called  Henson's  disc. 

(d.)  Each  fibre  presents  an  appearance  of  lonrjitudinal  striation  and 
after  hardening  in  alcohol  may  be  divided  by  teasing  with  needles  into 
longitudinal  fibrils,  more  or  less  cylindrical  or  angular,  which  are  named 
muscle  columns  or  sarcostyles,  and  extend  throughout  each  fibre.  Each 
of  these  appears  to  consist  of  short  columns  connected  together  by 
bright  intervals,  the  former  are  the  sarcous  elements  of  Bowman.  They 
may  possibly  be  further  longitudinally  striated,  and  so  made  uji  of  finer 
fibrilhB  still. 

After  treatment  with  reagents  the  fibre  may  be  split  up  into  trans- 
verse discs. 

(e.)  On  Transverse  Section. — The  fibre  presents  most  externally, 
the  outline  of  the  sarcolemma. 

(f.)  The  muscular  substance  proper  apj^ears  to  be  mapped  out  into 


Fip:.  S7.— Three  rrmscnlar  fibres  ruuninfr  lonfritudinally,  and  two  bundles  of  fibres  in  transverse  sec- 
tion, M,  from  the  tongue.    The  capillaries,  C,  are  injected,     x  150.     cKlein  and  Noble  Smith.; 

small  polygonal  areas  by  clear  lines  (fig.  83)  called  Cohnheim's  fields,  the 
lines  giving  the  appearance  of  a  mesh  work.  The  lines  represent  the 
transverse  section  of  the  cementing  material  between  the  sarcostyles, 
which  is  called  sarcoplasm. 

(g.)  Immediately  within  the  sarcolemma  iu  ordinary  muscle  or  in 
the  centre  of  the  fibre  as  in  the  muscle  of  some  insects,  are  seen  clear 
oval  nuclei  called  muscle  nuclei  or  nmscle  corpuscle,  surrounding  which 
is  a  certain  amount  of  granular  protoplasm  (fig.  85). 

The  appearances  of  the  muscle  fibre  when  seen  under  the  micro- 
scope, cannot  be  said  to  be  yet  thoroughly  understood,  and  have  given 
rise  to  various  theories  as  to  the  structure  of  striped  muscle,  to  several 
of  which  it  will  be  as  well  to  allude. 

Muscle  Caskets  (Krause)  Theory. — According  to  this  view  a 
muscle  fibre  is  made  up  of  transverse  compartments,  bounded  laterally 
by  the  sarcolemma,  and  above  and  below  by  a  fine  membrane,  called 


86 


HANDBOOK    OF    PHYSIOLOGY. 


Krause's  membrane,  whicli  passes  from  side  to  side  from  the  sarcolemma 
across  the  light  stripe.  This  membrane  corresponds  to  Dobie's  line. 
The  transverse  compartments  are  divided  longitudinally  into  smaller 
ones  by  lines  which  correspond  with  the  boundaries  of  Cohnheim's  areas, 
and  each  such  compartment  is  termed  a  muscle  casket.  Within  the 
middle  part  of  the  casket  is  a  muscle  prism  made  up  of  darker  rods  of 
contractile  material  called  muscle  rods,  and  above  and  below  the  muscle 
prism  is  a  more  fluid  substance.  When  the  muscle  contracts,  the  fluid 
substance  is  pressed  more  between  the  muscle  rods,  causing  them  to  be 
further  away  from  one  another. 

Muscle  Reticulum  Theory. — According  to  the  views  of  certain 
observers  (Eetzius,  Melland.  Marshall,  van  Gehuchten,  and  Carnoy),  the 


Fig.  88 


Fi^.  88a. 


Fig.  88— Transverse  section  of  one  of  the  trunk  muscles  of  the  Hippocampus,  stained  in  chloride 
of  gold.    (RoUett.) 

Fig.  88a. — Portion  of  muscle-fibre  of  Dytiscus.  showing  network  very  plainly.  One  of  the  trans- 
verse networks  is  split  off,  and  some  of  the  longitudinal  bars  are  shown  broken  off.    (After  Melland. ) 

part  of  fresh  muscle  which  is  stained  in  chloride  of  gold,  is  a  meshwork 
of  fibrils  which  corresponds  to  the  intracellular  meshwork  of  ordinary 
protoplasmic  cells,  i.e.,  the  spongioplasm,  and  is  the  part  which  is  the 
contractile  element  in  muscle.  The  meshwork  on  one  level  is  connected 
with  the  meshwork  on  another  level  by  means  of  longitudinal  fibres,  at 
the  junction  of  which  the  meshes  ajapear  more  or  less  knotted  (figs.  88 
and  88a).  The  longitudinal  fibres  of  the  network  are,  according  to  this 
theory,  the  chief  agents  in  the  active  contraction.  The  transverse  mesh- 
work is  more  passively  elastic,  and  may  be  the  cause  of  the  speedy  relax- 
ation of  muscle  after  contraction  has  ceased.  The  material  filling  up 
the  meshwork  is  a  more  fluid  and  non-contractile  material. 

Rollett  has   minutely  criticised  the  idea  of  the  gold-staining  sub- 
stance of  the  fibre  being  the  contractile  portion.     His  views  are  the 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


87 


following: — -That  the  muscle-fibre  consists  of  longitudinal  fibrillae 
grouped  together  into  muscle  columns,  which  are  seen  in  the  transverse 
section  as  Cohnheim's  fields,  and  that  the  intercolumnar  material  is 
semi-fluid  sarcoplasm.  A  muscle  column  consists  of  segments  alter- 
nately thin  and  thick,  while  in  the  centre  of  the  thin  portion  is  a  dark 
enlargement  forming  a  dot,  these  dots  in  Cohnheim's  arrangement  cor- 
respond to  Krause's  membrane. 

In  fresh  muscle,  at  low  focus,  according  to  this  view,  the  muscle- 
columns  appear  dark  and  the  sarcoplasma  appears  light,  the  former  are 
in  a  line  with  the  granules.  At  high  focus,  the  reverse  is  the  case,  but 
the  dark  sarcoplasma  is  now  seen  in  line  with  two  rows  of  granules 
(fig.  89). 

Also,  that  in  gold-stained  preparations,  the  dark  row  of  granules  are 
thicknesses  of  the  sarcoplasma  between  the  thin  segments  of  the  muscle 


ifftttttttttttftffT' 


■  I 

■ ' 


II I       I '     I    '     I        Ml         \        \ 

■    ,    ,    |.    .    .    1.    11    I 


ttt      tHlT    ' 







I 


Fig.  80.— Diagram  of  the  appearances  in  fresh  muscle-flbre.  A.  At  low  focus  (b)  the  muscle 
columns  appear  dark  and  in  a  line  with  tiie  granules,  sarcoplasm  light.  At  high  focus  (a)  the  sarco- 
plasm is  dark,  muscle  columns  light,  and  two  rows  of  granules  appear  in  a  line  with  the  sarcoplasm 
and  alternating  with  the  muscle  columns.    (Marshall,  after  Rolletl.) 


columns,  whereas  the  two  rows  of  granules  do  not  correspond  with 
these,  but  alternate  with  them,  belonging  as  they  do  to  the  muscle 
columns,  and  not  to  the  sarcoplasm. 

Schiifer  has  thrown  considerable  light  upon  the  controversy  by  hav- 
ing actually  observed  that  when  a  small  portion  of  the  living  wing- 
muscle  of  insects  is  teased  up  with  needles  in  a  small  drop  of  white  of 
egg,  the  sarcostyles  may  easily  be  separated  from  their  surrounding 
sarcoplasm ,  and  may  be  actually  seen  to  contract,  whereas  the  sarcoplasm 
shows  no  sucli  property.  According  to  this  observer  such  a  sarcostyle 
may  l)e  examined  thus  isolated,  both  living  and  after  treatment  with 
various  reagents,  and  it  shows  alternate  bright  and  light  stripes,  the 
latter  being  bisected  by  a  line  which  corresponds  Avtih  Krause's  mem- 
brane. Krause's  membrane  divides  the  sarcostyle  into  sarcomeres,  which 
contain  in  the  middle  the  strongly  refractive  disc-like  sarcous  element, 
and  above  and  below  it  hyaline  material,  which  is  bounded  by  Krause's 
membrane.  The  sarcous  substance  is  penetrated  by  canals,  which  ex- 
tend upward  and  downward  from  the  liyaline  substance  to  the  middle. 


88 


HAlJfDBOOK    OF    PHYSIOLOGY. 


The  sarcous  substance  stains  with  hsematoxylin.  A  light  interval  may 
bisect  the  sarcous  substance  if  the  fibre  is  stretched,  which  corresponds 
witli  Henseu's  disc. 

Appearances  under  Polarized  Light. — The  appearances  which 
muscle  presents  when  viewed  under  polarized  light  vary  according  as 
the  fibres  are  looked  at,  as  fresh  in  their  own  j)lasma,  or  as  hardened 
fibres  prepared  and  mounted  in  Canada  balsam. 

The  whole  of  the  living  fibre  may  be  doubly  refracting,  the  isotro- 
pous  part  aj)pearing  as  rows  of  dots  separating  transversely  the  princi- 
pal material  of  the  fibre.  Shortly,  according  to  Schafer,  it  may  be  said 
that  the  sarcoplasm  is  singly  refracting,  and  that  the  sarcostyle  is  in 
great  part  doubly  refracting.  In  a  fibre  which  is  extended,  after  it  has 
been  hardened  in  alcohol  aijd  mounted  in   Canada  balsam,  there  are 


(IIIIIHIIij 

ilillllillO 


m 


S.E. 


S.E. 


Fig.  90. 


Fig.  91. 


Fig.  90.— Sarcostyles  from  the  wing-muscles  of  a  wasp,  a,  a'.  Sarcostyles  showing  degrees  of 
retraction  (?  contraction),  b.  A  sarcostyle  extended  with  the  sarcous  elements  separated  into  two 
parts,    c.  Sarcostyles  moderately  exteiicled  (semidiagrammatic).    cE.  A.  Schafer.) 

Fig.  91. — Diagram  of  a  sarcomere  in  a  moderately  extended  condition,  a,  and  in  a  contracted 
condition,  b.  k,  k,  Krause's  membranes;  h,  plane  of  Henson;  s.e.,  poriferous  sarcous  element. 
(E.  A.  Schafer.) 

alternate  dark  and  light  bands,  the  former  corresponding  to  the  light 
intervals  as  seen  in  ordinary  light,  and  the  latter  bo  the  various  elements. 
When  the  fibre  is  more  contracted  the  dark  line  becomes  narrower,  and 
the  anisotropous  intervals  broader,  but  there  is  no  interval  of  the  bands 
on  contraction.  It  appears  further  that  the  chromatic  portion  only  of 
the  sarcostyles  is  anisotropous,  and  the  sarcoplasm  and  the  remainder  of 
the  fibre  is  isotropous. 

{b.)  Heart  Muscle. — The  muscular  fibres  of  the  heart,  unlike  those 
of  most  of  the  involuntary  muscles,  are  striated;  but  although,  in  this 
respect,  they  resemble  the  skeletal  muscles,  they  have  distinguishiug 
characteristics  of  their  own.  The  fibres  which  lie  side  by  side  are  united 
at  frequent  intervals  by  short  branches  (fig.  92).  The  fibres  are  smaller 
than  those  of  the  ordinary  striated  muscles,  and  their  striation  is  less 
marked.  No  sarcolemma  can  be  discerned^  The  muscle-corpuscles  are 
situate  in  the  middle  of  the  substance  of  the  fibre;  and  in  correspond- 


THE    STRUCTURE    OF   THE    ELEMEXTARY    TISSUES. 


89 


ence  with  these  the  fibres  appear  under  certain  conditions  subdivided 
into  oblong  portions  or  "cells,"  the  oft'sets  from  wliich  are  the  means  by 
whicli  tlie  fibres  branch  and  anastomose  one  witli  another. 

It  should  be  noted,  however,  that  tlie  heart  muscular  fibres  are  not 
the  only  ones  which  branch,  since  the  fibres  of  the  tongue  of  the  frog, 
especially  where  they  are  attached  to  the  mucous  membrane,  present 
this  peculiarity;  branching  muscular  fibres  have  also  been  noted  in  the 
tongue,  and  in  the  facial  muscles  of  other  animals.  And  again,  in  the 
animals  in  which  two  kinds  of  skeletal  muscles  occur,  red  and  pale,  in 
the  red  muscles  the  fibres  are  much  less  distinctly  striated  transversely, 
Avhereas  their  longitudinal  striation  is  more  marked  than  in  the  joale 
variety.     They  are  also  finer  than  other  skeletal  muscles.     It  should  also 


Fig.  93. 


Fig.  93. 


Fig.  92.— Muscular  fibre  cells  from  the  heart.    (E.  A.  Schafer.) 

Fig.  9.3.— From  a  preparation  of  the  nerve-tenuination  in  the  muscular  fibres  of  a  snake,    a, 
End  plate  seen  only  broad  surfaced.    6,  End  plate  seeu  as  narrow  surface.    (Lingard  and  Klein.) 

be  added  that  in  these  red  muscles  the  sarcoplasm  is  much  developed, 
and  the  muscle  nuclei  are  very  numerous,  and  may  be  situated  in  the 
middle  of  the  fibre,  as  is  the  case  with  heart  muscle  fibres. 

Blood  and  Nerve  Supply. — Tbe  voluntary  muscles  are  freely  sup- 
plied with  blood-vessels;  the  capillaries  form  a  network  with  oblong 
meshes  around  tlie  fibres  on  the  outside  of  the  sarcolemma.  No  vessels 
penetrate  the  sarcolemma  to  enter  the  interior  of  the  fibre.  Nerves  also 
are  supplied  freely  to  muscles;  the  voluntary  muscles  receiving  them 
from  the  cerebro-spinal  system,  and  the  unstriped  muscles  from  the 
sympathetic  or  ganglionic  system. 

The  nerves  terminate  in  the  muscuLir  fibre  in  the  following  ways:— 
(1.)  In  unstriped  muscle,  the  nerves  first  of  all  form  a  plexus,  called 
the  fifoiuid  pIv.vKs  (Arnold),  correspondiug  to  each  group  of  muscle 
bundles;  the  plexus  is  made  by  the  anastomosis  of  the  })rimitive  fibrils 
of  the  axis-cylinders.     From  the  ground  i)lexus,  branches  pass  oli,  and 


90 


HAISTDBOOK    OF    PHYSIOLOGY. 


again  anastomosing,  form  plexuses  which  correspond  to  each  muscle 
bundle — intermediary  plexuses.  From  these  plexuses  branches  consist- 
ing of  primitive  fibrils  pass  in  between  the  individual  fibres  and  anas- 
tomose. These  fibrils  either  send  off  finer  branches,  or  terminate  them- 
selves in  the  nuclei  of  the  muscle  cells. 

(2.)  In  striped  muscle  the  nerves  end  in  motorial  end-plates,  having 
first  formed,  as  in  the  case  of  unstriped  fibres,  ground  and  intermediary 


Fig.  94. — Two  striped  muscle-fibres  of  the  hyoglossus  of  frog,  a,  Nerve-end  plate;  b,  nerve- 
fibres  leaving  the  end  plate;  c,  nerve-fibres,  terminating  after  dividing  into  branches  d,  a  nucleus  in 
which  two  nerve-fibres  anastomose.    X  600.     (Arndt.) 


plexuses.  The  fibres  are,  however,  medullated,  and  when  a  branch  of 
the  intermediary  plexus  passes  to  enter  a  muscle-fibre,  its  primitive 
sheath  becomes  continuous  with  the  sarcolemma,  and  the  axis-cylinder 
forms  a  network  of  its  fibrils  on  the  surface  of  the  fibre.  This  network 
lies  embedded  in  a  flattened  granular  mass  containing  nuclei  of  several 
kinds;  this  is  the  r)iotorial  end-plate  (figs.  93  and  94).  In  batrachia,  be- 
sides end-plates,  there  is  another  way  in  which  the  nerves  end  in  the  muscle 
fibres,  viz.,  by  rounded  extremities,  to  which  oblong  nuclei  are  attached, 


THE   STRL'CTURE    OF  THE   ELEilENTARY   TISSUES.  91 

Development. —  (1.)  Unstriped. — The  cells  of  unstriped  muscle  are 
derived  directly  from  embryonic  cells,  by  an  elongation  of  the  cell,  and 
its  nucleus;  the  latter  changing  from  a  vesicular  to  a  rod  shape. 

(2.)  Striped. — Formerly  it  was  supposed  that  striated  fibres  were 
formed  by  the  coalescence  of  several  cells,  but  recently  it  has  been 
proved,  that  each  fibre  is  formed  from  a  single  cell,  the  process  involv- 
ing an  enormous  increase  in  size,  a  multiplication  of  the  nucleus  by  fis- 
sion, and  a  differentiation  of  the  cell-contents.  This  view  differs  but 
little  from  another,  that  the  muscular  fibre  is  produced,  not  by  multi- 
plication of  cells,  but  by  arrangement  of  nuclei  in  a  growing  mass  of 
protoplasm  (answering  to  the  cell  in  the  theory  just  referred  to),  which 
becomes  gradually  differentiated  so  as  to  assume  the  characters  of  a  fully 
developed  muscular  fibre. 

Growth  of  Muscle. — The  growth  of  muscles,  both  striated  and  non- 
striated,  is  the  result  of  an  increase  both  in  the  number  and  size  of  the 
individual  elements.  In  the  pregnant  uterus  the  fibre-cells  may  become 
enlarged  to  ten  times  their  original  length.  In  involution  of  the  uterus 
after  parturition  the  reverse  changes  occur,  accompanied  generally  by 
some  fatty  infiltration  of  the  tissue  and  degeneration  of  the  fibres. 

IV.  Nervous   Tissue. 

Xervous  tissue  has  usually  been  described  as  being  composed  of 
two  distinct  substances,  nerve-fibres  and  nerve-cells.  The  modern 
view  of  the  nature  of  nerve-tissue  is,  however,  that  it  is  composed 
of  one  element  alone,  called  the  neuron  or  nerve  unit,  embedded  in 
and  supported  by  a  substance  called  neuroglia.  This  neuron  consists  of 
a  cell-body,  a  number  of  branching  processes  termed  dendrites,  and  a 
long  process  running  out  from  it,  the  neuraxon,  which  becomes  eventu- 
ally a  nerve-fibre.  The  nerve-cell  and  the  nerve-fibre,  are  really  parts  of 
the  same  anatomical  unit,  and  the  nervous  centres  are  made  up  of  these 
units,  arranged  in  different  ways  throughout  the  nervous  system  (fig  94a). 
The  different  neurons  do  not  unite  anatomically  with  each  other,  but 
form  independent  units.  A  further  description  of  these  structures  will 
be  given  later. 

Nerve-Fibres. 

While  the  nerve-fibre  is  really  to  be  considered  as  a  process  of  the 
nerve-cell,  it  is  convenient  to  describe  it  separately. 

Varieties. — Nerve-fibres  are  of  two  kinds,  medullated  or  white  fibres^ 
and  )wn-))ir(liiHated  nr  firay  fibres. 

Medullated  Fibres. — Each  medullated  nerve-fibre  is  made  up  of 


92 


HANDBOOK    OF   PHTSIOLOGT. 


the  following  parts: — (1.)  An  external  sheath  called  the 2)rimitive  nerve'- 
sheath,  or  nucleated  sheath  of  Schwann;  (2.)  An  intermediate  or  pack- 
ing substance  known  as  the  medullary  or  myelin  sheath,  or  white  sub- 
stance of  Schwann;  and  (3)  internally  the  axis-cylinder,  primitive  band, 
axis  band,  or  axial  fibre. 

Although  these  parts  can  be  made  out  in  nerves  examined  some 
time  after  death,  in  a  recent  specimen  the  contents  of  the  nerve-sheath 
appear  to  be  homogeneous.     But  by  degrees  they  undergo  changes  which 


Fig.  94a. — Diagram  showing  the  arrangement  of  the  neurons  or  nerve-units  in  the  architee 
ture  of  the  nervous  system.  M.  Neurons  I.  and  II.,  motor  neurons;  &  Neurons  2.,  II.,  III., 
sensory  neurons;  A.  Neurun,  associative  or  commissural  neuron.     (Dana.) 


show  them  to  be  composed  of  two  different  materials.  The  internal  or 
central  part,  occupying  the  axis  of  the  tube,  viz.,  the  axis-cylinder,  be- 
comes grayish,  while  the  outer  or  cortical  portion,  or  white  substance 
of  Schwann,  becomes  opaque  and  dimly  granular  or  grumous,  as  if  from 
a  kind  of  coagulation.  At  tlie  same  time  the  fine  outline  of  the  previ- 
ously transparent  cylindrical  tube  is  exchanged  for  a  dark  double  con- 
tour (fig.  95,  b),  the  outer  line  beivig  formed  by  the  sheath  of  the  fibre, 
the  inner  by  the  margin  of  curdled  or  coagulated  medullary  substance. 


THE    STRLJ(.TL'KE    OP   THE    KLKMEXTAHY    TISSUE? 


93 


The  granuLir  inateriiil  shortly  collects  into  little  masses,  which  distend 
portions  of  the  tubular  membrane;  while  the  intermediate  spaces  col- 
lapse, giving  the  fibres  a  varicose,  or  beaded  appearance  (fig.  95,  c  and 
I)),  instead  of  the  previous  cylindrical  form.  The  whole  contents  of 
the  nerve-tubules  are  extremely  soft,  for  when  subjected  to  pressure 
they  readily  pass  from  one  part  of  the  tubular  sheath  to  another,  and 
often  cause  a  bulging  at  the  side  of  the  membrane.  They  also  readily 
escape,  on  pressure,  from  the  extremities  of  the  tubule,  in  tlie  form  of  a 
grumous  or  granular  material. 

The  external  nucleated  sheath  of  Schwann,  also  called  the  vcn- 
rilemma,  is  a  pellucid   membrane   forming  the  outer  investment  of  the 


M  BCD 


Fig-.  95. 


Fig.  9G. 


Fig.  05.- -Primitive  nerve-fibres,  a.  A  perfectly  fiv^sh  tuluile  -nitli  a  single  dark  outline,  n.  A 
tubule  or  libra  with  a  double  contour  from  coiumeiiciiiLr  ]iost-morteui  change,  c.  The  cliaiige.s 
further  advanced,  in-oducing  a  varicose  or  beaded  appearance,  d.  A  tubule  or  fibre,  the  central 
part  of  which,  in  consequiiice  of  still  further  changes,  ha«  accumulated  in  separate  portions  within 
the  sheath  (Wagner). 

Hg.  yii.— Two  nerve-fibres  of  sciatic  nerve,  a.  Node  of  Ranvier.  b.  Axis-cylinder,  c.  Sheath 
of  Schwann,  with  nuclei.     X  300.    cKlein  and  Noble  Smith.) 


nerve-fibre.  Within  this  delicate  structureless  membrane  nuclei  are 
seen  at  intervals,  surrounded  by  a  variable  amount  of  i)rotoplasm.  The 
sheath  is  structureless,  like  the  sarcolemma,  and  the  nuclei  appear  to  be 
within  it:  together  with  the  protoplasm  which  surrounds  them  they  are 
the  relics  of  embryonic  cells,  and  from  their  resemblance  to  the  muscle 
corpuscles  of  striated  muscle  may  be  termed  ucrve-corjnischs.  They  are 
easily  stained  with  logwood  and  other  dyes. 

The  medullary  or  myelin  sheath  or  Avhite  substance  of  Schwann 
is  the  ptirt  to  which  the  peculiar  opaciue  white  aspect  of  medullatcd 
nerves  is  due.     The  thickness  of  this  layer  in  nerve-fibres  varies  consid- 


94 


Handbook  of  physiology. 


erably,  at  one  time  being  very  well  developed,  at  another  forming  but  a 
very  thin  investment  of  the  axis  cylinder.  It  is  a  semi-fluid,  fatty  sub- 
stance, and  in  the  fibre  possesses  a  double  contour.  It  is  said  to  be 
made  up  of  a  fine  reticulum  (Stilling,  Klein),  in  the  meshes  of  which  is 
embedded  the  bright  fatty  material.     It  stains  well  with  osmic  acid. 

According  to  M'Carthy  this  sheath  is  composed  of  small  rods  radiat- 
ing from  the  axis-cylinder  to  the  external  sheath  of  Schwann.  Some- 
times the  whole  space  is  occupied  by  them,  while  at  other  times  the 
rods  appear  shortened  and  compressed  laterally  into  bundles  embedded 
in  some  homogeneous  substance.  According  to  other  ob- 
servers the  sheath  is  made  up  of  segments  which  are 
either  cylindrical  or  funnel-shaped  {sections  of  Lanter- 
man7i).  It  is  not  definitely  decided  that  these  divisions 
exist  naturally  in  the  nerve-fibre.     In  nerves  hardened  in 


Fig.  97.  Fig.  98. 

Fig.  97.— A  node  of  Ranvier  in  a  meduUated  nerve-fibre,  viewed  from  above.  The  medullary 
sheath  is  interrupied,  and  the  primitive  sheath  thickened.  Copied  from  Axel  Key  and  Ketzius. 
X  750.    (Klein  and  Noble  Smith.) 

Fig.  98. — Gray,  pale,  or  gelatinous  nerve-fibres.  A.  From  a  branch  of  the  olfactory  nerve  of  the 
sheep;  two  dark-bordered  or  white  fibres  from  the  fifth  pair  are  associated  with  the  pale  olfactory 
fibres.    B.  From  the  sympathetic  nerve.     X  450.     (Max  Schultze.) 

alcohol,  it  is  possible  to  demonstrate  a  very  chromatic  recticulum  in  the 
medullary  sheath,  which  is  supposed  to  be  of  a  horny  nature,  since  it 
offers  much  resistance  both  to  chemical  reagents  and  to  digestive  fluids 
{horny  reticulum  or  neuro-keratin  network). 

The  axis-cylinder  consists  of  a  large  number  of  primitive ^Z»n7/c?, 
This  is  well  shown  in  the  cornea,  where  the  axis-cylinders  of  nerves 
break  up  into  minute  fibrils  which  form  terminal  networks,  and  also  in 
the  spinal  cord,  where  these  fibrillse  form  a  large  part  of  the  gray  matter. 
From  various  considerations,  such  as  its  invariable  presence  and  un- 
broken continuity  in  all  nerves,  though  the  primitive  sheath  or  the 
medullary  sheath  may  be  absent,  there  can  be  little  doubt  that  the  axis- 
cylinder  is  the  essential  part  of  the  fibre,  the  other  parts  having  the 
subsidiary  function  of  support  and  possibly  of  insulation. 


THE   STKUCTL'KE   Ui'   THE   ELEiiE^lAUY    llSSUEri.  9.5 

Nodes  of  Ranvier. — At  regular  intervals  in  most  medullated  nerves 
the  nucleated  sheath  of  Schwann  possesses  annular  constrictions;  thfse 
live  c->x\\q(X  nodes  of  Ranvier.  At  these  points  (fig.  97),  the  contin- 
uity of  the  medullary  white  substance  is  interrupted,  and  the  primitive 
sheath  comes  into  immediate  contact  with  the  axis-cylinder.  The  seg- 
ment of  the  fibre  between  two  nodes  is  termed  an  internode,  and  the 
length  of  the  internodes  varies  in  different  nerves;  their  average  is  said 
to  be  1  mm.  There  is  only  one  nerve  nucleus  to  each  internode.  At 
each  node  the  internodes  are  united  within  the  external  sheath  by  a 
band,  constricting  hand  of  Ranvier  (fig.  101),  and  this  stains  black  with 
silver  nitrate;  the  axis-cylinders  at  the  nodes  also  are  capable  of  being 


Fiff.  90. — Transverse  section  of  soiatic  iumvp  of  the  rabbit,  hardened  in  chromic  acid  and 
stained  witli  pici'o-carniine,  and  sliowint;  lamellar  sheatli,  peripheric  connective  tissue,  and  intra- 
fascicidar  connective  tissue.  X  550  an(l  reduced  one-half.  «,  Perifasjicular  connective  tissue:  b, 
lamellar  >heath;  c,  intra-fascicular  connective  tissue;  d,  uerve-flbre  cut  across,  showing  nuclei  of 
the  same;  e,  axis-cylindei*. 

stained  with  the  same  reagent,  and  so  a  node  of  Ranvier  when  stained 
with  silver  nitrate  is  marked  by  a  black  cross. 

Size. — The  size  of  the  nerve-fibres  varies  (fig.  99);  it  is  said  that 
the  same  fibres  may  not  preserve  the  same  diameter  through  their  whole 
length.  The  largest  fibres  are  found  within  the  trunks  and  branches  of 
the  spinal  nerves,  in  which  the  majority  measure  from  1-4.4,'i  to  19//  in 
diameter.  In  tlie  so-called  visceral  nerves  of  the  brain  and  spinal  cord 
medullated  nerves  are  found,  (he  diameter  of  wliieh  varies  from  1.8//  to 
3.6//.  In  the  hypoglossal  nerve  they  are  intermediate  in  size,  and  gene- 
rally measure  7.2//  to  10.8//.. 

Non-medullated  Fibres.— The  fibres  of  the  second  kind  (fig.  98) 
which  are  also  called  -fibres  of  Ueinak,  constitute  the  principal  parr  of 
the  trunk  and  branches  of  the  si/mjjal/u'iio  nerves,  the  whole  of  the 


96 


HANDBOOK    OF    PHYSIOLOGY. 


olfactory  nerve,  and  are  mingled  in  various  proportions  in  the  cerebi'cj- 
spinal  nerves.  They  differ  from  the  preceding  chiefly  in  their  fineness, 
being  only  about  ^  to  -J  as  large  in  their  course  within  the  trunks  and 


Fig.  100.— Transverse  section  of  the  sciatic  nerve  of  a  cat  about  x  100.— It  consists  of  bundles 
(Funiculi)  of  nerve-flbres  ensheathecl  in  a  fibrous  supporting  capsule,  epineurium.  A;  each  bundle 
has  a  special  slieath  (not  sufficiently  marked  out  from  the  epineurium  in  tlie  figure)  or  perineurium 
B;  the  nerve-fibres  N  /  are  separated  from  one  another  by  endone^iriuni ;  L,  lymph  spaces;  Ar, 
artery;  V,  vein;  F,  fat.    Somewhat  diagrammatic.     (V.  D.  Harris.) 

branches  of  the  nerves;  in  the  absence  of  the  double  contour;  in  their 
contents  being  apparently  uniform;  and  in  their  having,  when  in  bun- 
dles, a  yellowish-gray  hue  instead  of  the  whiteness  of  the  cerebro-spinal 


Fig.  101.— Several  fibres  of  a  bundle  of  inedullatert  nerve-fibres  acted  upon  by  silver  nitrate  to 
show  peculiar  behavior  of  nodes  of  Ranvier,  N,  toward  this  reagent.  Tile  silver  has  penetrated  at 
the  nodes,  and  has  stained  the  axis-cyhnder,  M,  foi'  a  short  distance.  S,  the  white  substance. 
(Klein  and  Noble  Smith.) 

nerves.  These  peculiarities  depend  on  their  not  possessing  the  outer 
layer  of  medullary  substance;  their  contents  being  composed  exclusively 
of  the  axis-cylinder.  Yet,  since  many  nerve-fibres  may  be  found  which 
appear  intermediate  in  character  between  these  two  kinds,  and  since  the 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES.  97 

large  fibres,  as  they  approacli  both  their  central  and  their  peripheral 
end,  lose  their  medullary  sheath  and  assume  many  of  the  other  charac- 
ters of  the  fine  fibres  of  the  sympathetic  system,  it  is  not  necessary  to 
suppose  that  there  is  any  material  difference  in  the  two  kinds  of  fibres. 
The  non-medullated  fibres  frequently  branch. 

It  is  worthy  of  note  that  in  the  foetus,  at  an  early  period  of  develop- 
ment, all  nerve-fibres  are  non-medullated. 

Nerve-trunks. — Each  nerve-trunk  is  composed  of  a  variable  num- 
ber of  different-sized  bundles  {fnniculi)  of  nerve-fibres  which  have  a 
special  sheath  (perineurmm).  The  funiculi  are  inclosed  in  a  firm  fibrous 
sheath  (epineurium);  this  sheath  also  sends  in  processes  of  connective 


Fig.  102.— Small  branch  of  a  muscular  nerve  of  the  frog,  near  its  termination,  showing  dixisions 
of  the  fibres,     a,  into  two ;  b,  into  three,     x  350.     (Kolliker.) 

tissue  which  connect  the  bundles  together.  In  the  funiculi  between  tlie 
fibres  is  a  delicate  supporting  tissue  (the  endoneurium). 

There  are  numerous  lymph-spaces  both  beneath  the  connective  tissue 
investing  individual  nerve-fibres  and  also  beneath  that  which  surrounds 
the  funiculi. 

Every  nerve-fibre  in  its  course  proceeds  uninterruptedly  from  its 
origin  in  a  nerve-centre  to  near  its  destination,  whether  this  be  the 
periphery  of  the  body,  another  nervous  centre,  or  the  same  centre  whence 
it  issued. 

Bundles  of  fibres  run  together  in  the  nerve-trunk,  but  merely  lie  in 
apposition  to  each  other;  they  do  not  unite:  even  wlien  they  anas- 
tomose, there  is  no  union  of  fibres,  but  only  an  interchange  of  fibres 
between  the  anastomosing  funiculi.     Although  each  nerve-fibre  is  thus 


y»  HANDBOOK    OF    PHYSIOLOGY. 

single  and  undivided  through  nearly  its  whole  course,  yet  as  it  ap- 
proaches the  region  in  which  it  terminates,  individual  fibres  break  up 
into  several  subdivisions  before  their  final  ending. 

Nerve  Collaterals. — It  has  been  discovered  through  the  researches 
of  Golgi,  and  confirmed  by  the  further  studies  of  Cajal  and  other  an- 
atomists, that  each  individual  nerve-fibre  in  the  central  nervous  system 
gives  ofl:  in  its  course  branches  which  pass  out  from  it  at  right  angles 
for  a  short  distance,  and  then  turn  and  run  in  various  directions.  These 
branches  are  called  collaterals.  They  end  in  fine,  brush-like  termina- 
tions, known  as  end-brnsJies,  or  in  little  bulbous  swellings  which  come 
in  close  contact  with  some  nerve  cell  (fig.  103). 


Fig.  103.— Terminal  ramifications  of  a  collateral  branch  belonging  to  a  fibre  of  the  posterior 
column  in  lumbar  cord  of  an  embryo  calf. 

These  collaterals  form  a  very  important  part  of  the  nerve-unit.  At 
the  point  where  they  are  given  off,  there  is  usually  a  little  swelling  of 
the  ueuraxon  proper. 

The  nerve-fibre  itself  continues  on  and  finally  ends  in  various  ways, 
according  to  its  function  and  the  organ  with  which  it  is  connected.  In 
the  nerve-centres,  that  is,  in  the  brain  and  spinal-cord,  the  different 
nerve-fibres  end  just  as  the  collaterals  do,  by  splitting  up  into  fine 
branches  which  form  the  end-brushes.  Collaterals  of  the  nerve-fibres  and 
end-brushes  are  chiefly  found  in  the  nervous  centres.  The  nerve-fibres 
of  the  peripheral  nerves  end  in  the  muscles,  glands,  or  special  sensory 
organs,  such  as  the  eye  and  ear.  Here,  however,  some  analogy  to  the 
end-brush  can  also  be  discovered.  As  the  peripheral  nerve-fibres  ap- 
proach their  terminations,  they  lose  their  medullary  sheath,  and  consist, 
then  merely  of  an  axis-cylinder  and  primitive  sheath.  They  then  lose 
also  the  latter,  and  only  the  axis-cylinder  is  left.     Finally,   the  axis- 


THE    STPvUCTURE    OF   THE    ELEMENTARY   TISSUES.  99 

cylinder  breaks  up  iuto  its  eleuieutary  fibrillte,  to  end  in  various  ways  to 
be  described  later. 

Plexuses. — At  certain  parts  of  their  course,  nerves  form  plexuses, 
in  which  tliey  anastomose  Avith  each  other,  as  in  the  case  of  the  brachial 
and  lumbar  plexuses.  The  objects  of  such  interchange  of  fibres  are: — 
(a),  to  give  to  each  nerve  passing  off  from  the  plexus  a  wider  connec- 
tion with  the  spinal  cord  than  it  would  have  if  it  proceeded  to  its  desti- 
nation without  such  communication  with  other  nerves.  Thus,  each 
nerve  by  the  "wideness  of  its  con- 
nections is  less  dependent  on  the 
integrity  of  any  single  portion, 
whether  of  nerve-centre  or  of 
nerve-trunk,  from  which  it  may 
spring,  (b)  Each  part  supplied 
from  a  plexus  has  wider  relations 
with  the  nerve-centres,  and  more 
extensive  sympathies;  and,  by 
means  of  the  same  arrangement, 
groups  of  muscles  may  be  co- 
ordinated, every  member  of  the 
group  receiving  motor  filaments 
from  the  same  parts  of  the  nerve- 
centre,  (r)  Any  given  part,  say 
a  limb,  is  less  dependent  upon  the 
integrity  of  any  one  nerve. 

Nerve-Cells. 

The  nerve-cell  is  the  nodal  and 
important  part  of  the  neuron,  and 
from  it  are  given  off  the  dendrites 
and  axis-cylinder  process  or  neur- 
axou.  It  consists  of  a  mass  of 
protoplasm,  of  varying  shaiie  and  ,     ,  .      ,    , 

.  .    1  .        .  Fig:.  103a.— Nerve-cell  with  short  axis-cylinder 

Size,     containing    Wlthm    it    a    nu-    from  the  posterior  horn  of  the  lumbar  cord  of  au 

,  ,  ,      ,  .  ,,  embryo  calf  measuring  0.55  cm.       (.After  v.  Oo- 

cleus  and  nucleolus.  All  nerve-  huciuen.) 
cells  give  off  a  number  of  proc- 
esses which  branch  out  in  various  directions,  dividing  and  sub- 
dividing like  the  branches  of  a  tree,  but  never  anastomosing  with  each 
other  or  with  other  cells.  These  branches  are  what  have  already  been 
referred  to  as  the  dendrites  of  tiie  cell.  They  were  formerly  called  the ^;ro- 
toplasmic  jJrocesses  (figs.  103a,  104).  It  is  thus  seen  that  the  neuron  or 
nerve-unit  consists  of  a  number  of  subdivisions,  namely,  the  cell-body 
with  its  nucleus  and  nucleolus,  the  dendrites,  or  protoplasmic  processes^ 


100 


HANDBOOK    OF    PHYSIOLOGY. 


and  the  neuraxon  or  axis-cylinder  process,  which  is  continued  on  to  form 
"what  is  known  as  a  nerve-fibre.     The  nerve-cell  is  often  spoken  of  as  in- 


Fig.  104. — Large  nerve  cells  -with  processes,  from  the  ventral  cornua  of  the  cord  of  man,  X  350. 
On  the  cell  at  the  right  two  short  processes  of  the  cell-body  are  present,  one  or  the  other  of  which 
may  have  been  an  axis-cylinder  process  (Deiters).  A  similar  process  appears  also  on  the  cell  at 
the  left. 

eluding  the  cell-body  and  its  dendrites  and  the  axis-cylinder  process  for 
a  short  distance.     Strictly  speaking,  however,  the  name  should  be  ap- 


Fig.  ]04a.— Multipolar  nerve-ceU  of  the  cord  of  an  embryo  calf. 

plied  only  to  the  body  of  the  cell.      The  nerve-cell  is  provided  with  a  very 
large  round  nucleus  in  which  one  or  more  nucleoli  are  visible  (fig.  104). 


THE    STRUCTURE    OF   THE    ELEMENTARY    TISSUES. 


101 


The  protoplasm  of  the  cells  is  showD  by  various  djes  to  be  striated  or  re- 
ticulated. The  network  which  makes  up  this  cell-body  stains  more 
readily  with  certain  dyes  and  is  called  chvomophUlc.  The  material  which 
fills  in  the  spaces  between  the  network  of  the  cell-body  is  called  iha  jmra- 
plasm.  The  cells  often  contain  deposits  of  yellowish-brown  pigment 
(fig.  105).  The  nucleus  of  the  cell  is  sometimes  reticulated.  Within  the 
nucleus  is  sometimes  seen  a  nucleolus,  and  within  the  nucleolus  are 
bright  spots,  which  are  known  as  nucleolules. 

Nerve-cells  are  not  generally  present  iu  nerve-trunks,  but  are  found 

( 


Fig.  105.  —Cell  of  the  anterior  horn  of  the  human  spinal  cord,  stained  by  Nissl's  Method.    CAfter 

Edinger. ) 

in  collections  of  nervous  tissue  called  (janglia.     They  vary  considerably 
in  shape^  size,  and  stvn dure  in  dilferent  situations. 

a.  Some  nerve-cells  are  small,  generally  spherical  or  ovoid,  and  have 
a  regular  uninterrupted  outline.  These  single  nerve-cells  are  most  nu- 
merous in  the  sympathetic  ganglia ;  each  is  inclosed  iu  a  nucleated  sheath. 
b.  Others  (fig.  IOoa)  are  larger,  and  have  one,  two,  or  more  long  proc- 
esses issuing  from  them,  the  cells  being  called  respectively  ttnipolar, 
bipolar,  or  multipolar,  which  processes  often  divide  and  subdivide,  and 
appear  tubular  and  filled  with  the  same  kind  of  granular  material  that  is 
contained  within  the  cell.  These  jirocesses  are  the  dendrites.  Generally 
only  one  process  from  each  cell  is  continuous  with  a  nerve-fibre,  the 
prolongation  from   the  cell  1)y  degrees  assuming  the  characters  of    the 


102 


HAXDBOOK    OF    PHYSIOLOGY. 


nerve-fibre  with  "which  it  is  continuous.  This  process  is  the  neuraxon. 
In  bipolar  cells  one  pole  may  be  continuous  with  a  medullated  fibre,  and 
the  other  with  a  nou-medullated  one,  or  both  poles  may  pass  into  fibres 
of  the  one  or  the  other  kind. 

Ganglion-cells  are  generally  inclosed  in  a  transparent  membranous 
capsule  similar  in  appearance  to  the  external  nucleated  sheath  of  nerve- 
fibres;  Avithin  this  capsule  is  a  layer  of  small  flattened  cells. 

The  process  of  a  nerve-cell  or  neuraxon  which  becomes  continuous 
vvith  a  nerve-fibre  is  always  nnbranched  as  it  leaves  the  cell.  It  at  first 
has  all  the  characters  of  an  axis-cylinder,  but  soon  acquires  a  medullary 


Fig.  105a.— An  isolated  sympatlietic  ganglion-cell  of  man,  showing  sheath  with  nucleat^d-cell 
lining,  B.  A.  Ganglion-cell,  with  nucleus  and  nucleolus.  C.  Branched  process  or  dendrite.  D. 
Unbranched  process  or  neuraxon.    (Key  and  Retzius.)    x  750. 

sheath,  and  then  may  be  termed  a  nerve-fibre.  This  continuity  of  nerve- 
cells  and  fibres  may  be  readily  traced  out  in  the  anterior  coruua  of  the 
gray  matter  of  the  spinal  cord.  In  many  large  branched  nerve-cells  a 
distinctly  fibrillated  appearance  is  observable;  the  fibrillee  are  probably 
continuous  with  those  of  the  axis-cylinder  of  a  nerve. 

Other  points  in  the  structure  of  nerve-cells  will  be  mentioned  under 
the  account  of  the  central  nervous  system. 


Nerve  Terminations. 

Nerve-fibres  terminate  peripherally  in  four  different  ways:    1,  by  the 
terminal  subdivisions  which  pass  in  between   epithelial  cells,  and   are 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES. 


103 


known  as  inter-epithelial  arborizations;  2,  by  motor-plates  which  lie  in 
the  muscles;  3,  by  special  end -organs,  connected  with  the  senses  of 
sight,  hearing,  smell,  and  taste;  and,  4,  by  various  forms  of  tactile 
corpuscles. 

1.  The  inter-epithelial  arborizations  form  a  most  common  mode 
of  termination  of  tlie  sensory  nerves  of  the  body.  The  nerve-fibres  pass 
to  the  surface  of  the  skin  or  mucous  membrane;  they  then  lose  their  neu- 


Fig.  106.— Sensory   nerve  terminations  in  stratified  pavement  epithelium.      (jVfter  G.   Refc* 
zius.J    Golgi"s  rapid  method. 

rilemma  and  myeline  sheath,  the  bare  axis-cylinder  divides  and  subdi- 
vides into  minute  ramifications  which  pass  among  the  epithelial  cells 
of  the  skin  and  mucous  membrane.  In  the  various  glands  of  the  body 
this  form  of  termination  also  prevails.  The  hair-bulbs,  the  teeth,  and 
the  tendons  of  the  body  are  supplied  by  this  same  process  of  terminal 
arborization  (figs.  lOG,  lOT). 

2.   The  motor-nerv.es  passing  to  the  muscles  end  in  what  are  known 


Fig.  107.— Sensory  nerve  terminations  in  the  epithelium  of  the  mucosa  of  the  inferior  vocal 
cord  and  in  tlie  ciliated  epithelium  of  the  subglottic  region  of  the  larynx  of  a  cat  four  weeks  old. 
CAfter  G.  Retzius. )  Golgi"s  rapid  method,  ji,  Nerve-fibres  rising  from  the  connective-tissue  layer 
iuto  the  epithelial  iayer,  where  they  terminate  in  ramified  and  free  arborizations. 


as  muscle-plates,  the  details  of  whose  structure  have  been  already  de- 
scribed. , 

3.  The  special  sensory  end-organs  will  be  described  later  in  the 
chapter  on  the  Special  Senses. 

4.  A  fourth  form  of  termination  consists  of  corpuscles  that  are  more 
or  less  encapsulated,  and  these  are  known  as  the  corpuscles  of  Pacini,  the 
tactile  corpuscles  of  Mcissner,  the  tactile  corpuscles  of  Krause,  the  tactile 
menisques  and  the  corpuscles  of  Golyi. 


104 


HANDBOOK    OF    PHYSIOLOGY. 


The  Pacinian  bodies  or  corpuscles  (figs.  108  and  109),  named  after 
their  discoverer  Pacini,  also  called  corpuscles  of  Vator,  are  little  elon- 
gated oval  bodies,  situated  on  some  of  thecerebro-spiual  and  sympathetic 
nerves,  especially  the  cutaneous  nerves  of  the  hands  and  feet;  and  on 
branches  of  the  large  sympathetic  plexus  about  the  abdominal  aorta. 
They  often  occur  also  on  the  nerves  of  the  mesentery,  and  are  especially 
well  seen  even  by  the  naked  eye  in  the  mesentery  of  the  cat.  They  have 
been  observed  also  in  the  pancreas,  lym- 
phatic glands,  and  thyroid  glands,  as 
well  as  in  the  penis  of  the  cat.  Each 
corpuscle  is  attached  by  a  narrow  pedicle 
to  the  nerve  on  which  it  is  situated, 
and  is  formed  of  several  concentric 
layers  of  fine  membrane,  consisting  of  a 


Fig.  108. 


Fig.  109. 


Fig.  108. — Extremities  of  a  nerve  of  the  finger  witli  Pacinian  corpuscles  attached,  about  the 
natural  size  (adapted  from  Henle  and  Kolliker). 

Fig.  109. — Pacinian  corpuscle  of  the  cat's  mesentery.  The  stalk  consists  of  a  nerve-flbre  (N) 
with  its  thick  outer  sheath.  The  peripheral  capsules  of  the  Pacinian  corpuscle  are  continuous  wiih 
the  outer  sheath  of  the  stalk.  The  intermediary  part  becomes  much  narrower  near  the  entrance  of 
the  axis-cyUnder  into  the  clear  central  mass.  A  hook-shaped  termination  with  the  end-bulb  (T)  is 
seen  in  the  upper  part.  A  blood-vessel  (V)  enters  the  Pacinian  corpuscle,  and  approaches  the  end- 
bulb  ;  it  possesses  a  sheath  which  is  the  continuation  of  the  peripheral  capsules  of  the  Pacinian 
corpuscle.    X  100.    (Klein  and  Noble  Smith.) 

hyaline  ground  membrane  with  connective-tissue  fibres,  each  layer  being 
lined  by  endothelium  (fig.  109);  tlirough  its  pedicle  passes  a  single  nerve- 
fibre,  which,  after  traversing  the  several  concentric  layers  and  their 
immediate  spaces,  enters  a  central  cavity  and,  gradually  losing  its  dark 
border  and  becoming  smaller,  terminates  at  or  near  the  distal  end  of  the 
cavity,  in  a  knob-like  enlargement  or  in  a  bifurcation.     The  enlarge- 


THE   STRUCTURE   OF   THE    ELEMENTARY   TISSUES.  1U5 

ment  commonly  found  at  the  end  of  the  fibre  is  said  by  Pacini  to  re- 
semble a  ganglion  corpuscle;  but  this  observation  has  not  been  confirmed. 
In  some  cases  two  nerves  have  been  seen  entering  one  Pacinian  body, 
and  in  others  a  nerve  after  passing  unaltered  through  one  Las  been  ob- 


Fig.  110.— Summit  of  a  Pacinian  corpuscle  of  the  human  finger,  showingthe  endothelial  membranes 

lining  the  capsules.     X  220.     (Klein  aud  Noble  Smith.) 

served  to  terminate  in  a  second  Pacinian  corpuscle.      The  physiological 
import  of  these  bodies  is  still  obscure. 

2.  The  tactile  corpuscles  of  Meissner  (figs.  Ill,  112)  are  found  in  the 


Fig.  111.— A  touch-corpuscle  of  Meissner,  from  the  skin  of  the  human  hand 

papillae  of  the  skin  of  the  fingers  and  toes,  or  among  its  epithelium.  They 
may  be  simple  or  compound.  AVhen  simple  they  are  small,  slightly  flat- 
tened transparent  bodies  composed  of  nucleated  cells  enclosed  in  a  cap- 
sule. "When  compound,  the  capsule  contains  several  small  cells.  The 
corpuscles  are  about  ^j-^  of  an  inch  long  to  -j-lr  o^  ^'i"  i^ich  wide.  The 
nerve-fibre  penetrates  the  corpuscle,  loses  its  myeliue  sheath,  and  divides 


106 


HAXDBOOK    OF   PHYSIOLOGY. 


and  subdivides  to  form  a  series  of  arborizations,  more  or  less  distinct 
and  destined  for  the  different  parts  of  the  corpuscle.  The  terminal  ar- 
borizations occupy  the  central  part  of  the  corpuscle,  and  are  surrounded 
by  a  great  number  of  marginal  cells.     The  touch,  or  tactile  corpuscles 


Fig.  112. — Papillae  from  the  skin  of  the  hand,  freed  from  the  cuticle  and  exhibiting  tactile  cor- 
puscles. A.  Simple  papilla  with  four  nerve-fibres;  a,  tactile  corpuscles;  6,  nerves  with  winding 
fibres  c  and  e.  b.  Papilla  treated  with  acetic  acid;  a.  cortical  layer  with  cells  and  fine  elastic  fila- 
ments; 6,  tactile  corpuscle  with  tranverse  nuclei;  c,  entering  nerve  with  neurilemma  or  perineu- 
rium ;  d  and  e,  nerve-fibres  winding  round  the  corpuscle.    X  350.     (Kolhker.) 

of  Meissner,  have  been  regarded  at  one  time  as  epithelial,  ab  another 
time  as  nervous,  but  they  are  to-day  proved  to  be  mesodermic  cells,  and 
differentiated  for  the  special  purpose  of  the  sense  of  touch  (Dejerine). 


Fig.  113. — End-bulb  of  Krause.    a,  Medullated  nerve-fibre;  h,  capsule  of  corpuscle. 


3.  The  Corpuscles  of  Krause  or  End-Bulbs. — These  exist  in 
great  numbers  in  the  conjunctiva,  the  glans  penis,  clitoris,  lips,  skin, 
and  tendon  of  man;  they  resemble  the  corpuscles  of  Pacini,  but  have 
much  fewer  concentric  layers  to  the  corpuscle,  and  contain  a  relatively 
voluminous  central  mass  composed  of  polyhedral  cells.     In  man  these 


THE    STRUCTURE    OF   THE   ELEMEXTARY   TISSUES. 


107 


corpuscles  are  spherical  in  shape,  and  receive  many  nervous  fibres  which 
wind  through  the  corpuscle,  and  end  in  the  free  extremities  (fig.  113). 

4.  Tactile  Menisques. — ludifferentregionsof  theskinof  man,  one 
meets,  in  the  superficial  layers  and  in  the  Malpighian  layers,  nerves 
which,  after  having  lost  their  myeline  sheath,  divide  and  subdivide  to 
form  extremely  beautiful  arborizations.  The  branches  of  these  arboriza- 
tions are  flattened  down,  forming  the  tactile  menisques.  These  men- 
isques, which  simulate  the  form  of  a  leaf,  represent  a  mode  of  terminal 
nervous  arborization  (Eanvier). 

5.  The  corpuscles  of  Golgi  are  small  terminal  placques  placed  at  the 
union  of  tendons  and  muscles,  but  belonging  more  properly  to  the  tendon. 


Fig.  114.— A  termination  of  a  medullated  nerTC-fibre  in  tendon,  lower  half  -nith  convoluted  medul- 

lated  uerve-fibre.     (Golgi.) 


They  are  fusiform  in  shape  and  are  flattened  upon  the  surface  of  the 
tendon  close  to  its  insertion  into  the  muscular  fibres.  They  are  composed 
of  a  granular  substance,  enveloped  in  several  concentric  hyaline  mem- 
branes which  contain  some  nuclei.  The  nerve-fibre  passes  into  this 
little  corpuscle,  splitting  itself  up  into  fine  terminals.  The  corpuscles 
of  Golgi  are  believed  to  be  related  to  the  muscular  sense  (fig.  114). 

In  addition  to  the  special  end-organs,  sensory  fibres  may  terminate  in 
plexuses,  as  in  the  sub-epithelial  and  intra-epithelial  plexus  of  the 
cornea. 


The   Neuroglia. 

The  neuroglia,  while  not  a  nervous  tissue,  is  closely  mingled  with  it 
and  forms  an  important  constituent  of  the  nervous  system.  It  consists 
of  cells  giving  off  a  fine  network  of  richly  branching  fibres.  Neuroglia 
was  at  one  time  considered  to  be  a  form  of  connective  tissue,  and  it  is 
in  its  functions  strictly  comparable  to  the  connective  tissue  which  sup- 
ports the  special  structures  of  other  organs,  like  the  lungs  and  kidney 
(fig.  116).  It  is,  however,  derived  from  the  epiblastic  cells,  i.e.,  the 
same  cells  from  which  the  nerve-tissue  proper  also  develops.  In  the 
adult  animal  the  neuroglia-tissue  is  composed  of  cells  from  which  are 
given  off  immense  numbers  of  fine  processes.     These  extend  out  in  every 


108 


HANDBOOK    OF    PHYSIOLOGY. 


direction,  and  intertwine  among  the  nerve-fibres  and  nerve-cells  (fig.  115). 
The  neuroglia-cell  differs  in  size  and  shape  very  much  in  different  parts 

11 


Fig.  115.— Neuroglia  cells  in  the  cord  of  an  adult  frog.  (After  CI.  Sala.)  ^,  Ependyma  cells 
with  their  perip)ieral  extremities  atrophied  and  ramifled;  B,  C,  D,  neuroglia  cells  in  different  de- 
grees of  emigration  and  separation  from  the  ependymal  canal;  their  central  extremity  is  atro- 
phied and  much  contracted;  their  pe-ipheral  extremity,  on  the  other  hand,  is  greatly  extended; 
the  ramifications  of  the  latter  terminating  in  conical  buttons,  /,  end  under  the  pia  mater. 


Fig.  116.— Different  types  of  neuroglia  cells.     ("After  v.  Gehuchten.)    b.  Neuroglia  cells  of  the 
white  substance,  and  c,  of  the  gray  substance  of  the  cord  of  an  embryo  calf. 


THE    STRUCTURE    OF   THE    ELEMENTARY   TISSUES.  109 

of  the  nervous  system  in  accordance  with  the  arrangement  of  the  nerv- 
ous structures  about  it.  The  cell  is  composed  of  granular  protoplasm, 
and  lying  in  it  is  a  large  nucleus,  Avithiu  which  is  a  nucleolus.  The 
body  of  the  cell  is  small  in  amount  and  proportion  to  the  nucleus. 

Weigert  has  shown  that  the  processes  of  the  neuroglia-cells  branch 
and  prolong  themselves,  forming  in  many  places  an  extremely  thick  net- 
work. These  processes  become  changed  in  their  chemical  and  physical 
characters,  so  that  they  take  a  different  stain  from  that  of  the  cell-body 
itself,  and  they  thus  form  a  really  separate  structure,  distinct  almost 
from  the  mother-cell,  just  as  the  muscle  tissue  is  distinct  from  its  origi- 
nal cell-protoplasm,  or  just  as  the  substance  of  cartilage  is  distinct  from 
its  original  cell-body.  While  neuroglia-tissue  is  distributed  throughout 
the  whole  of  the  nervous  centres,  it  is  especially  deposited  in  certain  places. 
It  is  found  around  the  central  canal  of  the  spinal  cord,  and  upon  the 
superficial  surface  of  the  spinal  cord.  It  was  formerly  thought  to  com- 
pose part  of  the  gelatinous  substance  of  Eolando  in  the  spinal  cord,  but 
this  has  been  shown  by  Weigert  not  to  be  the  case. 

In  the  brain  a  deposit  of  neuroglia  is  found  beneath  the  ependymal 
lining  of  the  ventricles,  and  upon  the  superficial  surface  of  the  gray 
matter  of  the  cortex  beneath  thepia  mater.  It  is  distributed  to  some  ex- 
tent in  all  parts  of  the  brain  and  spinal  cord,  but  is  not  found  in  the 
peripheral  nerves. 


CHAPTER   lY. 

THE    CHEMICAL  COMPOSITION  OF  THE  BODY. 

Of  the  known  chemical  elements  of  which  about  seventy  have  been 
isolated  no  less  than  seventeen  combine,  in  larger  or  smaller  quantities, 
to  form  the  chemical  basis  of  the  animal  body. 

The  substances  which  contribute  the  largest  share  are  the  non-metallic 
elements,  Oxygen,  Carbon,  Hydrogen,  and  Nitrogen — oxygen  and  carbon 
making  up  altogether  about  85  per  cent  of  the  whole.  The  most  abun- 
dant of  the  metallic  elements  are  Calcium,  Sodium,  and  Potassium.* 

Few  of  the  elements',  however,  appear  free  or  uncombined  in  the  ani- 
mal body.  They  are  generally  united  together  in  variable  proportions  to 
form  compounds.  The  only  elements  which  have  been  found  free  in  the 
body  are  oxygen,  nitrogen,  and  hydrogen,  the  first  two  in  the  blood,  and 
hydrogen  as  Avell  as  oxygen  and  nitrogen  in  the  intestinal  canal. 

It  was  formerly  thought  that  the  more  complex  compounds  built  up 
by  the  animal  or  vegetable  organism  weve  peculiar  and  could  not  be  made 
artificially  by  chemists,  and  under  this  idea  they  Avere  formed  into  a  dis- 
tinct class,  termed  organic.  This  idea  has  long  been  given  up,  but  the 
name  is  still  in  use  with  a  different  signification.  The  term  is  now  ap- 
plied simply  to  the  compounds  of  the  element  carbon,  irrespective  of  their 
origin. 

A  large  number  of  the  animal  organic  compounds,  particularly  those 
of  the  albuminous  grouj),  are  characterized  by  their  complexity.  Many 
elements  enter  into  their  composition,  thereby  distinguishing  them  from 
simple  inorganic  compounds.  Many  atoms  of  the  same  element  occur  in 
each  molecule.  This  latter  fact  no  doubt  explains  the  reason  of  their 
instability.  Another  great  cause  of  the  instability  is  the  frequent  pres- 
ence of  nitrogen,  which  may  be  called  negative  or  undecided  in  its  affini- 
ties and  may  be  easily  separated  from  combination  with  other  elements. 

*Tiie  following  table  represents  the  relative  proportion    of    the  various  ele- 
ments.— (Marshall.) 

Fluorine 08 

Pot/imum      .....     .026 

Iron 01 

Magnesium 0013 

Silicon 0002 

(Traces  of  copper,  lead,  and  alu- 
minum)      


Oxygen 

.     72.0 

Carbon  .... 

13.5 

Hydroyen  . 

.       9.1 

Nitroyen 

2.5 

dtilriiiin 

.       1.3 

Phos|)horus  . 

1.15 

Sulphur     . 

.1476 

Sodium 

.i 

Chlorine     . 

.085 

100. 


110 


THE    CHEMICAL    COMPOSITION    OF   THE    BODY.  Ill 

Animal  tissues,  contaiMing  as  they  do  these  organic  nitrogenous  com- 
pounds, are  extremel}'  prone  to  undergo  decomposition.  They  also  con- 
tain much  looter,  a  circumstance  very  favorable  to  the  breaking  up  of  such 
substances.  It  is  due  to  this  tendency  to  decomposition  that  we  meet 
with  so  large  a  number  of  decomposition  products  among  the  chemical 
substances  forming  the  basis  of  the  animal  body. 

The  various  substances  found  in  the  animal  organism  may  be  conven- 
iently considered  according  to  the  following  classification:  1.  Ov(janic — 
a.  Nitrogenous  and  b.  Kon-Xitrogenous.     2.   Inovrjanic. 

Organic  Substances. 

Nlfrorji-nons  orf/ank  bodies  take  the  chief  part  in  forming  the  solid  tis- 
sues of  the  body,  and  are  found  also  to  a  Considerable  extent  in  the  circu- 
lating fluids  (blood,  lymph,  chyle),  the  secretions  and  excretions.  They 
often  contain  in  addition  to  carbon,  hydrogen,  nitrogen,  and  oxj'gen,  the 
elements  sulphur  and  phosphorus ;  but  although  the  comiiosition  of  most 
of  them  is  approximately  known,  no  general  rational  formula  can  at  pres- 
■ent  be  given. 

It  will  be  convenient  to  give  an  account  of  the  Proteid  substances  in 
this  Chapter,  as  these  constitute  the  most  important  classes  of  nitrogen- 
ous organic  substances.  According  to  their  chemical  composition  or  su- 
perficial differences  {e.y.,  solubility)  they  are  divided  into  three  main 
classes,  viz. :  (1)  Simple  proteids,  (2)  compound  proteids,  and  (o)  albu- 
menoids  or  i)roteoids.  The  other  members  are  Decoinposifiofi  2)ro(h(cfs,  the 
t'hief  of  which  is  Urea,  found  for  the  most  part  in  the  urine;  Ferments  ; 
Pitjiinnifs  :  and  other  bodies  and  will  be  more  appropriately  treated  of 
later  on.  , 

Proteids  (simple  proteids)  are  also  called  Albuminous  substances. 
They  are  the  chief  of  the  nitrogenous  organic  compounds  and  exist  in 
both  plants  and  animals,  one  or  more  of  them  entering  as  an  essential 
part  into  the  formation  of  all  living  tissue.  In  the  lymph,  chyle,  and 
blood,  they  exist  abundantly.  Very  little  is  known  with  any  certainty 
about  their  chemical  composition.  Xot  a  single  member  of  the  class  lias 
yet  been  synthesized.  Their  formula  is  unknown,  the  chemists  who  have 
attempted  to  construct  it  differing  very  greatly  among  themselves.  In 
fact  the  very  term  proteid  is  an  extremely  arbitrary  one.  It  simi)ly 
means  a  body  which,  according  to  Hoppe-Seyler,  contains  in  its  molecule 
the  elements  carbon,  hydrogen,  nitrogen,  oxygen,  and  suli)hur,  in  certain 
arbitrary  but  varying  amounts,  thus — Carbon,  from  51.5  to  54.5;  Hy- 
drogen, from  <).9  to  7..'V,  Nitrogen,  from  15.2  to  17. ;  Oxygen,  from 
20.9  to  23.5;  Sulphur,  from  3  to  2.  Some  lu-oteids  contain  from  .3  to 
1.5  of  phosphorus;  a  small  amount  c^f  iron  is  usually  associated  with 


112  HANDBOOK    OF    PHYSIOLOGY. 

jDroteids,  but  it  is  not  certain  whether  or  not  it  is  an  integral  part  of  the 
molecule.  Chittenden  defines  a  proteid  as  a  substance  which  contains 
carbon,  hydrogen,  oxygen,  nitrogen,  and  sulphur,  the  nitrogen  being  in  a 
form  which  serves  the  physiological  needs  of  the  body ;  and  yields,  on 
decomposition,  a  row  of  crystaUine  amido-acids  and  crystalline  nitrogen- 
ous bases;  nearly  all  contain  52  per  cent  of  carbon  and  16  per  cent  of  ni- 
trogen. 

Properties  of  Proteids. — Proteids  are  for  the  most  part  amorphous  and 
non-cry stallizable.  Certain  of  the  vegetable  proteids  have,  it  is  said, 
been  crystallized,  and  according  to  Hofmeister,  egg  albumin  is  also  capa- 
ble of  crystallization.  They  possess  as  a  rule  no  power  (or  scarcely  any) 
of  passing  through  animal  membranes.  They  are  soluble,  but  undergo 
alteration  in  composition  in  strong  acids  and  alkalies ;  some  are  soluble 
in  water,  others  in  neutral  saline  solutions,  some  in  dilute  acids  and  al- 
kalies, none  in  alcohol  or  ether.  Their  solutions  exercise  a  left-handed 
action  on  polarized  light. 

The  hope  that  it  may  be  possible  in  the  immediate  future  to  synthe- 
size proteids  is  rendered  all  the  weaker  because  of  the  extraordinary  va- 
riety of  compounds  obtained  by  the  decomposition  of  proteids  by  various 
chemical  methods,  the  compounds  differing  according  to  the  method  em- 
ployed. In  the  body  it  seems  clear  that  living  proteid  is  built  up  by  the 
food  supplied  to  it,  which  necessarily  contains  proteid  derived  either  from 
a  vegetable  or  an  animal  source ;  how  this  process  takes  place  we  are  yet 
unable  to  say.  In  the  course  of  later  chapters  in  this  book  we  shall  en- 
deavor to  trace  the  steps  of  the  breaking  up  of  proteid  in  the  body,  but 
we  may  anticipate  by  mentioning  that  it  is  now  generally  believed  that 
the  ultimate  products  of  this  decomposition  are  urea,  a  body  the  formula 
of  which  is  CO(iSfHj)„,  carbon  dioxide  and  water,  while  the  intermediate 
substances  or  by  products  are  probably  ammonia  compounds  (ammonium 
carbonate).  When  proteid  material  is  decomposed  by  putrefaction,  by 
the  action  of  chemical  reagents,  e.g.,  acids,  alkalies,  or  by  heat,  various 
bodies  are  produced,  of  which  amido-acids  (acids  in  which  one  or  more  of 
the  hydrogen  atoms  of  the  radical  of  the  acid  are  replaced  by  amidogen, 
NHj  and  bodies  belonging  to  the  aromatic  or  benzene  series  predominate. 
Hence  it  comes  that  various  theories  of  the  Avay  in  which  proteids  are 
built  up  have  arisen.  The  one  which  lias  appeared  to  have  received  the 
greatest  support  is  that  of  Latham.  This  observer  has  suggested  that 
proteid  may  be  considered  as  made  up  of  a  series  of  cyan-alcoJioh  (bodies 
obtained  by  the  union  of  any  aldehyde  with  hydrocyanic  acid)  with  a 
benzene  nucleus.  Taking  ordinary  ethyl  alcohol,  CH^CH^OH,  as  the 
type,  the  aldehyde  of  which  is  CH^CHO,  the  corresponding  cyan-alcohol 
would  be  CH3CHCNOH. 

Proteids  give  certain  general  chemical  reactions.     They  are  a  little 


THE    CHEMICAL   COMPOSITIOX    OF   THE    BODY.  113 

varied  in  the  case  of  each  particular  substance.     The  chief  of  these  are  as 
follows : 

i.  Xantho-Proteic  Reaction. — The  addition  of  strong  nitiic 
acitl,  drop  by  drop,  to  a  solution  of  any  proteid  produces  a 
Hocculent  ])recipitate  which  dissolves  in  an  excess  of  the  acid. 
The  solution  XwQomca  (-(nui ru  ijclhnr  \n  color;  wIumi  heated, 
this  color  is  more  marked ;  when  cooled,  the  addition  of  am- 
monia in  excess  changes  the  color  to  oraiKji'.  The  nitric  acid 
decom})oses  the  proteid  to  a  certain  extent  and  then  unites 
with  the  decomposition  products,  forming,  among  other 
things,  xanthoproteic  acidAvhich  gives  the  yellow  color.  The 
ammonia  unites  with  this  and  forms  ammonium  xanthoprote- 
ate  which  gives  the  orange  color. 

ii.  Biuret  (Piotrowski's)  Reaction. — With  a  trace  of  cupric 
sulphate  and  an  excess  of  potassium  or  sodium  hydrate  pep- 
tones and  proteoses  give  a  rose  fed  ;  Avith  ammonia  instead  of 
the  fixed  alkalies,  a  hhie  coloration.  jMost  proteids,  however, 
give  a  r/o/e^  (pinkish  purple)  color;  the  color  is  due  to  re- 
duced copper,  cuprous  hydroxide  being  formed  along  with 
other  compounds  of  red,  yellow,  and  blue  colors. 

iii.  Millon's  Reaction. — AVith  Millon's  reagent  (a  solution  of 
mercuric  nitrate)  proteids  give  a  heavy  Avhite  precipitate  of 
mercuric  albuminate  which,  with  an  excess  of  the  reagent,  be- 
comes brick  red  Avhen  heated.  This  test  is  said  to  be  due  to 
the  presence  of  ty rosin,  an  aromatic  compound  in  the  proteid 
molecule:  it  is  generally  used  for  solids  though  it  maybe 
used  for  liquids  also.  With  all  substances  containing  the 
C^H^OH  group,  e.ij.,  carbolic  acid,  this  reagent  gives  the  same 
color  reaction,  though  no  precipitate  is  formed,  the  solution 
itself  becoming  red. 

iv.  Ammonium  Sulphate  Reaction. — They  are,  with  the  ex- 
ci'ptiou  of  peptone,  entirely  }ireeipitated  from  their  solutions 
by  saturation  with  ammonium  sulphate. 

Many  of  the  proteids  give,  in  addition,  the  following  tests: 

v.   \\'ith  excess  of  acetic  aciil,  and  potassium  ferrocyanide,  a  white 

precipitate, 
vi.  A\'ith  excess  of  acetic  acid  and  a  saturated  solution  of  sodium 

sulphate,  on  boiling,  a  white  precipitate.     This  test  is  often 

used  to  get  rid  of  all  traces  of  proteids,  except  peptones,  from 

solutions. 
8 


114  HANDBOOK    OF    PHYSIOLOGY. 

vii.  Boiled  with  strong  hydrochloric  acid,  they  give  a  violet  red 

coloration, 
viii.  With  cane  sugar  and  strong  sulphuric  acid,  on  heating,  they 

give  2i  i^urjjlish  coloration, 
ix.  They  are  precipitated  on  addition  of — citric  or  acetic  acid, 

and  picric  acid ;  or  citric  or  acetic  acid,  and  sodium  tungstate ; 

or  citric  or  acetic  acid,  and  potassio-mercuric  iodide ;  and  with 

many  other  metallic  salts  in  solution  and  by  alcohol. 

Foriefii'es.— Proteids  are  divided  into  classes,  chiefly  on  the  basis  of 
their  solubilities  in  various  reagents.  Each  class,  however,  if  it  contains 
more  than  one  substance,  may  often  be  distinguished  by  other  properties 
common  to  its  members.  Not  every  one  of  the  proteids  enumerated  is 
contained  in  the  animal  tissues,  some  are  used  as  food. 

(1.)  Native- Albumins. — These  substances  are  soluble  in  water  and  in 
saline  solutions,  and  are  coagulated,  i.e.,  turned  into  coagulated  proteid, 
on  heating. 

(2.)  Albuminates. — These  are  soluble  in  acids  or  alkalies,  insoluble  in 
saline  solutions  and  in  water,  and  not  coagulated  on  heating. 

(3.)  Globulins. — These  are  soluble  in  weak  saline  solutions,  in  dilute 
acids  and  alkalies,  and  insoluble  in  water  and  in  strong  solutions  of  neu- 
tral salts.     They  are  coagulated  on  heating. 

(4.)  P7'oteoses. — These  are  soluble  in  water  and  dilute  saline  solutions, 
precipitated  by  saturation  with  ammonium  sulphate ;  precipitated  but  not 
coagulated  by  alcohol ;  precipitated  by  picric  acid :  cannot  be  coagulated 
by  heat. 

(5.)  Peptones. — These  are  soluble  in  water,  saline  solutions,  acids,  or 
alkalies ;  not  precipitated  on  saturation  with  any  neutral  salt ;  they  are 
not  coagulated  on  heating. 

(6.)  Coagulated  Proteids. — These  are  of  two  classes,  either  coagulated 
by  (a)  action  of  ferments,  or  (b)  heat.  These  are  soluble  only  in  gastric 
or  pancreatic  fluids,  forming  peptones,  or  (with  difficulty)  in  strong  acids 
and  alkalies. 

Native- Albumins.— Of  native-albumins  there  are  several  varieties : 
(a)  egg-albumin;  (b)  serum-albumin;  (c)  lact-albumin,  etc. 

Eijrj  Albumin  is  contained  in  the  white  of  the  egg. 

When  in  solution  in  water  it  is  a  transparent,  frothy,  yellowish  fluid, 
neutral  or  slightly  alkaline  in  reaction.  It  gives  all  of  the  general  pro- 
teid reactions.  It  yields  8  per  cent  of  argenin,  22.6  per  cent  of  leucin, 
and  2  per  cent  of  tyrosin. 

At  a  temperature  not  exceeding  40°  C.  it  is  dried  up  into  a  yellowish, 
transparent,  glassy  mass,  soluble  in  water.  At  a  temperature  of  70°  C. 
it  is  coagnkited,  i.e.,  changed  into  a  new  substance,  coagulated  proteid, 


THE    CHEMICAL   COMPOSITION   OF    THE    BODY.  115 

wliicli  is  quite  insoluble  in  water.  It  is  coagulated  also  by  the  prolonged 
action  of  alcohol ;  by  strong  mineral  acids,  especially  by  nitric  acid,  also 
by  tannic  acid,  or  carbolic  acid;  by  ethers  the  coaguluui  is  soluble  in 
caustic  soda. 

It  IS,  jjvec'qntated  without  coagulation,  i.e.,  forms  insoluble  compound 
with  the  reagent,  soluble  on  removal  of  the  salt  by  dialysis,  with  either 
mercuric  chloride,  lead  acetate,  copper  sulphate  or  silver  nitrate,  the  pre- 
cipitate in  each  case  being  soluble  in  slight  excess  of  the  reagent. 

With  strong  nitric  acid  the  albumin  is  precipitated  at  the  point  of 
contact  with  the  acid  in  the  form  of  a  fine  white  or  yellow  ring. 

Serum- Allni mi n.  is  contained  in  blood-serum,  lymph,  serous  and  syno- 
vial fluids,  and  in  the  tissues  generally ;  it  may  be  prepared  from  serum, 
after  removal  of  paraglobulin  by  saturation  with  magnesium  sulphaie,  by 
a  further  saturation  with  sodium  sulphate.  It  appears  in  the  urine  in  the 
condition  known  as  albuminuria. 

It  gives  similar  reactions  to  egg-albumin,  but  differs  from  it  in  not 
being  coagulated  by  ether.  It  also  differs  from  egg-albumin  in  not  being 
easily  precijiitated  by  hydrochloric  acid,  and  in  the  precipitate  being  easily 
soluble  in  excess  of  that  acid.  Serum-albumin,  either  in  the  coagulated 
or  precipitated  form,  is  inore  soluble  in  excess  of  strong  acid  than  egg- 
albumin. 

Albuminates. — ^There  are  two  principal  substances  belonging  to  this 
class,  a,  Acid-Albumin;  b,  Alkali-Albumin. 

Acid-Albttmin.—i\.ii\i\.-'Alh\xm.m.  is  made  by  adding  small  quantities  of 
dilute  acid  (of  wliich  the  best  is  hydrochloric,  .4  per  cent  to  1  per  cent), 
to  either  ei^^-  or  serum-albumin  diluted  Avith  five  to  ten  times  its  bulk  of 
water,  and  kee})ing  tlie  solution  at  a  temperature  not  higher  than  hO°  C. 
for  not  less  than  half  an  hour.  It  may  also  be  made  by  dissolving  coagu- 
lated native-albumin  in  strong  acid,  or  by  dissolving  any  of  the  globulins 
in  acids.  Solid  acid  albuminate  may  be  formed  by  adding  strong  acid 
drop  by  drop  to  a  strong  solution  of  proteid  matter  {<'.[/.,  undiluted  egg- 
albumin)  until  solidification  occurs. 

It  is  not  coagidated  on  heating,  but  on  e.iutrth/  neutralizing  the  solu- 
tion a  flocculent  precipitate  is  produced  (if  it  is  then  heated  to  70°  C'.  it 
will  coagulate  and  cannot  then  be  distinguished  from  any  other  form  of 
coagulated  jiroteids).  This  maybe  slunvn  by  adding  to  the  acid-albumin 
solution  a  little  aipieous  solution  of  litmus,  and  then  adding,  drop  by 
drop,  a  weak  solution  of  caustic  potash  from  a  burette  until  the  red 
color  disappears.  The  i)recipitate  is  the  derived-albumin.  It  is  soluble 
in  dilute  acid,  dilute  alkalies,  and  dilute  solutions  of  alkaline  carbonates. 
The  solution  of  acid-albuniin  gives  the  ])roteid  tests.  The  substance  it- 
self is  coagulated  by  strong  acids,  r.y. ,  nitric  acid,  and  by  strong  alcoliol; 
it  is  insoluble  in  distilled  water,  and  in  neutral  saline  solutions;  it  is  pre- 


116  HANDBOOK    OF    PHYSIOLOGY. 

cipitated  from  its  solutions  by  saturation  with  sodium  chloride.  On  boil- 
ing in  lime-water  it  is  partially  coagulated,  and  a  further  precipitation 
takes  place  on  addition  to  the  boiled  solution  of  calcium  chloride,  magne- 
sium sulphate,  or  sodium  chloride. 

Alkali-Albuinln. — If  solutions  of  native-albumin,  or  coagulated  or 
other  proteid,  be  treated  with  dilute  or  strong  fixed  alkali,  alkali-albumin 
is  produced.  Solid  alkali-albumin  (Lieberkuhn's  jelly)  may  also  be  pre- 
pared by  adding  caustic  soda  or  potash,  drop  by  drop,  to  undiluted  egg- 
albumin,  until  the  whole  forms  a  jelly.  This  jelly  is  soluble  in  an  excess 
of  the  alkali  or  in  dilute  alkalies  on  boiling.  A  solution  of  alkali-albu- 
min gives  the  tests  corresponding  to  those  of  acid-albumin.  It  is  not 
coagulated  on  heating  except  after  neutralization,  as  in  the  case  of  acid 
albumin.  It  is  thrown  down  on  neutralizing  its  solution,  except  in  the 
presence  of  alkaline  phosphates,  in  which  case  the  solution  must  be  dis- 
tinctly acid  before  a  precipitate  falls. 

To  differentiate  between  Acid-  and  Alkali-Albumin,  the  following 
method  may  be  adopted.  Alkali-albumin  is  not  precipitated  on  exact 
neutralization,  if  sodium  phosphate  has  been  previously  added.  Acid- 
albumin  is  precipitated  on  exact  neutralization,  whether  or  not  sodium 
phosphate  has  been  previously  added. 

Globulins. — The  globulins  give  the  general  proteid  tests;  are  insolu- 
ble in  water;  are  soluble  in  dilute  saline  solutions;  are  soluble  in  acids 
and  alkalies  forming  the  corresponding  derived-albumin. 

Most  of  them  are  j)recipitated  from  their  solutioirs  by  saturation  with 
solid  sodium  chloride,  magnesium  sulphate,  or  other  neutral  salt.  They 
are  coagulated,  but  at  different  temperatures,  on  heating. 

Globulin  or  CrystalUn. — It  is  obtained  from  the  crystalline  lens  by 
rubbing  it  up  with  powdered  glass,  extracting  with  water  or  with  dilute 
saline  solution,  and  by  passing  through  the  extract  a  stream  of  carbon 
iodide.  It  differs  from  other  globulins  in  not  being  precipitated  by  satu- 
ration with  sodium  chloride. 

Myosin. — The  relation  of  myosin  to  living  muscle  will  be  considered 
under  the  head  of  the  physiology  of  muscle.  It  may,  however,  be  prepared 
from  dead  muscle  by  removing  all  fat,  tendon,  etc.,  and  washing  repeatedly 
in  water  until  the  washing  contains  no  trace  of  proteids,  mincing  it  and 
then  treating  with  10  per  cent  solution  of  sodium  chloride,  or  similar 
solution  of  ammonium  chloride  or  magnesium  sulphate,  which  will  dis- 
solve a  large  portion  into  a  viscid  fluid,  which  filters  with  difficulty.  If 
the  viscid  filtrate  be  dropped  little  by  little  into  a  large  quantity  of  dis- 
tilled water,  a  white  flocculent  precipitate  of  myosin  will  occur. 

It  is  soluble  in  10  per  cent  saline  solution;  it  is  coagulated  at  60°  C. 
into  coagulated  proteid;  it  is  soluble  without  change  in  very  dilute  acids; 
it  is  precipitated  by  picric  acid,  the    precipitate  being  redissolved  on 


THE    CHEMICAL   COMPOSITION    OF   THE    BODY.  llY 

boiling;  it  may  give  a  l)lue  coloi-  "witli  ozoiiic  (^tliei'  and  tincture  of 
guaiaciim. 

Faraglohulu). — Paraglobulin  is  contained  in  i)lasma  and  in  serum,  in 
serous  and  synovial  fluids,  and  may  be  precipitated  by  saturating  plasma 
after  removal  of  fibrinogen  or  serum  with  solid  sodium  chloride  or  magne- 
sium suli)hate,  as  a  bulky  flocculent  substance  Avliich  can  be  removed  by 
filtration. 

It  may  also  be  prepared  by  diluting  blood  serum  with  ten  volumes  of 
water,  and  passing  carbonic  acid  gas  rapidly  through  it.  The  fine  pre- 
cipitate may  be  collected  on  a  filter,  and  washed  with  water  containing 
carbonic  acid  gas. 

It  is  very  soluble  in  dilute  saline  solutions  (5  to  8  per  cent),  from 
which  it  is  precipitated  by  carbonic  acid  gas  or  by  dilute  acids ;  its  solu- 
tion is  coagulated  at  70°  C. ;  even  dilute  acids  and  alkalies  convert  it 
into  acid-  or  alkali-albumin. 

Fibrinogen. — Fibrinogen  is  contained  in  Ijlood-plasma,  from  whii-h  it 
may  be  prepared  by  addition  of  sodium  chloride  to  the  extent  of  13  per 
cent.  It  may  also  be  prepared  from  hydrocele  fluid  or  from  other  serous 
transudation  by  a  similar  method. 

Its  general  reactions  are  similar  to  those  of  paraglobulin ;  its  solution 
is  coagulated  at  52°-55°  C.  Its  characteristic  property  is  that,  under 
certain  conditions,  it  forms  fibrin. 

Edcstrine. — Edestrine  is  a  globulin  which  is  found  in  many  edible 
vegetables,  grain,  etc.  A  solution  may  be  prepared  by  adding  hemp  seed 
to  a  10  per  cent  solution  of  sodium  chloride  and  heating  to  50°  C. 

Proteoses  are  intermediate  substances  of  the  digestion  of  other  pro- 
teids,  the  ultimate  product  of  which  is  peptone.  They  are  produced  by 
the  action  of  the  gastric  and  pancreatic  juices  and  also,  sloAvly,  by  boiling 
with  dilute  acids.  The  term  is  a  general  one,  the  proteose  of  albumin 
being  albumose,  that  of  globulin  being  globulose,  etc.  They  are  divided 
into  primary  and  secondary  groups  representing  the  stages  of  progression 
from  proteids  to  peptones,  so  that  there  may  be  a  primary  and  a  second- 
ary albumose,  etc.  As  digestion  is  a  process  of  hydration  with  cleavage, 
the  successive  stages  present  progressively  simpler  substances.  Each 
grou})  reacts  to  fewer  reagents  than  the  preceding  one;  e.g.,  none  of  the 
proteoses  can  be  coagulated  by  boiling,  nitric  acid  will  precipitate  the 
primary  proteoses  but  not  the  secondary  ones. 

Peptones. — Peptone  is  formed  b}-  the  action  of  the  digestive  fer- 
ments, pepsin,  or  tvyjisin,  on  other  proteids,  and  on  gelatin.  It  is  a  still 
simpler  form  of  substance  than  the  proteoses  and  reacts  to  still  fewer  re- 
agents. They  will  be  considered  in  connection  with  tlie  i)hysiology  of 
digestion,  as  will  also  the  intermediate  compounds. 

Coagulated  proteids  are  formed  by  the  action  of  heat  or  of  ferments 


118  HANDBOOK    OF    PHYSIOLOGY, 

upon  other  proteids ;  tlie  temperature  necessary  to  produce  coagulation 
varying  in  the  manner  previously  indicated.  They  may  also  be  produced 
by  the  prolonged  action  of  alcohol  upon  proteids ;  the  process  is  one  of 
dehydration.  They  are  soluble  in  strong  acids  or  alkalies ;  slightly  so  in 
dilute;  are  soluble  in  digestive  fluids  (gastric  and  pancreatic).  Are  in- 
soluble in  water  or  saline  solutions  (except  fibrin). 

Fibrin. — Eibrinis  formed  bytlie  action  of  fibrin  ferment  on  fibrinogen 
and  can  be  obtained  as  a  soft,  white,  fibrous,  and  very  elastic  substance 
by  whipping  blood  with  a  bundle  of  twigs  and  washing  the  adhering  mass 
in  a  stream  of  water  until  all  the  blood-coloring  matter  is  removed.  It 
is  soluble  to  a  certain  extent  in  strong  saline  solutions. 

Compound  Proteids. — Tlie  compound  proteids  are  compounds  of  a 
simple  proteid  with  some  other  molecule.  According  to  their  chemical 
composition  and  characteristics  they  are  divided  into  several  classes,  viz. : 

Cliromo- proteids. — A  combination  of  a  proteid  substance  with  some 
form  of  pigment.  For  example,  ha3moglobin  is  a  combination  of  a  globu- 
lin with  hsematin,  an  iron-containing  radicle. 

Gluco-proteids. — A  combination  of  a  proteid  substance  with  a  carbo- 
hydrate radicle.  Examples  are  mucin,  which  is  found  in  mucous  secre- 
tions ;  and  mucoids,  which  are  found  in  certain  tissues,  cartilages,  etc. 

Nudeo-proteids. — A  combination  of  a  proteid  substance  with  a  nucleic 
acid :  they  are  divided  into  two  groups  according  to  the  character  of  the 
acid.  The  true  nucleo-proteids  contain  true  nucleic  acid ;  the  para-nucleo- 
proteids,  or  pseudo-nucleo-proteids  contain  para-nucleic  acid.  Both  acids, 
and  therefore  both  groups,  contain  phosphorus ;  but  the  true  nuclo-prpteids 
yield  nuclein  (xanthin)  bases  while  the  para-nucleo-proteids  do  not.  They 
are  found  in  the  nucleus  and  protoplasm  of  every  cell,  and  also  in  milk, 
as  caseinogen,  and  in  the  yolk  of  egg,  as  vitellin. 

Gluco-n'Ucleo-])roteids' — A  combination  of  a  nucleo-proteid  with  a  car- 
bohydrate radicle. 

Mucin. — Mucin  is  a  compound  of  a  globulin  with  a  carbohydrate 
radicle,  and  is  the  characteristic  component  of  mucus ;  it  is  contained  also 
in  foetal  connective  tissue,  in  tendons,  and  salivary  glands.  It  can  be 
obtained  from  mucus  by  diluting  it  with  water,  filtering,  treating  the 
insoluble  portion  with  weak  caustic  alkali,  and  reprecipitating  with  acetic 
acid.  The  mucins  derived  from  different  sources  probably  have  different 
compositions. 

Frojjertias. — Mucin  has  a  ropy  consistency.  It  can  be  coagulated;  is 
insoluble  in  water,  salt  solution,  and  very  dilute  muriatic  acid ;  is  soluble  in 
alkalies  and  concentrated  sulphuric  acid.  It  gives  the  proteid  reaction 
with  Millon's  reagent  and  with  nitric  acid.  Neither  mercuric  chloride 
nor  tannic  acid  gives  a  precipitate  with  it   (?).     It  does  not  dialyse. 


THE    CHEMICAL   COMPOSITION"    OF   THE    BODY,  119 

When  treated  with  su]})liiuio  acid  and  then  neutralized  with  solid  potas- 
sium hydrate,  it  will  give  both  the  Biuret  test,  denoting  the  presence  of 
proteid  matter,  and  also  Fehling's  test,  shoAving  the  presence  of  a  sugar: 
the  acid  splits  it  into  a  globulin  and  a  carbohydrate. 

Nucleins. — The  substance  known  as  miclein  and  found  in  all  cells 
as  well  as  in  milk  (caseinogen)  and  the  yolk  of  egg  (vitellin)  is  really  a 
compound  proteid  and  consists  of  a  whole  series  of  bodies  made  up  of 
proteid  and  nucleic  acid  in  varying  proportions ;  there  is  almost  no  limit 
to  the  possible  variations.  At  one  end  of  the  series  is  nucleic  acid  (0^^ 
'K,,^^^V^O^^,  according  to  Kossel),  a  body  containing  the  maximum  (9  to 
11  per  cent)  of  phosphorus,  but  without  any  proteid,  and  found  as  such 
only  in  spermatozoa;  in  the  middle  slyq  the  luicleins  proper;  and  at  the 
other  end  are  the  inieleo-jjvofeids,  containing  the  minimum  of  phosphorus. 
As  phos]jhorus  is  the  characteristic  component  of  nucleic  acid,  its  amount 
will  measure  the  amount  of  the  acid  present  in  any  molecule. 

The  karyoplasm  (nucleus)  of  every  cell  is  richer  in  the  nucleins,  while 
the  cytoplasm  (cell  body)  is  richer  in  the  nucleo-proteids  which  contain  a 
smaller  proportion  of  nucleic  acid  and,  therefore,  of  phosphorus.  The 
difference  in  staining  power  of  the  nucleus  and  cell  body  is  thus  explained 
as  the  relative  affinity  of  these  substances  for  a  basic  dye  is  proportional 
to  the  amount  of  nucleic  acid  they  contain.  The  chemical  differences  in 
the  action  of  cjrtoplasm  and  karyoplasm  toward  solvents  are  due  also  to 
the  proportion  of  nucleic  acid  and  proteid  which  they  contain.  These 
differences  are  quantitative  and  not  qualitative.  All  of  the  nucleo-pro- 
teids in  the  cell  body  are  true  ones  in  that  they  yield  nuclein  bases. 

Nnclein  Bases. — These  are  xanthin,  hypoxanthin,  adenin,  and  guanin  ; 
they  are  closely  related  nitrogenous  bodies  which  are  always  present  in 
every  chemical  change  in  the  cell,  and  one  may  be  transformed  into  an- 
other. They  are  also  known  as  xanthin  or  j9«ri?i  bases,  and  all  can  be 
derived  from  the  so-called ^>»r//i  nucleus  C^N^  by  substitution  of  atoms; 
the  j9wrm  base,  as  isolated  by  Emil  Fischer,  is  C.H^N^. 

Hypoxanthin  or  oxj'purin  is      .         .         .         C5H4N4O 

Xanthin  or  dioxypurin  is        ...  .    05114X402 
Adenin  or  aniino-puvin  is            ...         C5H5N5 

Guanin  or  amino-oxypurin  is  .         .  .    CilljNsO. 

Uric  acid  is  closely  related,  though  not  one  of  the  nuclein  bases,  being 
trioxypurin,  C^H^IST^O.,.  Caffeine,  the  active  principle  of  coffee,  is  tri- 
methyl  dioxypurin,  0^.11,^X^0.,— simply  xanthin  with  three  atoms  re- 
placed by  the  methyl  group  CH3. 

Caseinogen. ^ — ^Caseinogen,  the  chief  proteid  of  milk,  is  strictly  a 
nucleo-albumin  and  does  not  yield  the  nuclein  bases ;  it  bears  the  same 
relation  to  casein  that  fibrinogen  does  to  fibrin.  When  acted  on  by  ren- 
nin  it   siilits  into  two  parts  of  which   one,  the   smaller,  is  peptone-like  in 


120  HANDBOOK   OP  PHYSIOLOCtY. 

character.  The  other,  and  hxrger  part,  is  known  as  sohible  casein  and 
does  not  solidify  in  the  absence  of  calcium  salts ;  as  these  are  always 
present  in  milk,  it  there  unites  Avith  them  and  forms  insoluble  calcium 
casein;  strictly  speaking,  therefore,  the  curd  of  milk  is  the  calcium 
compound  of  soluble  casein.  Caseinogen  may  be  prepared  by  adding  di- 
lute hydrochloric  acid  to  milk  until  the  mixture  is  distinctly  acid ;  a  floc- 
culent  precipitate  of  caseinogen  Avill  be  thrown  down  and  may  be  sepa- 
rated by  filtration ;  the  fat  which  is  carried  down  Avith  this  precipitate 
may  be  removed  by  washing  with  alcohol  and  then  with  ether. 

Caseinogen  may  also  be  prepared  liy  adding  to  milk  an  excess  of  crys- 
tallized magnesium  sulphate  or  sodium  chloride,  either  of  which  salt 
causes  it  to  separate  out. 

Caseinogen  gives  the  Biuret  and  Millon's  reactions  showing  the  pres- 
ence of  proteid  substances,  much  the  same  tests  as  alkali-albumin.  It  is 
soluble  in  distilled  water,  dilute  or  strong  alkalies,  and  sulphuric  acid, 
but  insoluble  in  sodium  chloride  and  .2  per  cent  of  hydrochloric  acid. 

Vitellin. — Yitellin  is  prepared  from  yolk  of  egg  by  washing  with 
ether  until  all  the  yellow  matter  has  been  removed.  The  residiie  is  dis- 
solved in  10  per  cent  saline  solution,  filtered,  and  poured  into  a  large 
quantity  of  distilled  water.  The  precipitate  which  falls  is  impure  vitellin. 
It  gives  the  same  tests  as  myosin,  but  is  not  precipitated  on  saturation 
with  sodium  chloride ;  it  coagulates  between  70°  and  83°  C. 

Albumenoids  or  Proteoids. — The  albumenoids  belong  to  the  sim- 
ple tissues  of  the  body  which  are  derived  from  the  epiblast  and  are  char- 
acterized by  a  lack  of  an}^  degree  of  activity,  either  physiological  or 
chemical.  They  are  proteid  derivatives,  nitrogenous  bodies  derived  from 
proteid  matter  in  the  cells,  and  give  crystalline  amido-acids  and  nitrogen- 
ous bases  on  decomposition,  but  differ  from  true  proteids  in  not  having 
their  nitrogen  in  a  form  lit  for  the  physiological  needs  of  the  bod}'.  In 
other  Avords,  they  are  not  true  foods,  though  gelatin  has  a  certain  indirect 
food  A'alue  as  it  protects  the  body  proteids  from  work  in  many  Avaj-s,  at 
times.  The  albumenoids  are  soluble  in  dilute  acids  or  alkalies ;  the}'  ma}' 
be  distinguished  from  albumin  or  globulin  by  being  insoluble  in  Avater  or 
salt  solution  respectively. 

Gelatin. — Gelatin  is  contained  in  the  form  of  collaf/eu,  its  anhj^dride, 
in  bone  (ossch/'),  teeth,  hbrous  connective  tissues,  tendons,  ligaments,  etc. 
It  ma}'  be  obtained  by  prolonged  action  of  boiling  Avater  in  a  Papin's  di- 
gester or  of  dilute  acetic  acid  at  a  Ioav  temperature  (15°  C). 

Projierties. — The  percentage  composition  is  0,  25.24  per  cent,  H,  6.56 
percent,  N,  17.81  per  cent,  C,  50 per  cent,  80,  25  per  cent.  It  contains 
more  nitrogen  and  less  carbon  and  sulphur  than  proteids.  It  is  amor- 
phous, and  transparent  when  dried.      It  does  not  dialyse ;  it  is  insoluble 


THE   CHEMICAL   COMPOSITION    OF   THE    BODY.  121 

in  cold  Avater,  but  swells  u})  to  about  six  times  its  volume:  it  dissolves 
readily  on  the  addition  of  very  dilute  acids  or  alkalies.  It  is  soluble  in 
hot  water,  and  forms  a  jelly  on  cooling,  even  when  only  1  per  cent  of 
gelatin  is  present;  it  is  also  soluble  in  hot  salt  solution.  Prolonged 
boiling  in  dilute  acids,  or  in  water  alone,  destroys  this  power  of  forming 
a  jelly  on  cooling.  Its  physical  properties  seem  to  indicate  a  closer  rela- 
tionship to  albumin  than  to  keratin,  but  decomposition  proves  the  reverse. 
On  decomposition  it  gives  2  per  cent  of  leucin  and  2.G  per  cent  of  argenin, 
but  no  tj^rosin ;  instead  there  is  a  large  amount  of  glycocoll  (amido-acetic 
acid  or  glycin),  a  crystalline  substance. 

A  fairly  strong  solution  of  gelatin— 2  per  cent  to  4  per  cent — gives 
the  following  reactions : 

(a)  IVlf/i  proteid  tests :  (i.)  Xantlioproteictesf. — A  3-ellow  color  but 
no  previous  precipitate  with  nitric  acid,  becoming  darker  on  the 
addition  of  ammonia,  (ii.)  Biuret  test. — A  blue  color,  (iii-) 
M'lllon'' s  test — A  pink  color  but  no  precipitate,  (iv.)  Potassium 
ferroei/anide  <in(]  arctic  (teid. — jSTo  reaction,  (v.)  Boiling  with 
sodium  sulphate  and  acetic  acid.  Ko  reaction, 
(p.)  Special  reactions  :  (i.)  Xo  precipitate  with  acetic  acid,  (ii.)  Ko 
precipitate  with  dilute  hj-drochloric  acid,  (iii.)  A  white  pre- 
cipitate with  tannic  acid,  not  soluble  in  excess  or  in  dilute  ace- 
tic acid,  (iv.)  No  precipitate  Avith  mercuric  chloride,  unlike 
the  reaction  with  albumose  and  peptone,  (v.)  A  white  precipi- 
tate Avith  alcohol.  (vi.)  A  yelloAvish-Avhite  precipitate  Avith 
picric  acid,  dissoh-ed  on  heating  and  reappearing  on  cooling. 
Colhujen  is  insoluble  in  almost  everything. 

Elastin  is  found  in  elastic  tissue,  in  the  ligamenta  subflaA'a,  ligamen- 
tum  nuchw,  etc.  It  is  insoluble  in  all  ordinary  reagents,  but  SAvells  up 
both  in  cold  and  hot  Avater.  Is  soluble  in  strong  caustic  soda  slowly, 
Avhen  heated.  It  is  precipitated  by  tannic  acid;  does  not  gelatinize. 
Gives  the  proteid  reactions  Avith  strong  nitric  acid  and  ammonia,  and  im- 
perfectly Avith  INIillon's  reagent.  On  decomposition  it  gives  4.5  per  cent 
of  leucin,  a  small  amount  of  argenin,  and  a  mere  trace  of  tyrosin.  It  is 
prejiarod  by  boiling  Avitli  Avater,  then  treating  Avith  artificial  gastric  and 
l)ancreatic  juices,  then  l)oiling  again  in  Avater,  and  then  extracting  Avith 
acids,  alcohol,  and  ethers;  the  remainder  is  elastin. 

Chondrin  is  found  in  the  condition  of  chondrigen  in  cartilage. 
It  is  a  mixture  of  gelatin  Avith  a  mucin-like  substance,  and  is  obtained 
from  chondrigen  by  boiling. 

Projicrties. — It  is  soluble  in  hot  Avater,  and  in  solutions  of  neutral 
salt,  cf/.,  sulphate  of  sodium,  in  dilute  mineral  acids,  cau.stic  potash,  and 
soda.  Insoluble  in  cold  Avater,  alcohol,  and  ether.  It  is  precii)itated 
from  its  solutions  by  dihitc  mineral  acids  (excess  redissoh'es  it),  by  alum. 


122  HANDBOOK    OF    PHYSIOLOGY. 

by  lead  acetate,  by  silver  nitrate,  and  by  chlorine  water.  On  boiling  \Yith 
strong  hydrochloric  acid,  it  yields  grape-sugar  and  certain  nitrogenous 
substances.  Prolonged  boiling  in  dilute  acids,  or  in  water,  destroys  its 
power  of  forming  a  jelly  on  cooling. 

Keratin  is  obtained  from  hair,  horns,  fingernails,  etc.  Its  composi- 
tion is  very  similar  to  that  of  ordinary  albumin  and  is  approximately 
C,  49.5,  H,  6.5,  N,  16.8,  S,  4.,  0,  23.2;  the  keratins  obtained  from  the 
various  substances  are  distinct  and  differ  slightly  though  closely  related. 
Sulphur  is  the  characteristic  body  found  in  keratin  and  occurs  as  a  sul- 
phur-containing radicle ;  a  large  amount  of  mercaptan  sulphur  can  usually 
be  obtained.  On  decomposition,  keratin  yields  argenin  2.26  per  cent, 
leucin  10  per  cent,  and  tyrosin  4  per  cent. 

Proj^erties. — Keratin  is  insoluble  in  water,  salt,  sodium  carbonate,  and 
dilute  hydrochloric  acid ;  is  soluble  slowly,  when  warmed,  in  caustic  pot- 
ash and  sulphuric  acid;  gives  Millon's  and  the  xanthoproteic  reactions. 

Neurokeratin  is  a  form  of  keratin  which  is  found  in  the  white  sub- 
stance of  Schwann  around  the  axis- cylinders  of  nerves.  It  yields  arge- 
nin 5  per  cent,  leucin  10  per  cent,  and  tyrosin  3.5  per  cent. 

Non-nitrogenous  organic  bodies  consist  of 

(a)  Oils  and  Fats,  which  are  for  the  most  part  mixtures  of  tri-pal- 
mitin,  C.jHggOj,,  tri-stearin  C^^H^j^^O^,  and  ti<-olein  C^^H^^p^,  in  different 
proportions.  They  are  formed  by  the  union  of  three  molecules  of  fatty 
acid  with  one  molecule  of  the  triatomic  alcohol,  glycerin  0^11^(011)3,  and 
are  ethereal  salts  or  esters  of  that  alcohol.  Palmitic  acid  is  Cj^H^^O^ ; 
stearic  acid  is  0  ,H^  O  :  oleic  acid  is  0  ,H,,0„.  Human  fat  consists  of 
a  mixture  of  tri-j)almiti?i,  tri-stearin,  and  tri-olein,  of  which  the  two  former 
contribute  three-quarters  of  the  whole.  Olein  is  the  only  liquid  constitu- 
ent.   The  fat  of  milk  (and  butter)  is  tri-butyrine ;  butyric  acid  is  0^,11^,0^. 

Fats  are  insoluble  in  water  and  in  cold  alcohol ;  soluble  in  hot  alcohol, 
ether,  and  chloroform.  Colorless  and  tasteless ;  easily  decomposed  or  sa- 
ponified by  alkalies  or  super-heated  steam  into  glycerin  and  the  fatty  acids. 

And  (b)  Carbohydrates,  which  are  bodies  composed  of  six  or  twelve 
atoms  of  carbon  with  hydrogen  and  oxygen,  the  two  latter  elements  being 
in  the  proportion  to  form  water.  There  are  three  main  classes  of  carbo- 
hydrates. 

Monosaccharides  or  Glucoses,  C^H^^O^,  containing  one  molecule  of  su- 
gar, and  comprising  Dextrose  or  Grape  Sugar,  Lsevulose  or  Fruit  Sugar, 
Inosite,  etc.  Disaccharides  or  Saccharoses,  Cj„H^^Ojj,  containing  two 
molecules  of  sugar  from  which  one  molecule  of  water  has  been  with- 
drawn, and  comprising  Saccharose  or  Cane  Sugar,  Lactose,  Maltose,  etc. 
Polysaccharides  or  Amyloses,  GJi^()^,  containing  a  large  but  unknown 
number  of  molecules  of  sugar  from  which  water  has  been  withdrawn,  and 
comprising  Starch,  Dextrin,  Glycogen,  etc. 


THE    CHEMICAL    COMPOSITION    OF   THE    BODY.  123 

Pyoj^^erf lira.— jMonosaceharides  are  especially  soluble  and  i^olysaccha- 
rides  are  especially  insoluble ;  monosaccharides  and  disaccliarides  do  not 
give  colored  solutions  Avith  iodine  while  polysaccharides  do ;  monosaccha- 
rides and  (except  saccharose)  disaccliarides  reduce  Fehling's  solution 
while  polysaccharides  do  not. 

Of  these  the  most  important  are : 

Starch  (C^Hj^O.),  which  is  contained  in  nearl}-  all  2'f'infs,  and  in 
many  seeds,  roofs,  steins,  and  some  fruits.  It  is  a  soft  white  powder  com- 
posed of  granules  having  an  organized  structure,  consisting  of  fjranulose 
(soluble  in  water)  contained  in  a  coat  of  cellulose  (insoluble  in  water) ; 
the  shape  and  size  of  the  granules  varying  according  to  the  source  whence 
the  starch  has  been  obtained.  It  is  not  crystalline  and  will  not  dialyze. 
It  is  insoluble  in  cold  water,  in  alcohol,  and  in  ether ;  it  is  soluble  after 
boiling  for  some  time,  and  may  be  filtered,  in  consequence  of  the  swelling 
up  of  the  granulose,  which  bursts  the  cellulose  coat,  and  becoming  free, 
is  entirely  dissolved  in  water.  This  solution  is  a  solution  of  soluble 
starch  or  amy  din.  It  gives  a  blue  coloration  with  iodine,  which  disap- 
pears on  heating  and  returns  on  cooling.  It  is  converted  into  maltose  by 
diastase,  and  by  boiling  with  dilute  acids  into  dextrose. 

Glycogen,  which  is  contained  in  the  liver,  is  also  present  in  all  mus- 
cles but  especially  in  those  of  very  young  animals,  in  the  placenta,  in 
colorless  corpuscles,  and  iu  embryonic  tissues.  It  is  sometimes  called 
animal  starch  and  gives  many  reactions  proper  to  starch  itself.  It  is 
freely  soluble  in  water,  and  its  solution  looks  opalescent ;  it  gives  a  port- 
wine  coloration  with  iodine,  which  disappears  on  heating  and  returns  on 
cooling.  It  is  precipitated  by  basic  lead  acetate  and  is  insoluble  in  abso- 
lute alcohol  and  in  ether.  It  exists  in  the  liver  during  life,  but  very  soon 
after  death  is  changed  into  sugar.  It  may  be  prepared  by  grinding  mus- 
cle with  sand  till  a  pasty  mass  is  formed,  boiling  the  mass  in  Avater  for 
twenty  minutes,  filtering,  and  then  precipitating  the  glj^cogen  from  the 
filtrate  by  adding  a  little  more  than  an  equal  quantity  of  95  per  cent  al- 
cohol. It  is  converted  into  sugar  by  diastase  ferments,  or  into  dex- 
trose by  boiling  Avith  dilute  acids. 

Dextrin. — This  substance  is  made  iu  commerce  b}-  heating  dry  pota- 
to-starch to  a  temperature  of  400^.  It  is  also  produced  in  the  process  of 
the  couA^ersion  of  starch  into  sugar  by  diastase,  and  by  the  salivary  and 
pancreatic  ferments.  A  yelloAvish  amorphous  poAvder,  soluble  in  Avater, 
but  insoluble  in  absolute  alcohol  and  in  ether.  It  corresi)onds  almost  ex- 
actly in  tests  Avith  glycogen ;  but  one  variety  (achroo-dextrin)  does  not 
give  the  port-wine  coloration  Avith  iodine. 

Cane  Sugar,  or  Saccharose,  is  contained  in  the  juices  of  many 
plants  and  fruits,  and  is  as  a  rule  extracted  from  the  sugar  cane,  from 
beetroot,  or  from  the  maple.     It  is  crystalline  and  is  precipitated  from 


124  HANDBOOK   OF   PHYSIOLOGY. 

concentrated  solutions  by  absolute  alcohol.  It  has  no  power  of  reducing 
copper  salts  on  boiling.  It  is  dextro-rotatory  (see  Appendix).  It  is  not 
subject  to  alcoholic  fermentation,  until  by  inversion  it  is  converted  into 
glucose,  it  chars  on  addition  of  sulphuric  acid,  and  on  heating  with  po- 
tassium or  sodium  hydrate. 

Lactose  is  the  chief  carbohydrate  of  milk.  It  is  less  soluble  in 
water  than  glucose ;  not  sweet,  and  is  gritty  to  the  taste ;  but  it  is  insolu- 
ble in  absolute  alcohol.  In  digestion  it  yields  a  molecule  of  dextrose  and 
a  molecule  of  galactose.  Undergoes  alcoholic  fermentation  with  extreme 
difficulty ;  gives  the  tests  similar  to  glucose,  but  less  readily.  It  is  dex- 
tro-rotatory -|-  69°. 

Maltose  is  produced  by  the  action  of  the  saliva  and  pancreatic  juice 
on  starch.  It  is  also  formed  by  the  action  of  malt  upon  starch  by  the 
ferment  diastase,  and  in  the  formation  of  glucose  from  starch.  It  is  con- 
verted into  dextrose  by  dilute  sulphuric  acid.  It  is  dextro-rotatory ;  fer- 
ments with  yeast;  reduces  copper  salts,  and  crystallizes  in  fine  needles. 

Glucose  occurs  widely  diffused  in  the  vegetable  kingdom,  in  diabetic 
urine,  in  the  blood,  etc. ;  it  is  usually  obtained  from  grape-juice,  honey, 
beet-root  or  carrots.  It  really  is  a  mixture  of  two  isomeric  bodies,  Dex- 
trose or  grape-sugar,  which  turns  a  ray  of  polarized  light  to  the  right 
(_|_  56°),  and  Lcevulose  or  fruit-sugar,  which  turns  the  ray  to  the  left. 

It  is  easily  soluble  in  water  and  in  alcohol ;  not  so  sweet  as  cane-su- 
gar ;  the  relation  of  its  sweetness  to  that  of  cane-sugar  is  as  3  to  6.  It  is 
not  so  easily  charred  by  strong  sulphuric  acid  as  cane-sugar.  It  is  not  en- 
tirely soluble  in  alcohol.     It  undergoes  alcoholic  fermentation  with  yeast. 

Dextrose  is  the  characteristic  carbohydrate  of  the  blood.  It  has  the 
power  of  reducing  the  salts  of  silver,  bismuth,  mercury,  and  copper,  either 
to  the  form  of  the  metal  in  the  first  three  cases,  or  to  the  form  of  the 
suboxide  in  the  case  with  cuprous  salts.  Upon  this  property  the  chief 
tests  for  the  sugar,  e.g.,  Trommer's  and  Bottcher's,  depend  (see  Appen- 
dix). When  boiled  with  potash,  glucic  and  melanic  acids  are  formed, 
awd  a  yellowish  fluid  results  (Moore's  test).  It  is  oxidized  by  the  action 
of  nitric  acid  to  saccharic  acid.  It  forms  compounds  with  acids  and  Avith 
potash  and  lime.  It  undergoes  alcoholic  fermentation  Avith  yeast,  and 
lactic-acid  fermentation  Avith  bacteria  lactis.  It  forms  caramel  when 
strongly  heated,  and  is  also  charred  with  strong  acids.  For  the  method 
of  quantitative  estimation,  etc.,  see  Appendix. 

Laevulose  is  one  of  the  products  of  the  decomposition  of  cane-sugar 
by  means  of  dilute  mineral  acids,  or  by  means  of  the  ferment  invertin  in 
the  alimentary  canal. 

It  reacts  to  the  same  test  as  glucose,  but  is  non-crystallizable,  and  is 
Isevo-rotatory  —  lOGO. .  It  is  soluble  in  water  and  in  alcohol.  Its  com- 
pound Avith  lime  is  solid,  whereas  that  with  dextrose  is  not. 


THE    CHEMICAL   COMPOSITION    OF   THE    BODY.  125 

Galactose  is  formed  from  lactose  by  tlie  action  of  dilute  mineral 
acids,  or  inverting  ferments;  it  may  also  be  obtained  from  cerebrin.  It 
undergoes  alcoholic  fermentation,  and  reduces  copper  salts  to  the  sub- 
oxide. 

Inosite.^ — Inosite  occurs  in  the  heart  and  voluntary  muscles,  as  well 
as  in  beans  and  other  plants.  It  crystallizes  in  the  form  of  large  color- 
less monoclinic  tables,  which  are  soluble  in  water,  but  insoluble  in  alco- 
hol or  ether.  It  has  the  formula  of  glucose,  but  is  not  a  sugar.  Inosite 
may  be  detected  by  evaporating  the  solution  containing  it  nearly  to  dry- 
ness, and  by  then  adding  a  small  droj:)  of  solution  of  mercuric  nitrate,  and 
afterward  evaporating  carefully  to  dryness,  a  yellowish-white  residue  is 
obtained ;  on  further  cautiously  heating,  the  yellow  changes  to  a  deep 
rose-color,  which  disappears  on  cooling,  but  reappears  on  heating.  If 
the  inosite  be  almost  pure,  its  solution  may  be  evaporated  nearly  to  dry- 
ness. After  the  addition  of  nitric  acid,  the  residue  mixed  with  a  little 
ammonia  and  calcium  chloride,  and  again  evaporated,  yields  a  rose-red 
coloration. 

Certain  of  the  monatomic  Fatty  Acids  are  found  in  the  body, 
viz.,  Formic  CH,0„,  acetic  Q^fi„,  and  propionic  C^H^Oj,  present  in 
sweat,  but  normally  in  no  other  human  secretion.  They  have  been  found 
elsewhere  in  diseased  conditions.  Butyric  acid,  C\II^O„,  is  found  in 
sweat.  A^arious  others  of  these  acids  have  been  obtained  from  blood, 
muscular  juice,  fteces  and  urine. 

Of  the  diatomic  fatty  acids,  one  acid,  Lactic  acid,  CH^O,,  exists  in  a 
free  state  in  muscle  plasma,  antl  is  increased  in  quantity  by  muscular 
contraction,  is  never  contained  in  healthy  blood,  and  when  present  in 
abnormal  amount  seems  to  produce  rheumatism. 

Of  the  aromatic  series,  Benzoic  acid,  CjHgO..,  is  ahva^-s  found  in 
the  urine  of  herbivora,  and  can  be  obtained  from  stale  human  urine.  It 
does  not  exist  free  elscAvhere. 

Phenol. — Phenyl  alcohol  or  carbolic  acid  exists  in  minute  quantity  in 
human  urine.     It  is  an  alcohol  of  the  aromatic  series. 

Inorganic  Principles. 

The  inorganic  proximate  principles  of  the  human  body  are  numerous. 
They  are  derived,  for  the  most  })art,  directly  from  food  and  drink,  and 
pass  through  the  system  unaltered.  Some  are,  however,  decomposed  on 
their  way,  as  chloride  of  sodium,  of  which  onl}^  four-fifths  of  the  quantity 
ingested  are  excreted  in  the  same  form ;  and  some  are  newly  formed 
within  the  body, — as,  for  example,  a  part  of  the  sulphates  and  carbo- 
nates, and  some  of  the  water. 

Much  of  the  inorganic  saline  matter  found  in  the  body  is  a  necessary 
constituent  of  its  structure, — as  necessar}-  in  its  way  as  albumin  or  any 


126  HANDBOOK    OF    PHYSIOLOGY. 

other  organic  principle ;  another  part  is  important  in  regulating  or  modi- 
fying various  physical  processes,  as  absorption,  solution,  and  the  like; 
while  a  part  must  be  reckoned  only  as  matter,  which  is,  so  to  speak, 
accidentally  present,  whether  derived  from  the  food  or  the  tissues,  and 
which  will,  at  the  first  opportunity,  be  excreted  from  the  body. 

Gases. — The  gaseous  matters  found  in  the  body  are  Oxygen,  Hydro- 
gen, Nitrogen,  Carhuretted  and  Sulphuretted  hydrogen,  and  Carbonic  acid. 
The  first  three  have  been  referred  to.  Carburetted  and  sulphuretted 
hydrogen  are  found  in  the  intestinal  canal.  Carbonic  acid  is  present  in 
the  blood  and  other  fluids,  and  is  excreted  in  large  quantities  by  the 
lungs,  and  in  very  minute  amount  by  the  skin.  It  will  be  specially  con- 
sidered in  the  chapter  on  Respiration. 

Water,  the  most  abundant  of  the  proximate  principles,  forms  a  large 
proportion, — more  than  two-thirds  of  the  weight  of  the  whole  body.  Its 
relative  amount  in  some  of  the  principal  solids  and  fluids  of  the  body  is 
shown  in  the  following  table  (from  Robin  and  Verdeil's)  : — 

Quantity  op  Water  in  1000  Pakts. 


Teeth 100 

Bones    ......        130 

Cartilage 550 

Muscles 750 

Ligament 768 

Brain 789 

Blood 795 

Synovia 805 


Bile 880 

Milk 887 

Pancreatic  juice        ....  900 

Urine 936 

Lymph 960 

Gastric  juice         ....  975 

Perspiration 986 

Saliva 995 


The  importance  of  water  as  a  constituent  of  the  animal  body  may  be 
assumed  from  the  preceding  table,  and  is  shown  in  a  still  more  striking 
manner  by  its  withdrawal.  If  any  tissue,  as  muscle,  cartilage,  or  ten- 
don, be  subjected  to  heat  sufficient  to  drive  off  the  greater  part  of  its 
water,  all  its  characteristic  physical  properties  are  destroyed ;  and  what 
was  previously  soft,  elastic,  and  flexible  becomes  hard  and  brittle,  and 
horny,  so  as  to  be  scarcely  recognizable. 

In  all  the  fluids  of  the  body — blood,  lymph,  etc., — water  acts  the 
part  of  a  general  solvent,  and  by  its  means  alone  circulation  of  nutrient 
matter  is  possible.  It  is  the  medium  also  in  which  all  fluid  and  solid 
aliments  are  dissolved  before  absorption,  as  well  as  the  means  by  which 
all,  except  gaseous,  excretory  products  are  removed.  All  the  various 
processes  of  secretion,  transudation,  and  nutrition  depend  of  necessity 
on  its  presence  for  their  performance. 

The  greater  part,  by  far,  of  the  water  present  in  the  body  is  taken 
into  it  as  such  from  without,  in  the  food  and  drink.  A  small  amount, 
however,  is  the  result  of  the  chemical  union  of  hydrogen  with  oxygen  in 
the  blood  and  tissue.     The  total  amount  taken  into  the  body  every  day 


THE    CHEMICAL   COMPOSITION    OF   THE    BODY.  127 

is  about  44  lbs. ;  while  an  uncertain  quantity  (perhaps  -k  to  f  lb.)  is 
formed  by  chemical  action  within  it. — (Dalton.) 

The  loss  of  water  from  the  body  is  intimately  connected  with  excre- 
tion from  the  lungs,  skin,  and  kidneys,  and,  to  a  less  extent,  from  the 
alimentary  canal.  The  loss  from  these  various  organs  may  be  thus  ap- 
portioned (quoted  by  Dalton  from  various  observers). 

From  the  Alimentary  canal  (fa?ces) 4  per  cent. 

Lungs 20        " 

«         Skin  (perspiration) 30        " 

"         Kidneys  (urine) 46        " 

100 

Sodium  and  Potassium  Chlorides  are  present  in  nearly  all  parts  of  the 
body.  The  former  seems  to  be  especially  necessary,  judging  from  the 
instinctive  craving  for  it  on  the  part  of  animals  in  whose  food  it  is  defi- 
cient, and  from  the  diseased  condition  which  is  consequent  on  its  with- 
drawal. In  the  blood,  the  quantity  of  sodium  chloride  is  greater  than 
that  of  all  its  other  saline  ingredients  taken  together.  In  the  muscles, 
on  the  other  hand,  the  quantity  of  sodium  chloride  is  less  than  that  of  the 
chloride  of  potassium. 

Caleiuni  Fluoride,  in  minute  amount,  is  present  in  the  bones  and  teeth, 
and  traces  have  been  found  in  the  blood  and  some  other  fluids. 

Calcium,  Potassium,  Sodium,  and  Magnesium  Phosphates  are  found  in 
nearly  every  tissue  and  fluid.  In  some  tissues — the  bones  and  teeth — the 
phosphate  of  calcium  exists  in  very  large  amount  and  is  the  principal 
source  of  that  hardness  of  texture  on  which  the  proper  performance  of 
their  functions  so  much  depends.  The  phosphate  of  calcium  is  intimately 
incorporated  with  the  organic  basis  or  matrix,  but  it  can  be  removed  by 
acids  without  destroying  the  general  shape  of  the  bone ;  and,  after  the 
removal  of  its  inorganic  salts,  a  bone  is  left  soft,  tough,  and  flexible. 

Potassium  and  sodium  phosphates  with  the  carbonates,  maintain  the 
alkalinity  of  the  blood. 

Calcium  Cavhonate  occurs  in  bones  and  teeth,  but  in  much  smaller 
quantity  than  the  phosphate.  It  is  found  also  in  some  other  parts.  The 
small  concietions  of  the  internal  ear  (otoliths)  are  composed  of  crystalline 
calcium  carbonate,  and  form  the  only  example  of  inorganic  crystalline 
matter  existing  as  such  in  the  body. 

Potassium,  and  Sodium  Carbonates  are  found  in  the  blood,  and  some 
other  fluids  and  tissues. 

Potassium,  Sodium,  aud  Calcium  Suljihates  are  met  with  in  small 
amount  in  most  of  the  solids  and  fluids. 

Silicon. — A  very  minute  quantity  of  silica  exists  in  the  uriue,  and  in 
the  blood.  Traces  of  it  have  been  found  also  in  bones,  hair,  and  some 
other  parts. 


128  HANDBOOK    OF    PHYSIOLOGY. 

Iron. — The  especial  place  of  iron  is  in  lieemogiobin,  the  coloriiig-uiat- 
ter  of  the  blood,  of  which  a  full  account  will  be  given  with  the  chemistry 
of  the  blood.  Peroxide  of  iron  is  found,  in  very  small  quantities,  in  the 
ashes  of  bones,  muscles,  and  many  tissues,  and  in  lymph  and  chyle, 
albmnin  of  serum,  fibrin,  bile,  milk  and  other  fluids;  and  a  salt  of  iron, 
probably  a  phosphate,  exists  in  the  hair,  black  pigment,  and  other  deeply 
colored  ej)ithelial  or  horny  snbstances. 

Aluminium,  Manganese,  Copper,  and  Lead. — It  seems  most  likely  that 
in  the  human  body,  copper,  manganesium,  aluminium,  and  lead  are 
merely  accidental  elements,  which,  being  taken  in  minute  quantities  with 
the  food,  and  uot  excreted  at  once  with  the  faeces,  are  absorbed  and  de- 
posited in  some  tissue  or  organ,  of  which,  however,  they  form  no  neces- 
sary part.  In  the  same  manner,  arsenic,  being  absorbed,  may  be  depos- 
ited in  the  liver  and  other  parts. 


CHAPTER  Y. 

THE  BLOOD. 

The  blood  is  the  fluid  medium  b}'  means  of  which  all  the  tissues  of 
the  body  are  directly  or  indirectly  nourished;  by  means  of  it  also  such 
of  the  materials  which  result  from  the  metabolism  of  the  tissues  as  are 
of  no  further  use  in  the  economy,  are  carried  to  the  excretory  organs  to 
be  removed  from  the  body.  It  is  a  somewhat  viscid  fluid,  and  in  man 
and  in  all  other  vertebrate  animals  with  the  exception  of  two,*  is  red 
in  color.  The  exact  shade  of  red  is  variable;  that  taken  from  the 
arteries,  from  the  left  side  of  the  heart  and  from  the  pulmonary  veins 
is  of  a  bright  scarlet  hue,  that  obtained  from  the  systemic  veins,  from 
the  right  side  of  the  heart,  and  from  the  iDulmonary  artery,  is  of  a  much 
darker  color,  and  varies  from  bluish-red  to  reddish-black.  At  first 
sight,  the  red  color  appears  to  belong  to  the  whole  mass  of  blood,  but 
on  further  examination  this  is  found  not  to  be  the  case.  In  reality  blood 
consists  of  an  almost  colorless  fluid,  called  plasma  or  liquor  sanguinis, 
in  which  are  suspended  numerous  minute  rounded  masses  of  proto- 
plasm, called  blood  corpuscles,  which  are,  for  the  most  part,  colored, 
and  it  is  to  their  presence  in  the  fluid  that  the  red  color  of  the  blood  is 
due. 

Even  when  examined  in  very  thin  layers,  blood  is  opaque,  on  account 
of  the  diiferent  refractive  powers  possessed  by  its  two  constituents,  viz., 
lihe  plasma  and  the  corpuscles.  On  treatmeiit  with  chloroform  and 
other  reagents,  however,  it  becomes  transparent  and  assumes  a  lake 
color,  in  consequence  of  the  coloring  matter  of  the  corpuscles  having 
been  discharged  iuto  the  plasma.  The  specifir  gravity  of  the  blood 
varies  slightly  at  difl'erent  times  in  accordance  with  the  changing  pro- 
portions of  its  component  parts.  Of  tiiesc,  wnter  is  the  most  variable 
constituent,  and  salts  the  next,  while  albumens  are  the  most  constant 
and  the  last  afl'ected  by  disease.  Under  normal  conditions  the  average 
specific  gravity  in  adults  is  about  1.059,  the  normal  limits  of  variation 
being  given  by  Becquerel  and  Rodier  as  1.054-1.060,  by  Ilammerschlag  as 
1.056-1.063,  and  by  Jones  as  1.045-1.066.  The  physiological  variations 
may  be  considerable,  depending  on  the  age,  sex,  time  of  day,  amount  of 
exercise  or  sleep,  etc.     The  specific  gravity  is  increased  by  residence  in 

*Thc'  tiiiip/tio.titi<  and  the  leptocejihahis. 


130  HANDBOOK    OF    PHYSIOLOGY. 

high  altitudes.  AccordiDg  to  JoEes  it  is  verj  high  (1.066)  in  new-born 
infants,  but,  after  the  second  week,  sinks  throughout  the  first  year  of 
life  (to  1.048-1.050)  and  then  rises  again,  becoming  almost  as  high  in  old 
age  as  in  infancy.  In  iJathological  conditions  the  variations  may  be 
most  marked,  e.g.,  the  specific  gravity  is  constantly  lowered  in  antemia, 
while  in  cachexia  resulting  from  malignant  new  growths  it  may  even  be 
reduced  to  1.030  (Lyonnet).  Various  drugs  {e.g.,  diuretics  and  dia- 
phoretics) also  affect  the  specific  gravity.  A  rapid  and  useful  method 
of  estimating  the  specific  gravity  of  blood  is  the  one  devised  by  Hammer- 
schlag  as  a  modification  of  Eoy's  method.  Chloroform  and  benzol, 
which  are  respectively  heavier  and  lighter  than  blood,  are  mixed  in  such 
proportions  that  the  resultant  specific  gravity  is  about  1.059.  A  drop  of 
blood  is  then  added  to  this  mixture,  with  which  it  does  not  mix  at  all, 
but  floats  as  a  red  bead.  Accordingly  as  it  sinks  to  the  bottom  or  rises 
to  the  top,  either  chloroform  or  benzol  is  added.  AYhen  the  drop  re- 
mains stationary  in  the  body  of  the  liquid  the  specific  gravity  of  the 
mixture  will  be  the  same  as  that  of  the  blood,  and  can  be  ascertained  by 
a  hydrometer.  The  reaction  of  blood  is  faintly  alkaline  and  the  taste 
saltish.  Its  temperature  varies  slightly,  the  average  being  37.8°  C.  (100° 
F.).  The  blood  stream  is  warmed  by  passing  through  the  muscles, 
nerve  centres,  and  glands,  but  is  somewhat  cooled  on  traversing  the 
capillaries  of  the  skin.  Eecently  drawn  blood  has  a  distinct  odor,  which 
in  many  cases  is  characteristic  of  the  animal  from  which  it  has  been 
taken.  It  may  be  further  developed  also  by  adding  to  blood  a  mixture 
of  equal  parts  of  sulphuric  acid  and  water. 

Quantity  of  the  Blood. — The  quantity  of  blood  in  any  animal 
under  normal  conditions  bears  a  fairly  constant  relation  to  the  body- 
weight.  The  methods  employed  for  estimating  it  are  not  so  simple  as 
might  at  first  sight  have  been  thought-  For  example,  it  would  not  be 
possible  to  get  any  accurate  information  on  the  point  from  the  amount 
obtained  by  rapidly  bleeding  an  animal  to  death,  for  then  an  indefinite 
quantity  would  remain  in  the  vessels,  as  well  as  in  the  tissues;  nor,  on 
the  other  hand,  would  it  be  possible  to  obtain  a  correct  estimate  by  less 
rapid  bleeding,  as,  since  life  would  be  more  prolonged,  time  would  be 
allowed  for  the  passage  into  the  blood  of  lymph  from  the  lymphatic 
vessels  and  from  the  tissues.  In  the  former  case,  therefore,  we  should 
under-estimate,  and  in  the  latter  over-estimate  the  total  amount  of  the 
blood. 

Of  the  several  methods  which  have  been  employed,  the  most  accurate 
appears  to  be  the  following.  A  small  quantity  of  blood  is  taken  from 
an  animal  by  venesection;  it  is  defibrinated  and  measured,  and  used  to 
make  standard  solutions  of  blood.  The  animal  is  then  rapidly  bled  to 
death,  and  the  blood  which  escapes  is  collected.  The  blood-vessels  are 
next  washed  out  with  saline  solution  until  the  washings  are  no  longer 


THE    BLOOD.  131 

colored,  and  these  are  added  to  the  previously  withdrawn  blood;  lastly 
the  whole  animal  is  finely  minced  with  saline  solution.  The  fluid  ob- 
tained from  the  mincings  is  carefully  filtered,  and  added  to  the  diluted 
blood  previously  obtained,  and  the  whole  is  measured.  The  next  step 
in  the  process  is  the  comparison  of  the  color  of  the  diluted  blood  with 
that  of  standard  solutions  of  blood  and  water  of  a  known  strength,  until 
it  is  discovered  to  what  standard  solution  the  diluted  blood  corresponds. 
As  the  amount  of  blood  in  the  corresponding  standard  solution  is  known, 
as  well  as  the  total  quantity  of  diluted  blood  obtained  from  the  animal, 
it  is  easy  to  calculate  the  absolute  amount  of  blood  which  the  latter  con- 
tained, and  to  this  is  added  the  small  amount  wdiich  was  withdrawn  to 
make  the  standard  solutions.  This  gives  the  total  amount  of  blood 
which  the  animal  contained.  It  is  contrasted  with  the  weight  of  the 
animal,  previously  known. 

The  result  of  maiiy  experiments  shows  that  the  quantity  of  blood  in 
various  animals  averages  -^.t  to  -^^  of  the  total  bod3'-weight. 

An  estimate  of  the  quantity  in  man  which  corresponded  nearly  Avith 
this  proportion,  has  been  more  than  once  made  from  the  following  data. 
A  criminal  was  weighed  before  and  after  decapitation;  the  difference  in 
the  weight  representing  the  quantity  of  blood  Avhich  escaped.  The 
blood-vessels  of  the  head  and  trunk  were  then  washed  out  by  the  injec- 
tion of  water,  until  the  fluid  which  escaped  had  only  a  pale  red  or  straw 
color.  This  fluid  was  then  also  weighed;  and  the  amount  of  blood 
which  it  represented  was  calculated  by  comparing  the  proportion  of 
solid  matter  contained  in  it  with  that  of  the  first  blood  which  escaped 
on  decapitation.  Two  experiments  of  this  kind  gave  precisely  similar 
results.     (Weber  and  Lehmann.) 

It  should  be  remembered,  in  connection  with  these  estimations,  that 
the  quantity  of  the  blood  must  vary  very  considerably,  even  in  the  same 
animal,  with  the  amount  of  both  the  ingesta  and  egesta  of  the  period 
immediately  preceding  the  experiment;  it  has  been  found,  for  example, 
that  the  quantity  of  blood  obtainable  from  the  body  of  a  fasting  animal 
rarely  exceeds  a  half  of  that  which  is  present  soon  after  a  full  meal. 

Coagulation  of  the  Blood. 

One  of  the  most  characteristic  properties  which  the  blood  possesses 
is  that  of  clotting  or  coagidating.  This  phenomenon  may  be  observed 
under  the  most  favorable  conditions  in  blood  which  has  been  drawn 
into  an  open  vessel.  In  about  two  or  three  minutes,  at  the  ordinary 
temperature  of  the  air,  the  surface  of  the  fluid  is  seen  to  become  semi- 
solid or  jelly-like,  and  this  change  takes  place,  in  a  minute  or  two  after- 
ward at  the  sides  of  the  vessel  in  which  it  is  contained,  and  then  extends 
throughout  the  entire  mass.  The  time  which  is  occupied  in  these 
changes  is  about  eight  or  nine  minutes.     The  solid  mass  is  of  exactly 


132  HANDBOOK    OF    PHYSIOLOGY. 

the  same  volume  as  the  previously  liquid  blood,  and  adheres  so  closely 
to  the  sides  of  the  contaiuing  vessel  that  if  the  latter  be  inverted  none 
of  its  contents  escape.  The  solid  mass  is  the  crassamentum  or  clot.  If 
the  clot  be  watched  for  a  few  minutes,  drops  of  a  light,  straw-colored 
fluid,  the  serum,  may  be  seen  to  make  their  appearance  on  the  surface, 
and,  as  they  become  more  and  more  numerous,  to  run  together,  form- 
ing a  complete  superficial  stratum  above  the  solid  clot.  At  the  same 
time  the  fluid  begins  to  transude  at  the  sides  and  at  the  under-surface 
of  the  clot,  which  in  the  course  of  an  hour  or  two  floats  in  the  liquid. 
The  first  drops  of  serum  appear  on  the  surface  about  eleven  or  twelve 
minutes  after  the  blood  has  been  drawn;  and  the  fluid  continues  to 
transude  for  from  thirty-six  to  forty-eight  hours. 

The  clotting  of  blood  is  due  to  the  development  in  it  of  a  substance 
called /5n'«,  which  appears  as  a  meshwork  (fig.  117)  of  fine  fibrils.  This 
meshwork  entangles  and  incloses  within  itself  the  blood  corpuscles. 
The  first  clot  formed,  therefore,  includes  the  whole  of  the  constituents 
of  the  blood  in  an  apparently  solid  mass,  but  soon  the  fibrinous  mesh- 
work begins  to  contract  and  the  serum  which  does  not  belong  to  the 
clot  is  squeezed  out.  When  the  whole  of  the  serum  has  transuded  the 
clot  is  found  to  be  smaller,  but  firmer  and  harder,  as  it  is  now  made  up 
of  fibrin  and  blood  corpuscles  only.  Thus  coagulation  rearranges  the 
constituents  of  the  blood;  liquid  blood  being  made  up  of  plasma  and 
blood  corpuscles,  and  clotted  blood  of  serum  and  clot. 

Liquid  Blood. 


Plasma.  Corpuscles. 


Serum. 


Clot. 


Clotted  Blood. 

Under  ordinary  circumstances  coagulation  occurs  before  the  red  cor- 
puscles have  had  time  to  subside;  and  thus  from  their  being  entangled 
in  the  meshes  of  the  fibrin,  the  clot  is  of  a  deep  red  color  throughout, 
probably  slightly  darker  at  the  most  dependent  part,  from  greater  accu- 
mulation of  red  corpuscles  there  than  elsewhere.  When,  however,  coag- 
ulation is  from  any  cause  delayed,  as  when  blood  is  kept  at  a  tempera- 
ture slightly  above  0°  C.  (32°  F.),  or  when  clotting  is  naturally  slow,  as 
is  the  case  with  horse's  blood,  or,  lastly,  in  certain  diseased  conditions, 
particularly  in  inflammatory  states,  time  is  allowed  for  the  colored  cor- 
puscles to  sink  to  the  bottom  of  the  fluid.  When  clotting  after  a  time 
occurs,  the  upper  layers  of  the  blood  are  free  of  colored  corpuscles  and 


THE    BLOOD. 


133 


consist  chiefly  of  fibrin.  This  forms  a  superficial  stratum  differing  in 
appearance  from  the  rest  of  the  clot,  and  is  of  a  grayish  yellow  color. 
This  is  known  as  the  huffy  coat  or  cmsta  phlogititica.  The  bulfy  coat 
produced  in  the  manner  just  described,  commonly  contracts  more  than 
the  rest  of   the   clot,  on  account  of  the  absence  of  colored  corpuscles 


Fig.  117.— Reticulum  of  fibrin,  from  a  drop  of  Imman  blood,  after  treatment  with  rosanilin. 

CRanvier.) 

from  its  meshes,  and  because  contraction  is  less  interfered  with  by  ad- 
hesion to  the  interior  of  the  containing  vessel  in  the  vertical  than  the 
horizontal  direction.  A  cup-like  appearance  of  the  buffy  coat  results, 
and  the  clot  is  not  only  bulfed  but  cupped  on  the  surface. 

Formation  of  Fibrin. — That  the  clotting  of  blood  is  due  to  the  grad- 
ual appearance  in  it  of  fibrin  may  be  easily  demonstrated.  For  example, 
if  recently  drawn  blood  be  whipped  with  a  bundle  of  twigs,  the  fibrin 
may  be  withdrawn  from  the  blood  before  it  can  entangle  the  blood  cor- 
puscles within  its  meshes,  as  it  adheres  to  the  twigs  in  stringy  threads 
almost  free  from  corpuscles;  the  blood  from  which  the  fibrin  has  been 
withdrawn  no  longer  exhibits  the  power  of  spontaneous  coagulability. 
Although  these  facts  have  long  been  known,  the  closely  associated 
problem  as  to  the  exact  manner  in  which  fibrin  is  formed  is  by  no  means 
so  simple.  It  will  be  most  convenient  to  treat  of  the  question  step  by 
step. 

Fibrin  is  derived  from  the  plasma. 

Pure  plasma  may  be  procured  by  delaying  coagulation  in  blood  by 
keeping  it  at  a  temperature  slightly  above  freezing  point,  until  the 
colored  corpuscles  have  subsided  to  the  bottom  of  the  containing  vessel; 
the  blood  of  the  horse  being  specially  suited  for  the  purposes  of  this 
experiment.  A  portion  of  the  colorless  supernatant  plasma,  if  decanted 
into  another  vessel  and  exposed  to  the  ordinary  temperature  of  the  air, 
will  coagulate  just  as  though  it  were  the  entire  blood,  producing  a  clot 
similar  in  all  res]iects  to  blood  clot,  except  that  it  is  almost  colorless 


134  HANDBOOK    OF    PHYSIOLOGY. 

from  the  absence  of  red  corpuscles.  If  some  of  the  plasma  be  diluted 
with  twice  or  three  times  its  bulk  of  normal  saline  solution,*  coagula- 
tion is  delayed,  and  the  stages  of  the  gradual  formation  of  fibrin  in  it 
may  be  conveniently  watched.  The  viscidity  which  precedes  the  com- 
plete coagulation  may  be  actually  seen  to  be  due  to  the  formation  of 
fibrin  fibrils— first  of  all  at  the  edge  of  the  fluid  containing  vessel,  and 
then  gradually  extending  throughout  the  mass. 

If  a  further  portion  of  plasma,  diluted  or  not,  be  whipped  with  a 
bundle  of  twigs,  the  fibrin  may  be  obtained  as  a  solid,  stringy  mass,  just 
in  the  same  ^vay  as  from  the  entire  blood,  and  the  resulting  fluid  no 
longer  retains  its  power  of  spontaneous  coagulability. 

It  is  not  indeed  necessary  that  the  plasma  shall  have  been  obtained 
by  the  process  of  cooling  above  described,  as  if  it  had  been  separated 
from  the  corpuscles  in  any  other  way,  e.g.,  by  allowing  blood  to  flow 
direct  from  the  vessels  of  an  animal  into  a  vessel  containing  a  third  or 
a  fourth  of  its  bulk  of  a  saturated  solution  of  a  neutral  salt  (preferably 
of  magnesium  or  sodium  sulphate)  and  mixing  carefully,  will  answer 
the  purpose  and,  just  as  in  the  other  case  the  colored  corpuscles  will 
subside  leaving  the  clear  superstratum  of  (salted)  plasma.  In  order 
that  salted  plasma  may  coagulate,  however,  it  is  necessary  to  get  rid  of 
the  salts  by  dialysis,  or  to  dilute  it  with  several  times  its  bulk  of  water. 
The  second  question  which  must  be  considered  is,  from  what  mate- 
rials of  the  plasma  is  fibrin  formed?  If  plasma  be  saturated  with  solid 
magnesium  sulphate  or  sodium  chloride,  a  white,  sticky  precipitate  called 
by  Denis,  by  whom  it  was  first  obtained,  plasmine,  is  thrown  down, 
after  the  removal  of  which,  by  filtration,  the  plasma  will  not  spontane- 
ously coagulate.  Plasraine  is  soluble  in  dilute  neutral  saline  solutions, 
and  the  solution  of  it  speedily  coagulates,  producing  a  clot  composed  of 
fibrin.  Blood  plasma  therefore  contains  a  substance  without  which  it 
cannot  coagulate,  and  a  solution  of  which  is  spontaneously  coagulable. 
This  substance  is  very  soluble  in  dilute  saline  solutions,  and  is  not, 
therefore,  fibrin,  which  is  insoluble  in  these  fluids. 

But  there  is  distinct  evidence  that  plasmine  is  a  compound  body 
made  up  of  two  or  more  substances,  not  all  of  which  are  requisite  to 
form  a  clot,  and  that  it  is  not  mere  soluble  fibrin.  There  exists  in  all 
the  serous  cavities  of  the  body  in  health,  e.g.,  the  pericardium,  the  peri- 
toneum, and  the  pleura,  a  certain  small  amount  of  transparent  fluid, 
generally  of  a  pale  straw  color,  which  in  diseased  conditions  may  be 
greatly  increased.  It  somewhat  resembles  serum  in  appearance,  but  in 
reality  differs  from  it,  being  in  a  measure  allied  to  plasma.  This  se- 
rous fluid  is  not,  as  a  rule,  spontaneously  coagulable,  but  may  be  made 
to  clot  on  the  addition  of  serum,  which  is  also  a  fluid  which  has  no 

*  Normal  saline  solution  commonly  consists  of  a  .6  per  cent  solution  of  com- 
mon salt  (sodium  chloi'ide)  in  water. 


THE    BLOOD.  135 

tendency  of  itself  to  coagulate.  The  clot  produced  consists  of  fibrin, 
and  the  clotting  is  identical  with  the  clotting  of  plasma.  From  the 
serous  fluid  (that  from  the  inflamed  tunica  vaginalis  testis  or  hydrocele 
fluid  is  mostly  used)  we  may  obtain,  by  half-saturating  it  with  solid 
sodium  chloride,  a  white  viscid  substance  as  a  precipitate  which  is 
caMed  fibrinogen.  If  fibrinogen  be  separated  by  filtration,  it  can  be  dis- 
solved in  water,  as  a  certain  amount  of  the  neutral  salt  used  in  precipi- 
tating it  is  entangled  Avith  the  precipitate,  and  is  sufficient  to  produce  a 
dilute  (6  to  8  per  cent)  saline  solution  in  which  fibrinogen,  being  a  body 
of  the  globulin  class,  is  soluble.  The  solution  of  fibrinogen  has  no 
tendency  to  clot  of  itself,  but  if  blood-serum  be  added  to  a  solution  of 
fibrinogen,  the  mixture  clots. 

On  the  other  hand  from  blood-serum  may  be  obtained,  by  saturation 
with  one  of  the  neutral  salts  above-mentioned,  a  globulin  very  similar 
in  properties  to  fibrinogen,  which  is  called  serumglobidin  or  paraglubu- 
lin,  and  it  may  be  separated  by  filtration  and  dissolved  in  a  dilute  saline 
solution  in  a  manner  similar  to  fibrinogen. 

If  the  solutions  of  fibrinogen  and  paraglobulin  be  mixed,  the  mix- 
ture cannot  be  distinguished  from  a  solution  of  plasmiue,  and  in  a  great 
majority  of  cases  firmly  clots  like  that  solution,  whereas  a  mixture  of 
the  hydrocele  fluid  and  serum,  from  winch  these  bodies  have  been  re- 
spectively taken,  no  longer  manifests  the  like  property. 

In  addition  to  this  evidence  of  the  compound  nature  of  plasmine,  it 
may  be  further  shown  that,  if  sufficient  care  be  taken,  both  fibrinogen 
and  paraglobulin  may  be  separately  obtained  from  plasma:  the  one, 
fibrinogen,  as  a  flaky  precipitate  by  adding  carefully  13  per  cent  of 
crystalline  sodium  chloride  to  it;  and  the  other,  paraglobulin,  may  be 
precipitated,  after  the  removal  of  fibrinogen  by  filtration,  on  the  further 
addition  (above  20  per  cent  and  to  saturation)  of  the  same  salt  or  of 
magnesium  sulphate  to  the  filtrate.  It  is  evident,  therefore,  that  both 
these  substances  must  be  thrown  down  together  when  plasma  is  at  once 
saturated  with  sodium  chloride  or  magnesium  sulphate,  and  that  the 
mixture  of  the  two  corresponds  with  plasmine. 

So  far  it  has  been  shown  that  plasmine,  the  antecedent  of  fibrin,  to 
the  possession  of  which  blood  owes  its  power  of  coagulating,  is  not  a 
simple  body,  but  is  composed  of  at  least  two  factors — viz.,  fibrinogeii 
and  paraglobulin;  there  is  reason  for  believing  that  yet  another  body 
is  precipitated  with  them  in  plasmine. 

It  was  at  one  time  thought  that  the  reason  why  hydrocele  fluid 
coagulated,  when  serum  was  added  to  it,  was  that  the  latter  fluid  sup- 
plied the  paraglobulin  which  the  former  lacked;  this,  however,  is  not 
the  case,  as  hydrocele  fluid  does  not  lack  this  body,  and  moreover,  if 
paraglobulin,  obtained  from  diluted  serum  by  passing  a  stream  of  car- 
bonic acid  gas  through  it,  be  added,  no  clotting  will  take  place.     But  if 


136  HANDBOOK    OF    PHYSIOLOGY. 

paraglobulin,  obtained  by  the  saturation  method,  be  added  to  hydrocele 
fluid,  clotting  soon  follows,  as  it  will  also  in  a  mixed  solution  of  fibrin- 
ogen and  paraglobulin,  both  obtained  by  the  saturation  method.  From 
this  it  is  evident  that  in  plasmiue  there  is  something  more  than  the  two 
bodies  above  mentioned,  and  that  this  something  is  precipitated  with 
the  paraglobulin  by  the  saturation  method,  and  is  not  precipitated  by 
the  carbonic  acid  method. 

The  following  experiments  show  that  this  substance  is  of  the  nature 
of  a  ferment.  If  defibrinated  blood  or  serum  be  kept  in  a  stoppered 
bottle  with  its  own  bulk  of  alcohol  for  some  weeks,  all  the  proteids  are 
precipitated  in  a  coagulated  form ;  if  the  precipitate  be  then  removed 
by  filtration,  dried  over  sulphuric  acid,  finely  powdered,  and  then  sus- 
pended in  water,  a  watery  extract  may  be  obtained  by  further  filtration, 
containing  but  little  proteid.  Yet  a  little  of  this  watery  extract  will 
produce  coagulation  in  fluids,  e.g.,  hydrocele  fluid  or  diluted  plasma, 
which  are  not  spontaneously  coagulable,  or  which  coagulate  slowly  and 
with  difficulty.  It  will  also  cause  a  mixture  of  fibrinogen  and  paraglob- 
ulin both  obtained  by  the  carbonic  acid  method  to  clot.  The  watery 
extract  appears  to  contain  the  body  which  is  precipitated  with  the 
paraglobulin  by  the  saturation  method.  Its  active  properties  are  en- 
tirely destroyed  by  boiling.  The  amount  of  the  extract  added  does  not 
influence  the  amount  of  the  clot  formed,  but  only  the  rapidity  of  clot- 
ting, and  moreover  the  active  substance  contained  in  the  extract  evi- 
dently does  not  form  part  of  the  clot,  as  it  may  be  obtained  from  the 
serum  after  blood  has  clotted.  So  that  the  substance  contained  in  the 
aqueous  extract  of  blood  appears  to  belong  to  that  class  of  bodies  which 
promote  the  union  of,  or  cause  changes  in,  other  bodies,  without  them- 
selves entering  into  union  or  undergoing  change;  these  are  known  as 
ferments.  It  has,  therefore,  received  the  Vi?i.mQ  jihrin  ferment  or  throm- 
bin. This  ferment  is  developed  in  the  blood  soon  after  it  has  been 
shed,  and  its  amount  continues  to  increase  for  some  little  time  (p. 
133). 

So  far  we  have  seen  that  plasmine  is  a  body  composed  of  three  sub- 
stances, viz.,  fibrinogen,  paraglobulin,  and  fibrin  ferment.  But  we  shall 
see  that  only  two  of  them  are  necessary  to  coagulation. 

Relation  of  Calcium  Salts  to  Coagulation.— Blood  will  not 
clot  except  in  the  presence  of  soluble  calcium  salts.  If  potassium  or 
sodium  oxalate  be  added  to  blood  as  it  is  drawn  from  the  vessels  in  quan- 
tities sufficient  to  precipitate  the  calcium  salts,  coagulation  will  no 
longer  occur.  But  blood  which  has  thus  lost  its  coagulability  may  be 
made  to  clot  upon  the  addition  of  soluble  calcium  salts  in  proper  propor- 
tion. This  fact  has  been  demonstrated  not  only  for  blood,  but  for  solu- 
tions of  pure  fibrinogen. 

Tlieories  of  Coagulation.— A]\  present  theories  of  coagulation  agree 


THE    liLOOD. 


137 


in  that  fibrin  is  formed  by  a  reaction  between  fibrinogen  and  tbronibin. 
Beyond  this,  however,  tliere  is  some  difference  of  opinion.  The  chief 
2ioints  at  issue  arc:  (1)  the  origin  of  fibrinogen;  (2)  the  nature  of 
tlirombin;  (3)  tlie  nature  of  t!ie  reaction  between  fibrinogen  and 
thrombin. 

1.  Hammarsteu  has  shown  tliat  the  presence  of  paraglobuliu  is  not 
necessary  for  coagulation.  Schmidt  believes,  however,  that  fibrinogen 
is  derived  from  paraglobulin  after  the  blood  is  shed  from  the  body. 

2.  The  nature  of  thi'ombin  is  not  as  yet  satisfactorily  determined. 
Pekelhariug  has  concluded  from  experiment  that  thrombin  is  a  com- 
pound of  a  nucleo-albumin  with  the  calcium  salts  of  the  blood.  He  has 
succeeded  in  separating  from  blocd-plasma  a  nncleo-albuniin,  which 
when  brought  into  solution  with  fibrinogen  and  calcium  salts  will  form 
fibrin.  If,  however,  this  nucleo-albumin  be  brought  into  contact  with 
either  fibrinogen  alone  or  calcium  salts  alone,  no  clotting  will  occur. 

Pekelharing  further  supposes  that  thrombin  is  not  present  in  blood 
circulating  in  the  body — at  any  rate  in  greater  than  minimal  quantities; 
but  that  when  blood  is  drawn  or  for  other  reasons  coagulates  in  the 
body,  the  white  blood-cells  break  down,  nucleo-albumin  is  liberated,  and 
then  unites  with  the  calcium  salts  to  form  thrombin. 

3.  The  nature  of  the  reaction  between  fibrinogen  and  thrombin  has 
not  been  definitely  determined.  Hammarsten  has  proved,  however,  that 
the  entire  fibrinogen  molecule  does  not  enter  into  the  reaction  to  become 
fibrin.     A  part  of  it  splits  ofl:  and  passes  into  solution  as  fibrin-globulin. 


Schema  of  Coagulation. 
Blood 


Plasma 


Neutral  Salts        Fibrinogen         Calcium  Salts 


(for  ,liss.i King 
tibriuogen) 


Fibriu-globullu 


Corpuscles 


White 


Nucleo-albumin 


Fibrin 


There  is  strong  evidence  that  fibrin  is  a  compound  of  calcium  with  a 
portion  of  the  fibrinogen  molecule.  There  are  three  factors,  then,  in 
the  reaction — fibrinogen,  nucleo-albumin,  calcium  salts.  According  to 
Pekelharing,  the  nueleo-albuuiin   first  combines  with  the  calcium  salts, 


138  HANDBOOK    OF    PHYSIOLOGY, 

forming  thrombin,  which  in  turn  causes  a  splitting  of  the  fibrinogeu 
molecule — the  calcium  remaining  with  one  portion  of  the  molecule  to 
form  insoluble  fibrin,  the  other  portion  passing  into  solution  as  fibrin- 
globulin.  According  to  Lilienfeld,  the  reaction  first  occurs  between  the 
fibrinogen  molecule  and  the  nucleo-albumin,  resulting  in  a  splitting  of 
the  former.  A  portion  of  the  fibrinogen  molecule  then  unites  with  the 
calcium  salts  to  form  fibrin. 

Sources  of  the  Fibrin  f^erment. — Fibrin  ferment  cannot  be  obtained 
in  any  appreciable  amount  from  blood  which  is  allowed  to  flow  direct 
from  the  living  vessel  into  absolute  alcohol.  It  is  almost  certainly  a. 
result  of  the  more  or  less  complete  disintegration  of  the  colorless  cor- 
puscles after  blood  is  shed,  or  of  the  third  corpuscles  which  will  be  de- 
scribed later  on.  under  the  name  of  Hood  platelets.  The  proofs  of  this 
may  be  briefly  summarized  as  follows: — (1)  That  ail  strongly  coagulable 
fluids  contain  these  corpuscles  almost  in  direct  proportion  to  their  coag- 
ulability; (2)  That  clots  formed  on  foreign  bodies,  such  as  needles  pro- 
jecting into  the  interior  or  lumen  of  living  blood-vessels,  are  preceded 
by  an  aggregation  of  colorless  corpuscles;  (3)  That  plasma  in  which 
these  corpuscles  happen  to  be  scanty  clots  feebly ;  (4)  That  if  horse's 
blood  be  kept  in  the  cold,  so  that  the  corpuscles  subside,  it  will  be 
found  that  the  lowest  stratum,  containing  chiefly  colored  corpuscles, 
will,  if  removed,  clot  feebly,  as  it  contains  little  of  the  fibrin  factors; 
whereas  the  colorless  plasma,  especially  the  lower  layers  of  it  in  which 
the  colorless  corpus  les  are  most  numerous,  will  clot  well,  but  if  filtered 
in  the  cold  will  not  clot  so  well,  indicating  that  when  filtered  nearly 
free  from  colorless  corpuscles  even  the  plasma  does  not  contain  sufficient 
of  all  the  fibrin  factors  to  produce  thorough  coagulation;  (o)  In  a  drop 
of  coagulating  blood  observed  under  the  microscope  the  fibrin  fibrils  are 
seen  to  start  from  the  colorless  corpuscles. 

Conditions  affecting  Coagulation.— The  coagulation  of  the  blood 
is  hastened  by  the  following  means: — 

1.  Moderate  warmtJi,— from  about  37.8-49°  C.  (100°  to  130°  F.). 

2.  Rest  is  favorable  to  the  coagulation  of  blood.  Blood,  of  which 
the  whole  mass  is  kept  in  uniform  motion,  as  when  a  closed  vessel  com- 
pletely filled  with  it  is  constantly  moved,  coagulates  very  slowly  and 
imperfectly. 

3.  Contact  with  foreign  matter,  Q.x\(\.  especially  multiplication  of  the 
points  of  contact.  Thus,  as  before  mentioned,  fibrin  may  be  quickly 
obtained  from  liquid  blood  by  stirring  it  with  a  bundle  of  small  twigs; 
and  even  in  the  living  body  the  blood  will  coagulate  upon  rough  bodies 
projecting  into  the  vessels. 

4.  Injury  to  the  walls  of  the  Hood-vessels. 

5.  The  addition  of  less  than  twice  the  hulk  of  water. 


THE    BLOOD.  ]'.]'.) 

The  blood  last  drawn  is  said,  from  being  more  watery,  to  coagulate 
more  quickly  than  the  first. 

The  coagulation  of  tlie  blood  is  retarded,  suspended,  or  pre- 
vented by  the  following  means: — 

1.  Cold  retiirds  coagulation;  and  so  long  as  blood  is  kept  at  a  tem- 
perature 0°  C.  (33°  F.),  it  will  not  coagulate  at  all.  Freezing  the  blood, 
of  course,  prevents  its  coagulation;  yet  it  will  coagulate,  though  not 
firmly,  if  thawed  after  being  frozen;  and  it  will  do  so  even  after  it  has 
been  frozen  for  several  months.  A  higher  temperature  than  49°  C.  (120° 
F.)  retards  coagulation  bji  coagulating  the  albumen  of  the  serum,  and 
a  still  higher  one  above  56°  0.  (133°  F.)  prevents  it  altogether. 

2.  The  addition  of  ivater  in  greater  proportions  than  twice  the  hnlJc 
of  the  blood,  also  the  addition  of  syriip,  glycerine,  and  other  viscid  sub- 
stances. 

3.  Contact  with  living  tissuch,  and  especially  with  the  interior  of  a 
living  blood-vessel.  Blood  may  be  kept  fluid  in  a  tortoise's  heart  after 
removal  from  the  body  for  several  days,  and  if  the  jugular  vein  of  a 
horse  be  ligatured  in  two  places  so  as  to  include  within  it  blood,  and 
then  be  removed  from  the  body  and  placed  in  a  cool  place,  the  contained 
blood  will  remain  unclotted  for  hours  or  even  days. 

4.  Tlie  addition  of  neutral  salts  in  the  proportion  of  2  or  3  per  cent 
and  upward.  When  added  in  large  proportion  most  of  these  saline  sub- 
stances prevent  coagulation  altogether.  Coagulation,  however,  ensues 
on  dilution  with  water.  The  time  during  which  blood  can  be  thus  pre- 
served in  a  liquid  state  and  coagulated  by  the  addition  of  water,  is  quite 
indefinite. 

5.  In  injlamrnatory  states  of  the  system  the  blood  coagulates  more 
slowly  although  more  firmly. 

6.  The  coagulation  of  the  blood  is  prevented  altogether  hy  tlie  addi- 
tion of  strong  acids  and  caustic  alkalies,  and  also  by  the  addition  of  a  0.1 
per  cent  solution  of  potassium  oxalate,  which  precipitates  the  soluble  cal- 
cium salt  present  in  the  blood,  in  the  form  of  insoluble  calcium  oxalate. 
Without  the  presence  of  soluble  calcium  salt,  blood  does  not  coagulate. 

7.  The  injection  of  commercial  peptone  containing  album oses,  or  of 
various  digestive  ferments,  e.g.,  trypsin  or  pepsin,  into  the  vessels  of 
an  animal  appears  to  prevent  or  stay  coagulation  of  its  blood  if  it  be 
killed  soon  after.  The  secretion  of  the  mouth  of  the  leech,  and  possibly 
the  blood  squeezed  out  of  its  body  when  full,  also  prevents  the  clotting 
if  added  to  blood. 

It  is  stated  that  the  reason  why  blood  does  not  coagulate  in  the  living 
vessels  is,  that  the  factors  which  arc  necessary  for  the  formation  of  fibrin 
are  not  in  the  exact  state  required  for  its  production,  and  that  at  any 
rate  the  fibrin  ferment  is  not  formed  or  is  not  free  in  the  living  blood, 
but  that  it  is  produced  (or  set  free)  at  the  moment  of  coagulation  by  the 


140  HANDBOOK    OF    PHYSIOLOGY. 

disintegration  of  the  colorless  corpuscles.  This  supposition  is  certainly 
plausible,  and,  if  _it  be  a  true  one,  it  must  be  assumed  either  that  the 
living  blood-vessels  exert  a  restraining  influence  upon  the  disintegration 
of  the  corpuscles  in  sufficient  numbers  to  form  a  clot,  or  that  they  ren- 
der inert  any  small  amount  of  fibrin  ferment,  which  may  have  been  set 
free  by  the  disintegration  of  a  few  corpuscles;  as  it  is  certain,  firstly, 
that  white  corpuscles  must  from  time  to  time  disintegrate  in  the  blood 
without  causing  it  to  clot;  and,  secondly,  that  shed  and  defibrinated 
blood  which  contains  blood  corpuscles,  broken  down  and  disintegrated, 
will  not,  when  injected  into  the  vessels  of  fn  animal,  under  ordinary 
conditions,  produce  clotting.  There  must  be  a  distinct  difference, 
therefore,  if  only  in  amount,  between  the  normal  disintegration  of  a  few 
colorless  corpuscles  in  the  living  uninjured  blood-vessels  and  the  abnor- 
mal disintegration  of  a  large  number  which  occurs  whenever  the  blood 
is  shed  without  suitable  precaution,  or  when  coagulation  is  unrestrained 
by  the  neighborhood  of  the  living  uninjured  blood-vessels. 


The  Blood  Corpuscles. 

There  are  two  principal  forms  of  corpuscles,  the  red  and  the  toliite,  or, 
as  they  are  now  frequently  named,  the  colored  and  the  colorless.  In  the 
moist  state,  the  red  corpuscles  form  about  45  per  cent  by  weight,  of  the 
whole  mass  of  the  blood.  The  proportion  of  colorless  corpuscles  is  only 
as  1  to  500  or  600  of  the  colored. 

Red  or  Colored  Corpuscles. — Human  red  blood-corpuscles  hi'*^ 
circular,  biconcave  discs  with  rounded  edges,  from  3-0V0"  ^o  xoVo  inch  in 
diameter  7/./.  to  8/^,  and  yg^-oo-  inch  or  about  2/./.  in  thickness,  becoming 
flat  or  convex  on  addition  of  water.  When  viewed  singly  they  appear 
of  a  pale  yellowish  tinge;  the  deep  red  color  which  they  give  to  the 
blood  being  observable  in  them  only  when  they  are  seen  en  masse. 
They  are  composed  of  a  colorless,  structureless,  and  transparent  filmy 
framework  or  stroma,  infiltrated  in  all  parts  by  a  red  coloring  matter 
termed  limmogloMn.  The  stroma  is  tough  and  elastic,  so  that,  as  the 
corpuscles  circulate,  they  admit  of  elongation  and  other  changes  of  form, 
in  adaptation  to  the  vessels,  yet  recover  their  natural  shape  as  soon  as 
they  escape  from  compression.  The  term  cell,  in  the  sense  of  a  bag  or 
sac,  although  sometimes  apjalied,  is  scarcely  applicable  to  the  red  blood 
corpuscle;  it  must  be  considered,  if  not  solid  throughout,  yet  as  having 
no  such  marked  difl:erence  of  consistence  in  different  parts  as  to  justify 
the  notion  of  its  being  a  membranous  sac  with  fluid  contents.  The 
stroma  exists  in  all  parts  of  its  substance,  and  the  coloring-matter  uni- 
formly pervades  this;  but  at  the  same  time  it  is  probable  that  the  con- 
sistence of  the  peripheral  part  of  the  protoplasm  is  more  solid  than  that 
of  the  more  central  mass. 


THE    BLOOD.  141 

The  red  corpuscles  have  no  nuclei,  althougli,  in  their  usual  state,  the 
unequal  refraction  of  transmitted  light  gives  the  appearance  of  a  cen- 
tral spot,  brighter  or  darker  than  the  border,  according  as  ic  is  viewed 
in  or  out  of  focus.      Their  specilic  gravitv  is  about  1088. 

The  corpuscles  of  all  mammals  with  the  exception  of  the  camelidfe 
are  circular  and  biconcave.  In  the  camelida^  they  are  oval  and  bicon- 
vex. In  all  mammals  the  corpuscles  are  non-nucleated,  and  in  all  other 
vertebrates  (birds,  reptiles,  amphibia,  and  fish),  the  corpuscles  are  oval 
biconvex  and  nucleated  (tig.  121). 

N^imbers. — The  normal  number  of  red  blood  cells  in  a  cubic  milli- 
metre of  human  blood  was  estimated  by  Welcker,  in  1854,  to  be  5,000,000 
in  men  and  4,500,000  in  women.  Recent  observations,  however,  have 
shown  that  these  estimates  are  a  little  low,  especially  in  men,  and  the 
average  number  has  been  placed  by  different  authorities  at  various  points 
between  5,000,000  and  5,500,000,  or  even  6,000,000.  Still  the  original 
numbers  as  given  by  Welcker  are  accepted  at  the  present  day  as  being 
sufficiently  accurate  for  ordinary  purposes.  It  has  also  been  shown  that 
there  are  many  distinct  physiological  variations  in  the  number,  depend- 
ing on  the  time  of  day,  digestion,  sex,  and  pregnancy.  The  number 
of  red  cells  usually  diminishes  in  the  course  of  each  day,  w^hile  the 
leucocytes  increase  in  number.  It  has  been  suggested  that  this  is  due  to 
the  influence  of  digestion  and  exercise. 

It  lias  generally  been  found  that  within  half  an  hour  or  an  hour 
after  a  full  meal  the  number  of  red  cells  begins  to  diminish,  and  that 
this  keeps  up  for  from  two  to  four  hours,  when  it  is  followed  by  a 
gradual  rise  to  the  normal.  The  usual  fall  is  250,000  to  750,000  per 
cubic  millimetre.  These  results  are  most  marked  after  a  largely  fluid 
meal,  and  are  probably  due  to  dilution  of  the  blood  as  a  result  of  the  ab- 
sorption of  fluids.  In  animals  the  number  of  red  cells  is  increased  by 
fasting,  but  in  man  the  results  are  variable,  some  authorities  claiming 
an  increase  and  others  a  decrease.  In  childhood  there  is  no  difference 
between  the  sexes  in  the  number  of  red  cells  per  cubic  millimetre,  but 
after  menstruation  is  established,  a  relative  anaemia  develops  in  women. 
'W'elcker's  original  estimate  placed  the  diff'erence  at  500,000  per  cubic 
millimetre,  and  these  figures  have  been  generally  accepted,  though  one 
observer  (Leichtenstein)  asserted  that  the  difference  was  1,000,000. 
Recent  investigations,  however,  seem  to  show  that  Welcker's  estimate  is 
a  little  too  great. 

Menstruation  in  healthy  subjects  has  practically  no  effect,  as  not  more 
than  100-200  cubic  centimetres  are  lost  normally  in  the  course  of  several 
days.  Under  such  circumstances  the  normal  diminution  of  red  cells  per 
cubic  millimetre  is  probably  less  than  150,000,  though  one  observer 
(Sfameni)  has  placed  the  loss  at  about  225,000.     Some  observers,  on  the 


142  HANDBOOK    OF    PHYSIOLOGY. 

other  hand,  claim  an  increase.  The  leucocytes  are  slightly  increased 
during  menstruation.  It  is  now  the  general  opinion  that  pregnancy  has 
little  or  no  effect  on  the  number  of  red  cells,  and  that  any  anaemia 
must  be  due  to  abnormal  conditions.  Post-partum  ansemia  should  not 
last  longer  than  two  weeks. 

Varieties. — The  red  corpuscles  are  not  all  alike.  In  almost  every 
specimen  of  blood  a  certain  number  of  corpuscles  smaller  than  the  rest 
may  be  observed.  They  are  termed  microcytes,  or  hmnatohlasts^  and  are 
probably  immature  corpuscles. 

A  peculiar  property  of  the  red  corpuscles,  which  is  exaggerated  in 
inflammatory  blood,  may  be  here  again  noticed,  i.e.,  their  great  tendency 
to  adhere  together  in  rolls  or  columns  (rouleaux),  like  piles  of  coins, 
These  rolls  quickly  fasten  together  by  their  ends,  and  cluster;  so  that, 
when  the  blood   is  spread  out  thinly  on  a  glass,  they  form  a  kind  of 


Fig.  118.-  Fig.  119. 

Fig.  118.— Red  corpuscles  in  rouleaux.    The  rounded  corpuscles  are  white  or  uncolored. 
Fig.  119. — Corpuscles  of  the  frog.    The  central  mass  consists  of  nucleated  colored  corpuscles. 
The  other  corpuscles  are  two  varieties  of  the  colorless  form. 

irregular  network,  with  crowds  of  corpuscles  at  the  several  points  cor- 
responding Avith  the  knots  of  the  net  (fig.  118).  Hence  the  clot  formed 
in  such  a  thin  layer  of  blood  looks  mottled  with  blotches  of  pink  upon 
a  white  ground,  and  in  a  larger  quantity  of  blood  such  masses  help,  by 
the  consequent  rapid  subsidence  of  the  corpuscles,  in  the  formation  of 
the  bufPy  coat  already  referred  to. 

Action  of  Re-agents. — Considerable  light  has  been  thrown  on  the  physical 
and  chemical  constitution  of  red  blood-cells  by  studying  the  effects  produced 
by  mechanical  means  and  by  various  reagents :  the  following  is  a  brief  sum- 
mary of  these  re-actions  : — 

Pressure. — If  the  red  blood-cells  of  a  frog  or  man  are  gently  squeezed,  they 
exhibit  a  wTinkling  of  the  surface,  which  clearly  indicates  that  there  is  a 
superficial  pellicle  partly  differentiated  from  the  softer  mass  within ;  again,  if 
a  needle  be  rapidly  drawn  across  a  drop  of  blood,  several  corpuscles  will  be 
found  cut  in  two,  but  this  is  not  accompanied  by  any  escape  of  cell  contents ; 
the  two  halves,  on  the  contrary,  assume  a  rounded  form,  proving  clearly  that 
the  corpuscles  are  not  mere  membranous  sacs  with  fluid  contents  like  fat-cells. 


THE    BLOOD. 


143 


Fluids,  i.  Wdtt'f. — When  watrr  is  aildcil  icradually  to  frog's  blood,  the  oval 
disc-shaped  corpuscles  become  spherical,  and  gradually  discharge  their  haemo- 
globin, a  pale,  transparent  stroma  being  left  behind  ;  human  red  blood-cells 
■change  from  a  discoidal  to  a  splieroidal  form,  and  discharge 
their  cell- contents,  becoming  quite  transparent  and  all  but  in- 
visible. 

ii.  Saline  solution  produces  no  appreciable  effect  on  the  red 
blood- cells  of  the  frog.     In  tlie  red  blood-cells  of  man   the  dis- 
coid shape  is  exchanged  for  a  spherical  one,  with  spinous  pro- 
jections, like  a  horse-chestnut  (fig.  120j.     Their  original  forms  can  be  at  once 
restored  by  the  use  of  carbonic  acid. 

iii.  Acetic  acid  (dilute)  causes  the  nucleus  of  the  red  blood-cells  in  the  frog 
to  become  more  clearly  defined  ;  if  the  action  is  prolonged,  the  nucleus  becomes 
strongly  granulated,  and  all  the  coloring  matter  seems  to  be  concentrated  in  it, 


1^ 

Fig.  120. 

Effect  cf  saline 

solution. 


MAMMALS. 


ELEPHANT  MOUSE  /     HORSE  MUSK   DEER  CAMEL 


Fig.  121. — The  above  illustration  is  isomewhat  altered  from  a  drawing  by  Gulliver,  in  the  Proceed. 
Zool.  Society,  and  exhibits  the  typical  characters  of  the  red  blood-cells  inthe  main  divisions  of  the 
Vertebrata.  The  fractions  are  those  of  an  incti.  and  represent  the  average  diameter.  In  the  case 
of  the  oval  cells,  only  the  l<ing  diameter  is  here  given.  It  is  remarkable,  that  although  the  size  of 
the  red  blood-cells  varies  so  much  in  the  different  classes  of  the  vertebrate  icingdom,  that  of  the 
white  corpuscles  remains  comparatively  uniform,  and  thus  they  are,  in  some  animals,  much  greater, 
in  others  much  less  than  the  red  corpuscle  existing  side  by  side  with  them. 


the   surrouiuliiii^   cell-substance    and    outline    of   the   cell   becoming  almost   invisi- 
ble;   after  a   tune  the  cells  lose  their  color  altogether.      The  cells  m  the  figure 


144  HANDBOOK    OF    PHYSIOLOGY. 

(fig.  122j  represent  the  successive  stages  of  the  change.  A  similar  loss  of  color 
occurs  in  the  red  cells  of  human  blood,  which,  however,  from  the  absence  of 
nuclei,  seem  to  disappear  entirely. 

iv.  Alkalies  cause  the  red  blood-cells  to  swell  and  linally  to  disappear. 

V.  Chlorofor'm  added  to  the  red  blood-cells  of  the  frog  causes  them  to  part 
with  their  haemoglobin ;  the  stroma  of  the  cells  becomes  gradually  broken  up. 
A  similar  effect  is  produced  on  the  human  red  blood-cell. 

vi.  Tannin.— When  a  2  per  cent  fresh  solution  of  tannic  acid  is  applied  to 
frog's  blood  it  causes  the  appearance  of  a  sharply-delined  little  knob,  project- 
ing from  the  free  surface  {Roberts'  macula)  :  the  coloring  matter  becomes  at 
the  same  time  concentrated  in  the  nucleus,  which  grows  more  distinct  (fig. 
123) .     A  somewhat  similar  effect  is  produced  on  the  human  red  blood  corpuscle. 

vfi.  Magenta,  when  applied  to  the  red  blood-cells  of  the  frog,  produces  a 
similar  little  knob  or  knobs,  at  the  same  time  staining  the  nncleus  and  causing 
the  discharge  of  the  haemoglobin.  The  first  effect  of  the  magenta  is  to  cause 
the  discharge  of  the  haemoglobin,  then  the  nucleus  becomes  suddenly  stained, 
and  lastly  a  finely  granular  matter  issues  through  the  wall  of  the  corpuscle, 
becoming  stained  by  the  magenta,  and  a  macula  is  formed  at  the  point  of  es- 
cape.    A  similar  macula  is  produced  in  the  human  red  blood-cells. 

viii.  Boric  acid. — A  2  per  cent  solution  applied  to  nucleated  red  blood-cells 
(frog)  will  cause  the  concentration  of  all  the  coloring  matter  in  the  nucleus ; 
the  colored  body  thus  formed  gradually  quits  its  central  position,  and  comes  to 
be  partly,  sometimes  entirely,  protruded  from  the  surface  of  the  now  colorless 
cell  (fig.  124).     The  result  of  this  experiment  led  Briicke  to  distinguish  the 


oo 


Fig.  122.  E'ig.  123.  Fig.  124.  Fig.  125. 

Efcect  of  acetic  acid.      Effect  of  tannin.     Effect  of  boric  acid.     Effect  of  gases. 

colored  contents  of  the  cell  (zooid)  from  its  colorless  stroma  (cecoid) .  When 
applied  to  the  non-nucleated  mammalian  corpuscle  its  effect  merely  resembles 
that  of  other  dilute  acids. 

ix.  Ammonia. — Its  effects  seem  to  vary  according  to  the  degree  of  concen- 
tration. Sometimes  the  outline  of  the  corpuscles  becomes  distinctly  crenated ; 
at  other  times  the  effect  resejnbles  that  of  boracic  acid,  while  in  other  cases 
the  edges  of  the  corpuscles  begin  to  break  up. 

Gases.  Carbonic  acid. — If  the  red  blood- cells  of  a  frog  be  first  exposed  to 
the  action  of  water- vapor  (which  renders  their  outer  pellicle  more  readily  per- 
meable to  gases),  and  then  acted  on  by  carbonic  acid,  the  nuclei  immediately 
become  clearly  defined  and  strongly  granulated  ;  when  air  or  oxygen  is  admitted 
the  original  appearance  is  at  once  restored.  The  upper  and  lower  cell  in  fig. 
125  show  the  effect  of  carbonic  acid  ;  the  middle  one  the  effect  of  the  re-admis- 
sion of  air.  These  effects  can  be  reproduced  five  or  six  times  in  succession. 
If,  however,  the  action  of  the  carbonic  acid  be  much  prolonged,  the  granula- 
tion of  the  nucleus  becomes  permanent ;  it  appears  to  depend  on  a  coagulation 
of  the  paraglobulin. 

Heat.— The  effect  of  heat  up  to  50^—60°  C.  (120—140°  F.)  is  to  cause  the 
formation  of  a  number  of  bud-like  processes  (fig.  126) . 


THE    BLOOD.  145 

Electricity  causes  the  red  blc)ocl-eor])useles  to  become  crenated,  and  at  length 
mvdbeiTV-likc.     Flmdly  they  i-eeover  their  round  t'oi'ni  and  In-come  quite  pale. 

The  Colorless  Corpuscles. — In  human  blood  the  white  or  color- 
less corjjiiscles  or  Icucoci/tcs  are  nearly  splierical  masses  of  granular  pro- 
toplasm without  cell  wall.  In  all  cases  one  or  more  nuclei  exist  in  each 
corpuscle.  The  corpuscles  vary  considerably  in  size,  but  average  j-^^fw  o^ 
an  inch  (IO/j.)  in  diameter. 

There  was  for  some  time  a  general  accejitance  of  the  original  estimate 
of  "Welcker  that  there  were  about  13,500  leucocytes  in  each  cubic  milli- 
metre of  normal  luiman  blood.  But  improved  methods  and  appliances, 
especially  the  introduction  of  the  Thoma  h;i:^matocytometer,  soon  proved 
that  these  figures  were  too  high,  and  that  the  number  was  about  '7,500. 
The  latter  estimate  is  upheld  by  the  results  of  the  most  recent  investiga- 
tions, Eieder  placing  the  number  in  adults  at  7,680,  Limbeck  at  8,000  to 
9,000,  and  Eeinert  at  5,125  at  6  a.m.  and  8,2G2  at  4  p.m.  Therefore  the 
proportion  of  white  to  red  cells  (counting  5,000,000  of  the  latter  to  each 
cubic  millimetre)  is  about  1  to  6GG.  This  jiroportion  is  in  noway  to  be 
regarded  as  a  constant  one  in  health,  as  considerable  variations  occur  fre- 
quently, even  in  the  course  of  the  same  day.  The  chief  physiological 
variations  are  those  due  to  the  influence  of  digestion,  of  pregnane}-,  and 
of  infancy. 

After  a  full  meal  the  white  cells  in  a  healthy  adult  are  increased  in 
number  about  one-third  (Eieder),  the  increase  beginning  within  an  hour, 
attaining  a  maximum  in  three  or  four  hours,  and  then  gradually  falling 
to  normal.  This  jDrocess  is  frequently  modified  by  the  character  of  the 
food,  the  greatest  increase  occurring  with  an  exclusively  meat  diet,  while 
a  purely  vegetarian  diet  has  usually  no  effect.  The  increase  is  also  more 
marked  in  children,  and  especially  in  infants.  The  essential  factor  is 
probably  the  absorption  of  albuminous  matter  in  considerable  quantities; 
this  causes  proliferation  of  leucocytes  in  the  adenoid  tissue  of  the 
gastro-intestinal  tract.  In  pregnancy  there  is  often  ti  moderate  increase 
in  the  number  of  white  cells  during  the  latter  months.  This  does  not 
begin  until  after  the  third  month,  and  is  most  marked  and  constant  in 
primipartB.  After  parturition  the  leucocytes  gradually  diminish  utider 
normal  conditipns,  and  usually  reach  the  normal  within  a  fortnight. 
The  essential  factor  is  probably  the  general  stimulation  in  the  maternal 
organism.  It  is  well  established  that  the  white  cells  are  very  numerous 
in  the  new-born,  though  diiferent  observers  have  made  very  conflicting 
estimates.  Still  all  agree  that  there  is  a  very  rapid  decrease  in  tlieir  num- 
bers during  the  first  few  days,  and  that  this  is  followed  by  a  less  marked 
increase,  Avhich  continues  for  many  months.  According  to  Eieder,  who 
is  perhaps   the  most   reliable,  there  are  at  birth   frdtn   14,200  to  27,400 

lO 


146  HANDBOOK    OF    PHYSIOLOGY. 

per  cubic  millimetre,  on  the  second  to  fourth  day  from  8,700  to  12,400, 
and  after  the  fourth  day  from  12,400  to  14,800. 

Varieties. — :The  colorless  corpuscles  present  greater  diversities  of 
form  than  the  red  ones.  They  are  usually  classified  according  to  their 
reaction  to  staining  agents,  or  to  the  presence  or  absence  of  granules  in 
their  cytoplasm,  Kanthack  and  Hardy  offer  the  following  classification 
based  upon  both  phenomena: 

A    Oxyphil  (staining  with  acid  dyes).  ]  I  ^Sf  l^^^. 
B,  Basophil  (staining  with  basic  dyes). — 1,  Finely  granular. 

r,    -n       y  \  l-     Small. 

^-  Hy^li°« i2„  Large. 

Thejinely  granular  oxyphil  constitutes  75  per  cent  of  all  leucocytes. 

It  has  an  average  diameter  of  10,'j.,  and  possesses  phagocytic  action  to  a 

marked  degree — that  is,  it  possesses  the  power  of  ingesting  foreign  par- 

A  B  tides.     Its  nucleus  consists  of  several 

lobes  united  by  threads  of  chromatin. 
This  cell    was    formerly  known  under 
the  term  iieutrophil,  because  of  its  sup- 
posed reaction  to  neutral  dyes. 
,      ,   ,,     ,  The  coarsehi  qranular  form  or  eo- 

_„.     127.— A.     Three    colored    blood-cor-  ~'    "^ 

puscies.    B.  Three  colorless  blood-cor-  sinopliil  Constitutes    ouly    2    per    cent 

puscles  acted    on    by    acetic   acid:    the  -^  .^  x 

nuclei  are  very  clearly  visible.     X  900.        of   the    leuCOCytcS.       It    haS    a    diameter 

of  12^1  and  a  reniform  nucleus. 

The  Ija&opliil  cell  is  rarely  found  in  normal  blood.  It  may  occur  oc- 
casionally during  periods  of  digestion.  It  is  a  small,  spherical  cell, 
with  an  irregular  nucleus  and  a  diameter  of  7/-i. 

The  small  liyaline  leucocyte  is  also  called  a  lymphocyte,  because  of  the 
large  numbers  found  in  adenoid  tissue,  and  is  supposed  to  be  an  imma- 
ture form.  The  nucleus  is  proportionately  large,  and  is  surrounded  by 
but  little  protoplasm  in  which  no  granules  can  be  detected.  The  cell  is 
about  the  size  of  a  red  blood  cell,  and  constitutes  from  10  to  20  per  cent 
of  all  leucocytes. 

The  large  hyaline  or  myelocyte  varies  in  diameter  from  8.5  to  10/^..  Its 
nucleus  is  spherical  or  reniform,  and  is  surrounded  by  more  protoplasm 
than  in  the  case  of  the  lymphocyte.  It  forms  about  10  per  cent  of  the 
leucocytes. 

Amoeboid  Movement. — The  remarkable  property  of  the  colorless 
corpuscles  of  spontaneously  changing  their  shape  was  first  demonstrated 
by  Wharton  Jones  in  the  blood  of  the  skate.  If  a  drop  of  blood  be  ex- 
amined with  a  high  power  of  the  microscope,  under  conditions  by  which 
loss  of  moisture  is  prevented,  and  at  the  same  time  the  temperature  is 
mnintained  at  about  that  of  the  body,  37°  C.  (98.5°  F.),  the  colorless 


THE    BLOOD.  147 


corpuscles  will  be  observed  slowly  to  alter  their  shapes,  and  to  send  out 
processes  at  various  parts  of  their  circumference.  The  aniceboid  move- 
ment which  can  be  demonstrated  in  human  colorless  blood-corpuscles, 
can   be  most  conveniently  studied  in  the  newt's  blood.     The  processes 


mmi 


Fig.  138.— Human  colorless  blood-corpuscles,  showing  its  successive  changes  of  outline  withiC 
ten  minutes  when  kept  moist  on  a  warm  stage.     fSchofield.) 

which  are  sent  out  from  the  corpuscle  are  either  lengthened  or  with- 
drawn. If  lengthened,  the  protoplasm  of  the  whole  corpuscle  flows  as 
it  were  into  its  process,  and  the  corpuscle  changes  its  position;  if  with- 
drawn, protrusion  of  another  process  at  a  different  point  of  the  circum- 
ference speedily  follows.  The  change  of  position  of  the  corpuscle  can 
also  take  place  by  a  flowing  movement  of  the  whole  mass,  and  in  this 
case  the  locomotion  is  comparatively  rapid.  The  activity  both  in  the 
processes  of  change  of  shape  and  also  of  cliange  in  position  is  much 
more  marked  in  some  corpuscles  than  in  others.  Klein  states  that  in 
the  newt's  blood  the  changes  are  especially  noticeable  in  a  variety  of  the 
colorless  corpuscle,  which  consists  of  a  mass  of  finely  granular  proto- 
plasm w'ith  jagged  outline,  and  contains  three  or  four  nuclei,  or  in  large 
irregular  masses  of  protoplasm  containing  from  five  to  twenty  nuclei. 

Action  of  reagents  upon  the  colorless  corpuscles. — Feeding  the  corpus- 
cles.— If  some  fine  pigment  granules,  e.g.,  j^owdered  vermilion,  be  added  to  a 
fluid  containing  colorless  blood-corpuscles,  on  a  glass  slide,  these  will  be 
observed,  under  the  microscope,  to  take  up  the  pigment.  In  some  cases 
colorless  corpuscles  have  been  seen  with  fragments  of  colored  ones  thus  em- 
bedded in  their  substance.  They  have  also  been  seen,  in  diseased  states,  to 
contain  micro-organisms,  e.g.,  bacilli,  and  according  to  some  pathologists  are 
capable  of  destroying  them  (phagocytosis) .  They  may  too  take  up  other  for- 
eign matter  or  even  other  colorless  corpuscles.  This  propertj'  of  the  colorless 
corpuscles  i5  especially  interesting  as  helping  still  further  to  connect  them  with 
the  lowest  forms  of  animal  life,  and  to  connect  both  with  the  organized  cells  of 
which  the  higher  animals  are  composed. 

The  property  which  the  colorless  corpuscles  possess  of  passing 
through  the  walls  of  the  blood-vessels  wall  be  described  later  on. 

The  Blood-Plates. — A  third  variety  of  corpuscle  is  found  in  the 
blood,  and  is  known  as  the  llood-platc.  It  is  circular  or  elliptical  in 
shape,  of  nearly  homogeneous  structure,  and  varies  in  size  from  .5-5.5/^. 
Hence  it  is  smaller  than  the  red  cell.  Though  found  in  the  circulating 
blood,  tlicy  arc  not  independent  cells.  It  is  altogether  probable  that  they 
are  derived  chiefly  from  the  red  cells,  being  extruded  therefrom  in  the 


148 


HANDBOOK    OF    PHYSIOLOGY. 


form  of  masses  or  chains  of  globular  material.  Chemically  they  contain 
a  nncleo-proteid,  and  it  is  supposed  that  they  take  part  in  the  phenom- 
enon of  coagulation. 


Healthy  bacillus 
Healthj-  bacillus  - 


Healthy  bacillus 
Partially  digested  baciUus 


Partially  digested  leucocyte 

Nuclei  vacuolated ^\  ^ 


-    Nucleus 
^^   ^    BaciUus  in  leucocyte 
^— TT^ft. .  Partially  digested  leucocyte 

.  Foreign  matter 


Foreign  matter 


Leucocytes 


Particles  of  foreign  m.atter 

Particles  of  foreign  matter 
Particles  of  foreign  matter 


Fig.  129.— Macrophages  containing  bacilli  and  other  structures  supposed  to  be  undergoing  digestion. 

(Ruffer.) 


Enumeration  of  the  blood-corpuscles. — Several  methods  are  employed  for 
counting  the  blood-corjsuscles,  most  of  them  depending  upon  the  same  princi- 
ple, i.  e. ,  the  dilution  of  a  minute  volume  of  blood  Tvlth  a  given  volume  of  a 
colorless  solution  similar  in  s])ecific  gravity  to  blood  plasma,  so  that  the  size 
and  shape  of  the  corpuscles  is  altered  as  little  as  possible.  A  minute  quantity 
of  the  well-mixed  solution  is  then  taken,  examined  under  the  microscope, 
either  in  a  flattened  capillary  tube  (Malassez)  or  in  a  cell  (Hayem  &  Nachet, 
Gowers)  of  known  capacitj",  and  the  number  of  corpuscles  in  a  measured  length 
of  the  tube,  or  in  a  given  area  of  the  cell  is  counted.  The  length  of  the  tube 
and  the  area  of  the  cell  are  ascertained  by  means  of  a  micrometer  ^cale  in  the 
microscope  ocular ;  or  in  the  case  of  Gowers'  modification,  by  the  division  of 
the  cell  area  into  squares  of  known  size.  Having  ascertained  the  number  of 
coi-puscles  in  the  diluted  blood,  it  is  easy  to  find  out  the  number  in  a  given 
volume  of  normal  blood.  Gowers'  modification  of  Hayem  &  Nachet's  instru- 
ment, called  by  him  Hcemacytometer,  consists  of  a  small  pipette  (a)  ,  which, 
when  filled  up  to  a  mark  on  its  stem,  holds  995  cubic  millimetres.  It  is  fur- 
nished with  an  india-rubber  tube  and  glass  mouth-piece  to  facilitate  filling  and 
emptying ;  a  capillary  tube  (b)  marked  to  hold  5  cubic  millimetres,  and  also 
furnished  with  an  india-rubber  tube  and  mouth-piece;  a  small  glass  jar  (d)  in 
which  the  dilution  of  the  blood  is  performed ;  a  glass  stirrer  (e)  for  mixing 
the  blood  thoroughly,  (f)  a  needle,  the  length  of  which  can  be  regulated  by  a 
screw;    a  brass   stage   plate  (g)    carrying   a  glass   slide,  on    which   is  a  cell  one- 


THE    BLOOD. 


149 


fifth  of  a  millimetre  deep,  and  tlie  bottom  of  wliich  is  divided  into  one-tenth 
millimetre  squares.  On  the  top  of  the  cell  rests  the  cover-glass,  which  is  kept 
in  its  place  by  the  pressure  of  two  springs  proceeding  from  the  stage  plate  A 
standard  saline  solution  of  sodium  sulpliate,  or  similar  salt,  of  specific  gravity 
1025,  is  made,  and  995  cubic  millimetres  are  measured  by  means  of  the  pipette 
into  the  glass  jar,  and  with  this  five  cubic  millimetres  of  blood,  obtained  by 
pricking  the  finger  with  a  needle,  and  measured  in  the  capillary  pipette  (b) 
are  thoroughly  mixed  by  the  glass  stirring-rod.  A  drop  of  this  diluted  blood 
is  then  placed  in  the  cell  and  covered  with  a  cover-glass,  which  is  fixed  in 
position  by  means  of  the  two  lateral  springs.  The  layer  of  diluted  blood  be- 
tween the  slide  and  cover-glass  is  -}  inch  thick.  The  preparation  is  then 
examined  under  a  microscope  with  a  power  of  about  400  diametei-s,  and  focussed 
until  the  lines  dividiuti-  the  cell  into  squares  are  visible. 


Fig.  1.30.— Haemacj-tometer.    (Gower?.) 


After  a  short  delay,  the  red  corpuscles  which  have  sunk  to  the  bottom  of 
the  cell,  and  are  resting  on  the  squares,  are  counted  in  ten  squares,  and  the 
number  of  white  corpuscles  noted.  By  adding  together  the  numbers  counted 
in  ten  (one-tenth  millimetre)  squares,  and,  as  the  blood  has  been  diluted,  mul- 
tiplying by  ten  thousand,  the  number  of  corpuscles  in  one  cubic  millimetre  of 
blood  is  obtained.  The  average  number  of  corpuscles  per  each  cubic  millimetre 
of  healthy  blood,  according  to  Vierordt  and  Welcker,  is  5,000,000  in  adult 
men,  and  4, 500, 000  in  women. 

A  luiemacytometer  of  another  form,  and  one  that  is  much  used  at  the  jn-esent 
time,  is  known  as  the  Thoma-Zeiss  Iuvuku  ytometer.  It  consists  of  a  carefully 
graduated  pipette,  in  which  the  dilution  of  the  blood  is  done  ;  this  is  so  formed 
that  the  capillary  stem  has  a  capacity  equalling  one- hundredth  of  the  ball 
above  it.  If  the  blood  is  drawn  up  in  the  capillary  tube  to  the  line  marked  1 
(fig.  133)  the  saline  solution  may  afterward  be  drawn  up  the  stem  to  the  line 
101 ;   in  this  way  we  have   101   inirts  of  which  the  blood  forms  1.     As  the  con- 


150 


HANDBOOK    OF    PHYSIOLOGY. 


tents  of  the  stem  can  be  displaced  unmixed  we  shall  have  in  the  mixture  the 
proper  dilution.  The  blood  and  the  saline  solution  are  well  mixed  by  shaking 
the  pipette,  in  the  ball  of  which  is  contained  a  small  glass  bead  for  the  pur- 
pose of  aiding  the  mixing.  The  other  part  of  the  instrument  consists  of  a 
glass  slide  (fig.  131)  upon  which  is  moimted  a  covered  disc,  m,  accurately  ruled 
so  as  to  present  one  square  millimetre  divided  into  400  squares  of  one-twentieth 


jm: 


Fig.  131. — Thoma-Zeiss  Haemacytometer. 


of  a  millimetre  each.  The  micrometer  thus  made  is  surrounded  by  another 
annular  cell,  c,  which  has  such  a  height  as  to  make  the  cell  project  exactly 
one-tenth  millimetre  beyond  m.  If  a  drop  of  the  diluted  blood  be  placed  vipon 
m,  and  c  be  covered  with  a  perfectly  flat  cover-glass,  the  volume  of  the  diluted 
blood  above  each  of  the  squares  of  the  micrometer,  i.e.,  above  each  :j^,  will 
be  ^00  of  a  cubic  millimetre.  An  average  of  ten  or  more 
squares  are  then  taken,  and  this  number  multiplied  by  4000X 100 
gives  the  number  of  corpuscles  in  a  cubic  millimetre  of  un- 
diluted blood. 


Chemical  Composition'  of  the  Blood. 

Before  considering  tlie  chemical  composition  of  the 
blood  as  a  whole,  it  will  be  convenient  to  take  in  order 
the  composition  of  the  various  chief  factors  which  have 
been  set  out  in  the  table  on  p.  132,  into  which  the  blood 
may  be  separated,  viz. : — (1.)  The  Plasma ;  (2.)  The 
Serum;  (3.)   The  Corpuscles ;  (4.)   The  Fibrin. 

(1.)  The  Plasma. — The  Plasma,  or  liquid  part  of 
the  blood,  in  which  the  corpuscles  float,  may  be  ob- 
tained free  from  colored  corpuscles  in  either  of  the  ways 
mentioned  below. 

In  it  are  the  fibrin  factors,  inasmuch  as  when  ex- 
posed to  the  ordinary  temperature  of  the  air  it  under- 
goes coagulation  and  splits  up  into  fibrin  and  serum. 
It  differs  from  the  serum  in  containing  fibrinogen,  but 
in  appearance  and  in  reaction  it  closely  resembles  that 
fluid  ;  its  alkalinity,  however,  is  greater  than  that  of  the 
serum  obtained  from  it.  It  may  be  freed  from  white  corjDuscles  by  filtra^ 
tion  at  a  temperature  below  5°  C.  (41°  F.)  or  by  the  centrifugal  machine 


Fig.  133.— Thoma- 
Zeiss  Haemacyto- 
meter. 


The  chief  methods  of  obtaining  plasma  free  from  coriDuscles  may  be  here 
epitomized :  (1)  by  cold,  the  temperature  should  be  about  0°  C.  and  may  be 
two  or  three  degrees  higher,  but  not  lower.  (2)  The  addition  of  nevitral  salts, 
in  certain  proportions,  either  solid  or  in  solution,  e.g.  of  sodium  sulphate,  if 
solid  1  part  to  12  parts  of  blood ;  if  a  saturated  solution  1  part  to  6  parts  of 
blood ;  of  magnesium  sulphate,  of  a  23^,  or  if  saturated  solution  1  part  to  4  of 


THE    BLOOD. 


151 


blood.  (3)  A  third  waj'  is  to  mix  frog's  blood  with  an  equal  part  of  a  ofc  of 
cane  sugar,  and  to  get  rid  of  the  coipuscles  by  filtration ;  or  (4)  bj"  the  injec- 
tion of  commercial  peptone  into  the  veins  of  certain  mammals,  previous  to 
bleeding  them  to  death,  allowing  the  corpuscles  to  subside,  and  afterward 
subjecting  the  supernatant  plasma  to  the  action  of  a  centrifugal  machine ;  by 


Fig.  133.— Plan  cand  section  of  centrifugal  machine,  a.  An  iron  socket  secured  to  top  of  table  b; 
c,  a  steel  spindle  oarrying  the  turntable  d,  and  turning  freely  in  a  :  e.  a  flange  rounil  turntable  d: 
F  F,  shallow  grooves  on  face  of  d.  in  which  the  test  tubes  are  fixed  by  clamp^  g  g:  h.  a  pulley  fixed 
to  end  of  spindle  c,  and  turned  by  the  cord  k;  ii  are  two  guide-pulleys  for  cord  k.     (Gamgee.) 

the  rapid  rotation  of  which  (fig.  133)  the  whole  of  the  remaining  solid  parti- 
cles, if  any,  is  driven  to  the  outer  end  of  the  test-tubes  in  which  the  plasma  is 
placed. 


Composition  of  Plasma. 


Water        .... 
Solids— 

Proteids : 

1.  Yield  of  fibrin 

2.  Other  proteids     . 
Extractives  includiug  fat 
Inorganic  salts 


4.05 

78.84 
5.66 
8  5 


902.9 


07. 1 


1000 


152  HANDBOOK    OF    PHYSIOLOGY. 

Inorganic  Substances. — In  1,000  parts  of  plasma  there  are  — ■ 

ChloriDe                    3.536 

Sulphuric  acid    .,.,.,.  .129 

Phosphoric  acid      .......  .145 

Potassium                    ......  .814 

Sodium   ...,...,.  3.410 

Phosphate  of  lime       ,,,...  .298 

Phosphate  of  magnesia    , 218 

Oxygen      ........  .455 

8. 505 

(2.)  The  Serum. — The  serum  is  tlie  liquid  part  of  the  blood  or  of 
the  plasma  which  remains  after  the  separation  of  the  clot.  It  is  a  traus- 
pareut,  yellowish,  alkaline  fluid,  with  a  specific  gravity  of  from  1025  to 
1032.  In  the  usual  mode  of  coagulation,  part  of  the  serum  remains  in 
the  clot,  and  the  rest,  squeezed  from  the  clot  by  its  contraction,  lies 
around  it.  Since  the  contraction  of  the  clot  may  continue  for  thirty-six 
or  more  hours,  the  quantity  of  serum  in  the  blood  cannot  be  even 
roughly  estimated  till  this  period  has  elapsed.  There  is  nearly  as  much, 
by  weight,  of  serum  as  there  is  clot  in  coagulated  blood. 

Serum  may  be  obtained  from  blood  corjDuscles  by  allowing  blood  to 
clot  in  large  test  tubes,  and  subjecting  the  test  tubes  to  the  action  of  a 
centrifugal  machine  (fig.  133)  for  some  time. 

In  tabular  form  the  comjDosition  may  be  thus  summarized.  In  1000 
parts  of  serum  *  there  are : — 

Water about  900 

Proteids : 

a.   Serum- albumin         .......  ) 

(3.  Serum-globulin   .         .         .         .         .         .         .         .       |-  80 

y.  Fibrin  ferment         .......  ) 

Salts.  1 

Fats — including  fatty  acids,   cholesterin,   lecithin ;    and       | 
some  soaps        .........       | 

Grape  sugar  in  small  amount  .....  I  ^j^ 

Extractives — creatin,  creatinin,  urea,  etc.        .         .         . 

Yellow  pigment,  which  is  independent  of  heemoglobin. 

Gases — small  amounts  of  oxygen,  nitrogen,  and  carbonitj 
acid  .......... 

1000 

a.  Water. — The  water  of  the  serum  varies  in  amount  according  to 
the  amount  of  food,  drink,  and  exercise,  and  with  many  other  circum- 
stances. 

b.  Proteids. — «.  Serum  albumin  is  the  chief  proteid  found  in  serum. 
The  proportion  which  it  bears  to  serum-globulin,  the  other  proteid,  is 
as  3  to  4.5  in  human  blood. 

Serum-albumin  has  been  shown  by  Halliburton  to  be  a  compound 
body    which  may  be  called   serine,  made  up  of  three  proteids,  which 

*This  table  is  more  detailed  than  that  of  the  plasma  given  above.  The 
salts,  extractives,  etc.,  are  the  same  in  both  serum  and  plasma,  but  the  proteids 
are  somewhat  different  in  nature  and  amount. 


THE    BLOOD.  153 

coagulate  at  different  temperatures,  «  at  73°  C,  ^3  at  77°  C,  and  y  at  84° 
C.  The  serine  is  coagulated  by  the  addition  of  strong  acids,  such  as 
nitric  and  hydrochloric;  by  long  contact  with  alcohol  it  is  precipitated. 
It  is  not  precipitated  on  addition  of  ether,  and  so  differs  from  the  other 
native  albumin,  viz.,  e/7(/-albumin.  When  dried  at  40°  C.  (104°  F.) 
serum-albumin  is  a  brittle,  yellowish  substance,  soluble  in  water,  pos- 
sessing a  Iffivorotary  power  of  —  56°.  It  is  with  great  difficulty  freed 
from  its  salts.  It  is  precipitated  by  solutions  of  metallic  salts,  e.g.,  of 
mercuric  chloride,  copper  sulphate,  lead  acetate,  sodium  tungstate,  etc. 
If  dried  at  a  temperature  over  75°  C.  (167°  F.),  the  chief  part  of  the 
residue  is  insoluble  in  water,  having  been  changed  into  coagulated  pt-o- 
teid.  Serum-albumin  may  be  precipitated  from  serum,  from  which  the 
serum-globulin  has  been  previously  se2:)arated  by  saturation  with  mag- 
nesium sulphate,  by  further  saturation  with  sodium  sulphate,  sodium 
nitrate,  or  iodide  of  potassium. 

/?.  Serum-globulin  can  be  obtained  as  a  white  precipitate  from  cold 
serum  by  adding  a  considerable  excess  of  water  over  ten  times  its  bulk, 
and  passing  through  the  mixture  a  current  of  carbonic  acid  gas  or  by 
the  cautious  addition  of  dilute  acetic  acid.  It  can  also  be  obtained  by 
saturating  serum  with  either  crystallized  magnesium  suliDhate,  or  sodium 
chloride,  nitrate,  acetate,  or  carbonate.  When  obtained  iu  the  latter 
way,  precipitation  seems  to  be  much  more  complete  than  by  means  of 
the  former  method.  Serum-globulin  coagulates  at  75°  0.  (167°  F.). 
There  seems  to  be  more  globulin  in  the  serum  than  in  the  corresponding 
plasma,  and  supposing  Halliburton  is  correct  iu  believing  the  fibrin  fer- 
ment to  belong  to  the  globulin  class,  its  presence  arising  from  the  dis- 
integration of  the  colorless  corpuscles  (cell-globulin)  would  account  for 
part  of  the  increase,  while  possibly  another  part  might  be  due,  as  sug- 
gested by  Hammersten,  to  the  fact  that  fibrinogen  splits  up  into  fibrin, 
leaving  a  globulin  residue  which  appears  in  the  serum. 

c.  The  salts  of  sodium  predominate  in  serum  as  in  plasma,  and  of 
these  the  chloride  generally  forms  by  far  the  largest  proportion. 

d.  Fats  are  quite  constantly  present  in  a  free  state  {i.e.,  aspalmitin, 
stearin,  and  olein),  though  usually  in  very  small  quantities.  Gumprecht, 
however,  asserts  that  they  may  be  present  in  such  quantities  as  to  give 
the  blood  a  milky  hue.  Fatty  acids  have  been  found  by  some  observers 
in  pathological  conditions,  but  on  the  other  hand  it  is  claimed  that  this 
is  merely  the  result  of  faulty  technique.  The  amount  of  fatty  matter 
varies  according  to  the  time  after,  and  the  ingredients  of,  a  meal. 

e.  Grape  sitgar  is  found  principally  in  tlio  blood  of  the  hepatic  vein, 
to  the  extent  of  about  two  parts  in  a  thousand. 

f.  The  mY/t/c/'/ws  vary  from  time  to  time;  sometimes  hippuric  acid 
is  fouiul  in  addition  to  \irea,  uric  acid,  crcatin  and  croatiniu,  xanthin, 
hypoxanthin,  and  cholesteriu.  Vrea  exists  in  pro|iortion  from  .(yi  to 
.04  per  cent. 


154  HANDBOOK    OF    PHYSIOLOGY. 

g.  The  yellow  j92>7???e;?^  of  the  serum  and  the  odorous  matter  which 
gives  the  blood  of  each  particular  animal  a  peculiar  smell,  have  not  yet 
been  exactly  diSerentiated.  The  former  is  probably  of  the  nature  of  a 
lipochrome,  and  might  be  called  serum  lutein.  It  is  soluble  in  alcohol 
and  ether,  and  has  two  hazy  absorption  bands  toward  the  violet  end  of 
the  spectrum. 

(3.)  The  Corpuscles. — a.  Colored. — Analysis  of  a  thousand  parts 
of  moist  blood  corpuscles  shows  the  following  result: — 

Water 688 

Solids- 
Organic  303.88 

Mineral 8.12—312=1000 

Of  the  solids  the  most  important  is  HcBmoglohi7i,  the  substance  to 
which  the  blood  owes  its  color.  It  constitutes,  as  will  be  seen  from  the 
appended  Table,  more  than  90  per  cent  of  the  organic  matter  of  the 
corpuscles.  Besides  hasmoglobin  there  are  proteid  and  fatty  matters, 
the  former  chiefly  consisting  of  globulins,  and  the  latter  of  cliolesterin 
and  lecithin. 

In  1000  parts  organic  matter  are  found: — 

Haemoglobin 90§.4 

Proteids       .         .         .         ....         .         .    .       86.7 

Fats 7.9=1000 

Of  the  inorganic  salts  of  the  corpuscles,  with  the  iron  omitted — 

In  1000  parts  corj)uscles  (Schmidt)  are  found: — 

Potassium  Chloride 3.679 

Potassium  Phosphate 2.343 

Potassium  sulphate         .......       .132 

Sodium .633 

Calcivmi 094 

Magnesium         ........  .060 

Soda 341=7.382 

The  projDerties  of  hsemoglobin  will  be  considered  in  relation  to  the 
Gases  of  the  blood. 

b.  Colorless. — In  consequence  of  the  difficulty  of  obtaining  color- 
less corpuscles  in  sufficient  number  to  make  an  analysis,  little  is  ac- 
curately known  of  their  chemical  composition;  in  all  probability, 
however,  the  protoplasm  of  the  corpuscles  is  made  up  of  proteid  mat- 
ter, and  the  nucleus  of  ?iuclein,  a  nitrogenous  phosphorus-containing 
body  akin  to  mucin,  capable  of  resisting  the  action  of  the  gastric  juice. 
The  proteid  matter  is  made  up  probably  of  one  or  more  nucleo-albumins, 
and  of  one  or  more  globulins  with  a  small  amount  of  serum  albumin. 
There  are  also  present  lecitJdn,  a  fatty  body  containing  phosphorus, 
fatty  granules  staining  black  with  osmic  acid,  cliolesterin,  a  monatomic 
alcohol,  glycogen,  and  salts  of  sodium,  potassium,  calcium,  and  magne- 
sium, of  which  the  phosphate  of  potassium  is  in  greatest  amount. 

(4.)  Fibrin. — The  part  played  by  fibrin  in  the  formation  of  a  clot 
and  its  tests  have  been  already  described,  and  it  is  only   necessary  to 


THE    BLOOD.  155 

consider  here  its  general  properties.  It  is  a  stringy  elastic  substance 
belonging  to  the  proteid  class  of  bodies.  Blood  contains  only  .3  per 
cent  of  fibrin.  It  can  be  converted  by  the  gastric  or  pancreatic  juice 
into  peptone.  It  possesses  the  power  of  liberating  the  oxygen  from 
solutions  of  hydric  peroxide  H2O2  or  ozonic  ether.  This  may  be  shown 
by  dipping  a  few  shreds  of  fibrin  in  tincture  of  guaiacum,  and  then 
immersing  them  in  a  solution  of  hydric  peroxide.  The  fibrin  becomes 
of  a  bluish  color,  from  its  having  liberated  from  the  solution  oxygen, 
which  oxidizes  the  resin  of  guaiacum  contained  in  the  tincture,  and 
thus  produces  the  coloration. 

The  Gases  of  the  Blood. 

The  gases  contained  in  the  blood  are  carbonic  acid,  oxygen,  and  ni- 
trogen, 100  volumes  of  blood  containing  from  50  to  60  volumes  of  these 
gases  collectively. 

Arterial  blood  contains  relatively  more  oxygen  and  less  carbonic  acid 
than  venous.  But  the  absolute  quantity  of  carbonic  acid  is  in  both 
kinds  of  blood  greater  than  that  of  the  oxygen. 

Oxygen.  Carbonic  Acid.         Nitrogen. 

Arterial  Blood  .         .         20  vol.  per  cent.       39  vol.  per  cent.       1  to  2  vols. 

Venous        " 

(from  muscles  at  rest)      8  to  13    "  "  46    "  "  1  to  2  vols. 

The  Extraction  of  the  Gases  from  the  Blood. — As  the  ordinary  air  pumps  are- 
not  sufficiently  powerful  for  the  purpose,  the  extraction  of  the  gases  from  the- 
blood  is  accomplished  by  means  of  a  mercurial  air-pump,  of  which  there  are- 
many  varieties,  those  of  Ludwig,  Alvergnidt,  Geissler,  and  Sprengel  being  the 
chief.  The  principle  of  action  in  all  is  much  the  same.  Ludwig's  pump, 
which  may  be  taken  as  a  type,  is  represented  in  fig.  134.  It  consists  of  two- 
fixed  glass  globes,  C  and  F,  the  upper  one  communicating  by  means  of  the 
stop-cock  D,  and  a  stout  india-rubber  tube  with  ano.ther  glass  globe,  L,  which 
can  be  raised  or  lowered  by  means  of  a  puUey ;  it  also  communicates  by  means 
of  a  stop-cock,  B,  and  a  bent  glass  tube,  A,  with  a  gas  receiver  (not  repre- 
sented in  the  figm-e) ,  A,  dipping  into  a  bowl  of  mercury,  so  that  the  gas  may 
be  received  over  mei-curj\  The  lower  globe,  F,  communicates  with  C  by 
means  of  the  stop-cock,  E,  with  /  in  which  the  blood  is  contained  by  the  stop- 
cock, O,  and  with  a  movable  glass  globe,  21,  similar  to  L,  by  means  of  the 
stopcock,  H,  and  the  stout  india-rubber  tube,  K. 

In  order  to  work  the  i^ump,  L  and  M  are  filled  with  mercury,  the  blood  from 
which  the  gases  are  to  be  extracted  is  placed  in  the  bulb  I,  the  stopcocks,  H, 
E,  D,  and  B,  being  open,  and  G  closed.  M  is  raised  by  means  of  the  pulley 
until  F  is  full  of  mercury,  and  the  air  is  driven  out.  E  is  then  closed,  and 
L  is  raised  so  that  C  becomes  full  of  mercury,  and  the  air  driven  off.  B  is- 
then  closed.  On  lowering  L  the  mercury  runs  into  it  from  C,  and  a  vacuum 
is  established  in  C.  On  opening  E  and  lowering  M,  a  vacuum  is  similarly 
established  in  J^;  if  C  be  now  opened,  the  blood  in  /will  enter  ebullition,  and 
the  gases  will  pass  off  into  F  and  C.  and  on  raising  M  and  then  L,  the  stopcock 
B  being  opened,  the  gas  is  driven  through  ^4,  and  is  received  into  the  receiver 


156 


HANDBOOK   OF    PHYSIOLOGY. 


over  mercury.     By  repeating  the  experiment  several  times  the  whole  of  the 
gases  of  the  specimen  of  blood  is  obtained,  and  may  be  estimated. 


A.  The  Oxygen  of  the  Blood. — It  has  been  found  that  a  very 
small  proportion  of  the  oxygen  which  can  be  obtained,  by  the  aid  of  the 
mercurial  pump  from  the  blood,  exists  in  a 
state  of  simple  solution  in  the  plasma.  If 
the  gas  were  in  simple  solution,  the  amount 
of  oxygen  in  any  given  quantity  of  blood, 
exposed  to  any  given  atmosphere,  ought  to 
vary  with  the  amount  of  oxygen  contained  in 
the  atmosphere.  Since,  speaking  generally, 
the  amount  of  any  gas  absorbed  by  a  liquid 
such  as  plasma  would  depend  upon  the  pro- 
portion of  the  gas  in  the  atmosphere  to 
which  the  liquid  is  ex]30sed — if  the  propor- 
tion is  great,  the  absorption  will  be  great;  if 
small,  the  absorption  will  be  similarly  small. 
The  absorption  continues  until  the  propor- 
tions of  the  gas  in  the  liquid  and  in  the  at- 
mosphere are  equal.  Other  things  will,  of 
course,  influence  the  absorption,  such  as  the 
nature  of  the  gas  employed,  the  nature  of 
the  liquid  and  the  tem'perature,  but  cceteris 
paribus,  the  amount  of  a  gas  which  a  liquid 
absorbs  depends  upon  the  proportion  —  the 
so-called  partial  pressure — of  the  gas  in 
the  atmosphere  to  which  the  liquid  is  sub- 
jected. And  conversely,  if  a  liquid  contain- 
ing a  gas  in  solution  be  exposed  to  an  atmo- 
sphere containing  none  of  the  gas,  the  gas 
will  be  given  up  to  the  atmosphere  until  the 
amount  in  the  liquid  and  in  the  atmosj)here  becomes  equal, 
dition  is  called  a  condition  of  equal  tensions. 


Fig.  134. — Ludwig's  Mercurial 
Pump. 


This  con- 


The  condition  may  be  understood  by  a  simple  illustration.  A  large  amount 
of  carbonic  acid  gas  is  dissolved  in  a  bottle  of  water  by  exposing  the  liquid  to 
extreme  pressure  of  the  gas,  and  a  cork  is  placed  in  the  bottle  and  wired  down. 
The  gas  exists  in  the  water  in  a  condition  of  tension,  and  therefore  exhibits 
a  tendency  to  escape  into  the  atmosphere,  in  order  to  relieve  the  tension ;  this 
produces  the  violent  expulsion  of  the  cork  when  the  wire  is  removed,  and  if 
the  aerated  water  is  placed  in  a  glass  the  gas  will  continue  to  be  evolved  until 
it  has  almost  entirely  passed  into  the  atmosphere,  and  the  tension  of  the  gas 
in  the  water  api^roximates  to  that  of  the  atmosphere,  in  which,  it  should  be 
remembered,  the  carbon  dioxide  is,  naturally,  in  very  small  amount,  viz., 
.04  per  cent. 


THE    BLOOD.  157 

The  oxygen  of  the  blood  does  not  obey  this  law  of  pressure.  For  if 
blood  which  contains  little  or  no  oxygen  be  exposed  to  a  succession  of 
atmospheres  containing  more  and  more  of  that  gas,  we  find  that  the 
absorption  is  at  first  very  great,  but  soon  becomes  relatively  very  small, 
not  being  therefore  regularly  in  jJi'oportion  to  the  increased  amount  (or 
tension)  of  the  oxygen  of  the  atmospheres,  and  that  conversely,  if  arte- 
rial blood  be  submitted  to  regularly  diminishing  pressures  of  oxygen,  at 
first  very  little  of  the  contained  oxygen  is  given  off  to  the  atmosphere, 
then  suddenly  the  gas  escapes  with  great  rapidit}'',  and  again  disobeys 
the  law  of  pressures. 

Very  little  oxygen  can  be  obtained  from  plasma  freed  from  blood 
corpuscles,  even  by  the  strongest  mercurial  air-pump,  neither  can  it  be 
made  to  absorb  a  large  quantity  of  that  gas;  but  the  small  quantity 
which  is  so  given  up  or  so  absorbed  follows  the  laws  of  absorption  ac- 
cording to  pressure. 

It  must  be,  therefore,  evident  that  the  chief  part  of  the  oxygen  is 
contained  in  the  corpuscles,  and  not  in  a  state  of  simple  solution.  The 
chief  solid  constituent  of  the  colored  corpuscles  is  hcemoglobin,  which 
constitutes  more  than  90  per  cent  of  their  bulk.  This  body  has  a  very 
remarkable  affinity  for  oxygen,  absorbing  it  to  a  very  definite  extent 
under  favorable  circumstances,  and  giving  it  up  when  subjected  to  the 
action  of  reducing  agents,  or  to  a  sufficiently  low  oxygen  jjressure.  From 
these  facts  it  is  inferred  that  the  oxygen  of  the  blood  is  combined  witli 
hcemoglobin,  and  not  simply  dissolved;  but  inasmuch  as  it  is  compara- 
tively easy  to  cause  the  hemoglobin  to  give  up  its  oxygen,  it  is  believed 
that  the  oxygen  is  but  loosely  combined  with  the  substance. 

Haemoglobin. — Haemoglobin  is  a  crystallizable  body  which  consti- 
tutes by  far  the  largest  portion  of  the  colored  corj^uscles.  It  is  intimately 
distributed  throughout  their  stroma,  and  must  be  dissolved  out  before 
it  will  undergo  crystallization.  Its  percentage  composition  is  C.  53.85; 
H.  7.32;  N.  16.17;  0.  21.84;  S.  .63;  Fe.  .42.  Jacquet  gives  the 
empirical   formula  for  the    luymoolobin    of    the   dog,    C.,Ji,„„,N,„^S,Fe 

X  O  O'  (59         1203         195      3 

0„jg.  The  most  interesting  of  the  properties  of  ha^noglobin  are 
its  powers  of  crystallizing  and  its  attraction  for  oxygen  and  other 
gases. 

Crystals. — The  haemoglobin  of  the  blood  of  various  animals  possesses 
the  power  of  crystallizing  to  very  different  extents  (haemoglobin).  In 
some  animals  the  formation  of  crystals  is  almost  spontaneous,  whereas 
in  others  it  takes  jjlace  either  with  great  difficulty  or  not  at  all.  Among 
the  animals  whose  blood  coloring-matter  crystallizes  most  readily  are 
the  guinea-pig,  rat,  squirrel,  and  dog;  and  in  these  cases  to  obtain 
crystals  it  is  generally  sufficient  to  dilate  a  drop  of  recently-drawn  blood 
with  water  and  to  expose  it  for  a  few  minutes  to  the  air.  Light  seems 
to  favor  the  formation  of  the  crystals.     In  many  instances  other  means 


158 


HANDBOOK    OF    PHYSIOLOGY. 


must  be  adopted,  e.g.,t}ie  addition  of  alcohol,  ether,  or  chloroform,  rapid 
freezing,  and  then  thawing,  an  electric  current,  a  temperature  of  60°  0. 
(140°  F.),  the  addition  of  sodium  sulphate,  or  the  addition  of  decom- 
posing serum  of  another  animal. 

The  haemoglobin  of  human  blood  crystallizes  with  difficulty,  as  does 
also  that  of  the  ox,  the  pig,  the  sheep,  and  the  rabbit. 

The  forms  of  hemoglobin  crystals,  as  will  be  seen  from  the  appended 
figures,  differ  greatly. 

Hsemoglobin  crystals  are  soluble  in  water.  Both  the  crystals  them- 
selves and  also  their  solutions  have  the  characteristic  color  of  arterial 
blood. 

A  dilute  solution  of  oxy-hemoglobin  gives  a  characteristic  appear- 
ance with  the  spectroscope.     Two  absorption  bands  are  seen  between 


A' 


^4' 


\cX 


X 


Fig:.  135.— Crystals  of  oxy-haemoglobin— 
prismatic,  from  human  blood. 


Fig.  136.— Oxy-hgemoglobin  crystals— tetra- 
hedral,  from  blood  of  the  guinea-pig. 


the  solar  lines  d  *  (which  is  the  sodium  band  in  the  yellow)  and  e  *  (see 
plate),  one  in  the  yellow,  with  its  middle  line  some  little  way  to  the  right 
of  D,  is  very  intense,  but  narrower  than  the  other,  which  lies  in  the 
green  near  to  the  left  of  e.  Each  band  is  darkest  in  the  middle  and 
fades  away  at  the  sides.  As  the  strength  of  the  solution  increases  the 
bands  become  broader  and  deeper,  and  both  the  red  and  the  blue  ends 
of  the  spectrum  become  encroached  upon  until  the  bands  coalesce  to 
form  one  very  broad  band,  and  only  a  slight  amount  of  the  green  re- 
mains unabsorbed,  and  part  of  the  red;  on  still  further  increase  of 
strength  the  former  disappears. 

If  the  crystals  of  oxy-haemoglobin  be  subjected  to  a  mercurial  air- 
pump  they  give  off  a  definite  amount  of  oxygen  (1  gramme  giving  off 
1.59  ccm.  of  oyxgen),  and  they  become  of  a  purple  color;  and  a  solution 
of  oxy-hgemoglobin  may  be  made  to  give  up  oxygen,  and  to  become  pur- 
ple in  a  similar  manner. 


*  These  letters  refer  to  '^  Fraunhofer' s^^  lines. 


THE    BLOOD.  159 

This  change  may  be  also  effected  l3y  passing  through  the  solntion  of 
blood  or  of  oxy-hfemoglobin,  hydrogen  or  nitrogen  gas,  or  by  the  action 
of  reducing  agents,  of  which  Stokes's  fluid  *  or  ammonium  sulphide  are 
the  most  convenient. 

With  the  spectroscope,  a  solution  of  deoxidized  or  redticed  hcemoglohin 
is  found  to  give  an  entirely  different  aj^pearance  from  that  of  oxidized 
haemoglobin.  Instead  of  the  two  bands  at  d  and  e  we  find  a  single 
broader  but  fainter  band  occupying  a  position  midway  between  the  two, 
and  at  the  same  time  less  of  the  blue  end  of  the  spectrum  is  absorbed. 
Even  in  strong  solutions  this  latter  appearance  is  found,  thereby  differ- 
ing from  the  strong  solution  of  oxidized  htemoglobin  which  lets  through 
only  the  red  and  orange  rays;  accordingly  to  the  naked  eye  the  one 
(reduced  h£emoglobin  solution)  appears  purple,  the  other  (oxy-ha3moglo- 


Fig.  137.— Hexagonal  oxy-haemoglobin  crystals,  from  blood  of  squirrel.    On  these  hexagonal  plates 
prismatic  crystals  grouped  in  a  stellate  manner  not  unfrequentlj'  occur  (^after  Fuuke). 

bin  solution)  red.  The  deoxidized  crystals  or  their  solutions  quickly 
absorb  oxygen  on  exposure  to  the  air,  becoming  scarlet.  If  solutions 
of  blood  be  taken  instead  of  solutions  of  haemoglobin,  results  similar  to 
the  whole  of  the  foregoing  can  be  obtained. 

Venous  blood  never,  except  in  the  last  stages  of  asphyxia,  fails  to 
show  the  oxy-hffimoglobin  bands,  inasmuch  as  the  greater  part  of  the 
haemoglobin  even  in  venous  blood  exists  in  the  more  highly  oxidized  con- 
dition. 

Action  of  Gases  on  Haemoglobin. — Carbonic  oxide  gas,  passed 
through  a  solution  of  hemoglobin,  causes  it  to  assume  a  cherry-red  color, 

*  Stokes's  Fluid  consists  of  a  solution  of  ferrous  sulphate,  to  which  ammonia 
has  been  added  and  sufficient  tartaric  acid  to  prevent  precipitation.  Another 
reducing  agent  is  a  solution  of  stannous  chloride,  treated  in  a  way  similar  to 
the  ferrous  sulphate,  and  a  third  reagent  of  like  nature  is  an  aqueous  solution 
of  yellow  ammonium  sulphide,  NHi  HS. 


160  HANDBOOK    OF    PHYSIOLOGY. 

and  to  present  a  slightly  altered  spectrum;  two  bands  are  still  visible, 
but  are  slightly  nearer  the  blue  end  than  those  of  oxj -haemoglobin  (see 
plate).  The  amount  of  carbonic  oxide  taken  up  is  equal  to  the  amount 
of  the  oxygen  displaced.  Although  the  carbonic  oxide  gas  readily  dis- 
places oxygen,  the  reverse  is  not  the  case,  and  upon  this  property  de- 
pends the  dangerous  eifect  of  coal-gas  poisoning.  Coal  gas  contains 
much  carbonic  oxide,  and  when  breathed,  the  gas  combines  with  the 
haemoglobin  of  the  blood,  and  produces  a  compound  which  cannot  easily 
be  reduced.  This  compound  (carb-oxy-haemogiobin)  is  by  no  means  an 
oxygen  carrier,  and  death  may  result  from  suffocation  due  to  the  want 
of  oxygen  notwithstanding  the  free  entry  of  pure  air  into  the  lungs. 
Crystals  of  carbonic-oxide  haemoglobin  closely  resemble  those  of  oxy- 
hajmoglobin. 

Nitric  oxide  produces  a  similar  compound  to  the  carbonic-oxide 
haemoglobin,  which  is  even  less  easily  reduced. 

Nitrous  oxide  reduces  oxy-hgemogiobin,  and  iherefore  leaves  the  re- 
duced haemoglobin  in  a  condition  to  actively  take  up  oxygen. 

Biilpliuretted  Hydrogen. — If  this  gas  be  passed  through  a  solution  of 
oxy-haemoglobin,  the  haemoglobin  is  reduced  and  an  additional  band 
appears  in  the  red.  If  the  solution  be  then  shaken  with  air,  the  two 
bands  of  oxy-haemoglobin  replace  that  of  reduced  haemoglobin,  but  the 
band  in  the  red  persists. 

Methaemoglobin. — If  an  aqueous  solution  of  oxy-haemoglobin  is 
exposed  to  the  air  for  some  time,  its  spectrum  undergoes  a  change;  the 
two  D  and  e  bands  become  faint,  and  a  new  line  in  the  red  at  c  is  devel- 
oped. The  solution,  too,  becomes  brown  and  acid  in  reaction,  and  is  pre- 
cipitable  by  basic  lead  acetate.  This  change  is  due  to  the  decomposition 
of  oxy-haemoglobin,  and  to  the  production  of  methcemoglohin.  On  add- 
ing ammonium  sulphide,  reduced  haemoglobin  is  produced,  and  on  shak- 
ing this  up  with  air,  oxy-haemoglobin  is  rej^roduced.  Methaemoglobin 
is  probably  a  stage  in  the  deoxidation  of  oxy-h^moglobin.  It  appears 
to  contain  less  oxygen  than  oxy-haemoglobin,  bat  more  than  reduced 
haemoglobin.  Its  oxygen  is  in  more  stable  combination,  however,  than 
is  the  case  with  the  former  compound. 

Estimation  of  Haemoglobin. — The  most  exact  method  is  by  the 
estimation  of  the  amount  of  iron  (dry  haemoglobin  containing  .42  ^ev 
cent  of  iron)  in  a  given  specimen  of  blood,  but  as  this  is  a  somewhat 
complicated  process,  various  methods  have  been  proposed  which,  though 
not  so  exact,  have  the  advantage  of  simplicity.  In  Gower's  haemoglobin- 
ometer,  this  consists  in  comparing  the  color  of  a  given  small  amount 
of  diluted  blood  with  glycerine  jelly  tinted  with  carmine  and  picro-car- 
mine  to  represent  a  standard  solution  of  blood  diluted  one  hundred 
times.  The  amount  of  dilution  which  the  given  blood  requires  will 
thus  approximately  represent  the  quantity  of  haemoglobin  it  contains. 


THE    BLOOD. 


161 


But  of  the  several  varieties  of  hgemoglobinometer  that  whiyh  appears  to 
be  the  best  adapted  to  its  purpose  is  that  invented  by  Professor  Fleischl, 
of  Vienna.  In  this  instrument,  the  amount  of  haemoglobin  in  a  solution 
of  blood  is  estimated  by  comparing  a  stratum  of  diluted  blood  with  a 
standard  solid  substance  of  uniform  tint  similar  spectroscopically  to  di- 
luted blood.  In  order  that  the  strength  of  color  in  the  standard  sub- 
stance may  be  varied,  the  red  tinted  glass  is  made  wedge-shaped.  This, 
which  is  called  the  comparison  wedge,  is  cemented  on  to  a  colorless 
plain  strip  of  glass,  and  is  mounted  in  a  frame  (fig.  138,  P)  made  to 
slide  in  a  V-shaped  groove,  on  the  under  surface  of  the  stage  of  the  in- 
ijcrament.     The  comparison  wedge,  A",  is  so  placed  that  one  of  its  longi- 


Fig  138.— Fleischrs  Hfemoglobinometer. 

tudinal  edges  bisects  the  circular  stage-opening,  so  that  one-half  of  the 
latter  is  cut  off  by  the  red-tinted  wedge.  Into  the  stage-opening  fits 
a  small  circular  trough,  G,  having  a  glass  bottom,  and  divided  into  equal 
compartments  by  a  thin  lamina.  One  compartment,  a,  is  filled  in  the 
manner  to  be  presently  indicated  witli  diluted  blood,  and  the  other,  a', 
with  water;  the  trough  is  so  placed  that  the  lamina  is  in  one  plane  with 
the  edge  of  the  wedge,  the  water  compartment  being  above  the  wedge 
and  the  blood  compartment  above  the  free  half  of  the  stage  opening. 
By  turning  the  screw  head,  T,  the  frame,  P,  with  the  wedge,  K,  may 
be  moved  backward  and  forward  until  a  position  is  found  where  the  in- 
tensity of  the  tints  due  to  the  stratum  of  blood  on  the  one  hand  and  the 
thickness  of  the  wedge  on  the  other  appears  to  be  equal.  The  required 
degree  of  dilution  is  obtained  by  the  use  of  small  capillary  tubes  of  a 
capacity  varying  from  6  to  8  cmm.  The  capillary  pipette  is  filled  with 
blood  and  is  held  over  the  blood  compartment  and  its  contents  thor- 


162  HANDBOOK   OF    PHYSIOLOGY, 

oughly  washed  out  into  that  compartment,  and  the  blood  and  water  are 
mixed  with  a  wire.  Water  is  then  added  until  the  blood  compartment 
is  quite  full.  The  other  compartment  is  filled  with  water.  Light  is 
then  reflected  by  the  mirror,  S,  so  as  to  illuminate  both  compartments. 
By  moving  K  by  means  of  the  milled  head,  T,  a  position  of  A"  may  be 
found  corresponding  to  the  exact  intensity  of  the  light  passing  through 
the  two  compartments;  this  is  read  off  at  Jf  on  the  scale  P,  the  division 
of  which  corresponds  to  standard  strengths  of  solutions  of  haemoglobin. 
Distribution  of  Haemoglobin. — Hgemoglobin  occurs  not  only  in  the 
red  blood-cells  of  all  vertebrata  (except  amphioxus  and  leptocephalus 
whose  blood-cells  are  all  colorless,)  but  also  in  similar  cells  in  many 
Worms;  moreover,  it  is  found  diffused  in  the  vascular  fluid  of  some 
other  worms  and  certain  Crustacea;  it  also  occurs  in  all  the  striated  mus- 
cles of  Mammals  and  Birds.  It  is  generally  absent  from  unstriated 
muscle  except  that  of  the  rectum.  It  has  also  been  found  in  Mollusca 
in  certain  muscles  which  are  specially  active,  viz.,  those  which  work  the 
rasp-like  tongue. 

Derivatives  of  Haemoglobin. 

Haematin. — By  the  action  of  heat,  or  of  acids  or  alkalies  in  the 
jiresence  of  oxygen,  haemoglobin  can  be  split  up  into  a  substance  called 
Hcematin,  which  contains  all  the  iron  of  the  haemoglobin  from  which  it 
was  derived,  and  a  proteid  residue.  Of  the  latter  it  is  impossible  to  say 
more  than  that  it  probably  consists  of  one  or  more  bodies  of  the  globu- 
lin class.  If  there  be  no  oxygen  present,  instead  of  haematin  a  body 
called  haemochromogen  is  jiroduced,  which,  however,  will  speedily 
undergo  oxidation  into  hsematin. 

Haematin  is  a  dark  brownish  or  black  non-crystallizable  substance  of 
metallic  lustre.  Its  percentage  composition  is  C.  G4.30;  H.  5.50;  N. 
^.06;  Fe.  8.82;  0.  12.32;  which  gives  the  formula  Cgs,  H70,  Ng,  Fe2, 
Oio  (Hoppe-Seyler).  It  is  insoluble  in  water,  alcohol,  and  ether;  solu- 
ble in  the  caustic  alkalies;  soluble  with  difflculty  in  hot  alcohol  to  which 
is  added  sulphuric  acid.  The  iron  may  be  removed  from  haematin  by 
heating  it  with  fuming  hydrochloric  acid  to  160°  C.  (320°  F.),  and  a 
new  body,  haematoporphyrin,  the  so-called  iron-free  haematin,  is  pro- 
duced. Haematoporphyrin  (Ces,  H74,  Ng,  O12,  Hoppe-Seyler)  may  also  be 
obtained  by  adding  blood  to  strong  sulphuric  acid,  and  if  necessary 
filtering  the  fluid  through  asbestos.  It  forms  a  fine  crimson  solution, 
which  has  a  distinct  spectrum,  viz.,  a  dark  band  just  beyond  d,  and  a 
second  all  but  midway  d  and  e.  It  may  be  precipitated  from  its  acid 
solution  by  adding  water  or  by  neutralization,  and  when  redissolved 
in  alkalies  presents  four  bands,  a  pale  band  between  c  and  d,  a  second 
between  d  and  e,  nearer  d,  another  nearer  e,  and  a  fourth  occupying 
the  chief  part  of  the  space  between  h  and  f. 


THE    BLOOD.  l03 

Hcematin  in  acid  solution.— li  an  excess  of  acetic  acid  is  added  to 
blood,  and  the  solution  is  boiled,  the  color  alters  to  brown  from  decom- 
position of  hsemoglobin  and  the  setting  free  of  h^matin ;  by  shaking 
this  solution  with  ether,  a  solution  of  haematin  in  acid  solution  is  obtained. 
The  spectrum  of  the  ethereal  solution  (colored  plate)  shows  no  less  than 
four  absorption  bands,  viz.,  one  in  the  red  between  c  and  d,  one  faint 
and  narrow  close  to  d  and  then  two  broader  bands,  one  between  d  and 
E,  and  another  nearly  midway  between  h  and  f.  The  first  band  is  by 
far  the  most  distinct,  and  the  acid  aqueous  solution  of  haematin  shows 
it  plainly. 

licBmatin  in  alkaline  solution. — If  a  caustic  alkali  is  added  to  blood 
and  the  solution  is  boiled,  alkaline  hasmatin  is  produced,  and  the  solu- 
tion becomes  olive  green  in  color.  The  absorption  band  of  the  new 
compound  is  in  the  red,  near  to  d,  and  the  blue  end  of  the  spectrum  is 


Fig.  l;39.— Haematoidin  crystals.    (Frey.)  Fig.  140.— Hsemin  crystals.    (Frey.) 

absorbed  to  a  considerable  extent.  If  a  reducing  agent  be  added,  two 
bands  resembling  those  of  oxy-hgemoglobin,  but  nearer  to  the  blue,  ap- 
pear; this  is  the  sj)ectrum  of  reduced  hcematin,  or  haemochromogen. 
On  violently  shaking  the  reduced  hsematin  with  air  or  oxygen  the  two 
bands  are  rej^laced  by  the  single  band  of  alkaline  hfematin. 

Haematoidin. — This  substance  is  found  in  the  form  of  yellowish 
crystals  (fig.  139)  in  old  blood  extravasations  and  is  derived  from  the 
haemoglobin.  Their  crystalline  form  and  the  reaction  they  give  with 
fuming  nitric  acid  seem  to  show  them  to  be  closely  allied  to  Bilirubin, 
the  chief  coloring  matter  of  tlie  bile,  and  in  composition  they  are  prob- 
ably either  identical  or  isomeric  with  it. 

Haemin. — One  of  the  most  important  derivatives  of  haematin  is 
haemin.  It  is  usually  called  HydrocMorote  of  Hwmatin  (or  hydrochlor- 
ide), but  its  exact  chemical  composition  is  uncertain.  Its  formula  is 
said  to  be  C52H3„]S[.Fe03liCl,  and  it  contains  5.18  per  cent  of  chlorine, 
but  by  some  it  is  looked  upon  as  simply  crystallized  hcematin.  Al- 
though difficult  to  obtain  in  bulk,  a  specimen  may  be  easily  made  for 
the  microscope  in  the  following  way: — A  small  drop  of  dried  blood  is 
finely  powdered  with  a  few  crystals  of  common  salt  on  a  glass  slide  and 


164  HANDBOOK    OF    PHYSIOLOGY. 

spread  out;  a  cover  glass  is  then  placed  upon  it,  and  glacial  acetic  acid 
added  by  means  of  a  capillary  pipette.  The  blood  at  once  turns  of  a 
brownish  color.  The  slide  is  then  heated,  and  the  acid  mixture  evapo- 
rated to  dryness  at  a  high  temperature.  The  excess  of  salt  is  washed 
away  with  water  from  the  dried  residue,  and  the  specimen  may  then  be 
dried  and  mounted.  A  large  number  of  small,  dark,  reddish  black  crys- 
tals of  a  rhombic  shape,  sometimes  arranged  in  bundles,  will  be  seen  if 
the  slide  be  subjected  to  microscopic  examination  (fig.  140). 

The  formation  of  these  h^emin  crystals  is  of  great  interest  and  im- 
portance from  a  medico-legal  j)oiut  of  view,  as  it  constitutes  the  most 
certain  and  delicate  test  we  have  for  the  presence  of  blood  (not  of  ne- 
cessity the  blood  of  man)  in  a  stain  on  clothes,  etc.  It  exceeds  in  deli- 
cacy even  the  spectroscopic  test.  Compounds  similar  in  composition  to 
hsemin,  but  containing  hydrobromic  or  hydriodic  acid,  instead  of  hydro- 
chloric, may  be  also  readily  obtained. 

B.  The  Carbon  Dioxide  Gas  in  the  Blood.— Of  this  gas  in  the 
blood  part  exists  in  a  state  of  simple  solution  in  the  plasma,  and  is  given 
up  in  vacuo  (35.2  per  cent),  and  the  rest  in  a  state  of  weak  chemical 
-combination.      Of  the  latter,   part  is  in  loose   combination  Avith  the 

haemoglobin  and  part  is  more  firmly  united  with  the  alkalies,  possibly 
with  the  carbonates  in  the  form  of  bicarbonate.  The  amount  which  can 
be  absorbed  depends  on  the  alkalescence  of  the  blood. 

C.  The  Nitrogen  in  the  Blood. — The  whole  of  the  small  quantity 
of  the  nitrogen  contained  in  the  blood  is  simply  dissolved  in  the  fluid 
plasma. 

Chemical  Composition  of  the  Blood  in  Bulk. — Analyses  of  the 
blood  as  a  whole  differ  slightly,  but  the  following  table  may  be  taken  to 
represent  the  average  composition : 

Water 784 

Solids- 
Corpuscles        130 

Proteids  (of  serum) 70 

Fibrin  (of  clot) 2.2 

Fatty  matters  (of  serum)    .         .         .         .  1.4 

Inorganic  salts  (of  serum)      ....         6 

Gases,  kreatin,  urea    and    other    extractive     [    g  . 

matter,  glucose  and  accidental  substances      ) 

216 

1000 

Variations  in  the  Composition  of  healthy  Blood. 

The  conditions  which  appear  most  to  influence  the  composition  of 
the  blood  in  health  are  these:  Sex,  Pregnancy,  Age,  and  Temperament. 
The  composition  of  the  blood  is  also,  of  course,  much  influenced  by  diet. 

1.  Sex. — The  blood  of  men  differs  from  that  of  women,  chiefly  in. 


THE    BLOOD.  165 

being  of  somewhat  higher  specific  gravity,  from  its  containing  a  rela- 
tively larger  quantity  of  red  corpuscles. 

2.  Pregnancy. — The  blood  of  pregnant  women  is  rather  lower  than 
the  average  specific  gravity.  The  quantity  of  the  colorless  corpuscles  is 
increased  in  the  latter  months,  especially  in  primipara^;  it  is  also  claimed 
that  the  fibrin  is  increased  in  amount. 

3.  Age. — The  blood  of  the  foetus  is  very  rich  in  solid  matter,  and 
especially  in  colored  corpuscles;  and  this  condition,  gradually  diminish- 
ing, continues  for  some  weeks  after  birth.  The  quantity  of  solid  matter 
then  falls  during  childhood  below  the  average,  rises  during  adult  life, 
and  in  old  age  falls  again. 

4.  Temperament. — There  appears  to  be  a  relatively  large  quantity  of 
solid  matter  in  those  of  a  plethoric  or  sanguineous  temperament. 

5.  Diet. — Such  differences  in  the  composition  of  the  blood  as  are  due 
to  the  temporary  presence  of  various  matters  absorbed  with  the  food  and 
drink,  as  well  as  the  more  lasting  changes  which  must  result  from  gen- 
erous or  poor  diet  respectively,  need  be  here  only  referred  to. 

6.  Effects  of  Bleeding. — The  result  of  bleeding  is  to  diminish  the 
sjDecific  gravity  of  the  blood;  and  so  quickly,  that  in  a  single  venesection, 
the  portion  of  blood  last  drawn  has  often  a  less  specific  gravity  than  that 
of  the  blood  that  flowed  first.  This  is,  of  course,  due  to  absorption  of 
fluid  from  the  tissues  of  the  body.  The  physiological  import  of  this 
fact,  namely,  the  instant  absorption  of  liquid  from  the  tissues,  is  the 
same  as  that  of  the  intense  thirst  which  is  so  common  after  either  loss 
of  blood,  or  the  abstraction  from  it  of  watery  fluid,  as  in  cholera,  dia- 
betes, and  the  like. 

For  some  little  time  after  bleeding  the  want  of  colored  corpuscles  is 
well  marked,  but  with  this  exception,  no  considerable  alteration  seems 
to  be  produced  in  the  composition  of  the  blood  for  more  than  a  very 
short  time;  the  loss  of  the  other  constituents,  including  the  colorless 
corpuscles,  being  very  quickly  repaired. 

Variations  in  different  parts  of  the  Bodij. — The  composition  of  tlie 
blood,  as  might  be  expected,  is  found  to  vary  in  different  parts  of  the 
body.  Thus  arterial  blood  differs  from  venous;  and  although  its  com- 
position and  general  characters  are  uniform  throughout  the  whole  course 
of  the  systemic  arteries,  they  are  not  so  throughout  the  venous  system 
— the  blood  contained  in  some  veins  differing  remarkably  from  that  in 
others. 

Differences  between  Arterial  and  Venous  Blood. — The  differences  be- 
tween arterial  and  venous  blood  are  these : — 

(a.)  Arterial  blood  is  bright  red,  from  the  fact  that  almost  all  its 
hgemoglobin  is  combined  with  oyxgen  (Oxy-hgemoglobin,  or  scarlet  hae- 
moglobin), while  the  purple  tint  of  venous  blood  is  due  to  the  deoxida- 


166  HANDBOOK    OF    PHYSIOLOGY. 

tion  of  a  certain  quantity  of  its  oxy-haemoglobin,  and  its  consequent 
reduction  to  the  purple  variety  (Deoxidized,  or  purple  haemoglobin). 

(b.)  Arterial  blood  coagulates  somewhat  more  quickly. 

(c.)  Arterial  blood  contains  more  oxygen  than  venous,  and  less  car- 
bonic acid. 

Some  of  the  veins  contain  blood  which  differs  from  the  ordinary 
standard  considerably.  These  are  the  Portal,  the  Hepatic,  and  the 
Splenic  veins. 

Portal  vein. — The  blood  which  the  portal  vein  conveys  to  the  liver 
is  supplied  from  two  chief  sources;  namely,  from  the  gastric  and  mes- 
enteric veins,  which  contain  the  soluble  elements  of  food  absorbed  from 
the  stomach  and  intestines  during  digestion,  and  from  the  splenic  vein; 
it  must,  therefore,  combine  the  qualities  of  the  blood  from  each  of  these 
sources. 

The  blood  in  the  gastric  and  mesenteric  veins  will  vary  much  ac- 
cording to  the  stage  of  digestion  and  the  nature  of  the  food  taken,  and 
can  therefore  be  seldom  exactly  the  same.  Speaking  generally,  and 
without  considering  the  sngar,  and  other  soluble  matters  which  may 
have  been  absorbed  from  the  alimentary  canal,  this  blood  appears  to  be 
deficient  in  solid  matters,  especially  in  colored  corpuscles,  owing  to  di- 
lution by  the  quantity  of  water  absorbed,  to  contain  an  excess  of  proteid 
matter,  and  to  yield  a  less  tenacious  kind  of  fibrin  than  that  of  blood 
generally. 

The  blood  from  the  splenic  vein  is  generally  deficient  in  colored  cor- 
puscles, and  contains  an  unusually  large  proportion  of  proteids.  The 
fibrin  obtainable  from  the  blood  seems  to  vary  in  relative  amount,  but 
to  be  almost  always  above  the  average.  The  proportion  of  colorless  cor- 
puscles is  also  unusually  large.  The  whole  quantity  of  solid  matter  is 
decreased,  the  diminution  appearing  to  be  of  colored  corpuscles.  The 
plasma  is  said  to  be  colored  in  consequence  of  its  containing  dissolved 
haematin. 

The  blood  of  the  portal  vein,  combining  the  peculiarities  of  its  two 
factors,  the  splenic  and  mesenteric  venous  blood,  is  usually  of  lower 
specific  gravity  than  blood  generally,  is  more  watery,  contains  fewer 
colored  corpuscles,  more  proteids,  and  yields  a  less  firm  clot  than  that 
yielded  by  other  blood,  owing  to  the  deficient  tenacity  of  its  fibrin. 

Guarding  (by  ligature  of  the  portal  vein)  against  the  possibility  of 
an  error  in  the  analysis  from  regurgitation  of  hepatic  blood  into  the 
portal  vein,  recent  observers  have  determined  that  hepatic  venous  blood 
contains  less  water,  proteids,  and  salts  than  the  blood  of  the  portal 
veins;  but  that  it  yields  a  much  larger  amount  of  extractive  matter, 
in  which  is  one  constant  element,  namely,  grape-sugar,  which  is  found, 
whether  saccharine  or  farinaceous  matter  has  been  present  in  the  food 
or  not. 


THE    BLOOD.  IfJ? 

Development  of  the  Blood-Corpuscles. 

The  first  formed  blood-corpuscles  of  the  human  embryo  differ  much 
in  their  general  characters  from  those  which  belong  to  the  later  periods 
of  intra-uterine,  and  to  all  periods  of  extra-uterine  life.  Their  manner 
of  origin  is  at  first  very  simple. 

Surrounding  the  early  embryo  is  a  circular  area,  called  the  vascular 
area,  in  which  the  first  rudiments  of  the  blood-vessels  and  blood-corpus- 
cles are  developed.  Here  the  nucleated  embryonal  cells  of  the  meso- 
blast,  from  which  the  blood-vessels  and  corpuscles  are  to  be  formed, 
send  out  processes  in  various  directions,  and  these  joining  together, 
form  an  irregular  meshwork.  The  nuclei  increase  in  number,  and  col- 
lect chiefly  in  the  larger  masses  of  protoplasm,  but  partly  also  in  the 


^v%',, 


Fig.  141.— Part  of  the  network  of  developing  blood-vessels  in  the  vascular  area  of  a  guinea-pig. 
bL  blood-corpuscles  becoming  free  in  an  enlarged  and  liollowed-out  part  of  the  network  ;  a,  process 
or  protoplasm.    (E.  A.  Schafer.) 

processes.  It  appears  that  haemoglobin  then  makes  its  appearance  in  cer- 
tain of  these  nucleated  embryonal  cells,  Avhich  thus  become  the  earliest 
red  blood-corpuscles.  The  protoplasm  of  the  cells  and  their  branched 
net-work  in  Avhicli  these  corpuscles  lie  then  become  hollowed  out  into  a 
system  of  canals  inclosing  fluid,  in  which  the  red  nucleated  corpuscles 
float.  The  corpuscles  at  first  are  from  about.  ^-gVo  to  y-g'^-o-  of  an  inch 
(10,a  to  16/^-)  iu  diameter,  mostly  spherical,  and  with  granular  contents, 
and  a  well-marked  nucleus.  Their  nuclei,  which  are  about  -g-g^^g  of  an  inch 
(5/4  in  diameter,  are  central,  circular,  very  little  prominent  on  the  sur- 
faces of  the  corjniscles,  and  apparently  slightly  granular  or  tuberculated. 

The  corpuscles  then  strongly  resemble  the  colorless  corpuscles  of  the 
fully  developed  blood,  but  are  colored.  They  are  capable  of  amoeboid 
movement  and  multiply  by  division. 

AVhen,  in  the  progress  of  embryonic  development,  the  liver  begins  to 
be  formed,  the  multiplication  of  blood-cells  in  the  whole  mass  of  blood 
ceases,  and  new  blood-cells  are  produced  by  this  organ,  and  also  by  the 


168  HANDBOOK    OF    PHYSIOLOGY. 

spleen.  These  are  at  first  colorless  and  nucleated,  but  afterward  ac- 
quire the  ordinary  blood-tinge,  and  resemble  very  much  those  of  the  first 
set.  They  also  multiply  by  division.  About  this  time  the  bone  marrow 
also  begins  to  form  red  corpuscles,  though  at  first  in  small  amounts 
only.  This  function  develops  rapidly,  however,  so  that  at  birth  the 
marrow  represents  the  chief  seat  of  production  of  the  red  cells.  Never- 
theless, nucleated  red  cells  are  usually  found  at  birth,  sometimes  in  con- 
siderable quantities,  in  the  liver,  and,  less  often,  the  spleen.  Non- 
nucleated  red  cells  begin  to  appear  soon  after  the  first  month  of  foetal 
life,  and  gradually  increase,  so  that  at  the  fourth  month  they  form  one- 
fourth  of  the  whole  amount  of  colored  corpuscles;  at  the  end  of  foetal  life 
they  almost  completely  replace  the  nucleated  cells.  In  late  foetal  life 
the  red  cells  are  formed  in  almost  the  same  way  as  in  extra-uterine  life. 

Various  theories  have  prevailed  as  to  the  mode  of  origin  of  the  non- 
nucleated  colored  corpuscles.  For  a  time  it  was  thought  that  they  were 
of  endoglobular  origin,  and  merely  fragments  of  some  original  cell,  be- 
ing produced  by  subdivision  of  the  cell  body  itself.  This  theory  easily 
accounted  for  the  absence  of  the  nuclei,  but  it  has  not  been  supported 
by  recent  investigations.     At  present  it  is  the  general  belief  that  the 


^        ^._-'V 


"  '>m 


n-  i 


142,  143. 

FiK  14'^.— MultipUcation  of  the  nucleated  red  corpuscles.  Marrow  of  young  kitten  after 
bleeding,  showing  above  karyokinetic  division  of  erythroblast,  and  below  the  formation  of 
mature  from  immature  erythrocysts.     (Adapted  from  Howell.) 

Fig.  143  — Sliows  the  way  in  wliich  the  nucleus  escapes  from  the  nucleated  red  corpuscles. 
1,  S,  3,  4,  represent  different  stages  of  the  extrusion  noticed  upon  the  living  corpuscles,  a, 
Specimen  from  the  circulating  blood  of  an  adult  cat,  bled  four  times;  6,  specimen  from  the  cir- 
culating blood  of  a  kitten  forty  days  old,  bled  twice;  c,  specimens  from  the  blood  of  a  foetal  cat, 
9  cm.  long.  Otlieis  from  the  marrow  of  an  adult  cat,  two  of  the  figures  showing  the  granules 
present  in  the  corpuscles  which  have  been  interpreted  erroneously  as  a  sign  of  the  disintegration 
of  the  nucleus.     tAfter  Howell.) 

non-nucleated  cells  are  derived  from  nucleated  cells  by  a  process  of  mi- 
totic division,  and  further  that  their  nuclei  gradually  shrink  or  fade  and 
are  then  extruded.  Extrusion  undoubtedly  occurs  with  great  frequency, 
but  the  use  of  some  of  the  more  recent  stains  seems  to  prove  that  there 


THE    BLOOD.  169 

are  traces  of  nuclear  material  in  the  non-nucleated  corpuscles.  Owing 
to  these  facts  and  other  recent  investigations,  Maxiniow  asserts  that 
while  the  greater  part  of  the  nucleus  is  extruded,  still  a  small  portion 
usually  remains  in  a  finely  granular  form  and  gives  a  basic  staining 
quality  to  the  centres,  especially  of  tlie  young  red  cells. 

Origin  of  the  Mature  Colored  Corpuscles. — It  has  already 
been  shown  that  during  uterine  life  the  marrow  gradually  assumes  more 
and  more  completely  the  function  of  forming  red  cells.  This  function 
prevails  after  birth,  and  most  authorities  now  regard  the  red  marrow  as 
the  exclusive  seat,  under  normal  conditions,  of  the'  production  of  red 
corpuscles.  The  original  cell,  or  erythroblast,  is  generally  considered  to 
be  a  large  colorless  cell  which  is  devoid  of  haemoglobin,  is  larger  than 
the  ordinary  red  cell,  and  has  a  single  nucleus  but  no  nucleolus;  it 
differs  but  very  slightly  from  the  original  mesoblastic  cell. 

By  mitotic  division  of  these  original  cells  there  are  derived  several 
series  of  cells  which  approach,  more  and  more  completely,  the  type  of 
nucleated  red  corpuscles,   becoming  rich  in  hsemoglobin.     The  nucleus 


• 


Fig.  144.— Colored  nucleated  corpuscles,  from  the  red  marrow  of  the  guinea-pig.     (E.  A.  Schafer. ) 

is  then  extruded  (or  partly  extruded  and  partly  broken  up)  and  the 
normtil  non-nucleated  red  corpuscle  results.  A  few  authorities,  how- 
ever, in  tracing  the  red  cells  back  to  colorless  cells,  think  that  all  the 
lymphoid  tissues  are  also  jDrobable  sources  of  the  erythroblasts.  In  in- 
fancy and  early  childhood  the  red  marrow,  which  produces  the  colored 
corpuscles,  is  found  in  large  amount  in  the  cavities  of  almost  all  the 
bones.  In  adult  life  it  is  normally  confined  to  the  ribs,  flat  bones, 
vertebra,  and  upper  and  lower  thirds  of  the  long  bones.  In  imtliological 
conditions  it  has  been  found  that  the  spleen  in  the  adult,  or  both  the 
spleen  and  the  liver  in  infancy  and  early  childhood,  can  resume  the 
function  of  producing  red  corpuscles. 

Without  doubt,  the  red  corpuscles  have,  like  all  other  parts  of  the 
organism,  a  tolerably  definite  term  of  existence,  and  in  a  like  manner 
die  and  waste  away  when  the  portion  of  work  allotted  to  tliem  has  been 
performed.  Neither  the  length  of  their  life,  however,  nor  the  fashion 
of  their  decay  has  been  yet  clearly  made  out.  It  is  generally  believed 
that  a  certain  number  of  the  colored  corpuscles  undergo  disintegration 
in  the  spleen;  and  indeed  corpuscles  in  various  degrees  of  degeneration 
have  been  observed  in  that  organ. 

Origin  of  the  Colorless  Corpuscles.— In  foetal  life  the  white 
corpuscles  are  not  found  in  the  blood  until  the  vascular  system  has  been 


170  HANDBOOK    OF    PHYSIOLOGY. 

Tcry  extensively  developed,  long  after  the  appearance  of  red  cells;  the 
exact  time  of  their  appearance,  however,  has  not  yet  been  fully  deter- 
mined. It  is  now  quite  generally  believed  that  in  the  foetus  both  red 
and  white  cells  are  derived  from  a  common  origin,  and  that  they  become 
differentiated  in  the  course  of  development.  The  earliest  known  pro- 
genitors of  the  leucocytes  are  the  primary  wandering  cells  of  mesodermal 
origin,  which  are  found  chiefly  in  the  connective  tissues,  thus  lying  out- 
side of  the  vessels.  Gathering  in  groups,  partly  at  the  sites  of  the 
future  lymph  nodes,  but  chiefly  in  the  embryonal  liver,  these  wandering 
cells  pass  through  several  generations  of  mitotic  division,  and  thus 
gradually  assume  the  type  of  leucocytes.  According  to  a  few  observers 
the  leucocytes  are  also  formed  in  the  circulating  blood  and  lymph  by 
amitotic,  less  frequently  by  mitotic,  division.  Later  on  in  foetal  life 
the  function  of  forming  leucocytes  is  gradually  transferred  from  the 
liver  to  the  lymphoid  and  adenoid  tissues,  i.e.,  the  lymph  nodes,  spleen, 
marrow,  and  thymus. 

In  adult  life,  under  normal  conditions,  the  leucocytes  are  only 
formed  in  the  lymphoid  tissues,  including  the  lymph  nodes,  spleen  and 
marrow.  The  process  is  also  one  of  mitotic  division  (a  few  authorities 
claim  that  it  is  amitotic),  and  the  resulting  cells  pass  into  the  circulation 
by  way  of  the  thoracic  duct. 

Uses  of  the  Blood, 

1.  To  be  a  medium  for  the  reception  and  storing  of  matter,  e.g.y 
oxygen  and  digested  food  material,  from  the  outer  world,  and  for  its 
conveyance  to  all  parts  of  the  body. 

2.  To  be  a  source  whence  the  various  tissues  of  the  body  may  take 
the  materials  necessary  for  their  nutrition  and  maintenance;  and  whence 
the  secreting  organs  may  take  the  constituents  of  their  various  secre- 
tions. 

3.  To  be  a  medium  for  the  absorption  of  refuse  matters  from  all  the 
tissues,  and  for  their  conveyance  to  those  organs  whose  function  it  is  t« 
separate  them  and  cast  them  out  of  the  body. 

4.  To  warm  and  moisten  all  parts  of  the  body. 


CHAPTER  TI. 

THE  CIRCULATION   OF   THE  BLOOD. 

The  blood  is  made  to  circulate  within  the  system  of  closed  tubes  in 
which  it  is  contained  by  means  of  the  alternate  contraction  and  relaxa- 
tion of  the  heart.  The  heart  is  a  hollow  muscular  organ  consisting  of 
four  chambers,  two  auricles  and  two  ventricles,  arranged  in  pairs.     On 


Pulmonary  artery 


Superior  cava  or  vein 
from  head  and  neck 

Right  auricle 
Inferior  vena  cava 


Right  ventricle   ^ 


Portal  circulatioD  __ 


Second  renal 
circulation 


Pulmonary 
capillaries 


Pulmonary  veins 

Aorta 

Arteries  to  head  and 
neck 


Left  auricle 


Left  ventricle 


Gastric  and  intestinal 
vessels 


First  renal  circulation 


Systemic  capillaries 


Fig.  145.— Diagram  of  the  circulation. 

the  right  and  left  sides  is  an  auricle  Joined  to  and  communicating  with 
a  ventricle,  but  the  chambers  on  the  right  side  do  not  directly  commu- 
nicate with  those  on  the  left  side.  The  blood  is  conveyed  away  from 
the  left  side  of  the  heart  (as  in  the  diagram,  fig.  145)  by  the  arteries, 
and  returned  to  the  right  side  of  the  heart  by  the  veins,  the  arteries  and 
veins  being  continuous  with  each  other  at  one  end  by  means  of  the 
heart,  and  at  the  other  by  a  fine  network  of  vessels  called  the  capillaries. 
From  the  right  side  of  the  heart  the  blood  passes  to  the  lungs 

171 


1.72  HANDBOOK    OF    PHYSIOLOGY. 

tlirougli  the  pulmonary  artery,  then  through  the  pulmonary  capillaries, 
and  through  the  pulmonary  veins  to  the  left  side  of  the  heart  (Fig.  145). 
Thus  there  are  two  circulations  through  which  the  blood  must  pass;  the 
one,  a  shorter  circuit  from  the  right  side  of  the  heart  to  the  lungs  and 
back  again  to  the  left  side  of  the  heart;  the  other  and  larger  circuit, 
from  the  left  side  of  the  heart  to  all  parts  of  the  body  and  back  again  to 
the  right  side;  strictly  speaking,  however,  there  is  but  one  complete 
circulation,  which  may  be  diagrammatically  represented  by  a  double 
loop,  as  in  fig.  145,  in  which  there  is  one  continuous  stream,  the  whole 
of  which  must,  at  one  part  of  its  course,  pass  through  the  lungs.  Sub- 
ordinate to  the  circulations  through  the  lungs  and  through  the  system 
generally,  respectively  named  the  Pulmonary  and  Systemic,  it  will  be 
noticed  also  in  the  same  figure  that  a  portion  of  the  stream  of  blood 
having  been  diverted  once  into  the  capillaries  of  the  intestinal  canal, 
and  some  other  organs,  and  gathered  up  again  into  a  single  stream,  is  a 
second  time  divided  in  its  passage  through  the  liver,  before  it  finally 
reaches  the  heart  and  completes  a  revolution.  This  subordinate  stream 
through  the  liver  is  called  the  Portal  circulation.  A  somewhat  similar 
accessory  circulation  is  that  through  the  kidneys,  called  the  Renal  cir- 
culation. Such  then  is  the  outline  of  the  course  of  the  circulation. 
The  problems  in  connection  with  its  maintenance  cannot  be  well  under- 
stood without  a  more  detailed  knowledge  of  the  structure  and  mode  of 
action  of  the  heart,  and  of  the  structure  and  properties  of  the  blood- 
vessels.    These  subjacts  will  now  be  considered  seriatim. 

The  Heart. 

The  heart  is  contained  in  the  chest  or  thorax,  and  lies  between  the 
right  and  left  lungs  (fig.  146),  inclosed  in  a  membranous  sac — the  Peri- 
cardium, which  is  made  up  of  two  distinct  parts,  an  external  fibrous 
membrane,  composed  of  closely  interlacing  fibres,  which  has  its  base 
attached  to  the  diaphragm  or  midriff,  the  great  muscle  which  forms  the 
floor  of  the  chest  and  divides  it  from  the  abdomen — both  to  the  central 
tendon  and  to  the  adjoining  muscular  fibres,  while  the  smaller  and 
upper  end  is  lost  on  the  large  blood-vessels  by  mingling  its  fibres  with 
that  of  their  external  coats;  and  an  internal  serous  layer,  which  not  only 
lines  the  fibrous  sac,  but  also  is  reflected  on  to  the  heart,  which  it  com- 
pletely invests.  The  part  which  lines  the  fibrous  membrane  is  called 
the  parietal  layer,  and  that  inclosing  the  heart,  the  visceral  layer  or  epi- 
carchum,  and  these  being  continuous  for  a  short  distance  along  the  great 
vessels  of  the  base  of  the  heart,  form  a  closed  sac,  the  cavity  of  whicli  in 
health  contains  just  enough  fluid  to  lubricate  tl^e  two  surfaces,  and  thus 
to  enable  them  to  glide  smoothly  over  each  other  during  the  movements 
of  the  heart.  The  vessels  passing  in  and  out  of  the  heart  receive  in- 
vestments from  this  sac  to  a  greater  or  less  degree. 


THE    CIRCULATION"    OF   THE    BLOOD. 


173 


The  heart  is  situated  in  the  chest  behind  the  sternum  and  costal 
cartilages,  being  placed  obliquely  from  right  to  left,  quite  two-thirds  of 
it  being  to  the  left  of  the  mid-sternal  line.  It  is  of  pyramidal  shape, 
with  the  apex  pointing  downward,  outward,  and  toward  the  left,  and  the 
base  backward,  inward,  and  toward  the  right.  It  rests  upon  the  dia- 
phragm, and  its  pointed  apex,  formed  exclusively  of  the  left  side  of  the 
heart,  is  in  contact  with  the  chest  wall,  and  during  life  beats  against  it 
at  a  point  called  the  cq^ex  beat,  situated  in  the  fifth  left  intercostal 
space,  and  about  three  inches  from  the  mid-sternal  line.  The  heart  is, 
as  it  were,  suspended  in  the  chest  by  the  large  vessels  which  proceed 
from  its  base,  but,  excepting  at  this  part,  the  organ  itself  lies  free  within 
the  sac  of  the  pericardium.     The  part  which  rests  upon  the  diaphragm 


Larynx 
Trachea 


Aort; 


7cLv  My 


Pulmonarj-  artery 


Left  lung 


Fig.  146. — View  of  heart  and  lungs  in  situ.  The  front  portion  of  the  chest-wall,  and  the  outer 
or  parietal  layers  of  the  pleurae  and  pericardium  have  been  I'emoved.  The  lungs  are  partly  col- 
lapsed. 

is  flattened,  and  is  known  as  the  posterior  surface,  while  the  free  upper 
part  is  called  the  anterior  surface.  The  margin  toward  the  left  is  thick 
and  obtuse,  while  the  lower  margin  toward  the  right  is  thin  and  acute. 

On  examination  of  the  external  surface  the  division  of  the  heart  into 
parts  which  correspond  to  the  chambers  inside  of  it  may  be  traced,  for 
a  deep  transverse  groove  called  the  auriculo-ventrioidar  groove  divides 
the  auricles  which  form  the  base  of  the  heart  from  the  ventricles  which 
form  the  remainder,  including  the  apex,  the  ventricular  portion  being 
by  far  the  greater;  and,  again,  the  inter-ventricular  groove  runs  between 
the  ventricles  both  front  and  back,  and  separates  the  one  from  the  other. 
The  anterior  groove  is  nearer  the  left  margin  and  the  posterior  nearer 
the  right,  as  the  front  surface  of  the  heart  is  made  up  chiefly  of  the 
right  ventricle  and  the  posterior  surface  of  the  left  ventricle.     In  the 


174 


HANDBOOK    OF    PHYSIOLOGY. 


furrows  or  grooves  run  the  coronary  vessels,  which  supply  the  tissue  of 
the  heart  with  blood,  as  well  as  nerves  and  lymphatics  imbedded  in 
more  or  less  fatty  material. 

The  Chambers  of  the  Heart. — The  interior  of  the  heart  is  divided 
by  a  longitudinal  partition  in  such  a  manner  as  to  form  two  chief  cham- 
bers  or  cavities — right  and  left.     Each  of  these  chambers  is  again  sub- 


Fig.  147.— The  nght  auricle  and  ventricle  opened,  and  a  part  of  their  right  and  anterior  walls 
removed,  so  as  to  show  their  interior.  ^. — 1,  Superior  vena  cava  ;  3,  inferior  veua  cava  ;  2',  hepatic 
veins  cut  short ;  .3,  right  auricle  ;  3',  placed  in  the  fossa  ovalis,  below  which  is  the  Eustachian  valve  ; 
3",  is  placed  close  to  the  aperture  of  the  coronary  vein  ;  +,  +,  placed  in  the  auriculo- ventricular 
groove,  where  a  narrow  portion  of  the  adjacent  walls  of  the  auricle  and  ventricle  has  been  preserved; 
4,  4,  cavity  of  the  right  ventricle,  the  upper  figure  is  immediately  below  the  semilunar  valves  ;  4', 
large  columna  carnea  or  musculus  papillaris  ;  5,  .5',  .5",  tricuspid  valve ;  6,  placed  in  the  interior  of 
the  pulmonary  artery,  a  part  of  the  anterior  wall  of  that  vessel  having  been  removed,  and  a  narrow 
portion  of  it  preserved  at  its  commencement,  where  the  semilunar  valves  are  attached  ;  7,  concavity 
of  the  aortic  arch  close  to  the  cord  of  the  ductus  arteriosus  ;  8,  ascending  part  or  sinus  of  the  arch 
covered  at  its  commencement  by  the  auricular  appenchx  and  pulmonary  artery  ;  9,  placed  between 
the  innominate  and  left  carotid  arteries  ;  10,  appendix  of  the  left  auricle  ;  11,  11,  outside  of  the  left 
ventricle,  the  lower  figure  near  the  apex.    (Allen  Thomson.) 


divided  transversely  into  an  upper  and  a  lower  portion,  called  respect- 
ively, as  already  incidentally  mentioned,  auricle  and  ventricle,  which 
freely  communicate  one  with  the  other;  the  aperture  of  communication, 
however,  is  guarded  by  valves,  so  disposed  as  to  allow  blood  to  pass 
freely  from  the  auricle  into  the  ventricle,  but  not  in  the  opposite  direc- 


THE   CIRCL'LATION    OF   THE    BLOOD. 


175 


tiou.     There  are  thus  four  cavities  in  the  heart — the  auricle  and  ventri- 
cle of  one  side  being  quite  separate  from  those  of  the  other  (fig.  147). 

Right  Aid'ide. — The  right  auricle  is  situated  at  the  right  part  of  the 
base  of  the  heart  as  viewed  from  the  front.  It  is  a  thin-walled  cavity 
of  more  or  less  quadrilateral  shape,  prolonged  at  one  corner  into  a 


Fij.  148.— The  left  auricle  and  ventricle  opened  and  a  part  of  their  anterior  and  left  walls  re- 
moved. Yi  — The  pulmonary  artery  has  been  divided  at  its  conimencenient ;  the  opening  into  the 
left  ventricle  is  carried  a  short  distance  into  the  aorta  between  two  of  the  segments  of  the  semilunar 
valves  ;  and  the  left  part  of  the  auricle  with  its  appendix  has  been  removed.  The  riglit  auricle  is 
out  of  view.  1,  The  two  right  pulmonary  veins  cut  snort ;  their  oiienings  are  seen  within  the  auricle; 
1',  placed  within  the  cavit.v  of  the  auricle  on  the  left  side  of  the  septum  ami  on  the  part  which  forms 
the  remains  of  the  valve  of  the  foramen  ovale,  of  which  the  cresceutic  fold  is  seen  toward  tlie  left 
band  of  1' ;  3,  a  narrow  portion  of  the  wall  of  the  auiicleand  ventricle  preserved  round  the  auriculo- 
ventricular  orifice  ;  3,  3',  the  cut  surface  of  the  walls  of  the  ventricle,  seen  to  become  very  much 
thinner  towards  3',  at  the  apex  :  4,  a  small  part  of  the  anterior  wall  of  the  left  ventricle  which  has 
been  preserved  with  the  principal  anterior  columna  carnea  or  nnisculus  papillaris  attached  to  it ; 
5,  .5,  musciili  papillares  ;  .5',  the  left  side  of  the  septum,  between  tlie  two  ventricles,  within  thecavity 
of  the  left  ventricle  ;  (i,  G',  the  mitral  valve  ;  7,  placed  in  the  interior  of  the  aorta  near  its  commence- 
ment and  above  the  three  segments  of  its  semilunar  valve  whicli  are  hanging  loosely  together  ;  7', 
the  exterior  of  the  great  aortic  sinus  ;  8,  the  root  of  the  pulmouarv  artery  and  its  sen'iilunar  valves  ; 
8',  the  separated  portion  of  the  pulmonary  artery  lemaiiiiiig  attached  tothe  aorta  by  (1,  the  cord  of 
the  ductus  arteriosus  ;  10,  the  arteries  rising  from  the  summit  of  the  aortic  arch.    (Allen  Thomson.) 


tongue-shaped  portion,  the  right  auricular  appendix,  which  slightly  over- 
laps the  exit  of  the  great  artery,  the  aorta,  from  the  heart. 

The  interior  is  smooth,  being  lined  with  the  general  lining  of  the 


176  HANDBOOK    OF    PHYSIOLOGY. 

heart,  the  endocardium,  and  into  it  open  the  superior  and  inferior  venae 
cavae,  or  great  veins,  which  convey  the  blood  from  all  parts  of  the  body 
to  the  heart.  The  former  is  directed  downward  and  forward,  the  latter 
upward  and  inward;  between  the  entrances  of  these  vessels  is  a  slight 
tubercle  called  tubercle  of  Lower.  The  opening  of  the  inferior  cava  is 
protected  and  partly  covered  by  a  membrane  called  the  EustacMan 
valve.  In  the  posterior  wall  of  the  auricle  is  a  slight  depression  called 
fhe  fossa  ovalis,  which  corresponds  to  an  opening  between  the  right  and 
left  auricles  which  exists  in  foetal  life.  The  right  auricular  appendix  is 
of  oval  form,  and  admits  three  fingers.  Various  veins,  including  the 
coronary  sinus,  or  the  dilated  portion  of  the  right  coronary  vein,  open 
into  this  chamber.  In  the  apjjendix  are  closely  set  elevations  of  the 
muscular  tissue  covered  with  endocardium,  and  on  the  anterior  wall  of 


Fig.  149. — Transverse  section  of  bullock's  heart  in  a  state  of  cadaveric  rigidity.    (Dalton.) 
6,  Cavity  of  riglit  ventricle,    a,  Cavity  of  left  ventricle. 

the  auricle  are  similar  elevations  arranged  parallel  to  one  another,  called 
musculi  fectinati. 

Right  Ventricle. — The  right  ventricle  occupies  the  chief  part  of  the 
anterior  surface  of  the  heart,  as  well  as  a  small  part  of  the  posterior 
surface:  it  forms  the  right  margin  of  the  heart.  It  takes  no  part  in 
the  formation  of  the  apex.  On  section  its  cavity,  in  consequence  of  the 
encroachment  upon  it  of  the  septum  ventriculorum,  is  semilunar  or 
crescentic  (fig.  149);  into  it  are  two  openings,  the  auriculo-ventricular 
at  the  base  and  the  opening  of  the  pulmonary  artery  also  at  the  base, 
but  more  to  the  left;  the  part  of  the  ventricle  leading  to  it  is  called  the. 
conus  arteriosus  or  infundihulum  ;  both  orifices  are  guarded  by  valves, 
the  former  called  tricuspid  and  the  latter  semilunar  or  sigmoid.  In 
this  ventricle  are  also  the  projections  of  the  muscular  tissue  called  co- 
lumncB  carnem  (described  at  length  p.  179). 

Left  Auricle. — The  left  auricle  is  situated  at  the  left  and  posterior 
part  of  the  base  of  the  heart,  and  is  best  seen  from  behind.  It  is  quad- 
rilateral, and  receives  on  either  side  two  pulmonary  veins.  The  auricu- 
lar appendix  is  the  only  part  of  the  auricle  seen  from  the  front,  and 
corresponds  with  that  on  the  right  side,  but  is  thicker,  and  the  interior 
is  more  smooth.  The  left  auricle  is  only  slightly  thicker  than  the  right. 
The  left  auriculo-ventricular  orifice  is  oval,  and  a  little  smaller  than 


THE    CIRCULATION    OF    THE    BLOOD. 


177 


that  on  the  right  side  of  the  heart.  There  is  a  slight  vestige  of  the 
foramen  between  the  auricles,  which  exists  in  fcetal  life,  on  the  septum 
between  them. 

Left  Venlricle. — Though  taking  part  to  a  comparatively  slight  ex- 
tent in  the  anterior  surface,  the  left  ventricle  occupies  the  chief  part  of 
the  posterior  surface.  In  it  are  two  openings  very  close  together,  viz. 
tlie  auriculo-ventricular  and  the  aortic,  guarded  by  the  valves  corre- 
sf)onding  to  those  of  the  riglit  side  of  the  heart,  viz.  the  hicus2^id  or 
mitral  and  the  semilunar  or  sigmoid.  The  first  opening  is  at  the  left 
and  back  part  of  the  base  of  the  ventricle,  and  the  aortic  in  front  and 
toward  the  right.  In  this  ventricle,  as  in  the  right,  are  the  columnae 
carneae,  which  are  smaller  but  more  closely  reticulated.  They  are  chiefly 
found  near  the  apex  and  along  the  j)Osterior  Avail.  They  will  be  again 
referred  to  in  the  description  of  the  valves.     The  walls  of  the  left  ven- 


Fig.  150.— Network  of  muscular  fibres  from  the  heart  of  a  pig.    The  nut-lei  of  the  muscle-corpus- 
cles are  well  shown.     X  450.      (Klein  and  Noble  Smith.) 

tricle,  which  are  nearly  half  an  inch  in  thickness,  are,  with  the  excep- 
tion of  the  apex,  twice  or  three  times  as  thick  as  those  of  the  right. 

Capacity  of  the  Chambers. — During  life  each  ventricle  is  capable 
of  containing  about  four  to  six  ounces  (about  ISO  grms.)  of  blood.  The 
capacity  of  the  auricles  after  death  is  rather  less  than  that  of  the  ven- 
tricles: the  thickness  of  their  walls  is  considerably  less.  The  latter 
condition  is  adapted  to  the  small  amount  of  force  which  the  auricles 
require  in  order  to  empty  themselves  into  their  adjoining  ventricles; 
the  former  to  the  circumstance  of  the  ventricles  being  partly  filled  with 
blood  before  the  auricles  contract. 

Size  and  Weight  of  the  Heart. — The  heart  is  about  5  inches 
long  (about  12.6  cm.),  3.]  inches  (S  cm.)  greatest  width,  and  2^  inches 
(6.3  cm.  )  in  its  extreme  thickness.  The  average  weight  of  the  heart  in 
the  adult  is  from  9  to  10  ounces  (about  300  grms.);  its  weight  gradually 
increasing  througliout  life  till  middle  age;  it  diminishes  in  old  age. 

Structure. — The  walls  of  the  heart  are  constructed  almost  entirely 
of  layers  of  muscular  fibres;  but  a  ring  of  connective  tissue,  to  which 
some  of  the  muscular  fibres  are  attached,  is  inserted  between  each  auri- 
cle and  ventricle,  and  forms  the  boundary  of  the  auriculo-ventricular 

12 


178  HANDBOOK    OF    PHYSIOLOGY. 

opening.  Fibrous  tissue  also  exists  at  the  origins  of  the  pulmonary 
artery  and  aorta. 

The  muscular  fibres  of  each  auricle  are  in  part  continuous  with  those 
of  the  other,  and  partly  separate;  and  the  same  remark  holds  true  for 
the  ventricles.  The  fibres  of  the  auricles  are,  however,  quite  separate 
from  those  of  the  ventricles,  the  bond  of  connection  between  them 
being  only  the  fibrous  tissue  of  the  auriculo-ventricular  openings. 

The  minute  structure  of  the  striated  muscular  fibres  of  the  heart 
has  been  already  described  (p.  88). 

Endocardium. — As  the  heart  is  clothed  on  the  outside  by  a  thin 
transparent  layer  of  pericardium,  so  its  cavities  are  lined  by  a  smooth 


Fig.  151.— Diagram  of  the  circulation  tlirough  the  heart  (Dalton). 

and  shining  membrane,  or  endocardium,  which-^is  directly  continuous 
with  the  internal  lining  of  the  arteries  and  veins.  The  endocardium  is 
composed  of  connective  tissue  with  a  large  admixture  of  elastic  fibres; 
and  on  its  inner  surface  is  laid  down  a  single  tesselated  layer  of  flat- 
tened endothelial  cells.  Here  and  there  unstriped  muscular  fibres  are 
sometimes  found  in  the  tissue  of  the  endocardium. 

Valves. — The  arrangement  of  the  heart's  valves  is  such  that  the 
blood  can  pass  only  in  one  direction  (fig.  151). 

The  tricuspid  YalYe  (5,  fig.  147)  presents  three  principal  cusps  or  sub- 
divisions, and  the  mitral  or  bicicspid  valve  has  tivo  such  portions  (6,  fig. 
148).  But  in  both  valves  there  is  between  each  two  principal  portions 
a  smaller  one;  so  that  more  properly,  the  tricuspid  may  be  described  as 
consisting  of  six,  and  the  mitral  of  four,  portions.  Each  portion  is  of 
triangular  form.     Its  base  is  continuous  with  the  bases  of  the  neighbor- 


THE    CIRCULATION    OF   THE    BLOOD.  179 

ing  portions,  so  as  to  form  an  annular  membrane  around  the  auriculo- 
ventricular  opening,  and  is  fixed  to  a  tendinous  ring  which  encircles  the 
orifice  between  the  auricle  and  ventricle  and  receives  the  insertions  of 
the  muscular  fibres  of  both.  In  each  principal  cusjd  may  be  distin- 
guished a  central  part,  extending  from  base  to  apex,  and  including  about 
half  its  width.  It  is  thicker  and  much  tougher  than  the  border  pieces 
or  edges. 

AVhile  the  bases  of  the  cusps  of  the  valves  are  fixed  to  the  tendinous 
rings,  their  ventricular  surface  and  borders  are  fastened  by  slender  ten- 
dinous fibres,  the  cliordcB  tendinea>,  to  the  internal  surface  of  the  walls  of 
the  ventricles,  the  muscular  fibres  of  which  project  into  the  ventricular 
cavity  in  the  form  of  bundles  or  columns — the  columnce  carnece.  These 
columns  are  not  all  alike,  for  while  some  are  attached  along  their  whole 
length  on  one  side,  and  by  their  extremities,  others  are  attached  only 
by  their  extremities;  and  a  third  set,  to  which  the  name  musculi papil- 
lares  has  been  given,  are  attached  to  the  wall  of  the  ventricle  by  one 
extremity  onl}^,  the  other  projecting,  papilla-like,  into  the  cavity  of  the 
ventricle  (4,  fig.  148),  and  having  attached  to  it  chordaj  tendine^e.  Of 
the  tendinous  cords,  besides  those  which  pass  from  the  walls  of  the 
ventricle  and  the  musculi  papillares  to  the  margins  of  the  valves,  there 
are  some  of  especial  strength,  which  pass  from  the  same  parts  to  the 
edges  of  the  middle  and  thicker  portions  of  the  cusps  before  referred  to. 
The  ends  of  these  cords  are  spread  out  in  the  substance  of  the  valve, 
giving  its  middle  piece  its  peculiar  strength  and  toughness;  and  from 
the  sides  numerous  other  more  slender  and  branching  cords  are  given 
off,  which  are  attached  all  over  the  ventricular  surface  of  the  adjacent 
border-pieces  of  the  principal  portions  of  the  valves,  as  well  as  to  those 
smaller  portions  which  have  been  mentioned  as  lying  between  each  two 
principal  ones.  Moreover,  the  musculi  papillares  are  so  placed  that, 
from  the  summit  of  each,  tendinous  cords  proceed  to  the  adjacent  halves 
of  two  of  the  principal  divisions,  and  to  one  intermediate  or  smaller 
division,  of  the  valve. 

The  preceding  description  applies  equally  to  the  mitral  and  tricus- 
pid valve;  but  it  should  be  added  that  the  mitral  is  considerably  thicker 
and  stronger  than  the  tricuspid,  in  accordance  with  the  greater  force 
which  it  is  called  upon  to  resist. 

The  semilunar  valves  guard  the  orifices  of  the  pulmonary  artery  and 
of  the  aorta.  They  are  nearly  alike  on  both  sides  of  the  heart;  but  the 
aortic  valves  are  altogether  thicker  and  more  strongly  constructed  than 
the  pulmonary  valves,  in  accordance  Avith  the  greater  pressure  which 
they  have  to  withstand.  Each  valve  consists  of  three  parts  which  are  of 
semilunar  shape,  the  convex  margin  of  each  being  attached  to  a  fibrous 
ring  at  the  place  of  junction  of  the  artery  to  the  ventricle,  and  the 
concave  or  nearly  straight  border  being  free,  so  as  to  form  a  little  pouch 


180  HANDBOOK    OF    PHYSIOLOGY. 

like  a  watch-pocket  {7,  fig.  148).  In  the  centre  of  the  free  edge  of  the 
pouch,  which  contains  a  fine  cord  of  fibrous  tissue,  is  a  small  fibrous 
nodule,  the  corpiis  Arantii,  and  from  this  and  from  the  attached  border 
fine  fibres  extend  into  every  part  of  the  mid  substance  of  the  valve, 
except  a  small  lunated  space  just  within  the  free  edge,  on  each  side  of 
the  corpus  Arantii.  Here  the  valve  is  thinnest,  and  composed  of  little 
more  than  the  endocardium.  Thus  constructed  and  attached,  the  three 
semilunar  pouches  are  placed  side  by  side  around  the  arterial  orifice  of 
each  ventricle,  which  can  be  separated  by  the  blood  passing  out  of  the 
ventricle,  but  which  immediately  afterward  are  pressed  together,  so  as 
to  prevent  any  return  (6,  fig.  147,  and  7,  fig.  148).  This  will  be  again 
referred  to.  Opposite  each  of  the  semilunar  cusps,  both  in  the  aorta 
and  pulmonary  artery,  there  is  a  bulging  outward  of  the  wall  of  the 
vessel :  these  bulgings  are  called  the  sinuses  of  Valsalva. 

Structure. — The  valves  of  the  heart  are  formed  essentially  of  thick 
layers  of  closely  woven  connective  and  elastic  tissue,  over  which,  on 
every  part,  is  reflected  the  endocardium. 

The  Arteries. 

Distribution. — The  arterial  system  begins  at  the  left  ventricle  in  a 
single  large  trunk,  the  aorta,  which  almost  immediately  after  its  origin 
gives  off  in  the  thorax  three  large  branches  for  the  supply  of  the  head, 
neck,  and  upper  extremities;  it  then  traverses  the  thorax  and  abdomen, 
giving  off  branches,  some  large  and  some  small,  for  the  supply  of  the 
various  organs  and  tissues  it  passes  on  its  way.  In  the  abdomen  it 
divides  into  two  chief  branches,  for  the  supply  of  the  lower  extremities. 
The  arterial  branches  wherever  given  off  divide  and  subdivide,  until  the 
calibre  of  each  subdivision  becomes  very  minute,  and  these  minute  ves- 
sels pass  into  capillaries.  Arteries  are,  as  a  rule,  placed  in  situations 
protected  from  pressure  and  other  dangers,  and  are,  with  few  exceptions, 
straight  in  their  course,  and  frequently  communicate  (anastomose  or 
inosculate)  with  other  arteries.  The  branches  are  usually  given  off  at 
an  acute  angle,  and  the  areas  of  the  branches  of  an  artery  generally  ex- 
ceed that  of  the  parent  trunk  j  and  as  the  distance  from  the  origin  is 
increased,  the  area  of  the  combined  branches  is  increased  also.  After 
death,  arteries  are  usually  found  dilated  (not  collapsed  as  the  veins  are) 
and  empty,  and  it  was  to  this  fact  that  their  name  [aprrjpia,  the  wind- 
pipe) was  given  them,  as  the  ancients  believed  that  they  conveyed  air 
to  the  various  parts  of  the  body.  As  regards  the  arterial  system  of  the 
lungs,  the  pulmonary  artery  is  distributed  much  as  the  arteries  belong- 
ing to  the  general  systemic  circulation. 

Structure. — The  walls  of  the  arteries  are  composed  of  three  principal 
coats,  termed  {a)  the  external  or  tunica  adventitia,  {b)  the  middle  or 
tunica  media,  and  (c)  the  internal  or  tunica  intima. 


THE    CIRCULATION    OF   THE    BLOOD. 


181 


(a)  The  external  coat  or  tunica  aclventitia  (figs,  152  and  153,  a),  tlie 
strongest  and  toughest  part  of  the  wall  of  the  artery,  is  formed  of 
areolar  tissue,  with  which  is  mingled  throughout  a  network  of  elastic 
fibres.  At  the  inner  part  of  this  outer  coat  the  elastic  network  forms  in 
most  arteries  so  distinct  a  layer  as  to  be  sometimes  called  the  external 
elastic  coat  (fig.  153,  e). 

(b)  The  middle  coat  (fig.  153,  m)  is  composed  of  both  muscular  and 
elastic  fibres,  with  a  certain  proportion  of  areolar  tissue.  In  the  larger 
arteries  (fig.  153)  its  thickness  is  comparatively  as  well  as  absolutely 
much  greater  than  in  the  small,  constituting,  as  it  does,  the  greater  jiart 

I 


Fig.  152. 


Fig.  153. 


Fig.  154. 


Fig.  152.— Minute  artery  viewed  in  longitudinal  section,  e,  Nucleated  endothelial  membrane, 
■with  faint  nuclei  in  lumen,  looked  at  from  above  ;  i.  thin  elastic  tunica  intima  ;  jh,  muscular  coat 
or  tunica  media  ;  a,  tunica  adventitia.     (Klein  and  Noble  Smith.)      X  Sf-O. 

Fig.  153.— Transverse  section  through  a  large  branch  of  the  inferior  mesenteric  artery  of  a  pig. 
e.  Endothelial  membrane  ;  f,  tunica  elastica  interna,  no  subendothehal  layer  is  seen  ;  m.  muscular 
tunica  media,  containing  only  a  few  wavy  elastic  fibres  ;  e,  c,  tunica  elastica  externa,  dividing  the 
media  from  the  connective  tissue  adventitia,  a.    (Klein  and  Noble  Smith.)     X  350. 

Fig.  154.— Muscular  fibre-cells  from  human  arteries,  magnified  350  diameters.  (Kolhker.)  a, 
Nucleus,     b,  a  fibre-cell  treated  with  acetic  acid. 


of  the  arterial  wall.  The  muscular  fibres  are  nnstriped  (fig.  154),  and 
are  arranged  for  the  most  part  transversely  to  the  long  axis  of  the  artery 
(fig.  155,  m);  while  the  elastic  element,  taking  also  a  transverse  direc- 
tion, is  disposed  in  the  form  of  closely  interwoven  and  branching  fibres, 
which  intersect  in  all  parts  the  layers  of  muscular  fibre.  In  arteries  of. 
various  size  there  is  a  difi'erence  in  ihe  proportion  of  the  muscular  and 
elastic  element,  elastic  tissue  preponderating  in  the  largest  arteries,  and 
unstriped  muscle  in  those  of  medium  and  small  size. 

(r)  The  internal  coat  is  formed  by  a  layer  of  elastic  tissue,  called 
the  fenestrated  coat  of  Henlc.  It  is  ]icculiar  in  its  tendency  to  curl  up, 
when  peeled  oil  from  the  artery,  and  in  the  perforated  and  streaked  ap- 
pearance which  it  presents  under  the  microscope.  Its  inner  surface  is 
lined    with  a  delicate  layer  of  elongated  cndotlielial  cells  (fig.  153,  c), 


182 


HANDBOOK    OF    PHYSIOLOGY. 


■which  make  it  smooth  and  polished,  and  furnish  a  nearly  impermeable 
surface,  along  -which  the  blood  may  flow  with  the  smallest  possible 
amount  of  resistance  from  friction. 

Immediately  external  to  the  endothelial  lining  of  the  artery  is  fine 
connective  tissue,  the  suh- endothelial  laijer,  with  branched  corpuscles. 
Thus  the  internal  coat  consists  of  three  parts,  (a)  an  endothelial  lining, 
{}))  the  sub-endothelial  layer,  and  (c)  elastic  layers. 

Vasa   Vasorum, — 'The  walls  of  the  arteries,  with  the  exception  of 

Endothelium. 

&v5^  Sub  endothelial  layer. 

Elastic  intima. 


A  Middle  coat. 


Fig,  155.— Transverse  section  of  aorta  through  internal  and  about  half  the  middle  coat, 


the  endothelial  lining  and  the  layers  of  the  internal  coat  immediately 
outside  it,  are  not  nourished  by  the  blood  which  they  convey,  but  are, 
like  other  parts  of  the  body,  supplied  with  little  arteries,  ending  in 
capillaries  and  veins,  which,  branching  throughout  the  external  coat, 
extend  for  some  distance  into  the  middle,  but  do  not  reach  the  internal 
coat.     These  nutrient  vessels  are  called  vasa  vasorum. 

Nerves. — Most  of  the  arteries  are  surrounded  by  a  plexus  of  sympa- 
thetic nerves,  which  twine  around  the  vessel  very  much  like  ivy  round 
a  tree:  and  ganglia  are  found  at  frequent  intervals.  The  smaller  arter- 
ies are  also  surrounded  by  a  very  delicate  network  of  similar  nerve-fibres, 
many  of  which  appear  to  end  near  the  nuclei  of  the  transverse  muscular 
fibres  (fig.  156). 


THE    CIRCULATION"   OF   THE   BLOOD.  IHPi 

The  Capillaries. 

Distribution. — In  all  vascular  textures  except  some  parts  of  the  cor- 
pora cavernosa  of  the  penis,  and  of  the  uterine  placenta,  and  of  the 
spleen,  the  transmission  of  the  blood  from  the  minute  branches  of  the 
arteries  to  the  minute  veins  is  effected  through  a  network  of  capillaries. 
They  may  be  seen  in  all  minutely  injected  preparations. 

The  point  at  which  the  arteries  terminate  and  the  minute  veins  com- 
mence, cannot  be  exactly  defined,  for  the  transition  is  gradual;  but  the 


Fig.  156.— Ramification  of  nerves  and  termination  in  the  muscular  coat  of  a  small  arterj'  of  the 

frog.    (.Arnold.) 

capillary  network  has,  nevertheless,  this  peculiarity,  that  the  small 
vessels  which  compose  it  maintain  the  same  diameter  throughout:  they 
do  not  diminioh  in  diameter  in  one  direction,  like  arteries  and  veins; 
and  the  meshes  of  the  network  that  they  compose  are  more  uniform 
in  shape  and  size  than  those  formed  by  the  anastomoses  of  the  minute 
arteries  and  veins. 

Structure. — This  is  much  more  simple  than  that  of  the  arteries  or 
veins.  Their  walls  are  composed  of  a  single  layer  of  elongated  or  radi- 
ate, flattened  and  nucleated  cells,  so  joined  and  dovetailed  together  as 
to  form  a  continuous  transparent  membrane  (fig.  157).  Outside  these 
cells,  in  the  larger  capillaries,  there  is  a  structureless  or  very  finely 
fibrillated  membrane,  on  the  inner  surface  of  which  they  are  laid  down. 
In  some  cases  this  external  membrane  is  nucleated,  and  may  then  be 
regarded  as  a  miniature  representative  of  the  tunicit  adventitia  of  arteries. 
Here  and  there  at  the  junction  of  two  or  more  of  the  delicate  endothe- 
lial cells  which  compose  the  capillary  wall,  pseudo-stomata  may  be  seen. 


184  HAJfDBOOK    OF    PHYSIOLOGY. 

The  diameter  of  thp  capillary  vessels  varies  somewhat  in  the  different 
textures  of  the  bod}',  the  most  common  size  being  about  -g-oVo^^^  of  an 
inch,  V2:j..  Among  the  smallest  may  be  mentioned  those  of  the  brain, 
and  of  the  follicles  of  the  mucous  membrane  of  the  intestines;  among 
the  largest,  those  of  the  skin,  and  especially  those  of  the  medulla  of 
bones.    - 

The  size  o£  capillaries  varies  necessarily  in  diiferent  animals  in  rela- 


Fig.  157.— Capillary  blood-vessels  from  the  omentum  of  rabbit,  showing  the  nucleated  endothelial 
membrane  of  which  they  are  composed.     (Klein  and  Noble  Smith.) 

tion  to  the  size  of  their  blood  corpuscles :  thus,  in  the  Proteus,  the  capil- 
lary circulation  can  just  be  discerned  with  the  naked  eye. 

Tlieform  of  the  capillary  network  presents  considerable  variety  in 
the  different  textures  of  the  body:  the  varieties  consisting  principally 
of  modifications  of  two  chief  kinds  of  mesh,  the  rounded  and  the  elon- 
gated. That  kind  in  which  the  meshes  or  interspaces  have  a  roundish 
form  is  the  most  common,  and  jDrevails  in  those  parts  in  which  the 
capillary  network  is  most  dense,  such  as  the  kings  (fig.  158),  most 
glands,  and  mucous  membranes,  and  the  cutis.  The  meshes  of  this 
kind  of  network  are  not  quite  circular  but  more  or  less  angular,  some- 
times jaresenting  a  nearly  regular  quadrangular  or  polygonal  form,  but 
being  more  frequently  irregular.  The  capillary  network  with  elongated 
meshes  is  observed  in  parts  in  which  the  vessels  are  arranged  among 
bundles  of  fine  tubes  or  fibres,  as  in  muscles  and  nerves.  In  such  parts, 
the  meshes  form  parallelograms,  the  short  sides  of  which  may  be  from 
three  to  eight  or  ten  times  less  than  the  long  ones;  the  long  sides  being 
more  or  less  parallel  to  the  long  axis  of  the  fibre.  The  rounded  and 
elongated  meshes  vary  according  as  the  vessels  composing  them  are 
straight  or  tortuous. 

The  number'  of  the  capillaries  and  the  size  of  the  meshes  in  different 
parts  determine  in  general  the  degree  of  vascutarity  of  those  parts. 


THE    CIRCULATION   OF   THE   BLOOD. 


185 


The  capillary  network  is  closest  in  the  lungs  and  in  the  choroid  coat  of 
-the  eye.  In  the  iris  and  ciliary  body,  the  interspaces  are  somewhat 
wider,  yet  very  small.  In  the  human  liver  the  interspaces  are  of  the 
same  size,  or  even  smaller  than  the  capillary  vessels  themselves.  In  the 
human  lung  they  are  smaller  than  the  vessels;  in  the  human  kidney, 
and  in  the  kidney  of  the  dog,  the  diameter  of  the  injected  capillaries, 
compared  with  that  of  the  interspaces,  is  in  the  proportion  of  one  to 
four,  or  of  one  to  three.  The  brain  receives  a  very  large  quantity  of 
blood;  but  its  capillaries  are  very  minute,  and  are  less  numerous  than 
in  some  other  parts.  In  tlie  mucous  membranes — for  example  in  the 
conjuiictiva  and  in  the  cutis  vera,  the  capillary  vessels  are  much  larger 
th-!n  in   the  brain,  and  the  interspaces  narrower, — namely,  not  more 


Fig.  158. 


Fig.  159. 


Fig.  1.58.— Network  of  capillary  vessels  of  the  air-cells  of  the  hoi-se's  lung  magnified,    a,  a, 
Capillaries  proceeding  from  b,  b,  terminal  branches  of  the  pulmonary  artery.    (Frey.)" 

Fig.  159.— Injected  capillary  vessels  of  muscle  seen  with  a  low  magnifying  power.      (Sharpey.) 

than  three  or  four  times  wider  than  the  vessels.  In  the  i^eriosteum 
the  meshes  are  much  larger.  In  the  external  coat  of  arteries,  the  width 
of  the  meshes  is  ten  times  that  of  the  vessels. 

It  may  be  held  as  a  general  rule,  that  the  more  active  the  functions 
of  an  organ  are,  the  more  vascular  it  is.  Hence  the  narrowness  of  the 
interspaces  in  all  glandular  organs,  in  mucous  membranes,  and  in  grow- 
ing parts;  their  much  greater  width  in  bones,  ligaments,  and  other  very 
tough  and  comparatively  inactive  tissues;  and  the  usually  complete 
absence  of  vessels  in  cartilage,  and  such  parts  as  those  in  Avhich,  proba- 
bly, very  little  vital  change  occurs  after  they  are  once  formed. 


186 


HANDBOOK   OF   PHYSIOLOGY. 


The  Veins. 


Distribution. — The  venous  system  begins  in  small  vessels  which  are 
slightly  larger  than  the  capillaries  from  which  they  spring.  These 
vessels  are  gathered  up  into  larger  and  larger  trunks  until  they  termi- 
nate (as  regards  the  systemic  circulation)  in  the  two  venas  cavas  and  the 
coronary  veins,  which  enter  the  right  auricle,  and  (as  regards  the  pul- 
monary circulation)  in  four  pulmonary  veins,  which  enter  the  left 
auricle.     The  total  capacity  of  the  veins  diminishes  as  they  approach 


::i#^=:»'-^ 


Fig.  160.— Transverse  section  through  a  small  artery  and  vein  of  the  mucous  membrane  of  a 
child's  epiglottis  :  the  artery  is  thick-walled  and  the  vein  thin-walled,  a.  Artery,  the  'etter  is  placed 
in  the  lumen  of  tlie  vessel,  e.  Endothelial  cells  with  nuclei  clearly  visible  ;  these  cells  appear  very 
thick  from  the  contracted  state  of  the  vessel.  Outside  it  a  double  wavy  line  Jiarks  the  elastic 
tunica  intiina.  m.  Tunica  media  consisting  of  unstriped  muscular  fibres  circularlj  arranged ;  their 
nuclei  are  well  seen.  a.  Part  of  the  tunica  adventitia  showing  bundles  of  connective-tissue  fibre  in 
section,  with  the  circular  nuclei  of  the  connective-tissue  corpuscles.  This  coat  gradually  merges 
into  the  surrounding  connective-tissue,  v.  In  the  lumen  of  the  vein.  The  other  letters  indicate  the 
same  as  in  the  artery.  The  muscular  coat  of  the  vein  (m)  is  seen  to  be  much  thinner  than  that  of 
the  artery,     x  350.     (Klein  and  Noble  Smith.) 


the  heart;  but,  as  a  rule,  their  capacity  exceeds  by  twice  or  three  times 
that  of  their  corresponding  arteries.  The  pulmonary  veins,  however, 
are  an  exception  to  this  rule,  as  they  do  not  exceed  in  capacity  the  pul- 
monary arteries.  The  veins  are  found  after  death  more  or  less  collapsed, 
and  often  contain  blood.  They  are  usually  distributed  in  a  superficial 
and  a  deep  set  which  communicate  frequently  in  their  course. 

Structure. — In  structure  the  coats  of  veins  bear  a  general  resemblance 
to  those  of  arteries  (fig.  160).  Thus,  they  possess  outer,  middle,  and 
internal  coats. 

The  outer  coat   is    constructed   of  areolar  tissue  like  that  of  the 


THE   CIRCULATION"    OF   THE   BLOOD. 


187 


arteries,  but  is  thicker.     In  some  veins  it  contains  muscular  fibre-cells, 
which  are  arranged  longitudinally. 

The  middle  coat  is  considerably  thinner  than  that  of  the  arteries;  it 
contains  circular  unstriped  muscula.r  fibres,  mingled  with  a  large  pro- 


rig.  161.— Diagram  showing  valves  of  veins,  a,  part  of  a  vein  laid  open  and  spread  out,  with  two 
pairs  of  valves,  b,  longitudiQal  section  of  a  vein,  showing  the  apposition  of  the  edges  of  the  valves 
in  their  closed  state,  c,  portion  of  a  distended  vein,  exhibiting  a  swelling  in  the  situation  of  a  pair 
of  valves. 

portion  of  yellow  elastic  and  white  fibrous  tissue.  In  the  large  veins, 
near  the  heart,  namely  the  vence  cava  and  pulmonary  veins,  the  middle 
coat  is  replaced,  for  some  distance  from  the  heart,  by  circularly  arranged 
striped  muscular  fibres,  continuous  with  those  of  the  auricles. 


Fig.  162.— A,  vein  with  valves  open,    b,  vein  with  valves  closed:    streana  of  blood  passing  off  by 

lateral  channel.    (Dalton.) 

The  intciiud  coat  of  veins  consists  of  a  fenestrated  membrane,  which 
may  be  absent  in  the  smaller  ones,  lined  by  endothelium. 

Valves. — The  chief  iuilucnce  which  the  veins  have  in  the  circula- 
tion, is  effected  with  the  help  of  the  valves,  contained  in  all  veins  sub- 
ject to  local  pressure  from  the  muscles  between  or  near  which  they  run. 


188 


HANDBOOK    OF    PHYSIOLOGY. 


The  general  construction  of  these  valves  is  similar  to  that  of  the  semi- 
lunar valves  of  the  aorta  and  pulmonary  artery,  already  described;  but 
their  free  margins  are  turned  in  the  opposite  direction,  i.  e.,  toward  the 
heart,  so  as  to  prevent  any  movement  of  blood  backward.  They  are 
commonly  placed  in  pairs,  at  various  distances  in  different  veins,  but 
almost  uniformly  in  each  (fig.  161).  In  the  smaller  veins  single  valves 
are  often  met  with;  and  three  or  four  are  sometimes  placed  together,  or 
near  one  another,  in  the  largest  veins, 
such  as  the  subclavian,  and  at  their  junc- 
tion with  the  jugular  veins.  The  valves 
are  semilunar;  the  unattached  edge  be- 
ing in  some  examples  concave,  in  others 
siraight.  They  are  composed  of  inexten- 
sile  fibrous  tissue,  and  are  covered  with 
endothelium  like  that  lining  the  veins. 
During  the  period  of  their  inaction,  Avhen 
the  venous  blood  is  flowing  in  its  proper 
direction,  they  lie  by  the  sides  of  the  veins; 
but  when  in  action,  they  come  together 
like  the  valves  of  the  arteries  (figs.  161  and 
162).  Their  situation  in  the  superficial 
veins  of  the  forearm  is  readily  discovered 
by  pressing  along  its  surface,  in  a  direc- 
tion opposite  to  the  venous  current,  i.e., 
from  the  elbow  toward  the  wrist;  when 
little  swellings  (fig.  161,  o)  appear  in  the 
position  of  each  pair  of  valves.  These 
swellings  at  once  disappear  when  the  pres- 
sure is  removed. 

Valves  are  not  equally  numerous  in  all 
veins,  and  in  many  they  are  absent  al- 
together. They  are  most  numerous  in 
the    veins   of   the   extremities,  and   more 

so  in  those  of  the  leg  than  the  arm.  They  are  commonly  absent  in 
veins  of  less  than  a  line  in  diameter,  and,  as  a  general  rule  there 
are  few  or  none  in  those  which  are  not  subject  to  muscular  pres- 
sure. Among  those  veins  which  have  no  valves  may  be  mentioned  the 
superior  and  inferior  vena  cava,  the  trunk  and  branches  of  the  portal 
vein,  the  hepatic  and  renal  veins,  and  the  pulmonary  veins;  those  in  the 
interior  of  the  cranium  and  vertebral  column,  those  of  the  bones,  and 
the  trunk  and  branches  of  the  umbilical  vein  are  also  destitute  of  valves. 

LyynpJiatics  of  Arteries  and  Veins. — Lymphatic  spaces  are  present 
in  the  coats  of  both  arteries  and  veins;  but  in  the  tunica  adventitia  or 
external  coat  of  large  vessels  they  form  a  distinct  plexus  of  more  or  less 


Fig.  163.— Surface  view  of  an  artery 
from  the  mesentery  of  a  frog,  en- 
slieathed  in  a  peri-vascular  lympliatic 
vessel,  o.  Tde  artery,  with  its  circular 
muscular  coat  (media)  indicated  by 
Ijroad,  transverse  markings,  with  an 
indication  of  the  adventitia  outside. 
/.  Lymphatic  vessel,  its  wall  is  a  sim- 
ple endotlielial  membrane.  (Klein  and 
Noble  Smith. 


THE    CIRCULATIOlsr    OF   THE    BLOOD.  ISO 

tubular  vessels.  In  smaller  vessels  tliey  appear  as  sinous  spaces  lined 
by  endothelium.  Sometimes,  as  in  the  arteries  of  the  omentum,  mesen- 
tery, and  membranes  of  the  brain,  in  the  pulmonary,  hepatic,  and  splenic 
arteries,  the  spaces  are  continuous  with  vessels  which  distinctly  ensheatli 
them — perivascula?-  lymjihatic  sheaths  (fig.  1G3).  Lymph  channels  are 
said  to  be  present  also  in  the  tunica  media. 

The  Action  of  the  Heart. 

The  heart's  action  in  propelling  the  blood  consists  in  the  successive 
alternate  contraction  (systole)  and  relaxation  (diastole)  of  the  mus- 
cular walls  of  its  two  auricles  and  two  ventricles. 

Action  of  the  Auricles. — The  description  of  the  action  of  the 
heart  may  be  commenced  at  that  period  in  each  cycle  which  imme- 
diately j)recedes  the  beat  of  the  heart  against  the  chest  wall.  The  whole 
heart  is  then  in  a  passive  state;  the  auricles  are  gradually  filling  with 
blood  flowing  into  them  from  the  veins;  and  a  portion  of  this  blood  is 
passing  at  once  through  them  into  the  ventricles,  the  opening  between 
the  cavity  of  each  auricle  and  that  of  its  corres]Donding  ventricle  being, 
during  all  the  jijawse,  free  and  jDatent.  The  auricles,  however,  receiving 
more  blood  than  at  once  passes  through  them  to  the  ventricles,  become, 
near  the  end  of  the  jDause,  fully  distended;  and  at  the  end  of  the  pause, 
they  contract  and  expel  their  contents  into  the  ventricles. 

The  contraction  of  the  auricles  is  sudden  and  very  quick;  it  com- 
mences at  the  entrance  of  the  great  veins  into  them,  and  is  thence  prop- 
agated toward  the  auriculo-ventricular  opening,  forcing  the  contained 
blood  into  the  ventricle.  The  reflux  of  blood  into  the  great  veins  dur- 
ing the  auricular  systole  is  resisted  not  only  by  the  mass  of  blood 
within  them,  but  also  by  the  simultaneous  contraction  of  the  mus- 
cular coats  with  which  the  large  veins  are  provided  near  their  en- 
trance into  the  auricles.  Any  slight  regurgitation  from  the  right  auri- 
cle is  limited  by  the  valves  at  the  junction  of  the  subclavian  and  internal 
jugular  veins,  beyond  which  the  blood  cannot  move  backward;  and  the 
coronary  vein  is  preserved  from  it  by  a  valve  at  its  mouth. 

The  force  of  the  blood  propelled  into  the  ventricle  at  each  auricular 
systole  is  transmitted  in  all  directions,  but  being  insuificient  to  open  the 
semilunar  valves,  it  is  expended  in  distending  the  ventricle. 

Action  of  the  Ventricles. — The  dilatation  of  the  ventricles  which 
proceeds  during  the  chief  part  of  the  dilatation  of  the  auricles  is  com- 
pleted by  the  forcible  injection  of  the  contents  of  the  latter.  Thus. 
distended,  the  ventricles  immediately  contract:  so  immediately,  indeed, 
that  their  systole  looks  as  if  it  were  continuous  with  that  of  the  auri- 
cles. The  ventricles  contract  much  more  slowly  than  the  auricles,  tind 
in    their   contraction    probably    always    thoroughly    empty  themselves,. 


190  HANDBOOK   OF   PHYSIOLOGY. 

differing  iu  this  respect  from  the  auricles,  in  which,  even  after  their 
complete  coutractiou,  a  small  quantity  of  blood  remains.  The  shape  of 
both  ventricles  during  systole  uudergoes  an  alteration  when  the  chest  is 
opened,  the  diameter  iu  the  plane  of  the  base  being  diminished,  but  the 
length  of  the  heart  as  a  whole  is  not  altered  (Ludwig).  Haycraft  states 
that  the  heart  undergoes  no  change  of  shape  in  the  unopened  chest. 
Daring  the  systole  of  the  ventricles,  too,  the  aorta  and  pulmonary 
artery,  being  filled  with  blood  by  the  force  of  the  ventricular  ac- 
tion against  considerable  resistance,  elongate  as  well  as  expand,  and 
the  whole  heart  moves  slightly  toward  the  right  and  forward,  twisting 
on  its  long  axis,  and  exposing  more  of  the  left  ventricle  anteriorly  than 
is  usually  in  front.  When  the  systole  ends  the  heart  resumes  its  former 
position,  rotating  to  the  left  again  as  the  aorta  and  pulmonary  artery 
contract.  After  the  whole  of  the  blood  has  been  expelled  from  the 
ventricles,  the  walls  are  believed  to  remain  contracted  for  a  short  period 
before  the  rapid  re-dilatation  of  the  chambers  begin. 

Action  of  the  Valves. — (1)  The  Auriculo-  Ventricular. — The  dis- 
tention of  the  ventricles  with  blood  continues  throughout  the  whole 
period  of  their  diastole.  The  auriculo-ventricular  valves  are  gradually 
brought  into  place  by  some  of  the  blood  getting  behind  the  cusps  and 
forcing  them  up;  and  by  the  time  that  the  diastole  is  complete,  the 
valves  are  no  doubt  in  apposition,  the  completion  of  this  being  brought 
about  by  the  reflux  current  caused  by  the  systole  of  the  auricles.  This 
elevation  of  the  auriculo-ventricular  valves  is  materially  aided  by  the 
action  of  the  elastic  tissue  which  has  been  shown  to  exist  so  largely  in 
their  structure,  especially  on  the  ventricular  surface.  At  any  rate  at 
the  commencement  of  the  ventricular  systole  they  are  completely  closed. 
It  should  be  recollected  that  the  diminution  in  the  breadth  of  the  base 
of  the  heart  in  its  transverse  diameters  during  ventricular  systole  is 
especially  marked  in  the  neighborhood  of  the  auriculo-ventricular  rings, 
and  this  aids  in  rendering  the  auriculo-ventricular  valves  competent  to 
close  the  openings,  by  greatly  diminishing  their  diameter.  The  mar- 
gins of  the  cusps  of  the  valves  are  still  more  secured  in  apposition  with 
another,  by  the  simultaneous  contraction  of  the  musculi  papillaves, 
whose  chordse  tendineae  have  a  special  mode  of  attachment  for  this 
object.  The  cusps  of  the  auriculo-ventricular  valves  meet  not  by  their 
edges  only,  but  by  the  opposed  surfaces  of  their  thin  outer  borders. 

The  form  and  position  of  the  fleshy  columns  on  the  internal  walls  oi 
the  ventricle  no  doubt  help  to  produce  the  obliteration  of  the  ventricu' 
lar  cavity  during  contraction;  and  the  completeness  of  the  closure  ma} 
often  be  observed  on  making  a  transverse  section  of  a  heart  shortly 
after  death,  in  any  case  in  which  rigor  mortis  is  very  marked  (fig.  149) 
In  such  a  case  only  a  central  fissure  may  be  discernible  to  the  eye  iu  thi 
place  of  the  cavity  of  each  ventricle. 


THE  CIRCULATION  OF  THE  BLOOD.  191 

If  there  were  ouly  circular  fibres  forming  the  ventricular  wall,  it  is 
evident  that  on  systole  the  ventricle  would  elongate;  if  there  were  only 
longitudinal  fibres,  the  ventricle  would  shorten  on  systole;  but  there 
are  both.  The  tendency  to  alter  in  length  is  thus  counterbalanced, 
and  the  whole  force  of  the  contraction  is  expended  in  diminishing  the 
cavity  of  the  ventricle;  or,  in  other  words,  in  expelling  its  contents. 

On  the  conclusion  of  the  systole  the  ventricular  walls  tend  to  expand 
by  virtue  of  their  elasticity,  and  a  negative  pressure  is  set  up,  which 
tends  to  suck  in  the  blood.  This  negative  or  suctional  pressure  on  the 
left  side  of  the  heart  is  of  the  highest  importance  in  helping  the  pul- 
monary circulation.  It  has  been  found  to  be  equal  to  23  mm.  of  mer- 
cury, and  is  quite  independent  of  the  aspiration  or  suction  power  of  the 
thorax  itself,  which  will  be  described  in  a  later  chapter. 

The  musculi  jjapillares  prevent  the  auriculo-ventricular  valves  from 
being  everted  into  the  auricle.  For  the  chordae  tendiuese  might  allow 
the  valves  to  be  pressed  back  into  the  auricle,  were  it  not  that  when  the 
wall  of  the  ventricle  is  brought  by  its  contraction  nearer  the  auriculo- 
ventricular  orifice,  the  musculi  papillares  more  than  compensate  for  this 
by  their  own  contraction — holding  the  chords  tight,  and,  by  pulling 
down  the  valves,  adding  slightly  to  the  force  with  which  the  blood  is 
expelled. 

These  statements  apply  equally  to  the  auriculo-ventricular  valves  on 
both  sides  of  the  heart;  the  closure  of  both  is  generally  complete  every 
time  the  ventricles  contract.  But  in  some  circumstances  the  tricuspid 
valve  does  not  completely  close,  and  a  certain  quantity  of  olood  is 
forced  back  into  the  auricle.  This  has  been  called  the  safety-valve  action. 
The  circumstances  in  which  it  usually  hapjDeus  are  those  in  which  the 
vessels  of  the  lung  are  already  completely  full  when  the  right  ventricle 
contracts,  as,  e.g.,  in  certain  pulmonary  diseases,  in  very  active  exertions, 
and  in  great  efforts.  In  these  cases,  the  tricuspid  valve  does  not  com- 
pletely close,  and  the  regurgitation  of  the  blood  may  be  indicated  by  a 
pulsation  in  the  jugular  veins  synchronous  with  that  in  the  carotid 
arteries. 

(2.)  Tlie  Semihmar. — It  has  been  shown  that  the  commencement  of 
the  ventricular  systole  precedes  the  opening  of  the  semilunar  valves  by  a 
fraction  of  a  second.  This  would  seem  to  show  that  the  intraventricular 
pressure  does  not  exceed  the  arterial  pressure  until  the  systole  has  actually 
begun,  for  the  opening  of  the  valves  takes  place  at  once  when  there  is  a 
distinct  difference  in  favor  of  the  intraventricular  over  the  arterial  press- 
ure, and  continues  open  only  as  long  as  this  difference  continues.  When 
the  arterial  begins  to  exceed  the  intraventricular  pressure,  there  is,  as  it 
were,  a  reflux  of  blood  toward  the  heart,  and  the  valves  close.  The  dila- 
tation of  the  arteries  is,  in  a  peculiar  manner,  adapted  to  bring  this  about. 


192  HANDBOOK    OF    PHYSIOLOGY. 

The  lower  borders  of  the  semilunar  valves  are  attached  to  the  inner 
surface  of  the  tendinous  ring,  which  is,  as  it  were,  inlaid  at  the  orifice 
of  the  artery,  between  the  muscular  fibres  of  the  ventricle  and  the 
elastic  fibres  of  the  walls  of  the  artery.  The  tissue  of  this  ring  is  tough, 
and  does  not  admit  of  extension  under  such  pressure  as  it  is  commonly 
exposed  to;  the  valves  are  equally  inextensile,  being,  as  already  men- 
tioned, formed  mainly  of  tough,  close-textured,  fibrous  tissue,  with 
strong  interwoven  cords.  Hence,  when  the  ventricle  propels  blood 
through  the  orifice  and  into  the  canal  of  the  artery,  the  lateral  pressure 
which  it  exercises  is  sufficient  to  dilate  the  walls  of  the  artery,  but  not 
enough  to  stretch  in  an  equal  degree,  if  at  all,  the  unyielding  valves  and 
the  ring  to  which  their  lower  borders  are  attached.  The  effect,  there- 
fore, of  each  such  propulsion  of  blood  from  the  ventricle  is,  that  the 
wall  of  the  first  portion  of  the  artery  is  dilated  into  three  pouches  behind 


Fig.  164.— Sections  of  aorta,  to  show  the  action  of  the  semilunar  valves,  a  is  intended  to  shovv 
the  valves,  represented  by  the  dotted  lines,  lying  near  the  arterial  walls,  represented  by  the  contin- 
uous outer  line.  B  (after  Hunter)  shows  the  arterial  wall  distended  into  three  pouches  (aj,  and 
drawn  away  from  the  valves,  which  are  straightened  into  the  form  of  an  equilateral  triangle  as 
represented  by  the  dotted  lines. 

the  valves,  while  the  free  margins  of  the  valves  are  drawn  inward  toward 
its  centre  (fig.  164,  b).  Their  positions  may  be  explained  by  the  dia- 
grams, in  which  the  continuous  lines  represent  a  transverse  section  of 
the  arterial  walls,  the  dotted  ones  the  edges  of  the  valves,  firstly,  when 
the  valves  are  nearest  to  the  walls  (a),  as  in  the  dead  heart,  and,  sec- 
ondly, when,  the  walls  being  dilated,  the  valves  are  drawn  away  from 
them  (b). 

This  position  of  the  valves  and  arterial  walls  is  retained  so  long  as 
the  ventricle  continues  in  contraction:  but  as  soon  as  it  relaxes,  and  the 
dilated  arterial  walls  can  recoil  by  their  elasticity,  the  blood  is  forced 
backward  toward  the  ventricles  and  onward  in  the  course  of  the  circu- 
lation. Part  of  the  blood  thus  forced  back  lies  in  the  pouches  (sinuses 
of  Valsalva)  {a,  fig.  164,  b)  between  the  valves  and  the  arterial  walls; 
and  the  valves  are  by  it  pressed  together  till  their  thin  lunated  margins 
meet  in  three  lines  radiating  from  the  centre  to  the  circumference  of 
the  artery  (7  and  8,  fig.  148). 

The  contact  of  the  valves  in  this  position  and  the  comj)lete  closure 


THE    CIKCLLATIOX    OF    THE    BLOOD.  193 

of  the  ai'terial  orifice  are  secured  by  the  peculiar  construction  of  their 
borders  before  mentioned.  Among  the  cords  which  are  interwoven  in 
the  substance  of  the  valve  are  two  of  greater  strength  and  prominence 
than  the  rest;  of  which  one  extends  along  the  free  border  of  each  valve, 
and  the  other  forms  a  double  curve  or  festoon  just  below  the  free 
border.  Each  of  these  cords  is  attached  by  its  outer  extremities  to  the 
outer  end  of  the  free  margin  of  its  valve,  and  in  the  middle  to  the 
corpus  Arantii;  they  thus  enclose  a  lunated  space  from  a  line  to  a  line 
and  a  half  in  width,  in  which  space  the  substance  of  the  valve  is  much 
thinner  and  more  pliant  than  elsewhere.  When  the  valves  are  j^ressed 
down,  all  these  parts  or  spaces  of  their  surfaces  come  into  contact,  and 
the  closure  of  the  arterial  orifice  is  thus  secured  by  the  apposition  not 
of  the  mere  edges  of  the  valves,  but  of  all  those  thin  lunated  parts  of 
each  which  lie  between  the  free  edges  and  the  cords  next  below  them. 
These  parts  are  firmly  pressed  together,  and  the  greater  the  pressure 
that  falls  ou  them  the  closer  and  more  secure  is  their  apposition.  The 
corpora  Arantii  meet  at  the  centre  of  the  arterial  orifice  when  the  valves 
are  down,  and  they  probably  assist  in  the  closure;  but  they  are  not 
essential  to  it,  for,  not  unfrequently,  they  are  wanting  in  the  valves  of 
the  pulmonary  artery,  which  are  then  extended  in  larger,  thin,  flapping 
margins.  In  valves  of  this  form,  also,  the  inlaid  cords  are  less  distinct 
than  in  those  with  corpora  Arantii;  yet  the  closure  by  contact  of  their 
surfaces  is  not  less  secure. 

Cardiac  Cycle. — Taking  72  as  the  average  number  of  cardiac  evolu^ 
tions  per  minute,  each  revolution  may  be  considered  to  occujiy  |  of  a 
second,  or  about  .8,  which  may  be  approximately  distributed  in  the 
following  way: — 

Auricular  systole,  about    .  1  +  Auricular  diastole    .         .         .     .7  —  .8 
Ventricular  systole    "         .3 -(- Ventricular  diastole    .         .  .5  =.8 

Period  of  joint  auricular 
and  ventricular  diastole  .4  -|-  Period  of  sj'stole  of 

auricles  or  ventricles    .         .     .4  =  .8 

If  the  speed  of  the  heart  be  quickened,  the  time  occupied  by  each 
cardiac  revolution  is  of  course  diminished,  but  the  diminution  affects 
only  the  diastole  and  pause.  The  systole  of  the  ventricles  occupies  very 
much  the  same  time,  whatever  the  pulse-rate. 

The  exact  period  in  which  the  several  valves  of  the  heart  are  in 
action  is  a  matter  of  some  uncertainty;  the  auriculo-ventricular  valves 
are  probably  closed  during  the  whole  time  of  the  ventricular  contrac- 
tion, while,  during  the  dilatation  and  distention  of  the  ventricles,  they 
are  open.  The  semilunar  valves  are  only  certainly  open  during  the 
middle  period  of  the  ventricular  contraction. 

1  7. 


194  HANDBOOK    OF    PHYSIOLOGY. 

The  Sounds  of  the  Heart. 

When  the  ear  is  placed  over  the  region  of  the  heart,  two  sounds  may- 
be heard  at  every  beat  of  the  heart,  which  follow  in  quick  succession, 
and  are  succeeded  by  a  pause  or  period  of  silence.  The  first  sound  is 
dull  and  prolonged;  its  commencement  coincides  with  the  impulse  of 
the  heart  against  the  chest  wall,  and  just  precedes  the  pulse  at  the  wrist. 
The  second  is  shorter  and  sharper,  with  a  somewhat  flapping  character, 
and  follows  close  after  the  arterial  pulse.  The  periods  of  time  occupied 
respectively  by  the  two  sounds  taken  together  and  by  the  pause  between 
the  second  and  the  first,  are  unequal.  According  to  Foster,  the  interval 
of  time  between  the  begiuDing  of  the  first  sound  and  the  second  sound 
is  .3  second,  while  between  the  second  and  the  succeeding  first  it  is 
nearly  .5  (see  fig.  165).  The  relative  length  of  time  occupied  by  each 
sound,  as  compared  with  the  other,  may  be  best  appreciated  by  consider- 
ing the  different  forces  concerned  in  the  production  of  the  two  sounds. 
In  one  case  there  is  a  strong,  comparatively  slow,  contraction  of  a  large 
mass  of  muscular  fibres,  urging  forward  a  certain  quantity  of  fluid 
against  considerable  resistance;  while  in  the  other  it  is  a  strong  but 
shorter  and  sharper  recoil  of  the  elastic  coat  of  the  large  arteries — shorter 
because  there  is  no  resistance  to  the  flapping  back  of  the  semilunar  valves, 
as  there  was  to  their  opening.  The  sounds  may  be  expressed  by  the 
words  luhh — du}). 

The  events  which  correspond,  in  point  of  time,  with  i\\ki  fii^st  sound, 
are  (1)  the  contraction  of  the  ventricles,  (2)  the  first  part  of  the  dilata- 
tion of  the  auricles,  (3)  the  tension  of  the  auriculo-ventricular  valves, 
(4)  the  opening  of  the  semilunar  valves,  and  (5)  the  propulsion  of  blood 
into  the  arteries.  The  sound  is  succeeded,  in  about  one-thirtieth  of  a 
second,  by  the  pulsation  of  the  facial  arteries,  and  in  about  one-sixth  of 
a  second,  by  the  pulsation  of  the  arteries  at  the  wrist.  The  second  sound, 
in  point  of  time,  immediately  follows  the  cessation  of  the  ventricular 
contraction,  and  corresponds  with  (a)  the  tension  of  the  semilunar 
valves,  {h)  the  continued  dilatation  of  the  auricles,  (c)  the  commencing 
dilatation  of  the  ventricles,  and  {d)  the  opening  of  the  auriculo-ventric- 
ular valves.  The  pause  immediately  follows  the  second  sound,  and 
corresponds  in  its  first  part  with  the  completed  distention  of  the  auri- 
cles, and  in  its  second  with  their  contraction,  and  the  completed  disten- 
tion of  the  ventricles ;  the  auriculo-ventricular  valves  being  all  the  time 
of  the  pause  open,  and  the  arterial  valves  closed. 

Causes. — The  exact  cause  of  the  first  sound  of  the  heart  is  not 
known.  Two  factors  probably  enter  into  it,  viz.,  firstly  the  vibration 
of  the  auriculo-ventricular  valves  and  of  the  chordae  tendinese.  This 
vibration  is  produced  by  the  increased  intraventricular  pressure  set  up 


THE    CIRCULATION    OF   THE    BLOOD. 


195 


when  the  ventricular  systole  commences,  which  puts  the  valves  on  the 
stretch.  The  question  whether  this  stretched  condition  of  the  valve 
continues  throughout  the  whole  of  the  ventricular  systole  cannot  be 
definitely  settled,  but  if  it  does  not,  the  valvular  element  may  possibly 
take  part  in  the  production  of  the  first  jiart  of  the  first  sound  only.  It 
is  not  unlikely  too  that  the  vibration  of  the  ventricular  walls  themselves, 
and  of  the  aorta  and  pulmonary  arter}^  all  of  Avhich  parts  are  suddenly 


IMPULSE 


Fig.  165. — Diagrammatic  representation  of  the  events  of  the  cardiac  C3-cIe.  For  events  which 
occur  la  sequence,  read  in  the  direction  of  the  curved  arrow;  for  synchronous  events,  read  from 
the  centre  to  the  periphery  in  any  direction.    (Coleman. ) 

put  into  a  state  of  tension  at  the  moment  of  ventricular  contraction, 
may  have  some  part  in  producing  the  first  sound.  tSecondly,  the  luus- 
cula?'  sound  j)roduced  by  contraction  of  the  mass  of  muscular  fibres 
which  form  the  ventricle.  Looking  upon  the  contraction  of  the  heart 
as  a  single  contraction  and  not  as  a  series  of  contractions  or  tetanus,  it 
is  at  first  sight  difficult  to  see  why  there  should  be  any  muscular  sound 
at  all  when  the  heart  contracts,  as  contraction  of  a  single  muscle  does 
not  produce  sound.  It  has  been  suggested,  however,  that  it  arises  from 
the  repeated  unequal  tension  produced  when  the  wave  of  muscular  con- 
tractions passes  along  the  very  intricately  arranged  fibres  of  the  vcntric- 


196  HANDBOOK    OF    PHYSIOLOGY. 

ular  walls.  The  valvular  element  is  probably  the  more  important  of 
the  two  factors. 

The  cause  of  the  second  sound  is  more  simple  than  that  of  the  first. 
It  is  entirely  due  to  the  vibration  consequent  on  the  sudden  closure  of 
the  semilunar  valves  when  they  are  pressed  down  across  the  orifices  of 
the  aorta  and  pulmonary  arterj^  The  influence  of  these  valves  in  pro- 
ducing the  sound  was  first  demonstrated  by  Hope  who  experimented 
with  the  hearts  of  calves.  In  these  experiments  two  delicate  curved 
needles  were  inserted,  one  into  the  aorta,  and  another  into  the  pulmo- 
nary artery,  below  the  line  of  attachment  of  the  semilunar  valves,  and, 
after  being  carried  upward  about  half  an  inch,  were  brought  out  again 
through  the  coats  of  the  respective  vessels,  so  that  in  each  vessel  one 
valve  was  included  betw^een  the  arterial  walls  and  the  wire.  Upon  ap- 
plying the  stethoscope  to  the  vessels,  after  such  an  operation,  the  second 
sound  had  ceased  to  be  audible.  Disease  of  these  valves,  when  sufficient 
to  interfere  with  their  efficient  action,  also  demonstrates  the  same  fact 
by  modifying  the  valvular  cause  of  the  second  sound  or  destroying  its 
distinctness. 

One  reason  that  the  second  sound  is  clearer  and  sharper  than  the  first 
may  be,  that  the  semilunar  valves  are  not  covered  in  by  the  thick  layer 
of  fibres  composing  the  walls  of  the  heart  to  such  an  extent  as  are  the 
auriculo-ventricular.  It  might  be  expected  therefore  that  their  vibra- 
tion would  be  more  easily  heard  by  means  of  a  stethoscope  -applied  to 
the  walls  of  the  chest. 

The  contraction  of  the  auricles  which  takes  place  in  the  end  of  the 
pause  is  inaudible  outside  the  chest,  but  is  said  to  be  heard,  when  the 
heart  is  exposed  and  the  stethoscope  placed  on  it,  as  a  slight  sound  pre- 
ceding and  continued  into  the  louder  sound  of  the  ventricular  contrac- 
tion. 

The  Impulse  of  the  Heart. 

With  each  contraction  the  heart  may  be  felt  to  beat  with  a  slight 
shock  or  impulse  against  the  walls  of  the  chest.  The  force  of  the  im- 
pulse and  the  extent  to  which  it  may  be  perceived  beyond  this  point 
vary  considerably  in  different  individuals,  and  in  the  same  individual 
under  different  circumstances.  It  is  felt  more  distinctly,  and  over  a 
larger  extent  of  surface,  in  emaciated  than  in  fat  and  robust  persons, 
and  more  during  a  forced  expiration  than  in  a  deep  inspiration;  for,  in 
the  one  case,  the  intervention  of  a  thick  layer  of  fat  or  muscle  between 
the  heart  and  the  surface  of  the  chest,  and  in  the  other  the  inflation  of 
the  portion  of  lung  which  overlaps  the  heart,  prevents  the  impulse  from 
being  fully  transmitted  to  the  surface.     An  excited  action  of  the  heart. 


THE    CIRCULATION    OI-    THE    HLOOl). 


197 


and  especially  a  hypertrophied  couditiou  of  the  ventricles,  will  increase 
the  impulse;  while  a  depressed  condition,  or  an  atrophied  state  of  the 
ventricular  walls,  will  diminish  it. 

Cause  of  the  Tmjnilse. — During  the  period  which  precedes  the  ven- 


Tube  to  fommunicate 
with  tambour. 


Ivory     Tape  to  attach  the  instmment 
knob.  to  the  chest. 


Tympanum. 
Fig.  166. — Cardiograph.     (Sanderson's.) 


tricular  systole  the  apex  of  the  heart  is  situated  upon  the  diaphragm  and 
against  the  chest-wall  in  the  fifth  intercostal  space.  When  the  ventri- 
cles contract,  their  walls  become  hard  and  tense,  since  to  expel  their 
contents  into  the  arteries  is  a  distinctly  laborious  action,  as  it  is  resisted 


Screw  to  regulate  elevation  of  lever. 


Writing  lever. 


Tambour. 


Tube  to  cardiograph. 


Fig.  167.— Marey's  Tambour,  to  wliich  the  movement  of  the  column  of  air  in  the  firet  tympanum 
is  conducted  by  a  tube,  and  from  which  it  is  communicated  by  the  lever  to  a  revolving  cylinder,  so 
that  the  tracing  of  the  movement  of  the  impulse  beat  is  obtained. 


by  the  elasticity  of  the  vessels.  It  is  to  this  sudden  hardening  that  the 
impulse  of  the  heart  against  the  chest-wall  is  due,  and  the  shock  of  the 
sudden  tension  may  be  felt  not  only  externally,  but  also  internally,  if 
the  abdomen  of  an  animal  be  opened  and  the  finger  be  placed  upon  the 


198 


SAKDBOOK    OF    PHYSIOLOGY. 


under  surface  of  the  diaphragm,  at  a  jnoiDt  corresponding  to  the  under 
surface  of  the  ventricle.  The  shock  is  felt,  and  possibly  seen  more  dis- 
tinctly because  of  the  partial  rotation  of  the  heart,  already  spoken  of^ 
along  its  long  axis  toward  the  right.  The  movement  produced  by  the 
ventricular  contraction  against  the  chest- wall  may  be  registered  by  means 
of  an  instrument  called  the  cardiograpli,  and  it  will  be  found  to  corre- 
spond almost  exactly  with  a  tracing  obtained  by  the  same  instrument 
applied  over  the  contracting  ventricle  itself. 

The  Cardiograph  (tig.  166)  consists  of  a  cup-shaped  metal  box  over  the  open 
front  of  which  is  stretched  an  elastic  India-rubber  membrane,  upon  which  is 
fixed  a  small  knob  of  hard  wood  or  ivory.  This  knob,  however,  may  be  at- 
tached, as  in  the  figure,  to  the  side  of  the  box  by  means  of  a  spring,  and  may 
be  made  to  act  upon  a  metal  disc  attached  to  the  elastic  membrane. 

The  knob  is  for  application  to  the  chest-wall  over  the  place  of  the  great- 
est impulse  of  the  heart.  The  box  or  tymi^anum  communicates  by  means  of 
an  air-tight  tube  with  the  interior  of  a  second  tympanum,  in  connection  with 
which  is  a  long  and  light  lever.  The  shock  of  the  heart's  impulse  being 
communicated   to   the    ivory   knob,    and  through    it    to    the    first  tympanum,   the 


Fig.  167  A. — Cardiogram  of  Frog's  Heart,     c,  Tracing  of  auricular  and  ventricular  sj'stole;  t,  time 

in  half  secouds. 

effect  is,  of  course,  at  once  transmitted  by  the  column  of  air  in  the  elastic  tube 
to  the  interior  of  the  second  tympanum,  also  closed,  and  through  the  elastic 
and  movable  lid  of  the  latter  to  the  lever,  which  is  placed  in  connection  with 
a  registering  apparatus.  This  generally  consists  of  a  cylinder  or  drum  covered 
with  smoked  paper,  revolving  by  clock-work  with  a  definite  velocity.  The 
point  of  the  lever  writes  upon  the  paper,  and  a  tracing  of  the  heart's  impulse 
or  cardiogram  is  thus  obtained. 


Endocardiac  Pressure. 


It  cannot  be  considered,  however,  that  the  cardiogram  represents 
what  is  actually  occurring  within  the  heart  itself.  For  determining 
this,  communication  must  be  established  with  the  cavities  of  the  heart. 


THE   CIRCULATION   OP   THE    BLOOD.  190 

By  placing  tliree  small  India-rubber  air-bags  or  cardiac  munds  in  tlie 
interior  respectively  of  the  right  auricle  and  the  right  ventricle,  and  in 
an  intercostal  space  in  front  of  the  heart  of  living  animals  (horse),  and 
placing  these  bags,  by  means  of  long,  narrow  tubes,  in  communication 
with  three  levers,  arranged  one  over  the  other  in  connection  with  a  reg- 


Fi^.  168.— Apparatus  of  MM.  Chanveau  and  Marey  for  estimating  the  variations  of  endocardial 
pressure,  and  jsroduction  of  impulse  of  the  heart. 

istering  apparatus  (fig.  168),  Chauveau  and  Marey  have  been  able  to  re- 
cord and  measure  with  much  accuracy  the  variations  of  the  endocardial 
pressure  and  the  comparative  duration  of  the  contractions  of  the  auricles 
and  ventricles.  By  means  of  the  same  apparatus,  the  synchronism  of 
the  impulse  with  the  contraction  of  the  ventricles,  is  also  well  shown ; 
and  the  causes  of  the  several  vibrations  of  which  it  is  really  composed, 
have  been  demonstrated. 

In  the  tracing  (fig.  1G9),  the  intervals  between  the  vertical  lines  rep- 
resent periods  of  a  tenth  of  a  second.  The  parts  on  which  any  given 
vertical  line  falls  represent  simultaneous  events.  It  will  be  seen  that 
the  contraction  of  the  auricle,  indicated  by  the  marked  curve  at  A  in 
first  tracing,  causes  a  slight  increase  of  pressure  in  the  ventricle  which 
is  shown  at  a'  in  the  second  tracing,  and  jn'oduces  also  a  slight  impulse, 
which  is  indicated  by  a"  in  the  third  tracing.  The  closure  of  the  semi- 
lunar valves  causes  a  momentarily  increased  pressure  in  the  ventricle  at 
d',  affects  the  pressure  in  the  auricle  d,  and  is  also  shown  in  the  tracing 
of  the  impulse  d". 

The  large  curve  of  the  ventricular  and  the  impulse  tracings,  between 
a' and  d',  and  a"  and  d",  are  caused  by  the  ventricular  contraction,  while 
the  smaller  undulations,  between  b  and  c,  b'  and  c',  b"  and  c",  are 
caused  by  the  vibrations  consequent  on  the  tightening  and  closure  of 
the  auriculo-ventricular  valves. 

It  seems  by  no  means  certain  that  j\rarey''s  curves  jDroperly  represent 
the  variations  in  intraventricular  pressure.     Much  objection  has  been 


200 


HANDBOOK    OF    PHYSIOLOGY. 


takeu  to  his  method  of  investigation.  Firstly,  because  his  tambour  ar- 
rangement does  not  admit  of  both  positive  and  negative  pressure  being 
simultaneously  recorded.  Secondly,  because  the  method  is  only  applicable 
to  large  animals,  such  as  the  horse.  And  thirdly,  because  the  intraven- 
tricular changes  of  j)ressure  are  communicated  to  the  recording  tambour 
by  a  long  elastic  column  of  air;  and  fourthly,  because  the  tambour  ar- 
rangement has  a  tendency  to  record  inertia  vibrations.  H.  D.  Eolleston, 
who  has  pointed  out  the  above  imperfections  of  Marey's  method,  has  re- 
investigated the  subject  with  a  more  suitable  apparatus.     The  method 


Fig.  169.— Tracings  of  (1),  Intra-auricular,  and  C2),  Intra-ventricular  pressures,  and  (3),  of  the  im- 
pulse of  the  heart,  to  be  read  from  left  to  right,  obtained  by  Chauveau  and  Marey's  apparatus. 


adopted  by  Rolleston  is  as  follows :  a  window  is  made  in  the  chest  of 
an  anaesthetized  and  curarized  animal,  and  an  appropriately  curved  glass 
canula  introduced  through  an  opening  in  the  auricular  appendix. 
The  canula  is  then  passed  through  the  auriculo-ventricular  orifice  with- 
out causing  any  appreciable  regurgitation,  into  the  auricle,  or  it  may  be 
introduced  into  the  cavity  of  the  right  or  left  ventricle  by  an  opening 
made  in  the  apex  of  the  heart.  In  some  experiments  the  trocar  is 
pushed  through  the  chest  wall  into  the  ventricular  cavity.  The  appa- 
ratus is  filled  with  a  solution  of  leech  extract  in  .75  per  cent  saline  so- 
lution, or  with  a  solution  of  sodium  bicarbonate  of  specific  gravity  1083. 
The  animals  employed  were  chiefly  dogs.  The  movement  of  the  column 
of  blood  is  communicated  to  the  writing  lever  by  means  of  a  vnlcanite 
piston  which  moves  with  little  friction  in  a  brass  tube  connected  with 
the  glass  canula  by  means  of  a  short  connecting  tube. 

When  the  lower  part  of  the  tiil)e  (a)  is  placed  in  communication  with 
one  of  the  cavities  nf  the  heart,  the  movements  of  the  piston  are  re- 
corded by  means  of  the  lever  (c).  Attached  to  the  lever  is  a  section  of 
a  pulley  (h),  the  axis  of  which  coincides  with  that  of  the  steel  ribbon 
(e);  while,  firmly  fixed  to  the  piston,  is  the  curved  steel  piston  rod  (1), 


THE    CIUCULATION    OF    THE    BLOOD. 


201 


fi'oni  tlie  top  of  which  a  strong  silk  thread  (j)  passes  downward  into  the 
groove  on  the  pulley. 

This  thread  (j),  after  being  twisted  several  times  round  a  small  piu 
at  the  side  of  the  lever,  enters  the  groove  in  the  pulley  from  above  down- 
ward, and  then  passes  to  be  fixed  to  the  lower  part  of  the  curve  on  the 
piston-rod  as  shown  in  the  smaller  figure. 

The  rise  and  fall  of  the  lever  (c)  is  controlled  by  the  resistance  to 


rig.  170.— Apparatus  for  recordiug  the  endocai  dial  pressure.     CRolIeston.) 


torsion  of  the  steel  ribbon  (e),  to  the  middle  of  whi.;h  one  end  of  the 
lever  is  securely  fixed  by  a  light  screw  clamp  (f).  At  some  distance 
from  this  clamp — the  distance  varying  with  the  degree  of  resistance 
which  it  is  desired  to  give  to  the  movements  of  the  lever — are  two  hold- 
ers (g.g')  which  securely  clamp  the  steel  ribbon. 

As  the  torsion  of  a  steel  wire  or  strip  follows  Hooke's  law,  the  tur- 
sion  being  proportional  to  the  twisting  force — the  movements  of  the 
lever  point  are  proportional  to  the  force  employed  to  twist  the  steel  strip 
or  ribbon — in  other  words  to  the  pressures  which  act  on  the  piston  (b). 

To  make  it  possible  to  record  satisfactorily  the  very  varying  ventric- 
uhir  and  auricular  pressures,  the  resistance  to  torsion  of  a  steel  ribbon 
adapts  itself  very  conveniently. 

This  resistance  can  be  varied  in  two  ways,  1st,  by  using  one  or  more 
pieces  of  steel  ribbon  or  by  using  strips  of  different  thicknesses;  or  2d, 


302 


HANDBOOK    OF    PHYSIOLOGY. 


by  varyiDg  the  distance  between  the  holders  (g.g.)  and  the  central  part 
of  the  steel  ribbon  to  which  the  lever  is  attached. 

Eolleston's  conclusions  are  as  follows : — 

1.  That  there   is   no   distinct   and   separate   auricular  contraction 


Fig.  171. — Endocardial  pressure  curve  from  the  left  ventricle.  The  thorax  was  opened  and  a 
canula  introduced  through  the  apex  of  the  ventricle;  abscissa  is  line  of  atmospheric  pressure,  a 
to  D  represents  ventricular  contraction;  from  d  to  the  next  rise  at  g  represents  the  ventricular 
diastole.  The  notch  at  the  top  of  which  is  f  is  a  post-ventricular  rise  in  pressure  from  below  that 
of  the  atmosphere  and  not  a  pre-systolic  or  auricular  rise  in  pressure. 

marked  in  the  curves  obtained  from  either  right  or  left  ventricles,  the 
auricular  and  ventricular  rises  of  pressure  being  merged  into  one  con- 
tinuous rise. 

2.  That  the  auriculo-ventricular  valves  are  closed  before  any  great 
rise  of  pressure  within  the  ventricle  above  that  which  results  from  the 
auricular  systole  {a,  fig.  172).     The  closure  of  the  valve  occurs  probably 


Fig.  172.— Curve  with  dicrotic  summit  from  left  ventricle;  abscissa  shows  atmospheric  pressure. 


in  the  lower  third  of  the  rise  a  b  (fig.  172),  and  does  not  produce  any 
notch  or  wave. 

3.  That  the  semilunar  valves  open  at  the  point  in  the  ventricular 
systole,  situated  (at  g)  about  or  a  little  above  the  junction  of  the  mid- 
dle or  upper  third  of  the  ascending  line  (a  b),  and  the  closure  about  or 
a  little  before  the  shoulder  (d). 

4.  That  the  minimum  pressure  in  the  ventricle  may  fall  below  that 
of  the  atmosphere,  but  that  the  amount  varies  considerably. 


THE    CIRCULATION    OP   THE    P.LOOD. 


203 


Frequency  of  the  Heart's  Action. 

The  heart  of  a  healthy  adult  man  contracts  about  72  times  in  a 
minute;  but  many  circumstances  cause  this  rate,  which  of  course  cor- 
responds with  that  of  the  arterial  pulse,  to  vary  even  in  health.  The 
chief  are  age,  temperament,  sex,  food  and  drink,  exercise,  time  of  day, 
posture,  atmospheric  pressure,  temperature;  as  follows: — 

(1.)  Age. — The  frequency  of  the  heart's  action  gradually  diminishes 
from  the  commencement  to  near  the  end  of  life,  but  is  said  to  rise 
again  somewhat  in  extreme  old  age,  thus: — 


About     the     seventh 


year 

from 

90  to 

85 

130 

About  the   fourteenth 

llf) 

year 

85  to 

80 

In  adult  age 

80  to 

70 

100 

lu  old  age 

70  to 

60 

90 

lu  decrepitude    . 

75  to 

65 

Before   birth  the  average  number  of 
pulsations  per  minute  is    150 

Just  after  birth      .      from  140  to 

During  the  first  year  130  to 

During    the     second 
year         .         .         .  115  to 

During  the  third  year  100  to 


(2.)  Temperament  and  Sex. — In  persons  of  sanguine  temperament, 
the  heart  acts  somewhat  more  frequently  than  in  those  of  the  phleg- 
matic; and  in  the  female  sex  more  frequently  than  in  the  male. 

(3  and  4.)  Food  and  Drinh.  Exercise. — After  a  meal  the  heart's 
action  is  accelerated,  and  still  more  so  during  bodily  exertion  or  mental 
excitement;  it  is  slower  during  sleep. 

(5.)  Dmrnal  Variation. — In  health  the  pulse  is  most  frequent  in  the 
morning,  and  becomes  gradually  slower  as  the  day  advances :  and  this 
diminution  of  frequency  is  both  more  regular  and  more  rapid  in  the 
evening  than  in  the  morning. 

(6.)  Posture. — The  pulse,  as  a  general  rule,  especially  in  the  adult 
male,  is  more  frequent  in  the  standing  than  in  the  sitting  posture,  and 
in  the  latter  than  in  the  recumbent  position;  the  difference  being 
greatest  bctv/een  the  standing  and  the  sitting  postures.  The  effect  of 
change  of  posture  is  greater  as  the  frequency  of  the  pulse  is  greater, 
and,  accordingly,  is  more  marked  in  the  morning  than  in  the  evening. 
By  supporting  the  body  in  diff'erent  positions,  without  the  aid  of  mus- 
cular effort  of  the  individual,  it  has  been  proved  that  the  increased  fre- 
quency of  the  pulse  in  the  sitting  and  standing  positions  is  dependent 
upon  the  muscular  exertion  engaged  in  maintaining  them;  the  usual 
effect  of  these  postures  on  the  pulse  being  almost  ent./ely  prevented 
when  the  usually  attendant  muscular  exertion  was  rendered  unnecessary. 

(7.)  Almos2)heHc  Pressure. — The  frequency  of  the  pulse  increases  in 
a  corresponding  ratio  with  the  elevation  above  the  sea. 

(8.)  Temperature. — The  rapidity  and  force  of  the  heart's  contrac- 
tions are  largely  influenced  by  variations  of  temperature.  The  frog's 
heart,  when  excised,  ceases  to  beat  if  the  temperature  be  reduced  to 


204  HANDBOOK    OF   PHYSIOLOGY. 

0°  C.  (32°  F.).  When  heat  is  gradually  applied  to  it,  botli  the  speed 
and  force  of  the  contractions  increase  till  they  reach  a  maximum.  If 
the  temperature  is  still  further  raised,  the  beats  become  irregular  and 
feeble,  and  the  heart  at  length  stands  still  in  a  condition  of  "heat- 
rigor."  Similar  effects  are  produced  in  warm-blooded  animals.  In  the 
rabbit,  the  number  of  heart-beats  is  more  than  doubled  when  the  tem- 
perature of  the  air  was  maintained  at  40".5  C.  (105°  F.).  At  45°  C.  (113° 
— 114°  F.),  the  rabbit's  heart  ceases  to  beat. 

In  health  there  is  observed  a  nearly  uniform  relation  between  the 
frequency  of  the  beats  of  the  heart  and  of  the  resjDirations;  the  propor- 
tion being,  on  an  average,  1  respiration  to  3  or  4  beats.  The  same  rela- 
tion is  generally  maintained  in  the  cases  in  which  the  action  of  the  heart 
is  naturally  accelerated,  as  after  food  or  exercise;  but  in  disease  this 
relation  may  cease.  In  many  affections  accompanied  with  increased 
frequency  of  the  heart's  contraction,  the  respiration  is,  indeed,  also 
accelerated,  yet  the  degree  of  its  acceleration  may  bear  no  definite  pro- 
portion to  the  increased  number  of  the  heart's  actions :  and  in  many 
other  cases,  the  heart's  contraction  becomes  more  frequent  without  any 
accompanying  increase  in  the  number  of  respirations;  or,  the  respiration 
alone  may  be  accelerated,  the  number  of  pulsations  remaining  station- 
ary, or  even  falling  below  the  ordinary  standard. 

The  Force  of  the  Cardiac  Action. 

(a.)  Ventricular. — The  force  of  the  left  ventricular  systole  is  more 
than  double  that  exerted  by  the  contraction  of  the  right  ventricle :  this 
difference  results  from  the  walls  of  the  left  ventricle  being  about  twice 
or  three  times  as  thick  as  those  of  the  right.  And  the  difference  is 
adapted  to  the  greater  degree  of  resistance  which  the  left  ventricle  has 
to  overcome,  compared  with  that  to  be  overcome  by  the  right:  the 
former  having  to  propel  blood  through  every  part  of  the  body,  the  latter 
only  through  the  lungs.  The  actual  amount  of  the  intraventricular 
pressures  during  systole  in  the  dog  has  been  found  to  be  2.4  inches  (60 
mm.)  of  mercury  in  the  right  ventricle,  and  6  inches  (150  mm.)  in  the 
left. 

During  diastole  there  is  in  the  right  ventricle  a  negative  or  suction 
pressure  of  about  |  of  an  inch  (  —  17  to  —16  mm.),  and  in  the  left  ven- 
tricle from  2  inches  to  ^  of  an  inch  (  —  52  to  —  20  mm.).  Part  of  this 
fall  in  pressure,  and  possibly  the  greater  part,  is  to  be  referred  to  the  in- 
fluence of  respiration;  but  without  this  the  negative  pressure  of  the  left 
ventricle  caused  by  its  active  dilatation  is  about  equal  to  |  of  an  inch 
(20  mm.  )of  mercury. 

The  right  ventricle  is  undoubtedly  aided  by  this  suction  power  of 
the  left,  so  that  the  whole  of  the  work  of  conducting  the  pulmonary 


THE    CIRCULATION    OF   THE    BLOOD.  205 

circulation  Joes  not  fall  upon  the  right  side  of  tlie  heart,  but  is  assisted 
by  the  left  side. 

(b.)  Auricular. — The  maximum  pressure  within  the  right  auricle  is 
equal  to  about  i  of  an  inch  (20  mm.)  of  mercury,  and  is  probably  some- 
what less  in  the  left.  It  has  been  found  that  during  diastole  the  pres- 
sure within  both  auricles  sinks  considerably  below  that  of  the  atmos- 
phere; and  as  some  fall  in  pressure  takes  place,  even  when  the  thorax 
of  the  animal  operated  upon  has  been  opened,  a  certain  proportion  of 
the  fall  must  be  due  to  active  auricular  dilatation  independent  of  respi- 
ration in  the  right  auricle,  this  negative  j)ressure  is  equal  to  about 
—  10  mm. 

In  estimating  the  work  done  by  any  machine  it  is  usual  to  express 
it  in  terms  of  the  unit  of  Avork.  In  England,  the  unit  of  work  is  the 
foot-pound,  and  is  defined  to  be  the  energy  expended  in  raising  a  unit 
of  weight  (1  lb.)  through  a  unit  of  height  (1  ft.) :  in  France,  the  kilo- 
gram-mefre.  The  work  done  by  the  heart  at  each  contraction  can  be 
readily  found  by  multiplying  the  weight  of  blood  expelled  by  the  ven- 
tricles by  the  height  to  which  the  blood  rises  in  a  tube  tied  into  an 
artery.  This  height  is  probably  about  9  ft.  3.21  metres  in  man.  Tak- 
ing the  Aveight  of  blood  expelled  from  the  left  ventricle  at  each  systole 
at  6  oz.,  i.e.,  y  lb.,  we  have  9  X  f  =  3.375  foot-pounds,  or  3.21  X  180  grms. 
or  578  gram- metres,  as  the  work  done  by  the  left  ventricle  at  each  sys- 
tole; and  adding  to  this  the  work  done  by  the  right  ventricle  (about 
one-fourth  that  of  the  left)  we  have  3.375  -f  .822  =  4.19  foot-pounds,  or 
722  gram-metres  as  the  work  done  by  the  heart  at  each  contraction. 

Blood  Pressure. 

The  subject  of  blood-pressure  has  been  already  incidentally  men- 
tioned more  than  once  in  the  preceding  pages,  the  time  has  now  arrived 
for  it  to  receive  more  detailed  consideration. 

That  the  blood  exercises  pressure  upon  the  walls  of  the  vessels  con- 
taining it,  is  due  to  the  following  facts: — 

Firstly,  that  the  heart  at  each  contraction  forcibly  injects  a  consid- 
erable amount  of  blood,  viz.,  I  to  G  oz.  (120  to  180  grms.)  suddenly  and 
quickly  into  the  arteries. 

Secondly,  that  the  arteries  are  already  full  of  blood  at  the  com- 
mencement of  the  ventricular  systole,  since  there  is  not  sufficient  time 
between  the  heart  beats  for  the  blood  to  pass  into  the  veins. 

Thirdly,  that  the  arteries  are  highly  distensible  and  stretch  to  ac- 
commodate the  extra  amount  of  blood  forced  into  them ;  and 

Fourthly,  that  there  is  a  distinct  resistance  interposed  to  the  pas- 
sage of  the  blood  from  the  arteries  into  the  veins,  from  the  enormous 
number  of  minute  vessels,  small  arteries  (arterioles)  and  capillaries  into 


20G  HANDBOOK   OF    PHYSIOLOGY. 

which  the  main  artery  has  been  ultimately  broken  up.  The  sectional 
area  of  the  capillaries  is  several  hundred  times  that  of  the  aorta,  and 
the  friction  generated  by  the  passage  of  the  blood  through  these  minute 
channels  opposes  a  considerable  hindrance  or  resistance  in  its  course. 
The  resistance  thus  set  up  is  called  peripheral  resistance.  The  fric- 
tion is  greater  in  the  arterioles  where  the  current  is  comparatively  rapid 
than  in  the  capillaries  where  it  is  slow. 

That  the  blood  exerts  considerable  pressure  upon  the  arterial  walls 
in  keeping  them  in  a  stretched  or  distended  condition,  may  be  readily 
shown  by  puncturing  any  artery;  the  blood  is  instantly  projected  with 
great  force  through  the  opening,  and  the  jet  rises  to  a  considerable 
height,  the  exact  level  of  which  varies  with  the  size  of  the  artery  expe- 
rimented with.  If  a  large  artery  be  j)unctured,  the  blood  may  be  pro- 
jected upward  for  many  feet,  whereas  if  a  small  artery  be  similarly  dealt 
with  the  jet  does  not  rise  to  such  a  height.  Another  marked  feature  of 
the  jet  of  blood  from  a  cut  artery,  particularly  well  marked  if  the  vessel 
be  a  large  one,  and  near  the  heart,  is  the  jerky  character  of  the  outflow. 
If  the  artery  be  cut  across,  the  jet  issues  with  force,  chiefly  from  the 
central  end,  unless  there  is  considerable  anastomosis  of  vessels  in  the 
neighborhood,  when  the  jet  from  the  peripheral  end  may  be  as  forcible 
and  as  intermittent  as  that  from  the  other  end.  The  intermittent  flow 
in  the  arteries  which  is  due  to  the  intermittent  action  of  the  heart,  and 
which  represents  the  systolic  and  diastolic  alterations  of  blood  pressure, 
may  be  felt  if  the  finger  be  placed  upon  a  sufficiently  superficial  artery. 
The  finger  is  apparently  raised  and  lowered  by  the  intermittent  systolic 
distention  of  the  vessel,  occurring  at  each  heart  beat.  This  intermittent 
distention  of  the  artery  is  what  is  known  as  the  Pulse,  to  the  further 
consideration  of  which  we  shall  persently  return,  but  we  may  say  here, 
that  in  a  normal  condition  the  pulse  is  a  characteristic  of  the  arterial, 
and  is  absent  from  the  venous  flow.  At  the  same  time  it  must  be  recol- 
lected that  in  the  veins  the  blood  exercises  a  pressure  on  its  containing 
vessel,  but  as  we  shall  see  presently  this  is  small  when  compared  with 
the  arterial  blood-pressure.  As  might  be  expected,  therefore,  the  blood 
is  not  expelled  with  so  much  force  if  a  vein  be  punctured  or  cut,  and 
further,  the  flow  from  the  cut  vein  is  continuous  and  not  intermittent, 
and  the  greater  amount  of  blood  comes  from  the  peripheral  and  not 
from  the  central  end  as  is  the  case  when  an  artery  is  severed. 

The  result  produced  by  the  experiment  of  cutting  or  imncturing  a 
blood  vessel  may  be  modified  by  introducing  into  the  vessel  a  glass 
tube  of  a  calibre  corresponding  to  that  of  the  vessel,  and  allowiug  the 
blood  to  rise  in  it.  If  the  vessel  be  an  artery,  the  blood  will  rise 
several  feet,  according  to  the  distance  of  the  vessel  from  the  heart,  and 
when  it  has  reached  its  highest  point  will  be  seen  to  oscillate  with 
the  heart's  beats.     This  experiment  shows  that  the  pressure  which  the 


THE   CIRCULATION    OF   THE    BLOOD. 


207 


blood  exerts  upon  the  Avails  of  the  contained  artery,  equals  the  pres- 
sure of  a  column  of  blood  of  a  certain  height;  in  the  case  of  the  rab- 
bit's carotid  it  is  equal  to  3  feet  of  blood,  or  rather  more  than  3  feet  of 
water.  In  the  case  of  the  vein,  if  a  similar  experiment  be  performed, 
blood  will  rise  in  the  tube  for  an  inch  or  two  only. 

The  usual  method  of  estimating  the  amount  of  blood  pressure  differs 
somewhat  from  the  foregoing  simple  experiment.  Instead  of  a  simple 
straight  tube  of  glass  inserted  into  the  vessel,  a  U-shaped  tube  contain' 


Fi^.  1T3.— Diaffram  of  mercurial  kymograph,  a,  revolving  cylinder,  worked  by  a  clock-work 
arrangement  contained  in  the  box  (b),  the  speed  being  regulated  by  a  fan  above  the  box;  cylinder 
supported  by  an  upright  (6),  and  capable  of  being  raised  or  lowered  by  a  screw  (a),  by  a  handle 
attached  to  "it;  d,  c,  e,  represent  mercurial  manometer,  a  somewhat  different  form  of  which  is 
shown  in  next  figure. 

ing  mercury,  or  a  mercurial  manometer  is  employed,  and  the  artery 
is  made  to  communicate  with  it  by  means  of  a  small  canula  which  is 
inserted  into  the  vessel,  and  a  connecting  tube,  an  arrangement  being 
made  whereby  the  canula,  tubes,  etc.,  are  filled  with  a  saturated  saline 
solution  to  prevent  the  clotting  of  blood  when  it  is  allowed  to  pass  from 
the  artery  into  the  apparatus.  The  passage  of  blood  is  prevented  during 
the  arrangement  of  the  details  of  the  experiment  by  a  pair  of  clamp  or 
bull-dog  forceps.  The  free  end  of  the  U-tube  of  mercury  contains  a 
yery  fine  glass  piston,  the  bulbous  end  of  which  floats  upon  the  surface 
of  the  mercury,  rising  with  its  rise  and  oscillating  with  its  oscillations. 


208 


HANDBOOK    OF   PHYSIOLOGY. 


As  soon  as  there  is  free  communication  between  the  artery  and  the  tube 
of  mercury,  the  blood  rushes  out  and  pushes  before  it  the  column  of 
mercury.  The  mercury  will  therefore  rise  in  the  free  limb  of  the  tube, 
and  will  continue  to  do  so  until  a  point  is  reached  which  corresponds  to 
the  mean  pressure  of  the  blood-vessel  used.  The  blood-pressure  is  thus 
communicated  to  the  upper  part  of  the  mercurial  column;  and  tiie 
depth  to  which  the  latter  sinks,  added  to  the  height  to  which  it  rises  in 
the  other,  will  give  the  height  of  the  mercurial  column  which  the  blood- 
pressure  balances;  the  weight  of  the  saline  solution  being  subtracted. 
For  the  estimation  of  the  amount  of  blood  pressure  at  any  given  mo- 
ment, no  further  apparatus  than  this,  which  is  called  Poiseuilles's  hcB- 


Fig.  174. — Ludwiff's  Kymograph.  The  manometer  is  shown  in  fig.  173,  D.  C.  E.  The  mercury 
which  partially  fills  the  tube  supports  a  float  in  form  of  a  piston,  nearly  filling  the  tube;  a  wire  is 
fixed  to  the  float,  and  the  writing  style  or  pen  is  guided  by  passing  through  the  brass  cap  of  the 
tube  fixed  to  the  wire;  the  pressure  is  communicated  to  the  mercury  by  means  of  a  flexible  metal 
tube  filled  with  fluid. 

inadynamometer,\&  necessary;  but  for  noting  the  variations  of  pressure 
in  the  arterial  system,  as  well  as  its  absolute  amount,  the  instrument  is 
usually  combined  with  a  recording  apparatus,  in  this  form  called  a 
kt/mograph  (fig.  173). 

The  recording  apparatus  consists  of  a  revolving  cylinder  (fig.  173, 
A),  which  is  moved  by  clockwork,  and  the  speed  of  which  is  capable  of 
regulation.  The  cylinder  is  covered  with  glazed  paper  blackened  in  the 
flame  of  a  lamp,  and  the  mercurial  manometer  is  so  fixed  (fig.  173,  D) 
that  its  float  provided  with  a  style  writes  on  the  cylinder  as  it  revolves. 
There  are  many  ways  in  which  the  mercurial  manometer  may  be  varied; 
in  fig.  174  is  seen  a  form,  which  is  known  as  Ludwig's  Kymograph.  In 
order  to  obviate  the  necessity  of  a  large  quantity  of  blood  entering  the 
tube  of  the  apparatus,  it  is  usual  to  have  some  arrangement  by  means 


THE   CIRCULATION    OF   THE    T.LOOD.  '-200 

of  which  the  mercury  may  be  made  to  rise  in  the  tube  of  the  manometer 
to  the  level  corresponding  to  the  mean  pressure  of  the  artery  experi- 
mented witli,  so  that  the  writing  style  simply  records  the  variations  of 
the  blood  pressure  above  and  below  the  mean  pressure.  This  is  done  by 
causing  the  saline  solution,  generally  a  saturated  solution  of  sodium 
carbonate  or  sulphate,  to  fill  the  apparatus  from  a  bottle  suspended  at  a 
height,  and  capable  of  being  raised  or  lowered  as  required  for  the  pur- 
pose, or  by  injecting  the  saline  solution  into  the  tube  by  means  of  a 
syringe.  The  canula  inserted  and  tied  into  the  artery  may  be  of  two 
kinds.  In  one  case  a  fine  glass  tube  is  used  with  the  end  drawn  out  and 
cut  so  that  its  end  is  oblique,  and  provided  with  a  shoulder  to  prevent 
its  coming  out  easily,  the  peripheral  end  of  the  cut  artery  being  tied  to 
obviate  the  escape  of  blood.  By  this  means,  the  pressure  communicated 
to  the  column  of  mercury  is  the  forward  and  not  the  lateral  pressure  of 
blood,  or  a  T- canula  may  be  employed  and  may  be  tied  into  the  two 
ends  of  a  divided  artery,  and  the  free  arm  of  the  T  piece  being  made 


Fig.  175. — Normal  tracina:  of  arterial  pressure  in  the  rabbit  obtained  with  the  mercurial  kymo- 
graph. The  smaller  undulations  correspond  with  the  heart  beats;  the  larger  curves  with  the  respi- 
I'atory  movements.     (^Burdon-Sanderson.) 

to  communicate  witli  the  manometer.  This  communicates  the  lateral 
blood  pressure. 

As  soon  as  the  experiment  is  completed,  the  writing  float  is  seen  to 
oscillate  in  a  regular  manner,  and  a  curve  of  blood  pressure  is  traced 
upon  the  smoked  paper  by  the  style  (or,  if  a  continuous  roll  of  unsmoked 
paper  be  usgd  instead,  by  an  inked  pen),  when  a  figure  similar  to  fig. 
175  will  be  obtained. 

This  indicates  two  main  variations  of  the  blood  jn-essure;  the  smaller 
excursions  of  the  lever  corresponds  with  Ihe  i^i/stole  and  diasfoh  of  the 
heart,  and  the  large  curves  correspond  with  the  respirations,  being  called 
the  respiratory  undulations  of  blood  pressure,  to  which  attention  will 
be  directed  in  the  next  chapter.  Of  course,  the  undulations  spoken  of 
are  only  seen  in  records  of  arterial  blood  pressure:  they  are  more  clearly 
marked  in  the  arteries  nearer  the  heart  than  in  those  more  remote,  in 
the  smaller  arteries  the  amount  of  the  pressure  as  well  as  the  indication 
of  the  systolic  rise  of  pressure,  being,  comparatively  speaking,  small. 

In  order  to  record  tlie  undulations  of  arterial  pressure,  for  some  pur- 
poses it  is  better  to  use  Fick's  Spring  Kymograph  than  the  mercurial 
manometer.     Two  forms  of  this  instrument  are  shown  in  figs.  17G  and 


210 


HAN"DBOOK    OF   PHYSIOLOGT. 


177.  It  consists  of  a  hollow  C-spring,  filled  witli  fluid,  the  interior  of 
which  is  made  to  communicate  with  the  artery  by  means  of  a  flexible 
metal  tube  and  canula.  In  response  to  the  pressure,  transmitted  to 
its  interior,  the  spring  tends  to  straighten  itself,  and  the  movement 
thus  produced  is  communicated  by  means  of  a  lever  to  a  writing  style 
and  so  to  a  recording  apparatus.  This  instrument  obviates  the  errors 
which  might  be  caused  by  the  inertia  of  the  mercury  in  the  mercurial 
manometer;  it  also  shows  in  more  detail  the  variations  of  the  blood 
pressure  in  the  vessel  during  and  after  each  individual  beat  of  the  heart. 


Fig.  176.— A  form  of  Fick's  Spring  Kymograph,  a,  Tube  to  be  connected  with  artery;  c,  hollow- 
spring,  the  movement  of  which  moves  b,  the  writing  lever;  e,  screw  to  regulate  height  of  b;  d,  out- 
side protective  spring;  g,  screw  to  fix  on  the  u  right  of  the  support. 


In  fig.  178  is  seen  a  tracing  taken  with  Fick's  Kymograph  from  an 
artery  of  a  dog. 

As  regards  the  actual  amount  of  blood  pressure,  from  observations 
which  have  been  made  by  means  of  the  mercurial  manometer,  it  has 
been  found  that  the  pressure  of  blood  in  the  carotid  of  a  rabbit  is  capa- 
ble of  supporting  a  column  of  2  to  3.5  inches  (50  to  90  mm.)  of  mercury, 
in  the  dog  4  to  7  inches  (100  to  175  mm.),  in  tlie  horse  5  to  8  inches 
(152  to  200  mm.),  and  in  man  the  pressure  is  estimated  to  be  about  the 
same. 

To  measure  the  absolute  amount  of  this  pressure  in  any  artery,  it  is 
necessary  merely  to  multiply  the  area  of  its  transverse  section  by  the 
height  of  the  column  of  mercury  which  is  already  known  to  be  sup- 


THE   CIRCULATION    OF   THE    liLOOD. 


211 


ported  by  the  blood-2:)ressure  in  any  j^art  of  the  arterial  system.  The 
weight  of  a  column  of  mercury  thus  found  will  represent  the  j)ressure 
of  the  blood.  Calculated  in  this  way,  the  blood-pressure  in  the  human 
aorta  is  equal  to  4  lbs.  4  oz.  avoirdupois;  that  in  the  aorta  of  the  horse 
being  11  lb.  9  oz.;  and  tliat  in  the  radial  artery  at  the  human  wrist  only 
4  drs.  Supposing  the  muscular  power  of  the  right  ventricle  to  be  only 
one-half  that  of  the  left,  the  blood-pressure  in  the  pulmonary  artery  will 
be  only  3  lb.  2  oz.  avoirdupois.  The  amounts  above  stated  represent  the 
arterial  tension  to  the  time  of  the  ventricular  contraction. 


Fig.  177. — Fick's  Kymograph,  improved  by  Hering  (after  McKendrick).  a,  HoUow  spring  filled 
with  alcohol,  bearing  lever  an-angement  b,  d,  c,  to  which  is  attached  the  marker  e;  the  rod  f  passes 
downward  into  tlietiibe/,  containing  castor  oil.  which  offers  resistance  to  the  oscillations  of  c:  </, 
syringe  for  filling  the  leaden  tube  /;  with  saturated  sulphate  of  sodium  solution,  and  to  apply  siilfi- 
cient  pressure  as  to  prevent  the  blood  from  jvissing  into  the  Iiibe /<  at /.  the  canula  inserted  iuto 
the  vessel;  /,  abscissa-markei',  whicla  can  be  applied  ti>  tlic moving  stu'face  by  turning  the  screw  m; 
A-,  .screw  for  adjusting  the  whole  apparatus  to  the  moving  sm-face:  o,  screw  for  elevating  or  de- 
pressing by  a  rack  and  pinion  movement  the  Kymograpli;  n,  screw  for  adjusting  the  position  of 
the  tube/. 

The  blood-pressure  is  greatest  in  the  left  ventricle  and  at  the  begin- 
ning of  the  aorta,  and  decreases  toward  the  capillaries.  It  is  greatest  in 
the  arteries  at  the  period  of  the  ventricular  systole.  The  blood-pressure 
gradually  lessens  then  as  we  proceed  from  tlie  arteries  near  tlie  heart  to 
those  more  remote,  and  again  from  these  to  the  capillaries,  and  thence 
along  the  veins  to  the  right  auricle.  The  blood-pressure  in  the 
veins  is  nowhere  very  great,  but  is  greatest  in  the  small  veins,  while  in 
the  large  veins  toward  the  heart  the  })ressure  becomes  net/afhr,  or,  in 
other  words,  when  a  vein  is  put  in  connection  with  a  mercurial  man- 


212  HANDBOOK    OF   PHYSIOLOGY. 

ometer  the  mercury  will  fall  in  the  arm  furthest  away  from  the  vein  and 
will  rise  in  the  arm  nearest  the  vein,  the  action  being  that  of  suction 
rather  than  jDressure  forward.  In  the  large  veins  of  the  neck  the  ten- 
dency to  suck  in  air  is  especially  marked,  and  is  the  cause  of  death  in 
some  surgical  operations  in  that  region.  The  amouut  of  pressure  in  the 
brachial  vein  is  said  to  support  9  mm.  of  mercury,  whereas  the  pressure 
in  the  veins  of  the  neck  may  fall  to  a  negative  pressure  of  rather  more 
than  ^  inch  or  —  about  -g^  to  -i-  inch  or  —  3  to  —  8  mm. 

The  variations  of  venous  pressure  during  systole  and  diastole  of  the 
heart  are  very  slight,  and  a  distinct  pulse  is  never  seen  in  veins  except 
under  extraordinary  circumstances.  From  observations  upon  the  web 
of  the  frog's  foot,  the  tongue  and  mesentery  of  the  frog,  the  tails  of 
newts,  and  small  fishes  (Roy  and  Brown),  as  well  as  upon  the  skin  of 
the  finger  behind  the  nail  (Kries),  by  careful  estimation  of  the  amount 
of  pressure  required  to  empty  the  vessels  of  blood  under  various  condi- 
tions, it  appears  that  the  blood-pressure  is  subject  to  variations  in 
the  capillaries,  apparently  following  the  variations   of   that   of   the 


ftWWmhf 


Fig.  178. — Normal  arterial  tracing^  obtained  with  Fick's  kymograph  in  the  dog. 
(Burdon-Sanderson.) 

arteries;  and  that  up  to  a  certain  point,  as  the  extravascular  pressure  is 
increased,  so  does  the  j)ulse  in  the  arterioles,  capillaries,  and  venules  be- 
come more  and  more  evident.  The  pressure  in  the  first  case  (web  of 
the  frog's  foot)  has  been  found  to  be  equal  to  about  i  to  f  inch  or  14  to 
20  mm.  of  mercury;  in  other  experiments  to  be  equal  to  about  -^  to  -j  of 
the  ordinary  arterial  pressure. 

The  arterial  blood-pressure  may  be  made  to  vary  by  variations  of 
either  of  the  two  chief  factors  ajDon  which  the  pressure  in  the  vessels 
depends,  viz.,  the  cardiac  contractions  and  the  peri]3heral  resistance. 
Thus,  increase  of  blood-pressure  may  be  brought  about  by  either  (a)  a 
more  frequent  or  more  forcible  action  of  the  heart,  or  (b)  by  increase  of 
the  perij)heral  resistance;  and  on  the  other  hand,  diminution  of  the 
blood-pressure  may  be  produced,  either  by  (a)  a  diminished  force  or  fre- 
quency of  the  contractions  of  the  heart,  or  by  (b)  a  diminished  periphe- 
ral resistance.  These  different  factors,  however,  although  varying  con- 
stantly, are  so  combined  that  the  general  arterial  pressure  remains  fairly 
constant;  for  example,  the  heart  may,  by  increased  force  or  frequency 
of  its  contractions,  distinctly  increase  the  blood-pressure,  but  this  in- 
creased action  is  almost  certainly  followed  by  diminished  peripheral 


THE   CIRCULATION"    OF   THE    BLOOD.  21o 

resistance,  and  thus  the  two  altered  conditions  may  balance,  with  the 
result  of  bringing  buck  the  blood-pressure  to  what  it  was  before  the 
heart  began  to  beat  more  rapidly  or  more  forcibly. 

It  will  be  clearly  seen  that  the  circulation  of  the  blood  within  the 
blood-vessels  must  depend  upon  the  diminution  of  the  pressure  from 
the  heart  to  the  capillaries,  and  from  the  capillaries  to  the  veins,  the 
blood  flowing  in  the  direction  of  least  resistance;  we  shall  presently  see 
further  that  the  general  or  local  flow  also  depends  upon  the  relations 
between  the  heart's  action  and  the  peripheral  resistance,  general  or  local. 

The  Arterial  Flow. 

The  character  of  the  flow  of  blood  through  the  arterial  system  de- 
pends to  a  very  considerable  extent  upon  the  structure  of  the  arterial 
walls,  and  particularly  upon  the  elastic  tissue  which  is  so  highly  devel- 
oped in  them. 

The  elastic  tissue  first  of  all  guards  the  arteries  from  the  suddenly 
exerted  pressure  to  which  they  are  subjected  at  each  contraction  of  the 
ventricles.  In  every  such  contraction  as  is  above  seen  the  contents  of 
the  ventricles  are  forced  into  the  arteries  more  quickly  than  they  can 
be  discharged  through  the  capillaries.  The  blood,  therefore,  being,  for 
an  instant,  resisted  in  its  onward  course,  a  part  of  the  force  with  which 
it  was  impelled  is  directed  against  the  sides  of  the  arteries;  under  this 
force  their  elastic  walls  dilate,  stretching  enough  to  receive  the  blood, 
and,  as  they  stretch,  becoming  more  tense  and  more  resisting.  Thus, 
by  yielding  they  break  the  shock  of  the  force  impelling  the  blood.  On 
the  subsidence  of  the  pressure,  when  the  ventricles  cease  contracting, 
the  arteries  are  able,  by  the  same  elasticity,  to  resume  their  former  cali- 
bre; the  elastic  tissue  also  equalizes  the  cnrrentof  blood  by  maintaining 
pressure  on  it  in  the  arteries  during  the  period  at  which  the  ventricles 
are  at  rest  or  are  dilating.  If  the  arteries  were  rigid  tubes,  the  blood 
instead  of  flowing,  as  it  does,  in  a  constant  stream,  would  be  propellca 
through  the  arterial  system  in  a  series  of  jerks  corresponding  to  the 
ventricular  contractions,  with  intervals  of  almost  complete  rest  during 
tlie  inaction  of  the  ventricles.  But  in  the  actual  condition  of  the  ves- 
sels, the  force  of  the  successive  contractions  of  the  ventricles  is  expended 
partly  in  the  direct  projDulsion  of  the  blood,  and  partly  in  the  dilatation 
of  the  elastic  arteries;  and  in  the  intervals  between  the  contractions  of 
the  ventricles,  the  force  of  the  recoil  is  employed  in  continuing  the  on- 
ward flow.  Of  course  the  pressure  exercised  is  equally  diffused  in  every 
direction,  and  the  blood  tends  to  move  backward  as  well  as  onward;  all 
movement  backward,  however,  is  prevented  by  the  closure  of  the  semi- 
lunar valves,  -which  takes  place  at  the  very  commencement  of  the  recoil 
of  the  arterial  walls. 


214  HANDBOOK    OF    PHYSIOLOGY. 

Thus  by  the  exercise  of  the  elasticity  of  the  arteries,  all  the  force  of 
the  ventricles  is  expended  upon  the  circulation;  for  that  part  of  the 
force  which  is  used  up  or  rendered  potential  in  dilating  the  arteries  is 
restored  or  made  active  or  kinetic,  in  full  when  they  recoil.  There  is 
no  loss  of  force;  neither  is  there  any  gain,  for  the  elastic  walls  of  the 
artery  cannot  originate  any  force  for  the  pro]3ulsion  of  the  blood — they 
only  restore  that  which  they  received  from  the  ventricles.  It  is  by  this 
equalizing  iniiuence  of  the  successive  branches  of  every  artery  that  at 
length  the  intermittent  accelerations  produced  in  the  arterial  current 
by  the  action  of  the  heart,  cease  to  be  observable,  and  the  jetting  stream 
is  converted  into  the  continuous  and  equable  movement  of  the  blood 
which  we  see  in  the  capillaries  and  veins.  In  the  production  of  a  con- 
tinuous stream  of  blood  in  the  smaller  arteries  and  capillaries,  the  re- 
sistance which  is  offered  to  the  blood-stream  in  these  vessels  is  a  neces- 
sary agent.  Were  there  no  greater  obstacle  to  the  escape  of  blood  from 
the  larger  arteries  than  exists  to  its  entrance  into  them  from  the  heart, 
the  stream  would  be  intermittent,  notwithstanding  the  elasticity  of  walls 
of  the  arteries. 

By  means  of  the  elastic  and  muscular  tissue  in  their  Avails  again  the 
arteries  are  enabled  to  dilate  and  contract  readily  in  correspondence 
with  any  temporary  increase  or  diminution  of  the  total  quantity  of 
blood  in  the  body;  and  within  a  certain  range  of  diminution  of  the 
quantity,  still  to  exercise  due  pressure  on  their  contents.  The  elastic 
tissue  further  assists  in  restoring  the  normal  channel  after  diminution 
of  its  calibre,  whether  this  has  been  caused,  by  a  contraction  of  the  mus- 
cular coat,  or  by  the  temporary  application  of  a  compressing  force  from 
without.  This  action  is  well  shown  in  arteries  which,  having  contracted 
by  means  of  their  muscular  element,  after  death  regain  their  average 
potency  on  the  cessation  of  post-mortem  rigidity. 

The  office  of  the  muscular  coat  also  is  employed  to  adjust  the  flow 
of  the  blood  locally,  to  regulate  the  quantity  of  blood  to  be  received  by 
each  part  or  organ,  and  to  adjust  it  to  the  requirements  of  each,  accord- 
ing to  various  circumstances,  but,  chiefly,  according  to  the  activity  with 
which  the  functions  of  each  are  at  different  times  performed.  The 
amount  of  work  done  by  each  organ  of  the  body  varies  at  different  times, 
and  the  variations  often  quickly  succeed  each  other,  so  that,  as  in  the 
brain,  for  example,  during  sleep  and  waking,  within  the  same  hour  a 
part  may  be  now  very  active  and  then  inactive.  In  all  its  active  exer- 
cise of  function,  such  a  part  requires  a  larger  supply  of  blood  than  is 
sufficient  for  it  during  the  times  when  it  is  comparatively  inactive.  It 
is  evident  that  the  heart  cannot  regulate  the  supply  to  each  part  at  dif- 
ferent periods;  neither  could  this  be  regulated  by  any  general  and  uni- 
form contraction  of  the  arteries;  but  it  may  be  regulated  by  the  power 
which  the  arteries  of  each  part  have,  in  their  muscular  tissue,  of  con- 


THE   CIRCULATION"   OF   THE    BLOOD.  215 

fcracting  so  as  to  diminish,  and  of  passively  dilating  or  yielding  so  as  to 
permit  an  increase  of,  the  supply  of  blood,  according  to  the  requirements 
of  the  part  to  which  they  are  distributed.  And  thus,  while  the  ventri- 
cles of  the  heart  determine  the  total  quantity  of  blood,  to  be  sent  onward 
at  each  contraction,  and  the  force  of  its  propulsion,  and  Avhile  the  large 
and  merely  elastic  arteries  distribute  it  and  equalize  its  stream,  the 
smaller  arteries,  in  addition,  regulate  and  determine,  by  means  of  their 
muscular  tissue,  the  proportion  of  the  whole  quantity  of  blood  which 
shall  be  distributed  to  each  part. 

This  regulating  function  of  the  arteries  is  governed  and  directed  by 
the  nervous  system  in  the  way  to  be  presently  described. 

The  muscular  element  of  the  middle  coat  also  co-operates  with  the 
elastic  in  adapting  the  calibre  of  the  vessels  to  the  quantity  of  blood 
which  they  contain.  For  the  amount  of  fluid  in  the  blood-vessels  varies 
very  considerably  even  from  hour  to  hour,  and  can  never  be  quite  con- 
stant; and  were  the  elastic  tissue  only  present  the  j^ressure  exercised 
by  the  walls  of  the  containing  vessels  on  the  contained  blood  would  be 
sometimes  very  small,  and  sometimes  inordinately  great.  The  presence 
of  a  muscular  element,  however,  provides  for  a  certain  uniformity  in  the 
amount  of  pressure  exercised;  and  it  is  by  this  adaptive,  uniform,  gen- 
tle, muscular  contraction,  that  the  normal  tone  of  tbe  blood-vessels  is 
maintained.  Deficiency  of  this  tone  is  the  cause  of  the  soft  and  yield- 
ing pulse,  and  its  unnatural^  excess  of  the  hard  and  tense  one. 

The  elastic  and  muscular  contraction  of  an  artery  may  also  be  re- 
garded as  fulfilling  a  natural  purpose  when,  the  artery  being  cut,  it  first 
limits  and  then,  in  conjunction  with  the  coagulated  fibrin,  arrests  the 
escape  of  blood.  It  is  only  in  consequence  of  such  contraction  and  co- 
agulation that  we  arc  free  from  danger  through  even  very  slight  wounds; 
for  it  is  only  when  the  artery  is  closed  that  the  processes  for  the  more 
permanent  and  secure  prevention  of  bleeding  are  established.  But  there 
appears  no  reason  for  supposing  that  the  muscular  coat  assists,  to  more 
than  a  very  small  degree,  in  propelling  the  onward  current  of  blood. 

The  Pulse. 

The  most  characteristic  feature,  then,  of  the  arterial  flow,  is  its  in- 
termittency,  and  this  intermittent  flow  is  seen  or  felt  as  the  Pulse. 

The  pulse  is  generally  described  as  an  expansion  of  the  artery  pro- 
duced by  the  wave  of  blood  set  in  motion  by  the  injection  of  blood  at 
each  ventricular  systole  into  the  already  full  aorta.  As  the  force  of  the 
left  ventricle,  however,  is  not  expended  in  dilating  the  aorta  only,  the 
wave  of  blood  passes  on,  expanding  the  arteries  as  it  goes,  running  as  it 
were  on  the  surface  of  the  more  slowly  travelling  blood  already  con- 
tained in  them,  and  producing  the  pulse  as  it  proceeds. 


21G 


HANDBOOK    OF   PHYSIOLOGY. 


The  distention  of  each  artery  increases  both  its  length  and  its  diam- 
eter. In  their  elongation,  the  arteries  ciiange  their  form,  the  straight 
ones  becoming  slightly  curved,  and  those  already  curved  becoming  more 
so;  but  they  recover  their  previous  form  as  well  as  their  diameter  when 
the  ventricular  contraction  ceases,  and  their  elastic  walls  recoil.  The 
increase  of  their  curves  which  accompanies  the  distention  of  arteries, 
and  the  succeeding  recoil,  may  be  well  seen  in  the  prominent  temporal 
artery  of  an  old  person.  In  feeling  the  pulse,  the  finger  cannot  distin- 
guish the  sensation  produced  by  the  dilatation  from  that  produced  by 
the  elongation  and  curving;  that  which  it  perceives  most  plainly,  how- 
ever, is  the  dilatation,  or  return,  more  or  less,  to  the  cylindrical  form,  of 
the  artery  which  has  been  partially  flattened  by  the  finger. 


Fig.  179.— Marey's  Sphygmograph,  moclifled  by  Mahomed. 


The  pulse — due  to  any  given  beat  of  the  heart — is  not  perceptible 
at  the  same  moment  in  all  the  arteries  of  the  body.  Thus,  it  can  be 
felt  in  the  carotid  a  very  short  time  before  it  is  perceptible  in  the  radial 
artery,  and  in  this  vessel  again  before  it  occurs  in  the  dorsal  artery  of 
the  foot.  The  delay  in  the  beat  is  in  proportion  to  the  distance  of  the 
artery  from  the  heart,  but  the  difference  in  time  between  the  beat  of 
any  two  arteries  probably  never  exceeds  ^  to  -J  of  a  second. 

A  distinction  must  be  carefully  made  between  the  passage  of  the 
wave  along  the  arteries  and  the  arterial  flow  itself.  Both  wave  and 
current  are  present;  but  the  rates  at  which  they  travel  are  very  different, 
that  of  the  wave  16.5  to  33  feet  per  second  (5  to  10  metres),  being  twenty 
or  thirty  times  as  great  as  that  of  the  current. 

The  Sphygmograph. — Much  light  has  been  thrown  on  what  may 
be  called  the  form  of  the  pulse  wave  by  the  sphygmograph  (figs.  179 
and  18;i).  The  principle  on  which  it  acts  will  be  seen  on  reference  to 
figs. 

The  small  button  reph'ces  the  finger  in  the  act  of  taking  tlie  pulse. 


THE   CIRCULATIOX    OF   THE    BLOOD. 


217 


and  is  made  to  rest  lightly  on  the  artery,  the  pulsations  of  which  it  is 
desired  to  investigate.  The  up-and-down  movement  of  the  button  is 
communicated  to  the  lever,  to  the  hinder  end  of  which  is  attached  a 
slight  spring,  which  allows  the  lever  to  move  up,  at  the  same  time  that 


Fig.  180.— Diagram  of  the  lever  of  the  Sphygmograph. 

it  is  just  strong  enough  to  resist  its  making  any  sudden  jerk,  and  in  the 
interval  of  the  beats  also  to  assist  in  bringing  it  back  to  its  original 
position.  For  ordinary  purposes  the  instrument  is  bound  on  the  wrist 
(fig.  181). 

It  is  evident  that  the  beating  of  the  pulse  Avith  the  reaction  of  the 
spring  will  cause  an  up-and-down  movement  of  the  lever,  the  pen  of 
which  will  write  the  effect  on  a  smoked  card,  which  is  made  to  move  by 
clockwork  in  the  direction  of  the  arrows  Thus  a  tracing  of  the  pulse 
is  obtained,  and  in  this  way  much  more  delicate  effects  can  be  seen  than 
can  be  felt  on  the  application  of  the  finger. 


Fig.  181.— The  Sphygmograph  applied  to  the  arm. 

Two  forms  of  sphygmograph  are  shown  in  figs.  179,  182,  viz.,  a  modifica- 
tion of  the  original  instrimient  of  Marey  and  Dudgeon's.  Marey's  instrument, 
and  indeed  all  modifications  of  it,  sufifer  from  the  defect  that  there  is  no  ade- 
quate method  of  measuring  the  pressure  exercised  by  the  button  of  the  instru- 
ment upon  the  artery,  and  that  it  is  difiicult  to  be  certain  of  the  exact  position 
it  occupies  over  the  artery.  Dudgeon's  sphygmograph,  although  very  conven- 
ient to  use,  is,  according  to  Ro\^  and  Adanii,  even  less  satisfactory,  and  the 
tracings  obtained  by  it  are  so  disfigured  by  inertia  vibrations  as  to  render 
them  more  or  less  worthless.  "The  mechanical  construction  cf  the  instrument 
is  such  as  to  render  great  inertia  vibrations  unavoidable."     Tkese  authoi,*s  have 


218 


HANDBOOK    OF   PHYSIOLOGY. 


invented  an   instrument  called  a  sphygmoraetpr,  in  which  these  defects  of  the 
sphygmograph  are  corrected. 


Fig.  183. — Dudgeon's  Sphygmograph. 


The  principle  of  the  sphygmometer  of  Roy  and  Adami  is  shown  in  the  dia- 
gram (fig.   183). 

The  apparatus  consists  of  a  box  (a)  which  is  moulded  to  fit  over  the  end  of 
the  radius  so  as  to  bridge  over  the  radial  artery.  Within  this  is  a  flexible  bag 
(b)  filled  with  water,  and  connected   by  a  T  tube  with  a  rubber  bag  (h)  and 

A 


To  manometer. 


Fig.  183.— Diagrammatic  sectional  representation  of  the  sphygmometer  (Roy  and  Adami) .  a, 
Box  in  which  the  portion  of  the  artery  is  inclosed;  b,  thin-walled  india-rubber  bag  filled  with  water, 
and  communicating  through  tap,  c,  with  matiometer  and  thick-walled  rubber  bag,  h;  d,  piston  con- 
nected by  rod,  e,  with  recording  lever,/;  g.  spiral  spring  attached  to  axis  of  lever,  and  by  which 
the  pressure  in  6,  against  the  piston,  d,  is  counterbalanced;  fc,  skin  and  subcutaneous  tissue;  m,  end 
of  radius  seen  in  section;  n,  radial  artery  seen  in  section. 


THE   CIKCULATION    OF   THE    BLOOD.  219 

mercurial  manometer.  The  fluid  in  the  box  may  be  raised  to  any  desired 
pressure,  and  may  then  be  shut  off  by  tap  (c) .  At  the  upper  part  of  the  box  is 
a  circular  opening,  and  resting  upon  (&)  is  a  flat  button  (d) ,  which  by  means 
of  a  short  light  rod(e)  communicates  the  movement  of  (&)  to  the  lever  (/).  To 
the  axis  of  rotation  of  this  lever  is  a  spiral  watch-spring  (g)  which  can  be  tight- 
ened at  will,  so  that  the  lever  can  be  made  to  take  a  vertical  position  at  any 
desired  hydrostatic  pressure  within  the  box.  The  movements  of  the  lever  are 
recorded  upon  a  piece  of  blackened  glazed  paper  made  to  move  in  a  vertical 
direction  past  it.  When  in  use,  the  box  is  fixed  upon  the  end  of  the  radius  by 
an  appropriate  holder,  and  the  pressure  is  raised  to  any  desired  height  to  which 
the  lever  is  adapted  by  tightening  or  slackening  the  spring.  The  tap  (c)  is 
then  closed.  The  pressure  within  the  box  acts  in  all  directions,  and  is  correctly 
indicated  by  the  manometer. 

The  tracing  of  the  pulse  (sphygmogram),  obtained  by  the  use  of 
the  sphygmogniph,  differs  somewhat  according  to  the  artery  upon  which 
it  is  applied,  but  its  general  characters  are  much  the  same  in  all  cases. 
It  consists  of :— A  sudden  upstroke    (fig.  184,  a),  which  is  somewhat 


Fig.  184,— Diapram  of  pulse  tracing,    a,  Up-stroke;  b,  down-stroke;  c,  pre-dicrotic  wave;  D,  di- 
crotic; E,  post-dicrotic  wave. 

higher  and  more  abrupt  in  the  jwlse  of  the  carotid  and  of  other  arteries 
near  the  heart  than  in  the  radial  and  other  arteries  more  remote;  and 
a  gradual  decline  (b),  less  abrupt,  and  therefore  taking  a  longer  time 
than  (a).  It  is  seldom,  however,  that  the  decline  is  an  uninterrupted 
fall;  it  is  usually  marked  about  half-way  by  a  distinct  notch  (c),  called 
the  (Ucroiic  notch,  which  is  caused  by  a  second  more  or  less  marked  as- 
cent of  tlie  lever  at  that  point  and  by  a  second  wave  called  the  dicrotic 
wave  (d)  ;  not  unfrequeutly  there  is  also  soon  after  the  commencement 
of  the  descent  a  slight  ascent  previous  to  the  dicrotic  notch:  this  is 
called  the  pre-dicrotic  wave  (c),  and  in  addition  there  may  be  one  or 
more  slight  ascents  after  the  dicrotic,  called  post-dicrotic  (e). 

The  interruptions  in  the  downstroke  are  called  the  katacrotic  waves, 
to  distinguish  them  from  an  interruption  in  the  upstroke,  the  anacrotic 
wave,  which  is  sometimes  met  with. 

The  explanation  of  these  tracings  presents  some  difficulties,  not, 
however,  as  regards  the  two  primary  factors,  viz.,  the  upstroke  and 
downstroke,  because  they  are  universally  taken  to  mean  tlie  sudden  in- 


220  HANDBOOK    OP   PHYSIOLOGY. 

jectioB  of  blood  iuto  the  already  full  arteries,  and  the  gradual  fall  of 
the  lever  signifying  the  recovery  of  the  arteries  by  their  recoil.  These 
points  may  be  demonstrated  on  a  system  of  clastic  tubes,  Avitli  a  syringe 
to  pnmp  in  water  at  regular  intervals,  just  as  well  as  on  the  radial 
artery,  or  on  the  more  complicated  system  of  tubes  in  which  the  heart, 
the  arteries,  the  capillaries  and  veins  are  represented,  Avhich  is  known 
as  an  arterial  scJiema.  If  we  place  two  or  more  sjDhygmographs  upon 
such  a  system  of  tubes  at  increasing  distances  from  the  pump,  we  may 
demonstrate  first,  that  the  rise  of  the  lever  commences  earliest  in  that 
nearest  the  pump,  and  secondly,  that  it  is  higher  and  more  sudden, 
while  at  a  longer  distance  from  the  pump  the  wave  is  less  marked,  and 
a  little  later.  So  in  the  arteries  of  the  body  the  Avave  of  blood  gradu- 
ally gets  less  and  less  as  we  approach  the  periphery  of  the  arterial  sys- 
tem, and  is  lost  in  the  capillaries. 

The  origin  of  the  secondary  waves  is  still  a  matter  of  uncertainty. 


Fig.  185. — Anacrotic  pulse  from  a  case  of  aortic  aneurism. 

The  anacrotic  wave  occurs  Avhen  the  peripheral  resistance  is  high;  that 
is,  when,  for  some  time  during  the  systole,  the  flow  from  the  aorta 
toward  the  jieriphery  is  slower  than  the  flow  from  the  ventricle  into  the 
aorta.  Thus,  it  is  seen  in  some  cases  of  nephritis  where  the  arteries  are 
rigid  and  the  peripheral  resistance  high. 

The  dicrotic  wave  is  the  most  important  of  the  secondary  waves,  and 
has  been  the  subject  of  much  discussion.  It  is  constantly  present  in 
pulse-tracings,  but  varies  in  height.  In  point  of  time  the  dicrotic  wave 
occurs  immediately  after  the  closure  of  the  aortic  semilunar  valves.  In 
certain  conditions,  generally  of  disease,  it  becomes  so  marked  as  to  be 
quite  plain  to  the  unaided  finger.  Such  a  pulse  is  called  dicrotic.  The 
most  generally  accepted  view  of  the  cause  of  the  dicrotic  wave  is  that  it 
represents  a  rebound  from  the  closed  aortic  valves.  During  systole,  as 
the  blood  is  forcibly  injected  into  the  aorta,  there  is  as  it  were  an  over- 
distention  of  the  artery.  The  systole  suddenly  ends,  the  aorta  by  rea- 
son of  its  elasticity  tends  to  recover  itself,  the  blood  is  driven  back 
against  the  semilunar  valves,  closing  them  and  at  the  same  time  giving 
rise  to  a  wave — ^the  dicrotic  wave^ — 'Which  begins  at  the  heart  and  travels 
onward  toward  the  periphery  like  the  primary  wave.     According  to  Fos- 


THE   CIRCULATrON"    OF   THE    BLOOD. 


221 


ter,  the  conditions  favoring  the  develoirment  of  dierotism  are:  (1)  a 
highly  extensible  and  elastic  arterial  wall;  (2)  a  coiniiaratively  low  mean 
blood  pressure,  leaving  the  extensible  reaction  free  scope  to  act;  (3)  a 
vigorous  and  rapid  stroke  of  the  ventricle,  discharging  into  the  aorta  a 
considerable  quantity  of  blood. 

The  other  secondary  waves  are  probably  due  to  the  elastic  recoil  of 
the  arteries,  though  some  of  thenx  at  least  may  be  due  to  the  inertia  of 
the  instruments  used. 


F'g.  186.— A,  Normal  pulse-t racing:  from  radial  of  lu-al thy  aflult.  obtained  by  the  sphygmometer. 
B,  From  same  artery,  with  the  same  extra-arterial  pressure,  taken  diu-mg  acute  uasal  cataiTh. 


In  the  use  of  the  sphygmograph  care  must  be  taken  as  to  the  careful 
regulation  of  the  pressure.  If  the  pressure  be  too  great,  the  characters 
of  the  pulse  may  he  almost  entirely  obscured,  or  the  artery  may  be 
entirely  obstructed,  and  no  tracing  is  obtained;  and  on  the  other  hand, 
if  the  pressure  is  too  slight,  a  very  small  part  of  the  characters  may  be 
represented  on  the  tracing. 


222  HANDBOOK    OF   PHYSIOLOGY. 

The  Capillary  Flow. 

It  is  in  the  capillaries  that  the  chief  resistance  is  offered  to  the  prog- 
ress of  the  blood ;  for  in  them  the  friction  of  the  blood  is  greatly  in- 
creased by  the  enormous  multiplication  of  the  surface  with  which  it  is 
brought  in  contact. 

When  the  capillary  circulation  is  examined  in  any  transparent  part 
of  a  full-grown  living  animal  by  means  of  the  microscope  (fig.  187),  the 
blood  is  seen  to  flow  with  a  constant  equable  motion;  the  red  blood- 
corpuscles  moving  along,  mostly  in  single  file,  and  bending  in  various 
ways  to  accommodate  themselves  to  the  tortuous  course  of  the  capillary, 
but  instantly  recovering  their  normal  outline  on  reaching  a  wider  vessel. 

At  the  circumference  of  the  stream  in  the  larger  capillaries,  but 
sepecially  well  marked  in  the  small  arteries  and  veins,  in  contact  with 


Fig.  187.— Capillaries  (C.)  in  the  web  of  the  frog's  foot  connecting  a  small  artery  (A)  with  a 
small  vein  V  (after  Allen  Thomson). 

the  walls  of  the  vessel,  and  adhering  to  them,  there  is  a  layer  of  liquor 
sanguinis  which  appears  to  be  motionless.  The  existence  of  this  still 
layer,  as  it  is  termed,  is  inferred  both  from  the  general  fact  that  such 
an  one  exists  in  all  fine  tubes  traversed  by  fluid,  and  from  what  can  be 
&een  in  watching  the  movements  of  the  blood-corpuscles.  The  red 
corpuscles  occupy  the  middle  of  the  stream  and  move  with  comparative 
rapidity;  the  colorless  corpuscles  run  much  more  slowly  by  the  walls  of 
the  vessel;  while  next  to  the  wall  there  is  often  a  transparent  space  in 
which  the  fluid  appears  to  be  at  rest;  for  if  any  of  the  corpuscles  hap- 
pen to  be  forced  within  it,  they  move  more  slowly  than  before,  rolling 
lazily  along  the  side  of  the  vessel,  and  often  adhering  to  its  wall.  Part 
of  this  slow  movement  of  the  colorless  corpuscles  and  their  occasional 
stoppage  may  be  due  to  their  having  a  natural  tendency  to  adhere  to 
the  walls  of  the  vessels.  Sometimes,  indeed,  when  the  motion  of  the 
blood  is  not  strong,  many  of  the  white  corpuscles  collect  in  a  capillary 
vessel,  and  for  a  time  entirely  prevent  the  passage  of  the  red  corpuscles. 


THE    CIRCULATION   OF   THE    BLOOD. 


223 


When  the  peripheral  resistance  is  greatly  diminished  by  the  dilata- 
tion of  the  small  arteries  and  capillaries,  so  mncli  blood  passes  on  from 
the  arteries  into  the  capillaries  at  each  stroke  of  the 
heart,  that  there  is  not  snflicient  remaining  in  the 
arteries  to  distend  them,  Thns,  the  intermittent 
current  of  the  ventricular  systole  is  not  converted 
into  a  continuous  stream  by  the  elasticity  of  the 
arteries  before  the  capillaries  are  reached;  and  so  in- 
Lermittency  of  the  flow  occurs  botli  in  cai^illaries 
and  veins  and  a  pulse  is  produced.  The  same  j^he- 
nomenon  may  occur  when  the  arteries  become  rigid 
from  disease,  and  when  the  beat  of  the  heart  is  so 
slow  or  so  feeble  that  the  blood  at  each  cardiac  sys- 
tole has  time  to  pass  on  to  the  capillaries  before  the 
next  stroke  occurs;  the  amount  of  blood  sent  at  each 
stroke  being  insufficient  to  properly  distend  the 
elastic  arteries. 

It  was  formerly  supposed  that  the  occurrence 
of  any  transudation  from  the  interior  of  the  capil- 
laries into  the  midst  of  the  surrounding  tissues  was 
confined,  in  the  absence  of  injury,  strictly  to  the 
fluid  part  of  the  blood;  in  other  words,  that  the 
corpuscles  could  not  escape  from  the  circulating 
stream,  unless  the  wall  of  the  containing  blood-vessel 
was  ruptured.  It  is  true  that  an  English  physiologist,  Augustus  Waller, 
affii-med,  in  1846,  that  he  had  seen  blood-corpuscles,  both  red  and  white, 
pass  bodily  through  the  wall  of  the  capillary  vessel  in  which  they  were 
contained  (thus  confirming  what  had  been  stated  a  short  time  previously 
by  Addison);  and  that,  as  no  opening  could  be  seen  before  their  escape, 
so  none  could  be  observed  -afterward — so  rapidly  was  the  part  healed. 
But  these  observations  did  not  attract  much  notice  until  the  phenome- 
non of  escape  of  the  blood-corpuscles  from  the  capillaries  and  minute 
veins,  apart  from  mechanical  injury,  were  re-discovered  by  Cohnheim 
in  1867. 

Cohnheim's  experiment  demonstrating  the  passage  of  the  corpuscles 
through  the  wall  of  the  blood-vessel  is  perfornu'd  in  the  following  man- 
ner. A  frog  is  urarized,  that  is  to  say,  paralysis  is  produced  by  ejecting 
under  the  skin  a  minute  quantity  of  the  poison  called  urari;  and  the 
abdomen  having  been  opened,  a  portion  of  small  intestine  is  drawn  out, 
and  its  transparent  mesentery  spread  out  under  a  microscope.  After 
a  variable  time,  occuijied  by  dilatation,  following  contraction  of  the 
minute  vessels  and  accompanying  quickening  of  the  blood-stream,  there 
ensues  a  retardation  of  the  current,  and  blood-corpuscles,  both  red  and 
white,  begin  to  make  their  way  through  the  capillaries  and  small  veins. 


Fig.  188.— A  large  ca- 
pillary froui  the  frog's 
mesentery  eight  hours 
utter  iri'itatiou  had 
heeu  set  up,  showing 
emigration  ot  leueo- 
oytes.  ((,  Cells  in  the 
act  of  traversing  the 
capillary  wall;  b,  some 
already  escaped. 

( Frey.; 


224  HANDBOOK    OF   PHySIOLOGY. 

The  white  corpuscles  pass  through  the  capillai-y  wall  chiefly  by  the 
amoeboid  movement  with  which  they  are  endowed.  This  migration  oc- 
curs to  a  limited  extent  in  health,  but  in  inflammatory  conditions  is 
much  increased. 

The  process  of  diapedesis  of  the  red  corpuscles,  which  occurs  under 
circumstances  of  impeded  venous  circulation,  and  consequently  increased 
blood-pressure,  resembles  closely  the  migration  of  the  leucocytes,  with 
the  exception  that  they  are  squeezed  through  the  wall  of  the  vessel,  and 
do  not,  like  them,  work  their  way  through  by  amoeboid  movement. 

Various  explanations  of  thzse  remarkable  phenomena  have  been 
suggested.  Some  believe  that  pseudo-stomata  between  contiguous  endo- 
thelial cells  provide  the  means  of  escape  for  the  blood-corpuscles.  But 
the  chief  share  in  the  process  is  probably  to  be  found  in  the  vital  en- 
dowments with  respect  to  mobility  and  contraction  of  the  parts  con- 
cerned— both  of  the  corpuscles  and  of  the  capillary  wall  itself. 

The  circulation  through  the  capillaries  must,  of  necessity,  be  largely 
influenced  by  that  which  occurs  in  the  vessels  on  either  side  of  them — 
in  the  arteries  or  the  veins;  their  intermediate  position  causing  them  to 
feel  at  once,  so  to  speak,  any  alteration  in  the  size  ox  rate  of  the  arterial 
or  venous  blood-stream.  Thus,  the  apparent  contraction  of  the  oapilla- 
riee,  on  the  application  of  certain  irritating  substances,  and  during  fear, 
and  their  dilatation  in  blushing  may  be  referred  primarily  to  the  action 
of  the  small  arteriss. 

The  Venous  Flow. 

The  blood-current  in  the  veins  is  maintained  (a)  primarily  by  the  vis 
a  tergo  of  the  contraction  of  the  left  ventricle;  but  very  effectual  assist- 
ance to  the  flow  is  aiforded  (b)  by  the  action  of  the  muscles  capable  of 
j^ressing  on  the  veins  with  valves,  as  well  as  (c)  by  the  suction  action  of 
the  heart,  and  (e)  aspiration  of  the  thorax. 

The  effect  of  muscular  pressure  upon  the  circulation  may  be  thus 
explained.  When  pressure  is  applied  to  any  part  of  a  vein,  and  the 
current  of  blood  in  it  is  obstructed,  the  portion  behind  the  seat  of  pres- 
sure becomes  swollen  and  distended  as  far  back  as  the  next  pair  of 
valves,  which  are  in  consequence  closed.  Thus,  whatever  force  is  exer- 
cised by  the  pressure  of  the  muscles  on  the  veins,  is  distributed  partly 
in  pressing  the  blood  onward  in  the  proper  course  of  the  circulation, 
and  partly  in  pressing  it  backward  and  closing  the  valves  behind. 

The  circulation  might  lose  as  much  as  it  gains  by  such  an  action,  if 
it  were  not  for  the  numerous  communications,  one  with  another;  for 
through  these,  the  closing  up  of  the  venous  channel  by  the  backward 


THE    CIIIOULATIONT    OF    THE    I'.LOOU.  225 

pressure  13  prevented  from  Lciiig  any  serious  liindranco  to  the  circnla- 
tion,  since  the  blood,  of  wliicdi  the  onward  course  is  arrested  by  tlie 
closed  valves,  can  at  once  pass  through  some  anastomosing  channel,  and 
proceed  on  its  way  by  another  vein.  Thus,  therefore,  the  effect  of  mus- 
cular pressure  upon  veins  which  have  valves,  is  turned  almost  entirely 
to  the  advantage  of  the  circulation;  the  pressure  of  the  blood  onward 
is  all  advantageous,  and  the  pressure  of  the  blood  backward  is  prevented 
from  being  a  hindrance  by  the  closure  of  the  valves  and  the  anastomoses 
of  the  veins. 

The  venous  flow  is  also  assisted  by  the  suction  action  of  the  heart, 
since  at  some  time  during  every  cardiac  cycle  the  pressure  falls  below 
that  of  the  atmosphere. 

The  aspiration  of  the  thorax  will  be  considered  more  fully  in  the 
chapter  on  Respiratiou.  In  this  connection  it  may  be  said,  however, 
tliat  the  pressure  in  the  great  veins  falls  during  inspiration  and  rises 
during  expiration. 

The  Velocity  of  the  Flow. 

The  velocity  of  the  blood-current  at  any  given  point  in  the  various 
divisions  of  the  circulatory  system  is  inversely  proportional  to  their  sec- 
tional area  at  that  point.  If  the  sectional  area  of  all  the  branches  of  a 
vessel  united  were  always  the  same  as  that  of  the  vessel  from  which  they 
arise,  and  if  the  aggregate  sectional  area  of  the  capillary  vessels  were 
equal  to  that  of  the  aorta,  the  mean  rapidity  of  the  blood's  motion  in  the 
capillaries  would  be  the  same  as  in  the  aorta;  and  if  a  similar  corre- 
spondence of  capacity  existed  in  the  veins  and  arteries,  there  would  be 
an  equal  correspondence  in  the  rapidity  of  the  circulation  in  them.  But 
the  arterial  and  venous  systems  may  be  represented  by  two  truncated 
cones  with  their  apices  directed  toward  the  heart;  the  area  of  their 
united  base  (the  sectional  area  of  the  capillaries)  being  400 — 800  times 
as  great  as  that  of  the  truncated  apex  representing  the  aorta.  Thus 
the  velocity  of  blood  in  the  capillaries  is  not  more  than  j;',-^  of  tliat  in 
the  aorta. 

In  the  Arteries. — The  velocity  of  the  stream  of  blood  is  greater  in 
the  arteries  than  in  any  other  part  of  the  circulatory  system,  and  in  thom 
it  is  greatest  in  the  neighborhood  of  the  heart,  and  during  the  ventricu- 
lar systole.  The  rate  of  movement  diminishes  during  the  diastole  of 
the  ventricles,  and  in  the  parts  of  the  arterial  system  most  distant  from 
the  heart.  Chauveau  has  estimated  the  rapidity  of  the  blood-stream  in 
the  carotid  of  the  horse  at  over  20  inches  per  second  during  the  heart's 
systole,  and  nearly  6  inches  during  the  diastole  (520-150  mm.). 
IS 


226 


HANDBOOK    OF    PHYSIOLOGY. 


Estimation  of  the  Velocity. — Various  instruments  hare  been  devised  for 
measuring  the  velocity  of  the  blood-stream  in  the  arteries.  Ludwig's  StromuJir 
(fig.  189)  consists  of  a  U-shaped  glass  tube  dilated  at  a  and  a',  the  ends  of 
which,  h  and  i.  are  of  known  calibre.  The  bulbs  can  be  filled  by  a  common 
opening  at  k.  The  instrument  is  so  contrived  that  at  5  and  b'  the  glass  part  is 
firmly  fixed  into  metal  cylinders,  attached  to  a  circu- 
lar horizontal  table,  c  c',  capable  of  horizontal  move- 
ment on  a  similar  table  cl  d'  about  the  vertical  axis 
marked  in  figure  by  a  dotted  line.  The  opening  in  c  c  , 
when  the  instrument  is  in  position,  as  in  fig.,  cor- 
!  li  responds  exactly  with  those  in  d  d' ;    but  if   c  c'  be 


Fig.  189. 


Fig.  190. 


Fig.  189. — Ludwig's  Stromuhr. 

Fig.  190.— Diagram  of  Chauveau's  Instrument,  a.  Brass  tube  for  introduction  into  the  lumen  of 
the  artery,  and  containing  an  index  needle,  which  passes  througli  the  elastic  membrane  in  its  side. 
and  moves  by  the  impulse  of  the  blood-cm'rent.  c.  Graduated  scale,  for  measimng  the  extent  of 
the  oscillations  of  the  needle. 


turned  at  right  angles  to  its  present  position,  there  is  no  communication  be- 
tween h  and  a,  and  i  and  a',  but  h  communicates  directly  with  i ;  and  if 
turned  through  two  right  angles  c'  communicates  with  d,  and  c  with  d',  and 
there  is  no  direct  communication  between  li  and  i.  The  experiment  is  per- 
formed in  the  following  way : — The  artery  to  be  experimented  upon  is  divided 
and  connected  with  two  canulae  and  tubes  which  fit  it  accurately  with  h  and 
i — h  the  central  end,  and  i  the  peripheral ;  the  bulb  a  is  filled  with  olive  oil  up 
to  a  point  rather  lower  than  fc,  and  a'  and  the  remainder  of  a  is  filled  with 
defibrinated  blood ;  the  tube  on  fc  is  then  carefully  clamped :  the  tubes  d  and 
d'  are  also  filled  with  defibrinated  blood.  When  everything  is  ready,  the  blood 
is  allowed  to  flow  into  a  through  h,  and  it  pushes  before  it  the  oil,  and  that 
the  defibrinated  blood  into  the  arterj^  through  i,  and  replaces  it  in  a' ;  Avhen  the 
blood  reaches  the  former  level  of  the  oil  in  a' ,  the  disc  c  c'  is  turned  rapidly 
through  two  riglit  angles,  and  the  blood  flowing  through  d  into  a'  again  dis- 
places the  oil  which  is  driven  into  a.  This  is  repeated  several  times,  and  the 
duration  of  the  experiment  noted.  The  capacity  of  a  and  a'  is  known ;  the 
diameter  of  the  artery  is  also  known  by  its  corresjwnding  with  the  canulae  of 
known  diameter,  and  as  the  number  of  times  a  has  been  filled  in  a  given  time 
is  known,  the  velocity  of  the  cm'rent  can  be  calculated. 


THE   CIUCULATIO>f    OF    THK    ]5L()()I).  227 

Chauveau's  instrument,  tig.  190,  consists  of  a  tliin  brass  tiibe,  o  in  one  side 
of  which  is  a  small  perforation  closed  bj^  thin  vulcanized  india-rubber.  Pa.ss- 
ing  through  the  rubber  is  a  fine  lever,  one  end  of  which,  slightly  flattened, 
extends  into  the  lumen  of  ,the  tube,  while  the  other  moves  over  the  face  of  a 
dial.  The  tube  is  inserted  into  the  interior  of  an  artery,  and  ligatures  applied  to 
fix  it,  so  that  the  movement  of  the  blood  may,  in  flowing  through  the  tube,  be 
indicated  by  the  movement  of  the  outer  extremity  of  the  lever  on  the  face  of 
the  dial. 

The  Hcemafochometer  of  Vierordt,  and  the  instrument  of  Lortet,  resemble  in 
principle  that  of  Chauveau. 

Intlie  Capillaries.— The  observution  of  Hales,  E.  11.  "Weber,  and  Val- 
entin agree  very  closely  as  to  the  rate  of  the  blood-current  in  the  capil- 
laries of  the  frog;  and  the  mean  of  their  estimates  gives  the  velocity  of 
the  systemic  capillary  circulation  at  about  one  inch  (25  mm.)  per  min- 
ute. The  velocity  in  the  capillaries  of  -warm-blooded  animals  is  greater. 
In  the  dog  j^  to  j  j] ,y^  inch  (.5  to  .75  mm.)  a  second.  This  may  seem 
inconsistent  with  the  facts,  which  show  that  the  whole  circulation  is 
accomplished  in  about  half  a  minute.  But  the  whole  length  of  capillary 
vessels,  through  which  any  given  portion  of  blood  has  to  pass,  probably 
does  not  exceed  from  yV^h  to  -Vth  of  an  inch  (.5  mm.);  and  therefore 
the  time  required  for  each  quantity  of  blood  to  traverse  its  own  appointed 
portion  of  the  general  capillary  system  will  scarcely  amount  to  a  second. 

J}L  till'.  Veins. — The  velocity  of  the  blood  is  greater  in  the  veins  than 
in  the  capillaries,  but  less  than  in  the  arteries:  this  fact  depending  upon 
the  relative  capacities  of  the  arterial  and  venous  systems.  If  an  accurate 
estimate  of  the  proportionate  areas  of  arteries  and  the  veins  correspond- 
ing to  them  could  be  made,  we  might,  from  the  velocity  of  the  arterial 
current,  calculate  that  of  the  venous.  A  usual  estimate  is,  that  the  ca- 
pacity of  the  veins  is  about  twice  or  three  times  as  great  as  that  of  tlie 
arteries,  and  that  the  velocity  of  the  blood's  motion  is,  therefore,  about 
twice  or  three  times  as  great  in  the  arteries  as  in  the  veins,  8  inches 
(200  mm.)  a  second.  The  rate  at  which  the  blood  moves  in  the  veins 
gradually  increases  the  nearer  it  approaches  the  heart,  for  the  sectional 
area  of  the  venous  trunks,  compared  \\\\\\  that  of  the  branches  opening 
into  them,  becomes  gradually  less  as  the  trunks  advance  toward  the  heart. 

Of  (lie  Circulation  as  a  ]]7iole. — It  would  appear  that  a  portion  of 
i)lood  can  traverse  the  entire  course  of  the  circulation,  in  the  horse,  in 
half  a  minute.  Of  course  it  would  require  longer  to  traverse  the  vessels 
of  the  most  distant  part  of  the  extremities  than  to  go  through  those  of 
the  neck;  but  taking  an  average  leugtli  of  vessels  to  be  traversed, 
it  may  be  concluded  that  half  a  minute  rejiresents  the  average  rate. 
Stewart  states  that  tlie  circulation  time  in  man  is  probably  not  less  than 
twelve  nor  more  than  fifteen  seconds. 


22S  HANDBOOK    OF    PHYSIOLOGY. 

Satisfactory  data  for  these  estimates  are  afforded  by  the  results  of 
experiments  to  ascertain  the  rapidity  with  whicli  poisons  introduced  into 
the  blood  are  transmitted  from  one  part  of  the  vascular  system  to  an- 
other. The  time  required  for  the  passage  of  a  solution  of  potassium 
ferrocyanide,  mixed  with  the  blood,  from  one  jugular  vein  (through  the 
right  side  of  the  heart,  the  pulmonary  vessels,  the  left  cavities  of  the 
heart,  and  the  general  circulation)  to  the  jugular  vein  of  the  opposite 
side,  varies  from  twenty  to  thirty  seconds.  The  same  substance  was 
transmitted  from  the  jugular  vein  to  the  great  saphena  in  twenty  sec- 
onds; from  the  jugular  vein  to  the  masseteric  artery  in  between  fifteen 
and  thirty  seconds;  to  the  facial  artery,  in  one  experiment,  in  between 
ten  and  fifteen  seconds;  in  another  experiment  in  between  twenty  and 
twenty-five  seconds;  in  its  transit  from  the  jugular  vein  to  the  metatar- 
sal artery,  it  occupied  between  twenty  and  thirty  seconds,  and  in  one 
instance  more  than  forty  seconds.  The  result  was  nearly  the  same 
whatever  was  the  rate  of:  the  heart's  action. 

In  all  these  experiments,  it  is  assumed  that  the  substance  injected 
moves  with  the  blood,  and  at  the  same  rate,  and  does  not  move  from 
one  part  of  the  organs  of  circulation  to  another  by  diffusing  itself 
through  the  blood  or  tissues  more  quickly  than  the  blood  moves.  The 
assumption  is  sufficiently  probable  to  be  considered  nearly  certain,  that 
the  times  above  mentioned,  as  occupied  in  the  passage  of  the  injected 
substances,  are  those  in  which  the  portion  of  blood,  into  which  each 
was  injected,  was  carried  from  one  part  to  another  of  the  vascular  system. 

Another  mode  of  estimating  the  general  velocity  of  the  circulating 
blood,  is  by  calculating  it  from  the  quantity  of  blood  supposed  to  br3 
contained  in  the  body,  and  from  the  quantity  which  can  pass  through 
the  heart  in  each  of  its  actions.  But  the  conclusions  arrived  at  by  this 
method  are  less  satisfactory.  For  the  total  quantity  of  blood,  and  tlie 
capacity  of  the  cavities  of  the  heart,  have  as  yet  been  only  approximately 
ascertained.  Still  the  most  careful  of  the  estimates  thus  made  accord 
very  nearly  with  those  already  mentioned;  and  it  may  be  assumed  that 
the  blood  may  all  j^ass  through  the  heart  in  about  twenty-five  seconds. 


Local  Peculiarities  of  the  Circulation. 

The  most  remarkable  peculiarities  attending  the  circulation  of  blood 
through  different  organs  are  observed  in  the  cases  of  the  brain,  the  3rec- 
tile  organfi,  the  lungs,  the  liver,  and  the  kidneys. 

In  the  Brain. — For  the  due  performance  of  its  functions  the  brain 
requires  a  large  supply  of  blood.  This  object  is  effected  through  the 
number  and  size  of  its  arteries,  the  two  internal  carotids,  and  the  two 
vertebrals.     It  is  further  necessary  that  the  force  with  which  this  blood 


THE   CIRCULATION    OF   THE    BLOOD.  229 

is  sent  to  tlie  brain  sliould  be  lc?s,  or  at  least  should  be  subject  to  less 
variation  from  external  circumstances  than  it  is  in  other  parts,  and  so 
tlie  large  arteries  are  very  tortuous  and  anastomose  freely  in  the  circle 
of  Willis,  which  thus  insures  that  the  supply  of  blood  to  the  brain  is 
uniform,  though  it  may  by  an  accident  be  diminished,  or  in  some  way 
changed,  through  one  or  more  of  the  principal  arteries.  The  transit  of 
the  large  arteries  tlirough  bone,  especially  the  carotid  canal  of  the  tem- 
poral bone,  may  prevent  any  undue  distention;  and  uniformity  of  sup- 
ply is  further  insured  by  the  arrangement  of  the  vessels  in  the  pia 
mater,  in  which,  previous  to  their  distribution  to  the  substance  of  the 
brain,  the  large  arteries  break  up  and  divide  into  innumerable  minute 
branches  ending  in  capillaries,  which,  after  frequent  communication 
with  one  another,  enter  the  brain,  and  carry  into  nearly  every  part  of  it 
uniform  and  equable  streams  of  blood.  The  arteries  are  also  enveloped 
in  a  special  lymphatic  sheath.  The  arrangement  of  the  veins  within 
the  cranium  is  also  peculiar.  The  large  venous  trunks  or  sinuses  are 
formed  so  as  to  be  scarcely  capable  of  change  of  size;  and  composed, 
as  they  are,  of  the  tough  tissue  of  the  dura  mater,  and,  in  some  instances 
bounded  on  one  side  by  the  bony  cranium,  they  are  not  compressible  by 
any  force  which  the  fulness  of  the  arteries  might  exercise  through  the 
substance  of  the  brain;  nor  do  they  admit  of  distention  Avhen  the  flow 
af  venous  blood  from  the  brain  is  obstructed. 

The  general  uniformity  in  the  supply  of  blood  to  the  l)raiii,  which 
is  thus  secured,  is  well  adapted,  not  only  to  its  functions,  but  also  to  its 
condition  as  a  mass  of  nearly  incompressible  substance  placed  in  a  cav- 
ity with  unyielding  walls.  These  conditions  of  the  brain  and  skull  for- 
merly appeared,  indeed,  enough  to  justify  the  opinion  that  the  quantity 
of  blood  in  the  brain  must  be  at  all  times  the  same.  But  it  was  found 
that  in  animals  bled  to  death,  without  any  aperture  being  made  in  the 
cranium,  the  brain  became  pale  and  anaemic  like  other  parts.  And  in 
death  from  strangling  or  drowning,  there  was  congestion  of  the  cerebral 
vessels;  while  in  death  by  prussic  acid,  the  quantity  of  blood  in  the 
cavity  of  the  cranium  was  determined  by  the  j^osition  in  which  the  ani- 
mal was  placed  after  death,  the  cerebral  vessels  being  congested  when 
the  animal  was  suspended  with  its  head  downward,  and  comparatively 
empty  when  the  animal  was  kept  suspended  by  the  ears.  Thus,  it  was 
concluded,  although  the  total  volume  of  the  contents  of  the  cranium  is 
}n-obably  nearly  always  the  same,  yet  the  quantity  of  blood  in  it  is  liable 
to  variation,  its  increase  or  diminution  being  accompanied  by  a  simul- 
taneous diminution  or  increase  in  the  quantity  of  the  cerebro-spinal 
Ihiid,  whicli,  by  readily  admitting  of  being  removed  from  one  part  of 
the  brain  and  spinal  cord  to  another,  and  of  being  rapidly  absorbed,  and 


230  HANDBOOK    OF    PHYSIOLOGY. 

as  readily  effused,  would  serve  as  a  kind  of  supplemental  fluid  to  tlie 
other  contents  of  the  cranium,  to  keep  it  uniformly  filled  in  case  of 
variations  in  their  quantity.  And  there  can  be  no  doubt  that,  although 
the  arrangements  of  the  blood-vessels,  to  which  reference  has  been  made, 
insure  to  the  brain  an  amount  of  blood  which  is  tolerably  uniform,  yet, 
inasmuch  as  with  every  beat  of  the  heart  and  every  act  of  respiration 
and  under  many  other  circumstances,  the  quantity  of  blood  in  the  cav- 
ity of  the  cranium  is  constantly  varying,  it  is  plain  that,  were  there 
not  provision  made  for  the  possible  displacement  of  some  of  the  contents 
of  the  unyielding  bony  case  in  which  the  brain  is  contained,  there  would 
be  often  alternations  of  excessive  pressure  with  insufficient  supply  of 
blood. 

Chemical  Composition  of  Cey^ebi'o- spinal  Fhdd. — The  cerebro-spinal  fluid  is 
ti'ansparent,  colorless,  not  viscid,  with  a  saline  taste  and  alkaline  reaction,  and 
is  not  affected  by  heat  or  acids.  It  contains  981-984  parts  water,  sodium 
chloride,  traces  of  potassium  chloride,  of  sulphates,  carbonates,  alkaline  and 
earthy  lihosphates,  minute  traces  of  urea,  sugar,  sodium  lactate,  fatty  matter, 
cholesterin,  and  albumen  (Flint). 

In  Erectile  Structures. — The  instances  of  greatest  variation  in  the 
quantity  of  blood  contained,  at  different  times,  in  the  same  organs,  are 
found  in  certain  structures  which,  under  ordinary  circumstances,  are 
soft  and  flaccid,  but,  at  certain  times,  receive  an  unusually  large  quan- 
tity of  blood,  become  distended  and  swollen  by  it,  and  pass  into  the  state 
which  has  been  termed  erection.  Such  structures  are  the  covpora  caver- 
nosa and  corpus  sjjongiosum  of  the  penis  in  the  male,  and  the  clitoris  in 
the  female;  and,  to  a  less  degree,  the  nipple  of  the  mammary  gland  in 
both  sexes.  The  corpus  cavernosum  penis,  which  is  the  best  example 
of  an  erectile  structure,  has  an  external  fibrous  membrane  or  sheath;  and 
frorn  the  inner  surface  of  the  latter  are  prolonged  numerous  fine  lamellae 
which  divide  its  cavity  into  small  com|5artments  looking  like  cells  when 
they  are  inflated.  Within  these  is  situated  the  plexus  of  veins  upon 
which  the  peculiar  erectile  property  of  the  organ  mainly  depends.  It 
consists  of  short  veins  which  very  closely  interlace  and  anastomose  with 
eaclx  other  in  all  directions,  and  admit  of  great  variations  of  size,  col- 
lapsing in  the  passive  state  of  the  organ,  but,  for  erection,  callable  of  an 
amount  of  dilatation  which,  exceeds  beyond  comparison  that  of  the 
arteries  and  veins  which  convey  the  blood  to  and  from  them.  The 
strong  fibrous  tissue  lying  in  the  intervals  of  the  venous  plexuses,  and 
the  external  fibrous  membrane  or  sheath  with  which  it  is  connected, 
limit  the  distention  of  the  vessels,  and,  during  the  state  of  erection,  give 
to  the  penis  its  condition  of  tension  and  firmness.  The  same  general 
condition  of  vessels  exists  in  the  corpus  spongiosum  urethras,  but  around 
the  urethra  the  fibrous  tissue  is  much  weaker  thtin  around  the  body  of 
the  penis,  and  around  the  glans  there  is  none.     The  venous  blood  is 


THE   CI-RCULATION    OF   THE    BLOOD.  231 

returned  from  the  plexuses  by  comj)aratively  small  veins;  those  from 
the  glans  and  the  fore  part  of  the  urethra  empty  themselves  into  the 
dorsal  veins  of  the  penis;  those  from  the  cavernosum  pass  into  deeper 
veins  which  issue  from  the  corpora  cavernosa  at  the  crura  j)enis;  and 
those  from  the  rest  of  the  urethra  and  bulb  j)ass  more  directly  into  the 
plexus  of  the  veins  about  the  prostate.  For  all  these  veins  one  condi- 
tion is  the  same;  namely,  that  they  are  liable  to  the  pressure  of  muscles 
when  they  leave  the  penis.  The  muscles  chiefly  concerned  in  this  action 
are  the  erector  penis  and  accelerator  urinffi.  Erection  results  from  the 
distention  of  tlie  venous  plexuses  Avith  blood.  The  j^i'incijjal  exciting 
cause  in  the  erection  of  the  penis  is  nervous  irritation,  originating  in 
the  part  itself,  or  derived  from  the  brain  and  spinal  cord.  The  nervous 
influence  is  communicated  to  the  penis  by  the  pudic  nerves,  which  ram- 
ify in  its  vascular  tissue;  and  after  their  division  in  the  horse  the  penis 
is  no  longer  capable  of  erection. 

This  influx  of  the  blood  is  the  first  condition  necessary  for  erection, 
and  through  it  alone  much  enlargement  and  turgescence  of  the  penis 
may  ensue.  But  the  erection  is  probably  not  complete,  nor  maintained 
for  any  time  except  when,  together  with  this  influx,  the  muscles  already 
mentioned  contract,  and,  by  compressing  the  veins,  stop  the  efflux  of 
blood,  or  prevent  it  from  being  as  great  as  the  influx. 

It  appears  to  be  only  the  most  perfect  kind  of  erection  that  needs 
the  help  of  muscles  to  compress  the  veins;  and  none  such  can  materially 
assist  the  erection  of  the  nipples,  or  that  amount  of  turgescence,  just 
falling  short  of  erection,  of  which  the  spleen  and  many  other  parts  are 
caj^able.  For  such  turgescence  nothing  more  seems  necessary  than  a 
large  plexiform  arrangement  of  the  veins,  and  such  arteries  as  may  ad- 
mit, upoii  occasion,  augmented  quantities  of  blood. 

The  circxilation  in  the  Lungs,  Liver,  and  Lvidneys  will  be  described 
under  their  respective  heads. 

The  Regulation  of  the  Blood-Flow. 

The  flow  of  blood  is  not  always  the  same,  but  varies: — 

(a.)  With  alterations  in  the  force  and  frequency  of  the  contractions 

of  the  heart ;  and 
(b.)  With  variations  of  the  peripheral  resistance. 

It  is  obvious  that  the  flow  of  blood  may  be  increased  under  the 
following  circumstances : — 

(a.)  If  the  force  and  frequency  of  the  heart's  beats  be  increased,  and 
the  peripheral  resistance  be  (1)  unchanged,  or  be  (2)  diminislied. 

(b.)  If  the  force  and  frequency  of  tlio  heart  be  unchanged,  ajid  the 
peripheral  resistance  be  diininisiied. 


232  HANDBOOK    OF   PHYSIOLOGY. 

And  may  on  tlie  other  hand  be  diminished: — 

(c.)  If  the  force  and  freqnency  of  the  heart's  beats  be  diminished, 
and  if  the  peripheral  resistance  be  (1)  unchanged,  or  be  (2)  in- 
creased. 

(d.)  If  the  force  and  freqnency  of  tlie  lieart's  beats  be  unchanged, 
and  the  periplieral  resistance  be  increased. 

When  the  force  and  freqnency  of  the  heart's  contractions  are  in- 
creased and  at  tlie  same  time  the  peripheral  resistance  is  increased,  the 
flow  may  be  increased,  diminished,  or  unchanged,  according  as  either  of 
the  two  factors,  one  of  which  tends  to  increase  the  flow,  and  the  other 
to  diminish  it,  is  more  markedly  increased,  or  if  they  are  balanced.  The 
complemented  proposition  is  also  true,  that  the  flow  may  be  increased, 
diminished,  or  unchanged,  when  the  force  and  frequency  of  the  heart's 
contractions  are  diminished,  and  the  peripheral  resistance  is  diminished. 

The  conditions  of  increased  flow  and  of  increase  of  blood  pressure 
are  not  the  same.  Indeed,  the  greatest  blood-flow  may  occur  when  the 
blood  pressure  is  low,  i.e.,  when  the  peripheral  resistance  is  diminished 
and  the  heart's  beat  is  increased  or  is  unchanged.  In  fact  there  is  only 
one  condition  in  which  increased  blood-flow  is  accompanied  by  increased 
blood-pressure,  viz.,  when  the  heart's  beat  is  increased  and  the  periphe- 
ral resistance  is  unchanged. 

It  will  be  necessary  now  to  consider  (a)  the  ways  in  which  the  force 
and  frequency  of  the  heart's  heats  are  regulated  ;  and  also  (b)  the  ways  in 
which  the  peripheral  resistance  is  increased  or  diminished.  We  shall 
afterward  be  in  a  better  position  to  discuss  the  A^ariations  of  blood- 
pressure  produced  by  different  combinations  of  cardiac  and  arterial 
alterations. 

(a.)  The  force  and  frequency  of  the  contractions  of  the  heart 
may  be  considered  to  depend  ujDon : 

1.  The  ]3roperties  and  condition  of  the  heart-muscle  itself; 

2.  The  influence  of  the  central  nervous  system; 

3.  The  amount  of  the  blood  passing  into  the  heart's  cavities ; 

4.  The  amount  of  pressure  to  be  overcome. 

5.  The  coronary  circulation. 

Each  of  these  factors  must  be  considered  seriatim. 

1.  Tlie  pyojjertics  of  tlie  heart-muscle.— It  has  already  been  pointed 
out  that  in  structure  the  muscular  fibres  of  the  heart  differ  from  skeletal 
muscle  on  the  one  hand,  and  from  uustriped  muscle  on  the  other,  occuj)y- 
ing,  as  it  were,  an  intermediate  position  between  the  two  varieties.  The 
heart-nuiscle,  however,  possesses  a  property  which  is  not  possessed  by  skele- 
tal muscle,  or  by  unstriped  muscle  to  such  a  degree,  namely,  the  property 
of  rhythmical  contractility.     The  jiroperty  of  rhythmic  contraction 


THE   CIRCULATION    OF    THE    DLOOl). 


133 


is  sliowii  by  the  action  of  tlie  licart  Avitliiii  tlie  body;  its  systole  is  fol- 
lowed by  its  diastole  in  regular  sequence  thronghont  the  life  of  the 
individual.  The  force  and  frequency  of  the  systole  may  vary  from  time, 
to  time  as  occasion  requires,  but  there  is  no  interru^ition  to  the  action 
of  the  normal  heart,  or  any  interference  Avith  its  rhythmical  contrac- 
tions. Further,  we  find  that  in  an  animal  rapidly  bled  to  deatli,  the  heart 
continues  to  beat  for  a  time,  varying  in  duration  with  the  kind  of  ani- 
mal experimentally  dealt  with,  and  in  the  entire  absence  of  blood  Avithin 
the  heart-chambers;  and  still  further,  if  the  heart  of  an  animal  be  re- 
moved from  the  body,  it  still,  for  a  varying  time,  continues  its  alternate 
systolic  and  diastolic  movements.  Thus  Ave  see  that  the  poAver  oi 
rhythmic  contraction  depends  neither  upon  connection  Avitli  the  centra] 


^^^^<5^-- 1*.  s.  d 


?^- A^ 


TPig.  101.  Fig.  191  A. 

Fig-.  101. — The  heart  of  a  frog  (Rana  esculen(a)  from  the  front.  T'.  A'entricle;  Ad,  riglit  carij)  • 
As,  left  auricle;  R,  bnlbus  arterio^is,  dividing  into  right  and  left  aortse.     ( Ecker.) 

Fig.  lui  A Tlie  heart  of  a  frog  (Rana  esculenta)  from  the  back.    s.  c,  Sinus  venosus  openeo  , 

c.  x.  s.,  left  vena  cava  superior;  c.  s.  d.,  right  vena  cava  superior;  c.  i.,  vena  cava  irforior  ;  v.  p  , 
vena  pulmouales;  A.d.,  right  auricle;  A.s.,  left  auricle;  A.p.,  opening  of  coiuumnicatior.  '^et  .veen  tm, 
riglit  auricle  and  the  sinus  venosus,     X  ~}^-3-    (Ecker.) 


nervous  system,  nor  yet  ujioii  (lie  stimulation  i)rodueed  by  the  presence 
of  blood  Avithin  its  chambers — it  is  automatic.  The  cause  of  tiiis 
rhythmic  power  has  been  the  subject  of  much  discussion  and  experi- 
mental observation.  Up  to  a  comparatively  short 'time  ago,  the  remark- 
able pro2)erty  of  the  lieart  to  continue  its  rhythmical  contractions  after 
removal  from  the  body  Avas  believed  to  be  connected  in  some  Avay  or 
other  Avitli  the  presence  of  collections  of  nerve  cells,  or  ganglia  in  sev- 
eral parts  of  its  tissue.  Although  this  idea,  as  Ave  shall  presently  see,  has 
now  been  very  generally  given  U}>,  it  may  be  as  Avell  to  describe  shortly 
these  ganglia  in  this  jjlace;  tliey  have  been  studied  more  particularly 


234 


HANDBOOK    OF    PHYSIOLOGY. 


iu  the  heart   of  the  frog,   of  the  tortoise,  and  of   other    cold-blooded 
animals. 

In  the  frog's  heart  (fig.  191)  these  ganglia  consist  of  three  chief 
groups.  The  first  grouj)  is  situated  in  the  wall  of  the  sinus  venosus 
at  the  junction  of  the  sinus  "with  the  right  auricle  {Remah'' s) ;  the 
second  group  is  placed  near  the  junction  between  the  auricles  and  ven- 
tricle (Bidder''s) ;  and  the  third  in  the  septum  between  the  auricles 
(v.  BezoIcPs). 

The  nerve  cells  of  which  these  ganglia  are  composed  are  generally 
unipolar,  and  seldom  bipolar;  sometimes  two  cells  are  said  to  exist  in 
the  same  envelope,  constituting  the  hvin  cells  of  Dogiel.  The  cells 
are  large,  and  have  very  large  round  nuclei  and  nucleoli  (fig.  193). 
Ganglion  cells  have  not  been  found  in  the  lower  part  of  the  ventricle. 

As  regards  the  automatic  movements 
of  the  heart  removed  from  the  body  our 
chief  knowledge  has  been  derived  from 
the  study  of  the  hearts  of  the  frog  and 
tortoise. 

JT 


Fig.  192. 

Fig.  192.— Course  of  the  nerves  in  the  auricular  partition  wall  of  the  heart  of  a  frog.  d.  Dorsal 
branch;  v.  ventral  branch.      (Ecker.) 

Fig.  19.3.— Isolated  nerve-cells  from  the  frog's  heart.  I.  Usual  form.  II.  Twin  cell.  C,  Capsule; 
N,  nucleus;  N',  nucleolus;  P,  process.      (Trom  Ecker.) 

If  removed  from  the  body  entire,  the  frog's  heart  will  continue  to 
beat  for  many  hours  and  even  days,  and  the  beat  has  no  apparent  differ- 
ence from  the  beat  of  the  heart  before  removal;  it  will  take  place,  as  we 
have  mentioned,  without  the  presence  of  blood  or  other  fluid  within  its 
chambers.  Not  only  is  this  the  case,  but  the  auricles  and  ventricle  may 
be  cut  off  from  the  sinus,  and  both  parts  continue  to  pulsate,  and  fur- 
ther the  auricles  may  be  divided  from  the  ventricle  with  the  same  result. 
If  the  heart  be  divided  lengthwise,  its  parts  will  continue  to  pulsate 
rhythmically,  and  the  auricles  may  be  cut  up  into  pieces,  and  the  pieces 
will  continue  their  movements  of  rhythmical  contraction. 

It  will  be  thus  seen  that  the  rhythmical  movements  appear  to  be 
more  marked  in  the  parts  supplied  by  the  ganglia,  as  the  apical  portion 


THE    CIRCULATION    OF   THE    BLOOD.  235 

of  tlie  ventricle,  iu  which  ganglia  have  not  been  found,  does  not,  under 
ordinary  circumstances,  possess  the  power  of  automatic  movement. 

It  has,  however,  been  shown  by  Gaskell  that  the  extreme  apex  of  the 
ventricle  of  the  heart  of  the  tortoise,  which  contains  no  ganglia,  may 
under  appropriate  stimuli  be  made  to  contract  rhythmically.  This 
proves  that  the  muscular  tissue  of  the  heart  itself  is  capable  of  rhyth- 
mical contraction  independent  of  the  ganglia.  Thus  it  seems  probable 
that  the  rhythmic  contractility  of  the  heart  is  a  power  inherent  in  the 
muscular  tissue,  which  is  quite  independent  as  far  as  its  commencement, 
at  any  rate,  is  concerned  of  nerve  influence. 

The  heart-muscle  exhibits  another  property  which  distinguishes  it 
from  ordinary  skeletal  muscle,  viz.,  the  way  in  which  it  reacts  to  stimuli. 
The  latter  as  will  be  described  at  greater  length  in  its  appropriate  place, 
reacts  slightly  to  a  slight  stimulus  above  the  minimal,  and  with  an  in- 
crease of  the  strength  of  the  stimuli  will  give  increasingly  ample  con- 
tractions until  the  maximum  contraction  is  reached;  in  the  case  of  the 
heart-beats  this  is  not  so,  since  the  •minimum  stimulus  ivhicli  has  any 
effect  is  followed  hij  the  maximum  contraction;  in  other  words  the  weak- 
est effectual  stimulus  brings  out  as  great  a  beat  as  the  strongest.  There 
is  another  great  difference  between  the  contraction  of  the  heart  and  of 
skeletal  muscle,  viz.,  the  inability  of  the  former  to  enter  into  a  state  of 
tetanus  under  the  influence  of  stimuli  repeated  very  rapidly.  If  the 
heart  be  stimulated  by  a  series  of  rapid  interrupted  induction  shocks, 
there  is  no  summation  of  the  contractions,  as  there  would  be  siipposing 
an  ordinary  skeletal  muscle  were  stimulated  in  the  same  Avay.  This 
phenomenon  is  said  to  be  due  to  the  following  fact,  viz.,  that  in  order  to 
produce  an  extra  contraction  of  the  excised  frog's  heart,  the  stimulus 
must  be  applied  during  diastole  or  period  of  rest  or  relaxation,  and  in 
that  case  the  next  contraction  happens  at  an  earlier  period  than  if  the 
stimulus  were  not  aj^plied.  If  applied  during  the  systole,  the  stimulus 
has  scarcely  any  effect;  the  period  during  which  the  muscle  is  refractory 
to  stimuli  is  much  longer  in  the  case  of  the  heart  than  in  the  case  of 
other  muscles.  In  order  to  produce  a  tetanus  in  skeletal  muscle,  the 
second  stimulus  must  be  sent  into  the  muscle  before  it  has  had  time  to 
recover  from  the  ett'ect  of  the  first  stimulus  and  relax,  and  so  on  with 
the  third,  fourth,  and  other  stimuli.  If,  as  we  may  suppose,  the  same 
conditions  for  the  production  of  tetanus  are  necessary  in  heart-muscle, 
the  I'easons  of  the  impossibility  of  producing  tetanus,  i.e.  that  a  stim- 
ulus applied  during  contraction  is  ineffectual,  are  sufficiently  obvious. 
It  appears,  however,  that  if  the  stimuli  are  sufficiently  strong  and  rap- 
idly repeated,  the  refractory  period  during  which  the  muscle  is  prac- 
tically insensible  to  stimuli  diminishes,  and  a  very  rapid  repetition  of 
the  beats  occurs.     As  a  rule  the  beats  are  fewer  with  rapid  stimulation. 


236  HANDBOOK    OF    PHTSIOLOGT. 

lu  conuectiou  with  the  rhythmic  contraction  of  ninscle,  it  is  neies- 
sary  to  alhide  briefly  to  what  is  known  as  Stannius'  experiment. 
Tins  experiment  consisted  originally  of  applying  a  tight  ligature  to  the 
heart  between  the  sinus  and  the  right  auricle,  the  eflEect  of  whicli  is  to  stop 
the  beat  of  tke  heart  below  the  ligature,  while  the  sinus  and  the  veins 
leading  into  it  continue  to  beat.  If  a  second  ligature  be  applied  at  the 
junction  of  the  auricles  and  ventricle,  the  ventricle  may  begin  to  beat 
slowly,  while  the  auricles  continue  quiescent.  In  both  cases  the  quies- 
cent parts  of  the  heart  may  be  made  to  give  single  contractions  in 
response  to  mechanical  stimulation.  A  considerable  amount  of  discussion 
has  arisen  as  to  the  explanation  of  these  phenomena.  It  was  suggested 
that  the  action  of  the  ligature  is  to  stimulate  some  inhibitory  nervous 
mechanism  in  the  sinus,  whereby  the  auricles  and  ventricle  can  no 
longer  continue  to  contract,  but  this  suggestion  must  certainly  be  given 
up  if  the  present  theory  as  to  the  functions  of  the  nerve  ganglia  be  cor- 
rect. It  may  be  that  the  effect  of  Stannius'  ligature  is  simply  an  exam- 
ple of  what  has  been  called  by  Gaskell  blocking.  The  explanation  of 
this  term  is  as  follows : — it  appears  that  under  normal  conditions  the 
wave  of  contraction  in  the  heart  starts  at  the  sinus  and  travels  down- 
ward over  the  auricles  to  the  ventricle,  the  irritability  of  the  muscle 
and  the  j^ower  of  rhythmic  contractility  being  greatest  in  the  sinus,  less 
in  the  auricles  and  still  less  in  the  ventricle,  while  under  ordinary  con- 
ditions the  apical  portion  of  the  ventricle  exhibits  ve]-y  slight  irritability 
and  still  less  power  of  spontaneous  contraction.  Thus  it  may  be  sup- 
posed that  the  wave  of  contraction  beginning  at  the  sinus  is  more  or 
less  blocked  by  a  ring  of  muscle  of  lower  irritability  at  its  junction  Avith 
the  auricles,  and.  again  the  wave  in  the  auricles  is  similarly  delayed  in 
its  passage  over  to  the  ventricle  by  a  ring  of  lesser  irritability,  and  thus 
the  wave  of  contraction  starting  at  the  sinus  is  broken  as  it  were  both 
at  the  auricles  and  at  the  ventricle.  By  an  arrangement  of  ligatures,  or 
better,  of  a  system  of  clamps,  one  part  of  the  heart  may  be  isolated  from 
the  other  portion,  and  the  contraction  when  stimulated  by  an  induction 
shock  may  be  made  to  stop  in  the  portion  of  the  heart-muscle  in  which 
it  begins.  It  is  not  unlikely  that  the  contraction  of  one  portion  of  the 
heart  acts  as  a  stimulus  to  the  next  portion,  and  that  the  sinus  contrac- 
tion generally  begins  first,  since  the  sinus  is  the  most  irritable  to  stimuli, 
and  possesses  the  power  of  rhythmic  contractility  to  the  most  highly 
developed  degree.  It  must  not  be  thought,  however,  that  the  wave  of 
contraction  is  incapable  of  passing  over  the  heart  in  any  other  direction 
than  from  the  sinus  downward;  it  has  been  shown  that  by  app>lication 
of  appropriate  stimuli  at  appropriate  instants,  the  natural  sequence  of 
beats  may  be  reversed,  and  the  contraction  starting  at  the  arterial  part 
of  the  ventricle  may  pass  upward  to  the  auricles  and  then  to  the  sinus 
in  order. 


TIIK    rruCULATION"    OF   THE    T'.LOOI).  237 

An  exceedingly  interesting  fuct  \vith  regard  to  tlio  passage  of  the 
wave  in  any  direction  lias  been  made  out  by  partial  division  of  tlie  mus- 
cular libres  at  any  point,  whereby  one  part  ol  the  wall  of  the  heart  is 
loft  connected  with  the  other  parts  by  a  small  portion  of  undivided 
muscular  tissue,  and  the  wave  of  contraction  then  being  only  able  to 
pass  to  the  next  portion  of  the  wall  every  second  or  third  beat.  Thus 
division  of  the  muscle  has  much  the  same  effect  as  partial  clamping  it 
in  the  same  position,  or  of  a  ligature  similarly  aj^plied,  but  not  tied 
tightly.  It  may,  therefore,  be  suggested  that  .Stannius'  ligature  acts  as 
a  partial  or  complete  block,  and  prevents  the  stimulus  of  the  sinus-beat 
from  passing  further  down  the  heart,  but  that  the  j^arts  below  the  liga- 
ture may  bo  made  to  contract  by  stimuli  applied  to  them  directly. 
Nearly  all  the  information  to  be  obtained  as  to  the  phenomena  of  the 
contraction  of  heart-muscle  apart  from  the  rhythmic  action  of  the 
organ  itself,  may  be  obtained  from  a  heart  to  which  a  Stannius'  ligature 
has  been  applied;  indeed,  the  effect  of  minimal  stimuli,  the  effect  of 
rapidly  repeated  shocks,  and  the  refractory  period  of  heart-muscle  may 
all  be  studied  from  a  heart  in  this  condition. 

The  velocity  of  the  wave  of  contraction  in  frog's  heart-muscle  has 
been  shown  to  be  |  to  |  inch,  or  10-15  mm.  a  second. 

In  pointing  out  the  differences  between  the  phenomena  of  contrac- 
tion in  skeletal  and  heart-muscle,  the  similarities  between  the  two  are 
not  to  bo  overlooked;  thus  it  has  been  shown  that  the  eifect  of  cold, 
heat,  fatigue,  and  other  influences  have  very  much  the  same  effect  in 
both  cases. 

2.   2'he  influence  of  the  rontral  nervous  system. 

The  heart  is  capable  of  automatic  rhythmic  movement,  as  has  been 
clearly  shown  by  its  behavior  when  removed  from  the  body,  and  it  has 
been  shown  further  that  there  is  reason  for  believing  that  the  power 
resides  in  the  inherent  proj^erty  of  its  muscle  fibres  themselves.  While 
in  the  body,  however,  the  heart's  beats  are  under  control  of  the  central 
nervous  system.  To  this  nervous  control,  we  must  next  direct  our  at- 
tentio7i.  The  influence  which  is  exerted  by  the  central  nervous  system 
appears  to  be  of  two  kinds,  firstly,  in  the  direction  of  slowing  or  inhibit- 
ing the  heats,  and  secondly,  in  the  direction  of  accelerating  or  augment- 
ing the  heats.  The  influence  of  the  first  kind  is  brought  to  bear  upon 
the  heart  through  the  libres  of  the  vagi  nerves,  and  that  of  the  second 
kind  through  the  sympathetic  fibres. 

Influence  of  the  Vagi. — It  has  long  been  known,  indeed  ever  since 
the  experiments  of  the  liros.  "Weber  in  1845,  that  stimulation  of  one  or 
both  vagi  produces  slowing  of  the  beats  of  the  heart.  It  has  since  been 
shown  in  all  of  the  vertebrate  animals  experimented  with,  that  this  is 
the  normal  action  of  vagus  stimulation.     Moreover,  section  of  one  nerve, 


238 


fiAUDBOOK    OF    PHYSIOLOGY. 


or  at  anj  rate  of  both  vagi,  produces  acceleration  of  tiie  pulse,  and  stim- 
ulation of  the  distal  or  peripheral  end  of  the  divided  nerve  produces 
normally  slowing  or  stopping  of  the  heart's  beats. 

It  appears  that  any  kind  of  stimulus  produces  the  same  effect,  either 
chemical,  mechanical,  electrical,  or  thermal,  but  that  of  these  the  most 
potent  is  a  rapidly  interrupted  induction  current.  A  certain  amount  of 
confusion  has  arisen  as  to  the  effect  of  vagus  stimulation  in  conse- 
quence of  the  fact  that  within  the  trunk  of  the  nerve  is  contained,  in 
some  animals,  fibres  of  the  sympathetic,  and  it  depends  to  some  extent 
upon  the  exact  position  of  the  application  of  the  stimulus,  as  to  the 
exact  effect  produced.  Speaking  generally,  however,  excitation  of  any 
part  of  the  trunk  of  the  vagus  produces  inhibition,  the  stimulus  being 
particularly  potent  if  applied  to  the  termination  of  the  vagi  in  the 
heart  itself,  where  they  enter  the  substance  of  the  organ  at  the  situation 
of  the  sinus  ganglia.  The  stimulus  may  be  applied  to  either  vagus  with 
effect,  although  it  is  frequently  more  potent  if  applied  to  the  nerve  on 
the  right  side.  The  effect  of  the  stimulus  is  not  immediately  seen;  one 
or  more  beats  may  occur  before  stoppage  of  the  heart  takes  place,  and 
slight  stimulation  may  produce  only  slowing  and  not  complete  stoppage 


^wififiiiii^ 


jwwuupiiwm™ 


Fig.  194. — ^Tracing  showing  the  actions  of  the  vagus  on  the  heart.  Aiu:,  Auricular;  vent.,  ven- 
tricular tracing.  The  part  between  perpendicular  lines  indicates  jjeriod  of  vagus  siiinulation.  C.8 
indicates  that  the  secondary  coil  was  8  cm.  from  the  primary.  The  part  of  tracing  to  the  left 
shows  the  legular  contractions  of  moderate  height  before  stimulation.  During  stimulation,  and  for 
some  time  after,  the  beats  of  auricle  and  ventricle  are  arrested.  After  they  commence  again  they 
are  single  at  first,  but  soon  acquire  a  much  gi'eater  amplitude  than  before  the  application  of  the 
stimulus.     (From  Brunton,  after  Gaskell.) 


of  the  heart.  The  stoppage  may  be  due  either  to  prolongation  of  the 
diastole,  as  is  usually  the  case,  or  to  diminution  of  the  systole.  Vagus 
stimulation  inhibits  the  spontaneous  beats  of  the  heart  only,  it  does  not 
do  away  with  the  irritability  of  the  heart-muscle,  since  mechanical  stim- 
ulation may  bring  out  a  beat  during  the  still-stand  caused  by  vagus 
stimulation.  The  inhibition  of  the  beats  varies  in  duration,  but  if  the 
stimulation  be  a  prolonged  one,  the  beats  may  reappear  before  the  cur- 
r(!iit  is  shut  off.  When  the  beats  reappear,  the  first  few  are  usually 
ft't'ble,  and  may  be  auricular  only;  after  a  time  the  contractions  become 
more  and  more  strong,  and  very  soon  exceed  both  in  amplitude  and 


THE   CIRCULATION"   OF   THE    BLOOI).  239 

frequency  those  which  occurred  before  the  application  of  the  stimulus 
(fig.  194). 

Influence  of  the  Sympathetic. — The  influence  of  the  sympathetic 
may  be  considered,  to  a  certain  extent,  as  the  reverse  of  that  of  the 
vagus.  Stimulation  of  the  sympathetic,  even  of  one  side,  produces  ac- 
celeration of  the  heart-beats,  and  according  to  certain  observers,  section 
of  the  same  nerve  produces  slowing.  The  acceleration  2:)roduced  by  stim- 
ulation of  the  sympathetic  fibres  is  accompanied  by  increased  force,  and 
so  the  action  of  the  nerve  is  more  properly  termed  augnientor.  The 
action  of  the  sympathetic  differs  from  that  of  the  vagus  in  several  par- 
ticulars besides  the  augmentation  which  is  produced :  firstly,  the  stimulus 
required  to  produce  any  effect  must  be  more  powerful  than  is  the  ease 
with  the  vagus  stimulation;  secondly,  a  longer  time  lapses  before  the 
effect  is  manifest;  and  thirdly,  the  augmentation  is  followed  by  exhaus- 
tion, the  beats  being  after  a  time  feeble  and  less  frequent. 

Origin  of  the  cardiac  nerve-fibres. — The  fibres  of  the  sympa- 
thetic system,  which  influence  the  heart-beat  in  the  frog,  leave  the 
spinal  cord  by  the  anterior  root  of  the  third  spinal  nerve,  and  pass 
thence  by  the  ramus  communicans  to  the  third  spinal  ganglion,  thence 
to  the  second  spinal  ganglion,  and  thence  by  the  annulus  of  Vieussens 


Fig.  195.— Tracing  showing- diminished  amplitude  and  slowing  of  the  pulsations  of  the  auricle 
and  ventricle  without  complete  stoppage  during  irritation  of  the  vagus.  (From  Brunton,  after 
Gaskell.) 

(round  the  subclavian  artery)  to  the  first  spinal  ganglion,  and  thence  in 
the  main  trunk  of  the  sympathetic,  to  near  the  exit  of  the  vagus  from 
the  cranium,  where  it  joins  that  nerve  and  runs  down  to  the  heart  within 
its  sheath,  forming  the  joint  vago-sympathetic  trunk. 

In  the  dog,  the  augmentor  fibres  leave  the  cord  by  the  second  and 
third  dorsal  nerves,  and  possibly  by  anterior  roots  of  two  or  more  lower 
nerves,  passing  by  the  rami  communicantes  to  the  ganglion  stellatum, 
or  first  thoracic  ganglion,  thence  by  the  annulus  of  Vieussens  to  the 
inferior  cervical  ganglion  of  the  sympathetic  fibres  from  the  annulus,  or 
from  the  inferior  cervical  ganglion  proceed  to  the  heart. 

From  the  fact  that  the  augmentor  fibres  are  joined  to  the  vagus 


240  HANDBOOK    OV    THYSIOLOGT. 

trunk,  it  may  be  understood  that  the  effect  of  the  stimulation  of  tlie 
vagus  in  the  frog  is  not  in  all  cases  purely  inhibitory,  but  may  be  aug- 
meutor,  according  to  the  position  where  the  stimulus  is  applied,  the 
intensity  of  the  stimulus,  and  the  condition  of  the  heart;  if  it  is  beating 
strongly  a  slight  "vagus  stimulation  will  produce  immediate  inhibition. 

The  fibres  of  the  vagus  which  pass  to  the  heart  arise  in  the  medulla 
oblongata,  in  the  floor  of  the  fourth  ventricle,  and  in  a  nucleus  of  gray 
matter,  the  exact  position  of  which  will  be  indicated  in  a  future  chap- 
ter. It  was  formerly  thought  that  the  inhibitory  fibres  in  the  vagus 
trunk  were  derived  from  the  spinal  accessory  nerve,  but  this  view  has 
been  largely  abandoned.  The  spinal  accessory  fibres  probably  supply 
certain  muscles  of  the  larynx.  It  has  been  found  that  stimulation  of 
this  nucleus,  Avhich  is  called  the  cardio-inhibitory  centre,  produces 
inhibition  of  the  heart-beat. 

Thus  there  is  no  doubt  that  the  vagi  nerves  are  simply  the  media  of 
an  inhibitory  or  restraining  influence  over  the  action  of  the  heart,  which 
is  conveyed  through  them  from  the  centre  in  the  medulla  oblongata 
which  is  always  in  operation.  The  restraining  influence  of  the  centre 
in  the  medulla  may  be  reflexly  increased  by  stimulation  of  almost  any 
afferent  nerve,  particularly  of  the  abdominal  sympathetic,  so  as  to  pro- 
duce slowing  or  stoppage  of  the  heart,  through  impulses  from  it  passing 
down  the  vagi.  As  an  example  of  this  reflex  stimulation,  the  well- 
known  effect  on  the  heart  of  a  violent  blow  on  the  epigastrium  may  be 
referred  to.  The  stoppage  of  the  heart's  action  in  this  case  is  due  to 
the  conveyance  of  the  stimulus  by  fibres  of  the  sympathetic  (afferent) 
to  the  medulla  oblongata,  and  its  subsequent  reflection  through  the  vagi 
(efferent)  to  the  muscular  substance  of  the  heart.  It  is  possible  that  the 
power  of  the  medullary  inhibitory  centre  may  in  a  similar  manner  be 
reflexly  lessened  so  as  to  joroduce  accelerated  action  of  the  heart. 

The  course  of  the  augmentor  fibres  in  the  spinal  cord  is  not  known, 
but  it  is  thought  that  in  all  probability  they  are  connected  with  an  aug- 
mentor centre  in  the  medulla.  The  circulation  of  venous  blood  appears 
to  stimulate  the  inhibitory  centre,  and  of  highly  oxygenated  the  aug- 
mentor centre. 

In  addition  to  direct  and  refiex  stimulation  it  is  almost  certain  that 
impulses  passing  down  from  the  cerebrum  may  have  a  similar  effect. 

Other  Influences  Affecting  the  Heart-Beat. — Alteration  of  tempera- 
ture.— The  effect  of  cold  is  to  slow  the  heart-beats,  and  if  the  heart  be 
cooled  down  to  3°  C.  (38°  F.)  it  will  stop  beating.  The  heart  may  be 
frozen,  and  when  thawed  will  continue  its  spontaneous  beats.  The 
eff'ect  of  heat  is  to  quicken  and  shorten  the  heart-beats,  but  at  a  moder- 
ate temperature,  20°  0.  (68°F,),  the  contractions  are  increased  in  force. 


THE    CIRCULATIOJ^"   OF   THE    BLOOD.  241 

At  or  below  40°  C.  (104°  F.)  tlie  contratious  are  so  rapid  as  to  pass  into 
heart-rigor;  this  may  be  stop2:>ed  by  cooling. 

Poisons  and  other  chemical  substances.— A  large  number  of 
chemical  substances  have  a  distinct  effect  upon  the  cardiac  contractions. 
Of  these  the  most  important  are  atroiyin  and  muscarin. 

Atrojnn  produces  considerable  augmentation  of  the  heart-beats,  and 
when  acting  upon  the  heart  prevents  the  results  of  vagus  stimulation, 

Muscarin  (obtained  from  various  sjDecies  of  poisonous  fungi)  pro- 
duces marked  slowing  of  the  heart-beats,  and,  in  larger  doses,  stoppage 
of  the  heart.  It  produces  a  similar  effect  to  that  of  prolonged  vagus 
stimulation,  and  as  in  that  case  the  effect  can  be  removed  by  the  action 
of  atropin. 

Digifalin  (the  active  principle  of  digitalis  purpurea),  slows  the  heart 
and  appears  to  act  by  stimulating  the  vagi.  Later  on  the  muscle  is  also 
more  excitable.  Veratrin  and  aconitin  have  a  similar  effect.  Nicotine 
prevents  the  effect  of  vagus  stimulation. 

Methods  of  investigating  the  Heart-beat. 

(1)  The  simplest  form  of  an  apparatus  to  be  used  for  recording  the  conti*ac- 
tions  of  the  frog's  heart  consists  of  a  small  closed  cylindrical  box  fixed  to  a 
stand.  At  the  bottom  of  the  box  are  two  tubes  by  means  of  which  water  at 
various  temperatures  may  be  made  to  circulate  through  it,  one  tube  being  the 
inlet  and  the  other  the  outlet,  and  they  are  connected  with  india-rubber,  suit- 
able for  the  purpose  of  conducting  water  to  and  from  the  apparatus.  The  lever 
is  made  of  a  piece  of  glass  rod  which  is  softened  and  drawn  out  in  the  flame 
of  the  blow-pipe  a  very  fine  thread,  leaving  a  small  piece  unaltered  to  act  as 
a  counterpoise.  The  lever  is  then  passed  through  a  piece  of  cork  and  through 
this  cork  a  fine  needle  is  inserted  at  right  angles  to  the  lever.  The  needle  is 
made  to  rest  on  a  support  attached  above  one  side  of  the  box  in  such  a  way 
that  the  lever  has  free  movement  up  and  down.  Another  small  piece  of  cork 
is  passed  along  the  lever  arm  and  is  adjusted  and  cut  so  that  its  point  directed 
downward  can  rest  upon  the  frog's  heart,  wdiicli  is  removed  from  the  bod}'  and 
placed  upon  the  top  of  the  box  in  serum  or  defibrinated  blood.  In  this  way 
the  contractions  of  the  auricles  and  ventricle  are  communicated  to  the  lever, 
and  this  may  be  made  to  write  upon  a  recording  cylinder. 

(2)  The  variations  of  endocardial  pressure,  which  correspond,  of  course, 
with  the  various  phases  of  the  cardiac  cycle,  may  be  recorded  by  a  modifica- 
tion of  the  ordinary  mercurial  manometer.  The  apparatus  is  best  used  with  a 
large  frog  (Rana  esculcnfa),  and  the  heart  is  exposed  in  the  usual  manner,  the 
pericardium  opened.  A  cut  is  made  into  the  bulb,  and  by  this  means  a  double 
or  perfusion  cannla  (fig.  19())  is  passed  into  the  ventricle,  a  ligature  is  passed 
round  the  heart,  and  the  canula  is  tied  in  tightly.  The  vessels  are  tlien  di- 
vided beyond  the  ligature,  and  the  canula.  with  the  heart  attached,  is  removed. 
To  one  stem  of  the  canula  a  tube  is  attached,  communicating  with  a  reservoir 
of  a  solution  of  dried  blood  in  .6  saline  solution,  and  filtered,  which  is  capa- 
ble of  being  raised  or  lowered  in  temperature  by  being  surrounded  by  a  metal 
box  which   contains  hot,  cold,  or  iced  water.     Attached  to  the  other  end  is  a 

i6 


242 


HANDBOOK   OF    PHYSIOLOGY. 


similar  tube,  which  communicates  by  a  T  piece  with  a  small  mercurial  man- 
ometer, provided  with  a  writing  style,  and  also  with  a  vessel  into  which  the 
serum  is  received.  The  apparatus  being  arranged  so  that  the  movements  of 
the  mercury  can  be  recorded  by  the  float  and  the  writing  style  on  a  slowly 
revolving  drum,  and  after  some  serum  has  been  allowed  to  pass  freely  through 
the  ventricle,  both  tubes  are  clipped,  the  second  one  beyond  the  T  piece,  and 
the  alterations  in  the  pressure  are  recorded.  The  effects  of  fluids  at  various 
temperatures  and  of  poisons  may  be  recorded  in  the  manner  indicated  above. 

(3)  By  Roy's  Tonovieter  (fig.  197)  the  alterations  in  volume  which  a  frog's 
heart  undergoes  during  contrac- 
tion are  recorded  by  the  folloAv- 
ing  means :  A  small  bell-jar, 
open  above,  but  provided  with  a 
firmly  fitting  cork,  in  which  is 
fixed  a  double  canula,  is  ad- 
justable by  a  smoothly  ground 
base  upon  a  circular  brass  plate. 


M 


Fig.  196. 


Fig.  197. 


Fig.  196.— Kronecker's  Perfusion  Canula,  for  supplying  Fluids  to  the  interior  of  the  Frog's 
Heart.  It  consists  of  a  double  tube,  one  outside  the  other;  the  end  view  is  shown  in  the  engraving. 
The  inner  tube  branches  out  to  the  left:  thus,  when  the  ventricle  is  tied  to  the  outer  tube  of  the  can- 
ula, a  current  of  liquid  can  be  made  to  pass  into  the  heart  by  one  tube  and  out  through  the  other. 

Fig.  197.— Roy's  Tonometer. 


about  2  to  3  inches  in  diameter.  The  junction  is  made  complete  by  greas- 
ing the  base  with  lard.  In  the  plate,  which  is  fixed  to  a  stand  adjustable  on 
an  upright,  are  two  holes,  one  in  the  centre,  a  large  one  about  one-third 
of  an  inch  in  diameter,  to  which  is  fixed  below  a  brass  grooved  collar, 
about  half  an  inch  deep ;  the  other  hole  is  the  opening  into  a  pipe  provided 
Avith  a  tap  (stopcock) .  The  opening  provided  with  the  collar  is  closed  at  the 
lower  part  with  a  membrane  of  animal  tissue,  which  is  loosely  tied  by  means 
of  a  ligature  around  the  groove  at  the  lower  edge  of  the  collar.  To  this  mem- 
brane a  piece  of  cork  is  fastened  by  sealing-wax,  from  which  passes  a  wire, 
which  can  be  attached  to  a  lever,  fixed  on  a  stage  below  the  apparatus. 

When  using  the  apparatus,  the  bell-jar  is  fixed  by  means  of  lard,  and  the 
jar  is  filled  with  olive  oil.  In  the  way  above  described,  the  heart  of  a  large 
frog  is  prepared  and  the  canula  fixed  in  the  cork  is  firmly  tied  into  the  heart ; 
the  tubes  of  the  canula  communicating  with  the  reservoir  of  serum  on  the 
Oxie  hand,  and  with  a  vessel  to  contain  the  serum  after  it  has  run  through  on 
t'i3  other.  The  canula  with  heart  attached  is  passed  into  the  oil,  and  the 
cork  firmly  secured.     By  these  means  the  lever  will  be  found   to  be  adjusted  to 


THE    CIRCULATION    OF   THE   BLOOD.  243 

a  convenient  elevation.  The  lever  is  allowed  to  write  on  a  moving  drum,  and 
serum  is  passed  through  at  various  temperatures.  After  a  short  time  the  heart 
may  stop  beating ;  but  two  wires  are  arranged,  the  one  in  the  canula,  the 
other  projecting  from  the  plate  in  such  a  way  that  the  lieart  can  be  moved 
against  them  by  shifting  the  position  of  the  bell- jar  a  little.  The  wires  act  as 
electrodes,  and  can  be  made  to  communicate  with  an  induction  apparatus,  so 
that  single  induction  shocks  can  be  sent  into  the  heart  to  produce  contractions, 
and  if  need  be,  by  means  of  the  trigger  key,  at  one  definite  point  in  the  revo- 
lution of  the  recording  cylinder. 

Electrical  Phenomena  of  the  Heart-beat. — The  phenomena  of 
the  natural  beut  of  the  heart  are  generally  considered  to  indicate  that 
the  systolic  contraction  is  a  single  and  not  a  tetanic  one.  The  electrical 
changes  support  this  view.  During  the  contraction  a  distinct  electrical 
change  occurs  which  is  similar  to  that  which  happens  in  skeletal  muscle 
with  each  contraction.  It  has  been  demonstrated  that  a  stanniused 
frog  heart  undergoes  two  changes  or  phases  as  regards  its  electrical  con- 
dition, the  first  immediately  before  the  contraction,  in  which  the  excited 
part  becomes  negative  to  the  other  parts,  contraction  following  the 
wave  of  excitation,  and  the  second  during  relaxation,  in  which  the  cur- 
rent flows  in  an  opposite  way. 

The  Metabolism  of  the  Heart. — Whatever  view  may  be  taken  of 
the  nature  of  the  rhythmic  cardiac  contractions,  it  will  be  generally 
acknowledged  that  the  contractions  cannot  long  be  maintained  without 
a  due  supply  of  blood  or  of  a  similar  nutritive  fluid.  Some  very  re- 
markable facts  have  been  made  out  about  this,  in  the  case  of  the  frog's 
heart.  For  instance,  it  has  been  shown  that  normal  saline  solution  is 
insufficient  to  maintain  the  contractions,  and  that  in  experiments  in 
which  it  is  necessary  to  maintain  the  beats  for  any  length  of  time  failing 
serum  or  saline  solution  of  dried  blood,  the  solution  should  contain 
some  serum-albumin,  and  that  there  should  also  be  present  some  potas- 
sium chloride,  and  Dr.  Ringer  has  composed  a  nutritive  fluid  which 
contains  chlorides  of  sodium,  potassium,  and  calcium  in  small  amounts, 
which  is  able  to  maintain  the  normal  beats  of  the  heart.  It  is  therefore 
very  reasonable  to  suppose  that  the  amount  and  quality  of  the  blood 
supplied  to  the  human  heart  has  the  greatest  influence  in  maintaining 
the  force  and  frequency  of  the  rhythmic  activity.  The  view  that  is 
taken  at  present  of  the  action  of  the  heart  is  one  propounded  by  Gaskell, 
viz.,  that  in  heart  muscle  as  in  protoplasm  generally,  the  metabolic  i)ro- 
cesses  are  those  of  anabolism  or  building  up,  which  takes  place  during 
the  diastole  of  the  heart,  that  vagus  stimulation  helps  on  this  process, 
and  of  catabolism  or  discharge,  which  is  manifested  in  the  contraction 
of  the  heart,  and  which  is  accelerated  by  stimulation  of  the  sympathetic 
fibres.  That  vagus  stimulation  is  therefore  ultimately  beneficial  to  the 
contractions.     The  electrical  currents  set  up  on  the  stimulation  of  the 


244 


HAN'DBOOK   OP    PHYSIOLOGY. 


vagus  and  of  the  sympathetic  are  in  opposite  directions,  and  so  if  Gas- 
kell's  contention  is  correct  that  the  negative  variation  of  the  muscle 
current  occurring  on  sympathetic  stimuhition  is  a  sign  of  catabolism,  the 
result  of  vagus  stimulation,  viz.,  a  positive  variation  of  the  muscle  cur- 
rent, may  be  supposed  to  indicate  the  complementary  condition  of  ana- 
bolism. 

3.  The  Amount  of  Blood  Passing  into  the  Heart's  Cavities. — It  is  found 
that  in  the  body  at  any  rate  the  amount  of  blood  which  passes  into  the 
cavities  of  the  heart  distinctly  affects  the  strength  of  its  beat.  Thus  if 
from  anj  cause  the  blood  is  diminished  the  contractions  become  much 


Fig.  198. — Plethysmograph.  By  means  of  this  apparatus,  the  alteration  in  volume  of  the  arm, 
E,  which  is  inclosed  in  a  glass  tube,  a,  filled  with  fluid,  the  opening  through  which  it  passes  being 
firmly  closed  by  a  thick  gutta-percha  band,  f,  is  communicated  to  the  lever,  d,  and  registered  by  a 
recording  apparatus.  The  fluid  in  a  communicates  with  that  in  b,  the  upper  limit  of  which  is 
above  that  in  a.  The  chief  alterations  in  volume  are  due  to  alteration  in  the  blood  contained  in  the 
arm.  When  the  volume  is  increased,  fluid  passes  out  of  the  glass  cylinder,  and  the  lever,  d,  also  is 
raised,  and  when  a  decrease  takes  place  the  fluid  returns  again  from  b  to  a.  It  will  therefore  be 
evident  that  the  apparatus  is  capable  of  recording  alterations  of  blood-pressure  in  the  arm.  Appa- 
ratus founded  upon  the  same  principle  have  been  used  for  recording  alterations  in  the  volume  of 
the  spleen  and  kidney. 


more  feeble,  although  they  may  possibly  be  increased  in  rapidity.  Simi- 
larly with 

4.  7he  Amount  of  Pressure  to  he  Overcome. — If  the  aortic  pressure  is 
too  low  the  muscle  contractions  of  the  heart  is  not  so  powerful  or  effec- 
tive as  if  the  pressure  is  normal,  whereas  too  great  arterial  pressure  may 
be  sufficient  to  delay  if  not  to  stop  altogether  the  heart's  beats,  dilata- 
tion of  its  cavities  taking  place  and  a  condition  of  asystolism  (Beau) 
resulting. 

Another  condition  sometimes  forgotten  should  be  added  as  influenc- 
ing the  potency  of  the  cardiac  contraction,  viz.,  the  heart  must  have 
sufficient  room  to  contract,  it  must  not  be  unduly  pressed  upon. 

6.  The  Coronary  Circulation. — The  nutrition  of  the  heart  wall  has 
been  fully  investigated  by  Porter  and  others.  The  coronary  arteries  are 
terminal  arteries;  that  is,  they  do  not  permit  the  establishment  of  a 
collateral  circulation  when   one  of  their  branches  is  blocked.     If  the 


THE   CIRCULATION   OF   THE    BLOOD.  245 

block  be  complete,  that  portiou  of  the  heart  wall  supplied  by  the  branch 
dies.  The  immediate  effect  of  the  closure  of  a  large  branch  in  the  dog 
may  be  occasional  and  transient  irregularity,  or  arrest  of  the  ventricular 
contractions,  preceded  by  irregularities  in  the  force  of  the  contractions 
and  a  diminution  in  the  amount  of  work  performed.  The  force,  rather 
than  the  rate,  of  the  ventricular  contractions  is  closely  dependent  upon 
the  blood-supply  to  the  coronary  arteries. 

(b.)  The  Peripheral  Resistance. — The  regulation  of  the  amount 
of  resistance  to  the  passage  of  blood  at  the  periphery  is  jirincipally  done 
by  the  alteration  of  the  calibre  of  the  arterioles.  This  regulating  power 
is  chiefly  invested  in  the  nervous  system.  Its  influence  is  exerted  upon 
the  muscular  coat  of  the  arteries  and  not  upon  the  elastic  element,  which 
possesses,  as  must  be  obvious,  rather  physical  than  vital  properties. 
The  muscular  tissue  in  the  walls  of  the  vessels  increases  in  amount  rel- 
atively to  the  other  coats  as  the  arteries  grow  smaller,  so  that  in  the 
arterioles  it  is  developed  out  of  all  proportion  to  the  other  elements; 
in  fact,  in  passing  from  capillary  vessels,  made  up  as  we  have  seen  of 
endothelial  cells  with  a  ground  substance,  the  first  change  which  occurs 
as  the  vessels  become  larger  (on  the  side  of  the  arteries)  is  the  ajjpear- 
ance  of  muscular  fibres.  Thus  the  nervous  system  is  more  powerful  in 
regulating  the  calibre  of  the  smaller  than  of  the  larger  arteries. 

It  was  long  ago  shown  by  Claude  Bernard  that  if  the  cervical  sym- 
pathetic nerve  is  divided  in  a  rabbit,  the  blood-vessels  of  the  correspond- 
ing side  of  the  head  and.  neck  become  dilated.  This  effect  is  best  seen 
in  the  ear,  which  if  held  up  to  the  light  is  seen  to  become  redder,  and 
the  arteries  are  seen  to  become  larger.  The  whole  ear  is  distinctly 
warmer  than  the  opposite  one.  This  effect  is  produced  by  removing 
the  arteries  from  the  influence  of  the  central  nervous  system,  which  in- 
fluence normally  passes  down  the  divided  nerve;  for  if  the  periiiheral 
end  of  the  divided  nerve  {i.e.,  that  farthest  from  the  brain)  be  stimulated, 
the  arteries  which  were  before  dilated  return  to  their  natural  size,  and 
the  parts  regain  their  primitive  condition.  And,  besides  this,  if  the 
stimulus  is  very  strong  or  very  long  continued,  the  point  of  normal  con- 
striction is  passed,  and  the  vessels  become  much  more  contracted  than  nor- 
mal. The  natural  condition,  which  is  about  midway  between  extreme  con- 
traction and  extreme  dilatation,  is  called  the  natural  tone  of  an  artery; 
if  this  is  not  maintained,  the  vessel  is  said  to  have  lost  tone,  or  if  it  is 
exaggerated,  the  tone  is  said  to  be  too  great.  The  effects  described  as 
having  been  produced  by  section  of  the  cervical  sympathetic  and  by 
subsequent  stimulation  are  not  peculiar  to  that  nerve,  as  it  has  been 
found  that  for  every  part  of  the  body  there  exists  a  nerve  the  division 
of  which  produces  the  same  effects,  viz.,  dilatation  of  the  vessels;  such 
may  be  cited  as  the  case  with  the  sciatic,  the  splanchnic  nerves,  and  the 


246  HANDBOOK   OF   PHYSIOLOGY. 

nerves  of  the  brachial  plexus:  when  these  are  divided,  dilatation  of  the 
blood-vessels  in  the  parts  supplied  by  them  takes  place.  It  appears, 
therefore,  that  nerves  exist  which  have  a  distinct  control  over  the  vas- 
cular supply  of  every  part  of  the  body.  These  nerves  are  called  vaso- 
motor. 

Eecently  Mall  has  shown  that  veins  possess  a  vaso-motor  nerve-supply 
as  well  as  arteries. 

Vaso-motor  nerves  may  be  divided  into  two  classes,  according  to  their 
function  of  causing  contraction  or  dilatation  of  the  blood-vessels,  into 
vaso-constrictor  and  vaso-dilator  nerves. 

Vaso-motor  Centres.  Bulbar  Centre. — The  bulbar  vaso-con- 
strictor centre  in  the  rabbit  lies  in  the  floor  of  the  fourth  ventricle,  a 
millimetre  or  two  caudal  to  the  corpora  quadrigemina,  and  extends 
longitudinally  over  an  area  of  about  3  millimetres.  Owsjanuikow  has 
shown  that  the  centre  is  composed  of  two  halves,  each  half  lying  in  the 
lateral  column  to  the  side  of  the  median  line.  This  centre  is  in  con- 
stant action,  as  is  shown  by  dilatation  of  the  blood-vessels  when  removed 
from  its  action  by  section  of  the  spinal  cord. 

The  existence  of  a  vaso-dilator  centre  in  the  spinal  bulb  has  not  been 
proved. 

Spinal  Centres. — Secondary  vaso-motor  centres  are  present  in  the 
spinal  cord  (Goltz).  Under  normal  conditions  they  do  not  act  indepen- 
dently of  the  bulbar  centre,  but  when  the  action  of  the  latter  has  been 
interrupted  by  section  of  tlie  cord,  certain  spinal  cells  below  the  section 
take  on  central  functions  and  bring  about  a  re-establishment  of  the  lost 
vascular  tone.  Moreover,  the  central  functions  disappear  if  the  cord 
below  the  section  be  destroyed. 

Sympathetic  Vaso-motor  Centres. — The  existence  of  sympathetic 
vaso-motor  centres  has  been  proved  by  the  experiments  of  Goltz  and 
Ewald.  It  was  found  by  these  observers  that  even  after  destruction  of 
the  lower  part  of  the  spinal  cord,  the  tone  of  the  vessels  of  the  hind 
limbs,  lost  as  a  result  of  the  operation,  was  re-established  later. 

Vaso-motor  Reflexes. — The  secondary  vaso-motor  centres,  when 
removed  from  the  influence  of  the  bulbar  centre,  respond  to  afferent  im- 
pulses by  vaso-motor  action.  But  under  normal  conditions  the  bulbar 
centre  controls  vaso-motor  reflexes.  The  afferent  impulses  which  excite 
reflex  vaso-motor  action  may  proceed  from  the  terminations  of  sensory 
nerves  in  general  or  from  the  blood-vessels  themselves,  and  the  constric- 
tion or  dilatation  which  follows  generally  occurs  in  the  area  whence  the 
impulses  arise.  Yet  the  reflex  may  appear  elsewhere,  e.g.,  the  vessels  of 
the  submaxillary  gland  dilate  when  the  tongue  is  stimulated — an  associa- 
tion in  function.     Impulsesproceeding  to  the  vaso-motor  centre  from  the 


THE  CIRCULATION    OF   THE    BLOOD. 


247 


cerebrum  may  cause  vaso-clilatation  as  in  IJusltuig,  or  "vaso-constriction 
as  in  the  pallor  of  fear.  An  important  reflex  association  exists  between 
the  vessels  of  the  skin  and  those  of  subjacent  jiarts.  It  is  generally  an 
inverse  relation;  that  is,  when  the  superficial  vessels  are  dilated  the 
deep  are  contracted.  This  reflex  is  made  use  of  in  medical  practice 
when  poultices  are  applied  to  the  chest  in  pneumonia,  the  lung  being  in 
a  state  of  inflammation. 

AfPcrcut  influence  upon  the  vaso-motor  centre  is  well  shown  by  the 
action  of  a  nerve  called  the  depressor,  the  existence  of  Avhich  was  de- 
monstrated by  Cyon  and  Ludwig. 


Fig.  199.  —Tracing  showing  the  effect  on  blood-pressure  of  stimulating  the  central  end  of  the 
Depressor  nerve  in  the  rabbit.  To  be  read  from  right  to  left.  T.  indicates  the  rate  at  which  the 
recording  surface  was  travelling,  the  intei-vals  correspond  to  seconds:  C.  the  moment  of  entrance  of 
current;  O.  moment  at  which  it  was  shut  off.  The  effect  is  some  time  in  developing  and  lasts  afr'»r 
the  current  has  been  taken  off.  The  larger  imdulalions  are  the  respiratory  nerves ;  the  pulse  oscilla- 
tions are  very  small.     (Foster.) 

It  is  a  small  afferent  nerve  and  passes  up  from  the  heart  in  which  it 
takes  its  origin,  and  in  the  rabbit  goes  upward  in  the  sheath  of  the  su- 
perior laryngeal  branch  of  the  vagus  or  with  that  branch  and  the  vagus 
itself,  communicating  by  filaments  with  the  inferior  cervical  ganglion 
as  it  proceeds  from  the  heart. 

If  during  a  blood-pressure  observation  in  a  rabbit  this  nerve  be  di- 
vided, and  the  central  end  {i.e.,  that  nearest  the  bniin)  be  stimulated,  a 
remarkable  fall  of  blood-pressure  takes  place  (fig.  199). 

The  cause  of  the  fall  of  blood-pressure  is  found  to  proceed  from  the 
dilatation  of  the  vascular  district  within  the  abdomen  supplied  by  the 
splanchnic  nerves,  in  consequence  of  which  the  vessels  hold  a  much 
larger  quantity  of  blood  tlian  usu::l.  The  engorgement  of  the  splanch- 
nic area  very  greatly  diminishes  the  amount  of  blood  in  the  vessels  else- 
where, and  so  materially  diminishes  the  blood-pressure.  The  function 
of  tlie  depressor  nerve  is  that  of  conveying  to  the  vaso-motor  centre  in- 
dications of  such  conditions  of  the  heart  as  require  a  diminution  of  the 


248  HANDBOOK    OF    PHYSIOLOGY. 

tension  in  the  blood-vessels;  as,  for  example,  that  the  heart  cannot, 
■U'ith  sufficient  ease,  propel  blood  into  the  already  too  full  or  too  tense 
arteries. 

The  action  of  the  depressor  nerve  in  causing  an  inhibition  of  the 
vaso-motor  centre  illustrates  the  more  unusual  effect  of  afferent  impulses. 
As  a  rule,  the  stimulation  of  the  central  end  of  an  afferent  nerve  pro- 
duces a  reverse  or  pressor  effect,  and  increases  the  tonic  influence  of 
the  centre,  and  by  causing  constriction  of  the  arterioles,  either  locally  or 
generally,  raises  the  blood-pressure.  Thus  the  effect  of  stimulating  an 
afferent  nerve  may  be  either  to  dilate  or  to  constrict  the  arteries.  Stim- 
ulation of  an  afferent  nerve  too  may  produce  a  kind  of  paradoxicnl  effect, 
causing  general  vascular  constriction  and  so  general  increase  of  blood- 
pressure,  but  at  the  same  time  local  dilatation  which  must  evidently  have 
an  immense  influence  in  increasing  the  flow  of  blood  through  the  part. 

Course  of  the  Vaso-motor  Nerves. — The  cell  bodies  forming 
the  bulbar  vaso-motor  centre  give  off  neuraxons  (axis-cylinder  processes), 
some  of  which  go  to  the  nuclei  of  certain  cranial  nerves,  while  others 
l^ass  down  the  cord  to  end  at  different  levels  in  contact  with  cells — prob- 
ably small  cells  in  the  anterior  horn  and  lateral  part  of  the  gray  matter. 
These  cells  constitute  the  spinal  centres.  The  neuraxons  of  the  spinal 
cells  leave  the  cord  in  certain  cranial  nerves  and  in  the  anterior  roots, 
and  end  in  sympathetic  ganglia  in  contact  with  their  cell  bodies.  From 
these  latter,  neuraxons  pass  uninterruptedly  to  their  termination  in  the 
vessel  wall. 

Besides  the  regulation  of  the  heart  beat  and  of  the  peripheral  resist- 
ance, it  must  be  recollected  that  other  circumstances  may  affect  the  blood 
pressure,  of  which  changes  in  the  blood  are  the  chief.  First  of  all — 
a.  As  regards  quantity.  At  first  sight  it  would  appear  probable  that 
one  of  the  easiest  ways  to  diminish  the  blood-pressure  would  be  to  re- 
move blood  from  the  vessels  by  bleeding.  It  has  been  found  by  experi- 
ment, however,  although  the  blood-pressure  sinks  while  large  abstractions 
of  blood  are  taking  place,  that  as  soon  as  the  bleeding  ceases  it  rises 
rapidly,  and  speedily  becomes  normal;  that  is  to  say,  unless  so  large  an 
amount  of  blood  has  been  taken  as  to  be  positively  dangerous  to  life, 
abstraction  of  blood  has  little  effect  upon  the  blood-pressure.  The  rapid 
return  to  the  normal  pressure  is  due  not  so  much  to  the  withdrawal  of 
lymph  and  other  fluids  from  the  body  into  the  blood,  as  was  formerly 
supposed,  as  to  the  regulation  of  the  peripheral  resistance  by  the  vaso- 
motor nerves;  in  other  words,  the  small  arteries  contract,  and  in  so  do- 
ing maintain  pressure  on  the  blood  and  favor  its  accumulation  in  the 
arterial  system.  This  is  due  to  the  stimulation  of  the  vaso-motor  cen- 
tre from  diminution  of  the  supply  of  blood,  and  therefore  of  oxygen. 
The  failure  of  the  blood-pressure  to  return  to  normal  in  the  too  great 


THE    CIRCULATION    OF   THE    BLOOD.  249 

abstraction  must  be  taken  to  indicate  a  condition  of  exhaustion  of  the 
centre,  and  consequently  of  want  of  regulation  of  the  periijheral  resist- 
ance. In  the  same  way  it  might  be  thought  that  injection  of  blood  into 
the  already  full  vessels  would  be  at  once  followed  by  rise  in  the  blood- 
pressure,  and  this  is  indeed  the  case  up  to  a  certain  point — the  pressure 
does  rise,  but  there  is  a  limit  to  the  rise.  Until  the  amount  of  blood 
injected  equals  about  2  to  3  per  cent  of  the  body-weight,  the  pressure 
continues  to  rise  gradually;  but  if  the  amount  exceed  this  proportion, 
the  rise  does  not  continue.  In  this  case,  therefore,  as  in  the  opposite 
when  blood  is  abstracted,  the  vaso-motor  apj^aratus  must  counter- 
act the  great  increase  of  pressure,  but  now  by  dilating  the  small  ves- 
sels, and  so  diminishing  the  peripheral  resistance,  for  after  each  rise 
there  is  a  partial  fall  of  pressure;  and  after  the  limit  is  reached  the 
whole  of  the  injected  blood  displaces,  as  it  were,  an  equal  quantity  which 
passes  into  the  small  veins,  and  remains  within  them.  It  should  be  re- 
membered that  the  veins  are  capable  of  holding  the  whole  of  the  blood 
of  the  body. 

Further,  as  we  have  seen,  the  amount  of  blood  supplied  to  the  heart, 
both  to  its  substance  and  to  its  chambers,  has  a  marked  effect  upon  the 
blood-pressure. 

h.  As  regards  qualitij.  The  quality  of  the  blood  supplied  to  the 
heart  has  a  distinct  effect  upon  its  contraction,  as  too  watery  or  too 
little  oxygenated  blood  must  interfere  with  its  action.  Thus  it  appears 
that  blood  containing  certain  substances  affects  the  peripheral  resistance 
by  acting  upon  the  muscular  fibres  of  the  arterioles,  and  so  directly  alter- 
ing the  calibre  of  the  vessels. 

Proofs  of  the  Circulation  of  the  Blood. 

It  seems  hardly  necessary  at  the  present  time  to  bring  forward  the 
proofs  that  during  life  the  blood  circulates  within  the  body;  they  are 
so  well  known.  It  is  interesting,  however,  to  recount  the  main  argu- 
ments by  which  Harvey  in  the  first  instance  established  the  fact  of  the 
circulation ;  they  were  as  follows : — 

1.  That  the  heart  in  half  an  hour  propels  more  blood  than  the  whole 
mass  of  blood  in  the  body; 

2.  That  the  blood  spurts  with  great  force  and  in  a  jerky  manner 
from  an  opened  artery,  such  as  the  carotid,  with  every  beat  of  the 
heart ; 

3.  That  if  true,  the  normal  course  of  the  circulation  would  explain 
why  after  death  the  arteries  are  commonly  found  empty  and  the  veins 
full; 

4.  That  if  the  large  veins  near  the  heart  be  tied  in  a  fish  or  snake, 
the  heart  becomes  pale,  flaccid,  and  bloodless;  and  that  on  moving  the 
ligature,  the  blood  again  flows  into  the  heart.     If  the  artcnj  is  tied,  tlie 


250  HANDBOOK   OF    PHYSIOLOGY. 

heart  becomes  distended,   the  distention  lasting  until  the  ligature   is 
removed ; 

5.  That  if  a  ligature  round  a  limb  be  drawn  very  tight,  no  blood  can 
enter  the  limb,  and  it  becomes  pale  and  cold.  If  the  ligature  be  some- 
what relaxed,  blood  can  enter  but  cannot  leave  the  limb;  hence  it  be- 
comes swollen  and  congested.  If  the  ligature  be  removed,  the  limb 
soon  regains  its  natural  appearance; 

6.  That  the  valves  in  the  veins  only  permit  the  blood  to  flow  toward 
the  heart; 

7.  That  there  is  general  constitutional  disturbance  resulting  from 
the  introduction  of  a  poison  at  a  single  point,  e.g.,  snake  poison; 

To  these  may  now  be  added  many  further  proofs  which  have  accu- 
mulated since  the  time  of  Harvey,  e.g. : — 

8.  That  in  wounds  of  arteries  and  veins;  in  the  former  case  hemor- 
rhage may  be  almost  stopped  by  pressure  between  the  heart  and  the 
wound,  in  the  latter  by  pressure  beyond  the  seat  of  injury; 

9.  That  the  passage  of  blood-corpuscles  from  small  arteries  through 
capillaries  into  veins  in  all  transparent  vascular  parts,  as  the  mesentery, 
tongue,  or  web  of  the  frog,  the  tail  or  gills  of  a  tadpole,  etc.,  may  actu- 
ally be  observed  under  the  microscope. 

Further,  it  is  obvious  that  the  mere  fact  of  the  existence  of  a  hollow 
muscular  organ  (the  heart)  with  valves  so  arranged  as  to  permit  the 
blood  to  pass  only  in  one  direction,  of  itself  suggests  the  course  of  the 
circulation.  The  only  part  of  the  circulation  which  Harvey  could  not 
follow  was  that  through  the  capillaries,  for  the  simple  reason  that  he 
had  no  lenses  sufficiently  powerful  to  enable  him  to  see  it.  Malpighi 
(1661)  and  Leeuwenhoek  (1668)  demonstrated  this  in  the  tail  of  the  tad- 
pole and  lung  of  the  frog. 


CHAPTER  VII. 

RESPIRATION. 

The  maintenunce  of  animal  life  necessitates  the  continual  absorption 
of  oxygen  and  excretion  of  carbonic  acid;  the  blood  being,  in  all  ani- 
mals which  possess  a  well-developed  blood-vascular  system,  the  medium 
by  which  these  gases  are  carried.  By  the  blood,  oxygen  is  absorbed 
from  without  and  conveyed  to  all  parts  of  the  organism;  and,  by  the 
blood,  carbonic  acid,  which  comes  from  within,  is  carried  to  those  parts 
by  which  it  may  escape  from  the  body.  The  two  processes, — absorption 
of  oxygen  and  excretion  of  carbonic  acid,  are  complementary,  and  their 
sum  is  termed  the  process  of  Respiration. 

In  all  Vertebrata,  and  in  a  large  number  of  Invertebrata,  certain  parts, 
either  lungs  or  gills,  are  specially  constructed  for  bringing  the  blood 
into  proximity  with  the  aerating  medium  (atmospheric  air,  or  water  con- 
taining air  in  solution).  In  some  of  the  lower  Vertebrata  (frogs  and 
other  naked  Amphibia)  the  skin  is  important  as  a  respiratory  orgaji, 
and  is  capable  of  supplementing,  to  some  extent,  the  functions  of  the 
•proper  hreatliing  apparatus;  but  in  all  the  higher  animals,  including 
man,  the  respiratory  capacity  of  the  skin  is  so  infinitesimal  that  it  may 
be  practically  disregarded. 

Essentially  a  lung  or  gill  is  constructed  of  a  fine  transparent  mem- 
brane, one  surface  of  which  is  exposed  to  the  air  or  water,  as  the  case 
may  be,  while,  on  the  other,  is  a  network  of  blood-vessels, — the  only  sep- 
aration between  the  blood  and  aerating  medium  being  the  thin  wall  of 
the  blood-vessels,  and  the  fine  membrane  on  one  side  of  which  vessels 
are  distributed.  The  difference  between  the  simplest  and  the  most 
complicated  respiratory  membrane  is  one  of  degree  only. 

The  various  complexity  of  the  respiratory  membrane,  and  the  kind 
of  aerating  medium,  are  not,  however,  the  only  conditions  which  cause 
a  difference  in  the  respiratory  capacity  of  different  animals.  The  num- 
ber and  size  of  the  red  blood-corpuscles,  the  mechanism  of  the  breathiTig 
apparatus,  the  presence  or  absence  of  a  pulmonari/  heart,  physiologically 
distinct  from  the  systemic,  are,  all  of  them,  conditions  scarcely  second 
in  importance. 

It  may  be  as  well  to  state  here  that  the  lungs  are  only  the  medium 
for  the  exchange,  on  the  part  of  the  blood,  of  carbonic  acid  for  oxygen. 
They  are  not  the  seat,  in  any  special  manner,  of  those  combustion-pro- 
Sol 


252 


HANDBOOK    OF    PHYSIOLOGY. 


cesses  of  which  the  production  of  carbonic  acid  is  the  final  result. 
These  processes  occur  in  all  parts  of  the  body  in  the  substance  of  the 
tissues. 

Of  the  Respiratory   Apparatus. 

The  object  of  respiration  being  the  interchange  of  gases  in  the  lungs, 
it  is  necessary  that  the  atmospheric  air  shall  pass  into  them  and  that 
the  changed  air  should  be  expelled  from  them.  The  lungs  are  contained 
in  the  chest  or  thorax,  which  is  a  closed  cavity  having  no  communica- 


Fig.  200. 


Fig.  201. 


Fig  200.— Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from 
before,  /i,  Tlie  great  cornu  of  the  hyoid  bone;  e,  epiglottis;  t,  superior,  and  t',  inferior  cornu  of  the 
thyroid  cartilage;  c,  middle  of  the  cricoid  cartilage  ;  tr,  the  trachea,  showing  sixteen  cartilaginous 
rings;  b,  tlie  right,  and  6',  the  left  bronchus.     (Allen  Thomson.)     x  J^- 

Fig.  201.— Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from 
behind,  /i.  Great  cornu  of  the  hyoid  bone;  t,  superior,  and  i',  the  inferior  cornu  of  the  thyroid 
cartilage;  e,  epiglottis;  o,  points  to  the  back  of  both  the  arytenoid  cartilages,  which  are  sur- 
mounted by  the  cornicula  ;  c,  the  middle  ridge  on  the  back  of  the  cricoid  cartilage;  tr,  the  pos- 
terior membranous  part  of  the  trachea;  b,  b',  right  and  left  bronchi.    (Allen  Thomson.)     x  ^. 


RESPIRATION".  253 

tion  with  the  outside,  except  by  means  of  the  respiratory  passages.  The 
air  enters  these  passages  through  the  nostrils  or  through  the  mouth, 
thence  it  passes  through  the  larynx  into  the  trachea  or  windpipe,  which 
about  the  middle  of  the  chest  divides  into  two  tubes,  bronchi,  one  to 
each  (right  and  left)  lung. 

The  Larynx  is  the  upper  part  of  the  passage  which  leads  exclusively 
to  the  lung;  it  is  formed  by  the  thyroid,  cricoid,  and  arytenoid  cartilages 
(fig.  200),  and  contains  the  vocal  cords,  by  the  vibration  of  whicii  the 
voice  is  chiefly  produced.  These  vocal  cords  are  ligamentous  bands 
attached  to  certain  cartilages  capable  of  movement  by  muscles.  By 
their  approximation  the  cords  can  entirely  close  the  entrance  into  the 
larynx;  but  under  ordinary  conditions,  the  entrance  of  the  larynx  is 
formed  by  a  more  or  less  triangular  chink  between  them,  called  the 
rima  glottidis.  Projecting  at  an  acute  angle  between  the  base  of  the 
tongue  and  the  larynx,  to  which  it  is  attached,  is  a  leaf-shaped  cartilage, 
with  its  larger  extremity  free,  culled  the  epiglottis  (fig.  201,  e).  The 
whole  of  the  larynx  is  lined  by  mucous  membrane,  which,  however,  is 
extremely  thin  over  the  vocal  cords.  At  its  lower  extremity  the  larynx 
joins  the  trachea.*  "With  the  exception  of  the  epiglottis  and  the  so- 
called  cornicula  laryngis,  the  cartilages  of  the  larynx  are  of  the  hyalin 
variety. 

The  Epiglottis. — The  supporting  cartilage  of  the  epiglottis  is  com- 
posed of  yellow  elastic  cartilage,  inclosed  in  a  fibrous  sheath  (perichon- 
drium), and  covered  on  both  sides  with  mucous  membrane.  The  ante- 
rior surface,  which  looks  toward  the  back  of  the  tongue,  is  covered  with, 
mucous  membrane,  the  basis  of  which  is  fibrous  tissue,  elevated  toward 
both  surfaces  in  the  form  of  rudimentary  papillae,  and  covered  with 
several  layers  of  squamous  epithelium.  In  it  ramify  capillary  blood- 
vessels, and  in  its  meshes  are  a  large  number  of  lymphatic  channels. 
Under  the  mucous  membrane,  in  the  less  dense  fibrous  tissue  of  which 
it  is  composed,  is  a  number  of  tubular  glands.  The  posterior  or  laryn- 
geal surface  of  the  epiglottis  is  covered  by  a  mucous  membrane,  similar 
in  structure  to  that  on  the  other  siirface,  but  its  epithelial  coat  is  thin- 
ner, the  number  of  strata  of  cells  is  less,  and  the  papilla  few  and  less, 
distinct.  The  fibrous  tissue  which  constitutes  the  mucous  membrane  is 
in  great  part  of  the  adenoid  variety,  and  is  here  and  there  collected  into 
distinct  masses  or  follicles.  The  glands  of  the  posterior  surface  are 
smaller  but  more  numerous  than  those  of  the  other  surface.  In  many 
places  the  glands  which  are  situated  nearest  to  the  perichondrium  are 
directly  continuous  through  apertures  in  the  cartilage  with  those  on  the 
other  side,  and  often  the  ducts  of  the  glands  from  one  side  of  the  carti- 

*  A  detailed  account  of  the  structure  and  function  of  the  Larynx  will  bo 
found  in  a  later  chapter. 


254 


HANDBOOK    OF    PHYSIOLOGY. 


lage  pass  tnrough  and  open  upon  the  mucous  surface  of  the  other  side. 
Taste  goblets  have  been  found  in  the  epithelium  of  the  posterior  surface 
of  the  epiglottis,  and  in  several  other  situations  in  the  laryngeal  mucous 
membrane. 

The  Trachea  and  Bronchi. — The  trachea  extends  from  the  cricoid 
cartilage,  which  is  on  a  level  with  the  fifth  cervical  vertebra,  to  a  point 
opposite  the  third  dorsal  vertebra,  where  it  divides  into  the  two  bronchi 


Fig.  202.— Section  of  the  trachea,  a,  Columnar  ciliated  epithelium;  6  aiid  c,  proper  structure  of 
the  mucous  membrane,  containing  elastic  fibres  cut  across  transversely;  d,  submucuous  tissue 
containing  mucous  glands,  e,  separated  from  the  hyaline  cartilage,  g,  by  a  fine  fibrous  tissue,  /;  h, 
external  investment  of  fine  fibrous  tissue.    (S.  K.  Alcock.) 


one  for  each  lung  (fig.  201).  It  measures,  on  an  average,  four  or  four- 
and-a-half  inches  in  length,  and  from  three-quarters  of  an  inch  to  an 
inch  in  diameter,  and  is  essentially  a  tube  of  fibro-elastic  membrane, 
within  the  layers  of  which  are  enclosed  a  series  of  cartilaginous  rings, 
from  sixteen  to  twenty  in  number.  These  rings  extend  only  around 
the  front  and  sides  of  the  trachea  (about  two-thirds  of  its  circumfer- 
ence), and  are  deficient  behind;  the  interval  between  their  posterior 
extremities  being  bridged  over  by  a  continuation  of  the  fibrous  mem- 


RESPIRATION".  255 

brane  in  which  they  are  closed  (fig.  202).  The  cartilages  of  the  trachea 
and  bronchial  tubes  are  of  the  hyaline  variety. 

Immediately  within  this  tube,  at  the  back,  is  a  layer  of  unstriped 
muscular  fibres,  which  extends,  transversely,  between  the  ends  of  the 
cartilaginous  rings  to  which  they  arc  attached,  and  opposite  the  inter- 
vals between  them,  also;  their  evident  function  being  to  diminish,  when 
required,  the  calibre  of  the  trachea  by  approximating  the  ends  of  the 
cartilages.  Outside  there  are  a  few  longitudinal  bundles  of  muscular 
tissue,  which,  like  the  preceding,  are  attached  both  to  the  fibrous  and 
cartilaginous  framework. 

The  mucous  membrane  consists  to  a  great  extent  of  adenoid  tissue, 
separated  from  the  stratified  columnar  epithelium  which  lines  it  by  a 
homogeneous  basement  membrane.  This  is  penetrated  here  and  there 
by  channels  which  connect  the  adenoid  tissue  of  the  mucosa  with  the 
intercellular  substance  of  the  epithelium.  The  stratified  columnar 
epithelium  is  formed  of  several  layers,  of  which  the  most  superficial  layer 
is  ciliated,  and  is  often  branched  downward  to  join  connective  tissue 
corpuscles;  while  between  these  branched  cells  are  smaller  elongated 
cells  prolonged  up  toward  the  surface  and  down  to  the  basement  mem- 
brane. Beneath  these  are  one  or  more  layers  of  more  irregularly-shaped 
cells.  Many  of  the  superficial  cells  are  of  the  goblet  variety.  In  the 
deeper  part  of  the  mucosa  are  many  elastic  fibres  between  which  lie 
connective-tissue  corpuscles  and  capillary  blood-vessels. 

Numerous  mucous  glands  are  situated  on  the  exterior  and  in  the 
substance  of  the  fibrous  framework  of  the  trachea;  their  ducts  perforat- 
ing the  various  structures  which  form  the  wall  of  the  trachea,  and  open- 
ing through  the  mucous  membrane  into  the  interior. 

The  two  bronchi  into  which  the  trachea  divides,  of  which  the  right 
is  shorter,  broader,  and  more  horizontal  than  the  left  (fig.  200),  resem- 
ble the  trachea  exactly  in  structure,  with  the  difference  that  in  them 
there  is  a  distinct  layer  of  unstriped  muscle  arranged  circularly  beneath 
the  mucous  membrane,  forming  the  muscularis  mucosce.  On  entering 
the  substance  of  the  lungs  the  cartilaginous  rings,  although  they  still 
form  only  larger  or  smaller  segments  of  a  circle,  are  no  longer  confined 
to  the  front  and  sides  of  the  tubes,  but  are  distributed  impartially  to  all 
parts  of  their  circumference. 

The  bronchi  divide  and  subdivide,  in  the  substance  of  the  lungs, 
into  a  number  of  smaller  and  smaller  branches,  which  penetrate  into 
every  part  of  the  organ,  until  at  length  they  end  in -the  smaller  sub- 
divisions of  the  lungs,  called  lohvles. 

All  the  larger  branches  have  walls  formed  of  tough  membrane,  con- 
taining portions  of  cartilaginous  rings,  by  which  they  are  held  open,  and 
unstriped  muscular  fibres,  as  well  as  longitudinal  bundles  of  elastic  tis- 
sue.    They  are  lined  by  mucous  membrane,  the  surface  of  which,  like 


256  HANDBOOK    OF    PHYSIOLOGY. 

that  of  the  larynx  and  trachea,  is  covered  with  ciliated  epithelium,  but 
the  several  layers  become  less  and  less  distinct  until  the  lining  consists 
of  a  single  layer  of  more  or  less  cubical  cells  covered  with  cilia  (fig.  203). 
The  mucous  membrane  is  abundantly  provided  with  mucous  glands. 

As  the  bronchi  become  smaller  and  smaller,  and  their  walls  thinner, 
the  cartilaginous  rings  become  scarcer  and  more  irregular,  until,  in  the 
smaller  bronchial  tubes,  they  are  represented  only  by  minute  and  scat- 
tered cartilaginous  flakes.  And  when  the  bronchi,  by  successive  branches 
are  reduced  to  about  ^L-  of  an  inch  (.6  mm.)  in  diameter,  they  lose  their 
cartilaginous  element  altogether,  and  their  walls  are  foi'med  only  of  a 
tough  fibrous  elastic  membrane,  with  circular  muscular  fibres;  they  are 
still  lined,  however,  by  a  thin  mucous  membrane,  with  ciliated  epithe- 
lium, the  length  of  the  cells  bearing  the  cilia  having  become  so  far 
diminished  that  the  cells  are  now  almost  cubical.     In  the  smaller  bron- 


gjn 


Fig.  20;b. —Transverse  section  of  a  bronchus,  about  V^  inch  in  diameter,  e,  Epithelium  (ciliated); 
immediately  beneath  it  is  the  mucous  membrane  or  internal  fibrous  layer,  of  varying  thickness;  m, 
muscular  layer  ;  s.  m,  submucous  tissue;  /,  fibrous  tissue  ;  c,  cartilage  enclosed  within  the  layers 
of  fibrous  tissue ;  g,  mucous  gland.    (F.  E.  Schulze.) 

chi  the  circular  muscular  fibres  are  relatively  more  abundant  than  in 
the  larger  bronchi,  and  form  a  distinct  circular  coat. 

The  Lungs  atid  Pleurm. — The  Lungs  occupy  the  greater  portion  of 
the  thorax.  They  are  of  a  spongy  elastic  texture,  and  on  section  appear 
to  the  naked  eye  as  if  they  were  in  great  part  solid  organs,  except  here 
and  there,  at  certain  points,  where  branches  of  the  bronchi  or  air-tubes 
may  have  been  cut  across,  and  show,  on  the  surface  of  the  section,  their 
tubular  structure.  In  fact,  however,  the  lungs  are  hollow  organs,  each 
of  which  communicates  by  a  separate  orifice  with  a  common  air-tube, 
the  trachea. 

Each  lung  is  enveloped  by  a  serous  membrane — the  pleura,  one  layer 
of  which  adheres  closely  to  its  surface,  and  provides  it  with  its  smooth 
and  slippery  covering,  while  the  other  adheres  to  the  inner  surface  of 
the  chest-wall.  The  continuity  of  the  two  layers,  which  form  a  closed 
sac,  as  in  the  case  of  other  serous  membranes,  will  be  best  understood 
by  reference  to  fig.  204.     The  appearance  of  a  space,  however,  between 


RESPIKATIOX. 


257 


the  pleura  which  covers  the  hmg  {visceral  layer),  and  that  which  lines 
the  inner  surface  of  the  chest  ( parietal  layer),  is  inserted  in  the  draw- 
ing only  for  the  sake  of  distinctness.  These  layers  are,  in  health,  every- 
where in  contact,  one  with  the  other;  and  between  them  is  only  just  so 
much  fluid  as  will  insure  gliding  easily,  in  their  expansion  and  contrac- 
tion, on  the  inner  surface  of  the  parietal  layer,  which  lines  the  chest- 
wall.  While  considering  the  subject  of  normal  respiration,  we  may 
discard  altogether  the  notion  of  the  existence  of  any  space  or  cavity 
between  the  lungs  and  the  wall  of  the  chest. 

If,  however,  an  opening  be  made  so  as  to  permit  air  or  fluid  to  enter 
the  pleural  sac,  the  lung,  in  virtue  of  its  elasticity,  recoils,  and  a  consid- 
erable space  is  left  between  it  and  the  chest-wall.  In  other  words,  the 
natural  elasticity  of  the  lungs  would  cause  them  at  all  times  to  contract 


Fig.  204.— Transverse  section  of  the  chest. 


away  from  the  ribs  were  it  not  that  the  contraction  is  resisted  by  atmos- 
pheric pressure  Avhicli  bears  only  on  the  inner  surface  of  the  air-tubes 
and  air-cells.  On  the  admission  of  air  into  the  pleural  sac,  atmospheric 
pressure  bears  alike  on  the  inner  and  outer  surfaces  of  the  lung,  and 
their  elastic  recoil  is  thus  no  longer  prevented. 

The  pulmonary  pleura  consists  of  an  outer  or  denser  layer  and  an 
inner  looser  tissue.  The  former  or  j^Uura  proper  consists  of  dense 
fibrous  tissue  with  elastic  fibres,  covered  by  endothelium,  the  cells  of 
which  are  large,  flat,  hyaline,  and  transparent  when  the  lung  is  ex- 
panded, but  become  smaller,  thicker,  and  granular  when  the  lung  col- 
lapses. In  the  pleura  is  a  lymph-canalicular  system;  and  connective 
tissue  corpuscles  are  found  in  the  fibrous  tissue  which  forms  its  ground- 
work. The  inner,  looser,  or  sub-pleural  tissue  contains  lanielloe  of  fibrous 
connective  tissue  and  connective-tissue  corpuscles  between  them.  Nu- 
merous lymphatics  are  to  be  met  with,  which  form  a  dense  plexus  of 
vessels,  many  of  which  contain  valves.  They  are  simple  endothelial 
17 


258 


HAl!fDBOOK    OF    PHYSIOLOGY. 


tubes,  and  take  origin  in  the  lympli-canalicular  system  of  the  pleura, 
proper.  Scattered  bundles  of  unstriped  muscular  fibre  occur  in  the 
pulmonary  pleura.  They  are  especially  strongly  developed  on  the  an- 
terior and  internal  surfaces  of  the  lungs,  the  parts  which  move  most 


Fig.  205.— Ciliary  epithelium  of  the  human  trachea,  a,  Layer  of  longitudinally  arranged  elastic 
fibres  ;  b,  basement  membrane  ;  c,  deepest  cells,  circular  in  form  ;  d,  intermediate  elongated  cells  ; 
c,  outermost  layer  of  cells  fully  developed  and  bearing  cilia.     X  350.    (Kolliker.) 

freely  in  respiration :  their  function  is  doubtless  to  aid  in  expiration. 
The  structure  of  the  parietal  portion  of  the  pleura  is  very  similar  to 
i;hat  of  the  visceral  layer. 

Each  lung  is  partially  subdivided  into  separate  portions  called  lobes; 
ihe  right  lung  into  three  lobes,  and  the  left  into  two.  Each  of  these 
lobes,  again,  is  composed  of  a  large  number  of  minute  parts,  called  lob- 


rig.206. 


Fig.  207 


Fig.  206.— Terminal  oranch  c-f  a  bronchial  tube,  with  its  inf undibula  and  air-cells,  from  the  mar- 
gin of  the  lung  of  a  monkey,  injected  with  quicksilver,  a,  Terminal  bronchial  twig;  b  b,  infundibula 
and  air-ct  lis.     X  10.    (F.  E.  Schulze.) 

Fig.  807. —Two  small  infundibula  or  groups  of  air-cells,  a  a,  with  air-cells,  6  6,  and  the  ultimate 
bronchial  tubes,  c  c,  with  which  the  air-cells  communicate.    From  a  new-born  child.    (Kolliker.) 

tiles.  Each  pulmonary  lobule  may  be  considered  to  be  a  lung  in  minia- 
ture, consisting,  as  it  does,  of  a  branch  of  the  bronchial  tube,  of  air-cells, 
blood-vessels,  nerves,  and  lymphatics,  with  a  sparing  amount  of  areolar 
tissue. 


RESPIRATION. 


259 


On  entering  a  lobule,  the  small  bronchial  tube,  the  structure  of 
which  has  been  just  described  {a,  fig.  206),  divides  and  subdivides;  its 
walls  at  the  same  time  becoming  thinner  and  thinner,  until  at  length 
they  are  formed  only  of  a  thin  membrane  of  areolar  and  elastic  tissue, 
lined  by  a  layer  of  squamous  epithelium,  not  provided  with  cilia.  At 
the  same  time,  they  are  altered  in  shape;  each  of  the  minute  terminal 
branches  widening  out  funnel-wise,  and  its  walls  being  pouched  out 
irregularly  into  small  saccular  dilatations,  called  air-cells  (fig.  206,  h). 
Such  a  funnel-shaped  terminal  branch  of  the  bronchial  tube,  with  its 


Fig.  208.— From  a  section  of  tbe  lung  of  a  cat,  stained  witli  silver  nitrate.  A.  D.  Alveolar  duct  or 
JntMcellular  passage.  S.  Alveolar  septa.  N.  Alveoli  or  air-cells,  lined  with  large  flat,  nucleated  cells, 
with  some  smaller  polyhedral  nucleated  cells.  M.  Unstriped  muscular  fibres.  Circular  muscular 
fibres  are  seen  surrounding  the  interior  of  the  alveolar  duct,  and  at  one  part  is  seen  a  group  of  small 
polyhedral  cells  continued  from  the  bronchus.    (Klein  and  Is'oble  Smith.) 


group  of  pouches  or  air-cells,  has  been  called  an  infundihidum  (figs.  206, 
207),  and  the  irregular  oblong  space  in  its  centre,  with  which  the  air- 
cells  communicate,  an  intercellular  passage. 

The  air-cells,  or  air-vesicles,  may  be  placed  singly,  like  recesses  from 
the  intercellular  passage,  but  more  often  they  are  arranged  in  groups  or 
even  in  rows,  like  minute  sacculated  tubes;  so  that  a  short  series  of  ves- 
icles, all  communicating  with  one  another,  open  by  a  common  orifice 
into  the  tube.  The  vesicles  are  of  various  forms,  according  to  the 
mutual  pressure  to  which  they  are  subject;  their  walls  are  nearly  in 
contact,  and  they  vary  from  -^  to  y^  of  an  inch  (.5  to  .3  mm.)  in  diam- 
eter.    Their  walls  are  formed  of  fine  membrane,  similar  to  that  of  the 


260 


HANDBOOK    OF    PHYSIOLOGY. 


intercellular  passages,  and  continuous  with  it,  which  membrane  is  folded 
on  itself  so  as  to  form  a  sharp-edged  border  at  each  circular  orifice  of 
communication  between  contiguous  air-vesicles,  or  between  the  vesicles 
and  the  bronchial  passages.  Numerous  fibres  of  elastic  tissue  are  spread 
out  between  contiguous  air-cells,  and  many  of  these  are  attached  to  the 
outer  surface  of  the  fine  membrane  of  which  each  cell  is  composed,  im- 
parting to  it  additional  strength,  and  the  power  of  recoil  after  disten- 
tion. The  cells  are  lined  by  a  layer  of  epithelium  (fig.  208),  not  pro- 
vided with  cilia.  Outside  the  cells,  a  network  of  pulmonary  capillaries 
is  spread  out  so  densely  (fig.  209)  that  the  interspaces  or  meshes  are 
even  narrower  than  the  vessels,  which  are,  on  an  average,  •g-gVo'  of  an 
inch  (8/j^)  in  diameter.  Between  the  atmospheric  air  in  the  cells  and 
the  blood  in  these  vessels,  nothing  intervenes  but  the  thin  walls  of  the 


Kg.  209.— Capillary  network  of  the  pulmonary  blood-vessels  in  the  human  lung.  X  SO,  CK311iker.> 

cells  and  capillaries;  and  the  exposure  of  the  blood  to  the  air  is  the- 
more  complete,  because  the  folds  of  membrane  between  contiguous 
cells,  and  often  the  spaces  between  the  walls  of  the  same,  contain  only  a 
single  layer  of  capillaries,  both  sides  of  which  are  thus  at  once  exposed 
to  the  air. 

The  air-vesicles  situated  nearest  to  the  centre  of  the  lung  are  smaller 
and  their  networks  of  capillaries  are  closer  than  those  nearer  to  the  cir- 
cumference. The  vesicles  of  adjacent  lobules  do  not  communicate;  and 
those  of  the  same  lobule  or  proceeding  from  the  same  intercellular  pas- 
sage, do  so  as  a  general  rule  only  near  angles  of  bifurcation;  so  that,, 
when  any  bronchial  tube  is  closed  or  obstructed,  the  supply  of  air  is  lost 
for  all  the  cells  opening  into  it  or  its  branches. 

Blood-supply. — The  lungs  receive  blood  from  two  sources,  (a)  the 
pulmonary  artery,  (b)  the  bronchial  arteries.  The  former  conveys  venous 
blood  to  the  lungs  for  its  arterialization,  and  this  blood  takes  no  share 


KESPIRATIOX.  261 

in  the  nutrition  of  the  pulmonary  tissues  through  which  it  passes,  (b) 
The  branches  of  the  bronchial  arteries  ramify  for  nutrition's  sake  in  the 
walls  of  the  bronchi^  of  the  larger  pulmonary  vessels,  in  tlie  interlobular 
connective  tissue,  etc.;  the  blood  of  the  bronchial  vessels  being  returned 
chiefly  through  the  bronchial  and  partly  through  the  pulmonary  veins. 

Lymphatics. — The  lymphatics  are  arranged  in  three  sets: — 1.  Irreg- 
ular lacunse  in  the  walls  of  the  alveoli  or  air-cells.  The  lymphatic 
vessels  which  lead  from  these  accompany  the  j)ulmonary  vessels  toward 
the  root  of  the  lung.  2.  Irregular  anastomosing  spaces  in  the  walls  of 
the  bronchi.  3.  Lymph-spaces  in  the  pulmonary  pleura.  The  lym- 
phatic vessels  from  all  these  irregular  sinuses  j)ass  in  toward  the  root 
of  the  lung  to  reach  the  bronchial  glands. 

Nerves. — The  nerves  of  the  lung  are  to  be  traced  from  the  anterior 
and  posterior  pulmonary  plexuses,  Avhich  are  formed  by  branches  of  the 
vagus  and  sympathetic.  The  nerves  follow  the  course  of  the  vessels  and 
bronchi,  and  in  the  walls  of  the  latter  many  small  ganglia  are  situated. 

The  Respiratory  Mechanism, 

Respiration  consists  of  the  alternate  expansion  and  contraction  of 
the  thorax,  by  means  of  which  air  is  drawn  into  or  expelled  from  the 
lungs.     These  acts  are  called  Inspiration  and  Expiration  respectively. 

For  the  inspiration  of  air  into  the  lungs  it  is  evident  that  all  that  is 
necessary  is  such  a  movement  of  the  side-walls  or  floor  of  the  chest,  or 
of  both,  that  the  capacity  of  the  interior  shall  be  enlarged.  By  such 
increase  of  capacity  there  will  be  of  course  a  diminution  of  the  j^ressure 
of  the  air  in  the  lungs,  and  a  fresh  quantity  will  enter  through  the 
larynx  and  trachea  to  equalize  the  pressure  on  the  inside  and  outside 
of  the  chest. 

For  the  expiration  of  ;iir,  on  the  other  hand,  it  is  also  evident  that, 
by  an  opposite  movement  which  shall  diminish  the  capacity  of  the  chest, 
the  pressure  in  the  interior  will  be  increased,  and  air  will  be  expelled, 
until  the  pressure  within  and  without  the  chest  are  again  equal.  In  both 
cases  the  air  passes  through  the  trachea  and  larynx,  whether  in  entering 
or  leaving  the  lungs,  there  being  no  other  communication  with  the  ex- 
terior of  the  body;  and  the  lung,  for  the  same  reason,  remains  under  all 
the  circumstances  described  closely  in  contact  with  the  walls  and  floor 
of  the  chest.  To  speak  of  expansion  of  the  chest,  is  to  speak  also  of  ex- 
pansion of  the  lung. 

We  have  now  to  consider  the  means  by  which  the  respiratory  move- 
ments are  effected. 

Inspiration. — The  enlargement  of  the  cnest  in  insjiiration  is  a 
muscular  act;  the  effect  of  the  action  of  the  inspiratory  muscles  being 
an  increase  in  the  size  of  the  chest-cavity  (a)  in  the  vertical,  and  (b) 


262 


HANDBOOK    OF    PHYSIOLOGY. 


in  the  lateral  and  antero-posterior  diameters.  The  muscles  engaged  in 
ordinary  inspiration  are  the  diaphragm;  the  scaleni ;  the  external  inter- 
costals;  parts  of  the  internal  iutercostals;  the  levatores  costarum ;  and 
serratus  posticus  superior. 

{a.)  The  vertical  diameter  of  the  chest  is  increased  by  the  contraction 
and  consequent  descent  of  the  diaphragm — the  sides  of  the  muscle  de- 
scending most,  but  the  central  tendon  also  descends  to  some  extent, 
while  the  intercostal  and  other  muscles,  by  actiug  at  the  same  time,  pre- 
vent the  diaphragm,  during  its  contraction,  from  drawing  in  the  sides 
of  the  chest. 

{b.)  The  increase  in  the  lateral  and  antero-posterior  diameters  of  the 


Fig.  810.— Diagram  of  axes  of  movement  of  ribs. 

chest  is  effected  by  the  raising  of  the  ribs,  the  greater  number  of  which 
are  attached  very  obliquely  to  the  spine  and  sternum. 

The  elevation  of  the  ribs  takes  place  both  in  front  and  at  the  sides 
— the  hinder  ends  being  prevented  from  performing  any  upward  move- 
ment by  their  attachment  to  the  spine.  The  movement  of  the  front 
extremities  of  the  ribs  is  of  necessity  accompanied  by  an  upward  and 
forward  movement  of  the  sternum  to  which  they  are  attached,  the  move- 
ment being  greater  at  the  lower  end  than  at  the  upper  end  of  the  latter 
bone. 

The  axes  of  rotation  in  these  movements  are  two;  one  corresponding 
with  a  line  drawn  through  the  two  articulations  which  the  rib  forms 
with  the  spine  {a,  h,  fig.  210) ;  and  the  other  with  a  line  drawn  from  one 
of  these  (head  of  rib)  to  the  sternum  (A  B,  fig.  210) ;  the  motion  of  the 
rib  around  the  latter  axis  being  somewhat  after  the  fashion  of  raising 
the  handle  of  a  bucket. 


RESPIRATIOlf. 


263 


The  elevation  of  the  ribs  is  accompanied  by  a  slight  opening  out  of 
the  angle  which  the  bony  part  forms  with  its  cartilage  (fig.  211,  A); 
and  thus  an  additional  means  is  provided  for  increasing  the  antero- 
posterior diameter  of  the  chest. 

The  muscles  by  which  the  ribs  are  raised,  in  ordinary  quiet  inspira- 
tion, are  external  intercostals,  and  that  portion  of  the  internal  intercostals 
which  is  situate  between  the  costal  cartilages;  and  these  are  assisted 
by  the  scaJeni,  which  fix  the  first  and  second  ribs,  the  levatores  costartim, 
and  the  serratus  posticus  superior.  The  action  of  the  levaiores  and  the 
serratus  is  "very  simple.  Their  fibres,  arising  from  the  spine  as  a  fixed 
point,  pass  obliquely  downward  and  forward  to  the  ribs,  and  necessarily 
raise  the  latter  when  they  contract.  The  action  of  the  intercostal  mus- 
cles is  not  quite  so  simple,  inasmuch  as,  passing  merely  from  rib  to  rib, 
they  seem  at  first  sight  to  have  no  fixed  point  toward  which  they  can 
pull  the  bones  to  which  they  are  attached. 


Fig.  211. — Diagram  of  movement  of  a  rib  in  inspiration. 


In  tranquil  breathing,  the  expansive  movements  of  the  lower  part  of 
the  chest  are  greater  than  those  of  the  upper.  In  forced  inspiration, 
on  the  other  hand,  the  greatest  extent  of  movement  appears  to  be  in 
the  upper  antero-posterior  diameter. 

In  extraordinarij  or  forced  inspiration,  as  in  violent  exercise,  or  in 
cases  in  which  there  is  some  interference  with  the  due  entrance  of  air 
into  the  chest,  and  in  which,  therefore,  strong  efforts  are  necessary,  other 
muscles  than  those  just  enumerated,  are  pressed  into  the  service.  It  is 
very  difhcult  or  impossible  to  separate  by  a  hard  and  fast  line  the  so- 
called  muscles  of  ordinary  from  those  of  extraordinary  inspiration;  but 
there  is  no  doubt  that  the  following  are  but  little  used  as  respiratory 
agents,  except  in  cases  in  which  unusual  elTorts  are  required — i\\Qsterno- 
mastoid,  the  serratus  magnus,  the  pectorales,  and  the  trapezitts. 


264  HANDBOOK   OF    PHYSIOLOGY. 

The  expansion  of  the  chest  in  inspiration  presents  some  peculiarities 
in  different  persons.  In  young  children,  it  is  effected  chiefly  by  the 
diaphragm,  which  being  highly  arched  in  expiration,  becomes  flatter  as 
it  contracts,  and,  descending,  presses  on  the  abdominal  viscera,  and 
pushes  forward  the  front  walls  of  the  abdomen.  The  movement  of  the 
abdominal  walls  being  here  more  manifest  than  that  of  any  other  part, 
it  is  usual  to  call  this  the  abdominal  type  of  respiration.  In  men,  to- 
gether with  the  descenb  of  the  diaphragm,  and  the  pushing  forward  of 
the  front  wall  of  the  abdomen,  the  chest  and  the  sternum  are  subject  to 
a  wide  movement  in  inspiration  (inferior  costal  type).  In  women,  the 
movement  appears  less  extensive  in  the  lower,  and  more  so  in  the  upper, 
part  of  the  chest  (superior  costal  type). 

Expiration. — From  the  enlargement  produced  in  inspiration,  the 
chest  and  lungs  return  in  ordinary  tranquil  expiration,  by  their  elastic- 
ity; the  force  employed  by  the  inspiratory  muscles  in  distending  the 
chest  and  overcoming  the  elastic  resistance  of  the  lungs  and  chest-walls, 
being  returned  as  an  expiratory  effort  when  the  muscles  are  relaxed. 
This  elastic  recoil  of  the  chest  and  lungs  is  sufficient,  in  ordinary  quiet 
breathing,  to  expel  air  from  the  lungs  in  the  intervals  of  inspiration, 
and  no  muscular  power  is  required.  In  all  voluntary  expiratory  efforts, 
however,  as  in  speaking,  singing,  blowing,  and  the  like,  and  in  many  in- 
voluntary actions  also,  as  sneezing,  coughing,  etc.,  something  more  than 
merely  passive  elastic  power  is  necessary,  and  the  proper  expiratory 
muscles  are  brought  into  action.  J3y  far  the  chief  of  these  are  the  ab- 
dominal muscles,  which,  by  pressing  on  the  viscera  of  the  abdomen,  push 
up  the  floor  of  the  chest  formed  by  the  diaphragm,  and  by  thus  making 
pressure  on  the  lungs,  expel  air  from  them  through  the  trachea  and 
larynx.  All  muscles,  however,  which  depress  the  ribs,  must  act  also  as 
muscles  of  expiration,  and  therefore  we  must  conclude  that  the  abdom- 
inal muscles  are  assisted  in  their  action  by  the  greater  part  of  the  inter- 
nal intercostals,  the  triangularis  ster7ii,  the  serratus  jjosticus  inferior 
and  quadratus  lumhorum.  When  by  tlie  efforts  of  the  expiratory  mus- 
cles, the  chest  has  been  squeezed  to  less  than  its  average  diameter,  it 
again,  on  relaxation  of  the  muscles,  returns  to  the  normal  dimensions 
by  virtue  of  its  elasticity.  The  construction  of  the  chest-walls,  there- 
fore, admirably  adapts  them  for  recoiling  against  and  resisting  as  well 
undue  contraction  as  undue  dilatation. 

In  the  natural  condition  of  the  parts  the  lungs  can  never  contract 
to  the  utmost,  but  are  always  more  or  less  "  on  the  stretch,"  being  kept 
closely  in  contact  with  the  inner  surface  of  the  walls  of  the  chest  by 
cohesion  as  well  as  by  atmospheric  pressure,  and  can  contract  away  from 
these  only  when,  by  some  means  or  other,  as  by  making  an  opening  into 
the  pleural  cavity,  or  by  the  effusion  of  fluid  there,  the  pressure  on  the 
exterior  and  interior  of  the  lungs  becomes  equal.     Thus,  under  ordinary 


RESPIEATION. 


265 


circumstances,  the  degree  of  contraction  or  dilatation  of  tlie  lungs  is 
dependent  on  that  of  the  boundar}^  walls  of  the  chest,  the  outer  surface 
of  the  one  being  in  close  contact  with  the  inner  surface  of  the  other, 
and  obliged  to  follow  it  in  all  its  movements. 

Methods  of  recording  Respiratory  Movements. 

The  movements  of  respiration  may  be  recorded  graphically  in  several  ways. 
The  ordinary  method  is  to  introduce  a  tube  into  the  trachea  of  an  animal,  and 
to  connect  this  tube  by  some  gutta-percha  tubing  with  a  T  piece  introduced 
into  the  cork  of  a  large-sized  bottle,  the  other  end  of  the  T  having  attached  to 
it  a  second  piece  of  tubing,  Avhich  can  remain  oiDen  or  can  be  partially  or 
completely  closed  by  means  of  a  screw  clamp.  Into  the  cork  is  inserted  a  sec- 
ond piece  of  glass  tubing  connected  with  a  Marey's  tambour  by  suitable  tubing. 
This  second  tube  communicates  any  alteration  of  the  pressm-e   in  the  bottle  of 


Fig:.  212.— Stethograph  or  Pneumograph,  h,  tamboiu-  fixed  at  right  angles  to  plate  of  steel/; 
€  and  d.  arms  by  which  instrument  is  attachpd  to  chest  by  belt  e.  Wheu  the  chest  expands,  the 
arms  are  puUed  asunder,  which  bends  tlie  steel  plate,  and  the  tambour  is  affected  by  the  pressure 
of  b  whicli  is  atraclie^l  to  it  on  the  one  hand,  and  to  the  upright  in  connection  with  horizontal  screw 
g.    (Modified  from  Marey"s  instrument.) 


the  tambour,  and  this  may  be  made  to  write  on  a  recording  surface  (fig. 
173).  If  the  tube  attached  to  the  T  piece  be  closed  the  movements  of  inspira- 
tion and  expiration  are  larger  than  if  it  were  closed.  The  alteration  of  the 
pressure  within  the  lungs  on  inspiration  and  expiration  is  shown  bj-  the  move- 
ment of  the  column  of  air  in  the  trachea.  By  these  means  a  record  of  the 
respiratory  movements  may  be  obtained. 

Various  instruments  for  recording  the  movements  of  the  chest  by  applica- 
tion of  apparatus  to  the  exterior.  Such  is  the  stethometer  of  Burton  Sander- 
son. This  consists  of  a  frame  formed  of  two  parallel  steel  bars  joined  by  a 
third  at  one  end.  At  the  free  end  of  the  bare  is  attached  a  leather  strap,  by 
means  of  which  the  apparatus  may  be  suspended  from  the  neck.  Attached  to 
the  inner  end  of  one  bar  is  a  tambour  and  ivory  button,  to  the  end  of  the 
other  an  ivory  button.  When  in  use,  the  apparatus  is  suspended  with  the 
ti-ansverse  bar  posteriorly,  the  button  of  the  tambour  is  placed  on  the  part  of 
the  chest  the  movement  of  which  it  is  desired  to  record,  and  the  other  button 


266 


HANDBOOK   OF    PHYSIOLOGY. 


is  made  to  press  upon  the  corresponding  side  of  the  chest,  so  that  the  chest  is, 
as  it  were,  held  between  a  pair  of  calipers.  The  tambour  is  connected  by 
tubing  and  a  T  piece  with  a  recording  tambour  of  Marey's,  and  with  a  baU, 
by  means  of  which  air  can  be  squeezed  into  the  cavity  of  the  tympanum. 
When  in  work  the  tube  connected  with  the  air  ball  is  shut  off  by  means  of  a 
screw  clamp.  The  movement  of  the  chest  is  thus  communicated  to  the  recording 
tambour. 

A  simpler  form  of  this  apparatus,  called  a  pneumograph  or  stethograph, 
consisting  of  a  thick  India-rubber  bag  of  elliptical  shape  about  three  inches 
long,  to  one  end  of  which  a  rigid  gutta-percha  tube  is  attached.  This  bag 
may  be  fixed  at  any  required  place  on  the  chest  by  means  of  a  strap  and  buckle. 
By  means  of  the  gutta-percha  tube  the  variations  of  the  presssure  of  air  in  the 


Tamlwur. 
Ivory  tutton. 


Tube  to  comma- 
nicate  with  re- 
cording tam- 
bour. 


Ball  to  fill  appa-  _ 
ratufl  -with  air. 


Fig.  213.— Stethometer.    CBurdon  Sanderson.) 


bag  produced  by  the  movements  of  the  chest  are  communicated  to  a  recording 
tambour.  This  apparatus  is  a  simplified  form  of  Marey's  pneumograph  (fig. 
212). 

The  variations  of  intrapleural  pressure  may  be  recorded  by  the  introducton 
of  a  canula  into  the  pleural  or  pericardial  cavity,  which  is  connected  with  a 
mercurial  manometer. 

Finally,  it  has  been  found  possible  in  various  ways  to  record  the  dia- 
phragmatic movements  by  the  insertion  of  an  elastic  bar  connected  with  a 
tambour  into  the  abdomen  below  it  (phrenograph) ,  by  the  insertion  of  needles 
into  different  parts  of  its  structure,  or  by  recording  the  contraction  of  isolated 
strips  of  the  diaphragm. 

The  acts  of  expansion  and  contraction  of  the  chest  take  up  under 
ordinary  circumstances  a  nearly  equal  time.     The  act  of  inspiring  air. 


RESPIRATION". 


267 


however,  especially  in  women  and  children,  is  a  little  shorter  than  that 
of  expelling  it,  and  there  is  commonly  a  very  slight  pause  between  the 
end  of  expiration  and  the  beginning  of  the  next  inspiration.  The  res- 
piratory rhythm  may  be  thus  expressed : — 


Inspiration 
Expiration 


6 

7  or  8 


A  very  slight  pause. 


If  the  ear  be  placed  in  contact  with  the  wall  of  the  chest,  or  be  sep- 
arated from  it  only  by  a  good  conductor  of  sound  or  stethoscope,  a  faint 
respiratory  murmur  is  heard  during  inspiration.     This  sound  varies 


Fig.  214.~Tracing  of  the  normal  diaphragm  respirations  of  rabbit,  a,  with  quick  movement  of 
drum,  b,  with  slow  movement,  j,  inspiration,  e,  expiration.  To  be  read  trom  left  to  right. 
(Marckwald.) 

somewhat  in  different  parts — being  loudest  or  coarsest  in  the  neighbor- 
hood of  the  trachea  and  large  bronchi  (tracheal  and  bronchial  breathing), 
and  fading  off  into  a  faint  sighing  as  the  ear  is  placed  at  a  distance  from 
these  (vesicular  breathing).  It  is  best  heard  in  children,  and  in  them 
a  faint  murmur  is  heard  in  expiration  also.  The  cause  of  the  vesicular 
murmur  has  received  various  explanations.  Most  observers  hold  that 
the  sound  is  produced  in  the  glottis  and  larger  bronchial  tubes,  but  that 
it  is  modified  in  its  passage  to  the  pulmonary  alveoli.  In  disease  of 
the  lungs  the  vesicular  murmur  undergoes  various  modifications,  for 
a  description  of  which  one  must  consult  text-books  on  physical  diag- 
nosis. 

Respiratory  Movements  of  the  Nostrils  and  of  the  Glottis. — During 


268  HANDBOOK   OF    PHYSIOLOGY. 

the  action  of  the  muscles  which  directly  draw  air  into  the  chest,  those 
which  guard  the  opening  through  which  it  enters  are  not  passive.  In 
hurried  breathing  the  instinctive  dilatation  of  the  nostrils  is  well  seen, 
although  under  ordinary  conditions  it  may  not  be  noticeable.  The 
opening  at  the  upper  part  of  the  larynx,  however,  or  rima  glottidis,  is 
dilated  at  each  inspiration  for  the  more  ready  passage  of  air,  and  be- 
comes smaller  at  each  expiration;  its  condition,  therefore,  corresponding 
during  respiration  with  that  of  the  walls  of  the  chest.  There  is  a  fur- 
ther likeness  between  the  two  acts  in  that,  under  ordinary  circumstan- 
ces, the  dilatation  of  the  rima  glottidis  is  a  muscular  act-  and  its  contrac- 
tion chiefly  an  elastic  recoil;  although,  under  various  conditions  to  be 
hereafter  mentioned,  there  may  be  in  the  latter  considerable  muscular 
power  exercised. 

Terms  used  to  express  Quantity  of  Air  breathed. — a.  Breath- 
ing or  tidal  air,  is  the  quantity  of  air  which  is  habitually  and  almost 
uniformly  changed  in  each  act  of  breathing.  In  a  healthy  adult  man 
it  is  about  30  cubic  inches,  or  about  500  ccm.,  or  half  a  litre. 

b.  Gomplemental  air,  is  the  quantity  over  and  above  this  which  can 
he  drawn  into  the  lungs  in  the  deepest  inspiration;  its  amount  varies, 
but  may  be  reckonded  as  100  cubic  inches,  or  about  1,600  ccm. 

c.  Reserve  air. — After  ordinary  expiration,  such  as  that  which  expels 
the  breathing  or  tidal  air,  a  certain  quantity  of  air,  about  100  cubic 
inches  (1,600  ccm.)  remains  in  the  lungs,  which  may  be  expelled  by  a 
forcible  and  deeper  expiration.  This  is  termed  reserve  or  supplemental 
air. 

d.  Residual  air  is  the  quantity  which  still  remains  in  the  lungs  after 
the  most  violent  expiratory  effort.  Its  amount  depends  in  great  meas- 
ure on  the  absolute  size  of  the  chest,  but  may  be  estimated  at  about  100 
cubic  inches,  or  about  1,600  ccm.  to  2,000  ccm. 

The  total  quantity  of  air  which  jDasses  into  and  out  of  the  lungs  of 
an  adult,  at  rest,  in  24  hours,  is  about  686,000  cubic  inches.  This  quan- 
tity, however,  is  largely  increased  by  exertion ;  the  average  amount  for 
a  hard-working  laborer  in  the  same  time  being  1,568,390  cubic  inches. 

e.  Respiratory  Capacity. — The  greatest  respiratory  capacity  of  the 
chest  is  indicated  by  the  quantity  of  air  which  a  person  can  expel  from 
his  lungs  by  a  forcible  expiration  after  the  deepest  inspiration  possible; 
it  expresses  the  power  which  a  person  has  of  breathing  in  the  emergen- 
cies of  active  exercise,  violence,  and  disease.  The  average  capacity  of 
an  adult,  at  15.4°  C.  (60°  F.),  is  about  225  to  250  cubic  inches,  or  3,500 
to  4,000  ccm. 

The  respiratory  capacity,  or  as  John  Hutchinson  called  it,  vital  capacity, 
is  usually  measured  by  a  modified  gasometer  or  spirometer,  into  which  the 
experimenter  breathes, — making  the  most  prolonged  expiration  possible  after 
the  deepest  possible  inspiration.     The  quantity  of  air  which  is  thus  expelled 


RESPIRATION.  269 

from  the  lungs  is  indicated  by  the  height  to  which  the  aii'  chamber  of  the 
spirometer  rises  ;  and  by  means  of  a  scale  placed  in  connection  with  this,  the 
number  of  cubic  inches  is  read  off. 

In  healtliy  men,  the  respiratory  capacity  varies  cliiefly  with  the 
stature,  weight,  and  age. 

It  was  found  by  Hutchinson,  from  whom  most  of  our  information 
on  this  subject  is  derived,  that  at  a  temperature  of  15.4°  C.  (60°  F.), 
225  cubic  inches  is  the  average  vital  or  respiratory  capacity  of  a  healthy 
person,  five  feet  seven  inches  in  height. 

Circumstances  affecting  the  amount  of  respirator y  capacity. — For  every  inch 
of  height  above  this  standard  the  capacity  is  increased,  on  an  average,  by  eight 
inches ;  and  for  every  inch  below,  it  is  diminished  by  the  same  amount. 

The  influence  of  tceight  on  the  capacity  of  respiration  is  less  manifest  and 
considerable  than  that  of  height :  and  it  is  difficult  to  arrive  at  any  definite 
conclusions  on  this  point,  because  the  natural  average  weight  of  a  healthy 
man  in  relation  to  stature  has  not  yet  been  determined.  As  a  general  state- 
ment, however,  it  may  be  said  that  the  capacity  of  respiration  is  not  affected 
by  weights  under  161  pounds,  or  11+  stones ;  but  that,  above  this  point,  it  is 
diminished  at  the  rate  of  one  cubic  inch  for  every  additional  pound  up  to  196 
pounds  or  14  stones. 

By  age,  the  capacity  appears  to  be  increased  from  about  the  fifteenth  to  the 
thirty-fifth  year,  at  the  rate  of  five  cubic  inches  per  year ;  from  thirty-five  to 
sixty-five  it  diminishes  at  the  rate  of  about  one  and  a  half  cubic  inch  per  year ; 
so  that  the  capacity  of  respiration  of  a  man  of  sixty  years  old  would  be  about 
30  cubic  inches  less  than  that  of  a  man  of  forty  years  old,  of  the  same  height 
and  weight.      (John  Hutchinson.) 

The  number  of  respirations  in  a  healthy  adult  person  usually  ranges 
from  14  to  18  per  minute.  It  is  greater  in  infancy  and  childhood.  It 
varies  also  much  according  to  different  circumstances,  such  as  exercise 
or  rest,  health,  or  disease,  etc.  Variations  in  the  number  of  respirations 
correspond  ordinarily  with  similar  variations  in  the  pulsations  of  the 
heaxt.  In  health  the  proportion  is  about  1  to  4,  or  1  to  5,  and  when  the 
rapidity  of  the  heart's  action  is  increased,  that  of  the  chest  movement  is 
commonly  increased  also;  but  not  in  every  case  in  equal  proportion.  It 
happens  occasionally  in  disease,  especially  of  the  lungs  or  air-passages, 
that  the  number  of  respiratory  acts  increases  in  quicker  proportion  than 
the  beats  of  the  pulse;  and,  in  other  affections,  much  more  commonly, 
that  the  number  of  the  pulses  is  greater  in  proportion  than  that  of  the 
respirations. 

The  Force  of  Inspiratory  and  Expiratory  Muscles. — ^The  force  with 
which  the  inspiratory  muscles  are  capable  of  acting  is  greatest  in  indi- 
viduals of  the  height  of  from  five  feet  seven  inches  to  five  feet  eight 
inches,  and  will  elevate  a  column  of  three  inches  of  mercury.  Above 
this  height  the  force  decreases  as  tlie  stature  increases;  so  that  the  aver- 
age of  men  of  six  feet  can   elevate  only  about  two  and  a  half  inches  of 


270  HANDBOOK    OF   PHYSIOLOGY. 

mercury.  The  force  manifested  in  the  strongest  expiratory  acts  is,  on 
the  average,  one-third  greater  than  that  exercised  in  inspiration.  But 
this  difference  is  in  great  measure  due  to  the  power  exerted  by  the 
elastic  reaction  of  the  walls  of  the  chest;  and  it  is  also  much  influenced 
by  the  disproportionate  strength  which  the  expiratory  muscles  attain, 
from  their  being  called  into  use  for  other  purposes  than  that  of  simple 
expiration.  The  force  of  the  inspiratory  act  is,  therefore,  better  adapted 
than  that  of  the  expiratory  for  testing  the  muscular  strength  of  the 
body.     (John  Hutchinson.) 

The  instrument  used  by  Hutchinson  to  gauge  the  inspiratory  and  expiratory 
power  was  a  mercurial  manometer,  to  which  was  attached  a  tube  fitting  the 
nostrils,  and  through  which  the  inspiratory  or  expiratory  effort  was  made. 
The  following  table  represents  the  results  of  numerous  experiments : 


Power  of 

Power  of 

Inspiratory  Muscles. 

Expiratory  Muscles. 

1.5  in.      . 

.     Weak 

.     2.0  in. 

2.0  "  . 

Ordinary 

2.5  " 

2.5   " 

.     Strong 

.     8.5  " 

3.5   "   . 

Very  strong     . 

4.5  " 

4.5   " 

.     Eemarkable 

.     5.8  " 

5.5   "  . 

Very  remarkable     . 

7.0  " 

6.0   *' 

.     Extraordinary 

.     8.5  " 

7.0   "   . 

Very  extraordinary 

10.0  " 

The  greater  part  of  the  force  exerted  in  deep  inspiration  is  employed 
in  overcoming  the  resistance  offered  by  the  elasticity  of  the  lungs. 

The  amount  of  this  elastic  resistance  was  estimated  by  observing  the  ele\a- 
tion  of  a  column  of  mercuiy  raised  by  the  return  of  air  forced,  after  deavh, 
into  the  lungs,  in  quantity  equal  to  the  known  capacity  of  respiration  during 
life ;  and  Hutchinson  calculated,  according  to  the  well-known  hydrostatic  law 
of  equality  of  pressures  (as  shown  in  the  Bramah  press),  that  the  total  force  to 
be  overcome  by  the  muscles  in  the  act  of  inspiring  200  cubic  inches  of  air  is 
more  than  450  lbs. 

The  elastic  force  overcome  in  ordinary  inspiration  is,  according  to  the  same 
authority,  equal  to  about  170  lbs. 

Douglas  Powell  has  shown  that  within  the  limits  of  ordinary  tran- 
quil respiration  the  elastic  resilience  of  the  walls  of  the  chest  favors  in- 
spiration; and  that  it  is  only  in  deep  inspiration  that  the  ribs  and  rib- 
cartilages  offer  an  opposing  force  to  their  dilatation.  In  other  words, 
the  elastic  resilience  of  the  lungs,  at  the  end  of  an  act  of  ordinary 
breathing,  has  drawn  the  chest-walls  within  the  limits  of  their  normal 
degree  of  expansion.  Under  all  circumstances,  of  course,  the  elastic 
tissue  of  the  lungs  opposes  inspiration  and  favors  expiration. 

It  is  possible  that  the  contractile  power  which  the  bronchial  tubes 
and  air-vesicles  possess,  by  means  of  their  muscular  fibres  may  (1)  assist 
in  expiration;  but  it  is  more  likely  that  its  chief  purpose  is  (3)  to  regu- 
late and  adapt,  iu  some  measure,  the  quantity  of  air  admitted  to  the 


RESPIRATION.  271 

lungs,  and  to  each  part  of  them,  according  to  the  supply  of  blood;  (3) 
the  muscular  tissue  contracts  upon  and  gradually  expels  collections  of 
mucus,  which  may  have  accumulated  within  the  tubes,  and  which  cannot 
be  ejected  by  forced  expiratory  efforts,  owing  to  collapse  or  other  mor- 
bid conditions  of  the  portion  of  lung  connected  with  the  obstructed 
tubes  (Gairdner).  (4)  Aj^art  from  any  of  the  before-mentioned  func- 
tions, the  presence  of  muscular  fibre  in  the  walls  of  a  hollow  viscus, 
such  as  a  lung,  is  only  what  might  be  expected  from  analogy  with  other 
organs.  Subject  as  the  lungs  are  to  such  great  variation  in  size,  it 
might  be  anticipated  that  the  elastic  tissue,  which  enters  so  largely  into 
their  composition,  would  be  supplemented  by  the  presence  of  much 
muscular  fibre  also. 

Respiratory  Changes  in  the  Air  Breathed. 

Compositio?i  of  the  At/nosphere. — The  atmosphere  we  breathe  has,  in 
every  situation  in  which  it  has  been  examined  in  its  natural  state,  a 
nearly  uniform  composition.  It  is  a  mixture  of  oxygen,  nitrogen,  car- 
bon dioxide,  argon,  and  watery  vapor,  with,  commonly,  traces  of  other 
gases,  as  ammonia,  sulphuretted  hydrogen,  etc.  Of  every  100  volumes 
of  pure  atmospheric  air,  79  volumes  (on  an  average)  consist  of  nitrogen, 
the  remaining  21  of  oxygen.  By  weight  the  proportion  is  N.  77,  0.  23. 
The  proportion  of  carbon  dioxide  is  extremely  small;  10,000  volumes  of 
atmospheric  air  contain  only  about  4  or  5  of  that  gas. 

The  quantity  of  watery  vapor  varies  greatly  according  to  the  temper- 
ature and  other  circumstances,  but  the  atmosi^here  is  never  without 
some.  In  this  country,  the  average  quantity  of  watery  vaj)or  in  the  at- 
mosiDhere  is  1.40  per  cent. 

Composition  of  Air  wliich  has  been  hreatlied. — The  changes  effected 
by  respiration  in  the  atmospheric  air  are:  1,  an  increase  of  temperature; 
2,  an  increase  in  the  quantity  of  carbonic  acid;  3,  a  diminution  in  the 
quantity  of  oxygen;  4,  a  diminution  of  volume;  5,  an  increase  in  the 
amount  of  watery  vapor;  G,  the  addition  of  a  minute  amount  of  organic 
matter  and  of  free  ammonia. 

1.  The  expired  air,  heated  by  its  contact  with  the  interior  of  the 
lungs,  is  (at  least  in  most  climates)  hotter  than  the  inspired  air.  Its 
temperature  varies  bet^veen  36°— 37.5°  C.  (97°  and  99.5°  F.),  the  lower 
temperature  being  observed  when  the  air  has  remained  but  a  short  time 
in  the  lungs.  "Whatever  may  be  the  temperature  of  the  air  when  in- 
haled, it  acquires  nearly  that  of  the  blood  before  it  is  expelled  from  the 
chest. 

2.  The  Carbonic  dioxide  is  increased;  but  the  quantity  exhaled  in  a 
given  time  is  subject  to  change  from  various  circumstances.  From 
every  volume  of  air  inspired,  from  4  to  5  per  cent  of  oxygen  is  abstracted  ; 


272  HAXDBOOK    OF    PHYSIOLOGY. 

while  a  rather  smaller  quantity,  4.0  of  carbon  dioxide  is  added  in  its 
place :  the  expired  air  will  contain,  therefore,  400  vols,  of  carbon  dioxide 
in  10,000.  The  quantity  of  carbon  dioxide  exhaled  into  the  air  breathed 
by  a  healthy  adult  man,  calculating  that  20  ccm.  of  the  500  ccm.  of  the 
air  breathed  out  at  each  expiration  consists  of  carbon  dioxide,  and  that 
the  rate  of  respiration  is  on  an  average  16,  the  total  amount  would  be 
about  460  litres  in  the  24  hours.  From  actual  experiment  this  amount 
seems  to  be  too  high,  since  from  the  average  of  many  investigations  the 
total  amount  of  carbon  dioxide  excreted  per  diem  has  been  found  to  be 
about  400  litres,  weighing  800  grms.,  consisting  of  218  grms.  of  C,  and 
582  grms.  of  0.  From  this  has  to  be  deducted  about  10  grms.  excreted  in 
any  other  way  than  by  the  lungs,  it  leaves  about  215  grms.  as  the  amount 
of  C.  excreted  by  the  average  healthy  man  by  respiration  each  day  and 
night,  that  is  about  7  oz.,  about  half  a  pound.  These  quantities  must 
be  considered  approximate  onl}^,  inasmuch  as  various  circumstances,  even 
in  health,  influence  the  amount  of  carbon  dioxide  excreted,  and,  correla- 
tively,  the  amount  of  oxygen  absorbed. 

Circumstances  influencing  the  amount  of  carbon  dioxide  excreted. — a.  Age 
and  Sex. — The  quantity  of  carbon  dioxide  exhaled  into  the  air  breathed  by 
males,  regularly  increases  from  8  to  30  years  of  age  ;  from  30  to  50  the  quantity, 
after  remaining  stationary  for  a  while,  gradually  diminishes,  and  from  50  to 
extreme  age  it  goes  on  diminishing,  till  it  scarcely  exceeds  the  quantity  ex- 
haled at  ten  years  old.  In  females  (in  whom  the  quantity  exhaled  is  always 
less  than  in  males  of  the  same  age)  the  same  regular  increase  in  quantity  goes 
on  from  the  8th  year  to  the  age  of  puberty,  when  the  quantity  abruptly  ceases 
to  increase,  and  remains  stationary  so  long  as  they  continue  to  menstruate. 
When  menstruation  has  ceased,  it  soon  decreases  at  the  same  rate  as  it  does  in 
old  men. 

&.  Respiratoi'y  Movements. — The  quicker  the  respirations,  the  smaller  is  the 
proportionate  quantity  of  carbon  dioxide  contained  in  each  volume  of  the  expired 
air.  Although  the  proportionate  quantity  of  carbon  dioxide  is  thus  diminished, 
the  absolute  amount  exhaled  within  a  given  time  is  increased  thereby,  owing  to 
the  larger  quantity  of  air  which  is  breathed  in  the  time.  The  last  half  of  a  vol- 
ume of  expired  air  contains  more  carbonic  acid  than  the  half  first  expired  ;  a 
circumstance  which  is  explained  by  the  one  portion  of  air  coming  from  the 
remote  part  of  the  lungs,  where  it  has  been  in  more  immediate  and  prolonged 
contact  with  the  blood  than  the  other  has,  which  comes  chiefly  from  the  larger 
bronchial  tubes. 

c.  External  temperature. — The  observation  made  by  Vierordt  at  various 
temperatures  between  3.4° — 28.8°  C.  (38°  F.  and  75°  F.)  show,  for  warm-blooded 
animals,  that  within  this  range,  every  rise  equal  to  5.5°  C.  (10°  F.)  causes  a 
diminution  of  about  33  ccm.  (2  cubic  inches)  in  the  quantity  of  carbonic  acid 
exhaled  per  minute. 

d.  Season  of  the  Year.  — The  season  of  the  year,  independently  of  tempera- 
ture, materially  influences  the  respiratory  phenomena ;  spring  being  the  season 
of  the  gi-eatest,  and  autumn  of  the  least  activity  of  the  respiratory  and  other 
functions. 

e.  Purity  of  the  Respired   Air. — The  average  quantity    of  carbon  dioxide 


EESPIRATION.  273 

given  out  by  the  lungs  constitutes  about  4.3  per  cent,  of  the  expired  air:  but 
if  the  air  which  is  breathed  be  previously  impregnated  with  carbon  dioxide 
(as  is  the  case  when  the  same  air  is  frequently  respired) ,  then  the  quantity  of 
carbon  dioxide  exhaled  becomes  relatively  much  less. 

/.  Hygrometric  State  of  Atmosphere. — The  amount  of  carbon  dioxide  exhaled 
is  considerably  influenced  by  the  degree  of  moisture  of  the  atmosphere,  much 
more  being  given  off  when  the  air  is  moist  than  when  it  is  dry. 

g.  Period  of  the  Day. — During  the  day-time  more  carbon  dioxide  is  exhaled 
than  corresponds  to  the  oxygen  absorbed  ;  while,  on  the  other  hand,  at  night 
very  much  more  oxygen  is  absorbed  than  is  exhaled  in  carbon  dioxide.  There  is, 
thus,  a  reserve  fund  of  oxygen  absorbed  by  night  to  meet  the  requirements  of  the 
day.  If  the  total  quantity  of  carbon  dioxide  exhaled  in  24  hours  be  repre- 
sented by  100,  52  parts  are  exhaled  during  the  day,  and  48  at  night.  While 
similarly,  33  parts  of  the  oxygen  are  absorbed  during  the  day,  and  the  remain- 
ing 67  by  night. 

h.  Food  and  Drink. — By  the  use  of  food  the  quantity  is  increased,  while 
by  fasting  it  is  diminished ;  it  is  greater  when  animals  are  fed  on  farinaceous- 
food  than  when  fed  on  meat.  The  effects  produced  by  spirituous  drinks  de- 
pend much  on  tlie  kind  of  drink  taken.  Pure  alcohol  tends  rather  to  increase 
than  to  lessen  respiratory  changes,  and  the  amount  therefore  of  carbon  dioxide 
expired ;  rum,  ale,  and  porter,  also  sherry,  have  very  similar  effects.  On  the 
other  hand,  brandy,  whiskey,  and  gin,  particularly  the  latter,  almost  always 
lessened  the  respiratory  changes,  and  consequently  the  amount  of  the  gas 
exhaled. 

i.  Exercise.  — Bodily  exercise,  in  moderation,  increases  the  quantity  to  about 
^  more  than  it  is  during  rest :  and  for  about  an  hour  after  exercise  the  volume 
of  the  air  expired  in  the  minute  is  increased  nearly  2,000  ccm.,  or  118  cubic 
inches  :  and  the  quantity  of  carbon  dioxide  about  125  ccm.,  or  7.8  cubic  inches 
per  minute.  Violent  exercise,  such  as  full  labor  on  the  tread-wheel,  still  fur- 
ther increases  the  amount  of  the  acid  exhaled. 

A  larger  quantity  is  exhaled  when  the  barometer  is  low  than  when  it  is 
high. 

3,  Tlic  o.njgen  is  diminished.  Pettenkofer  and  Voit  have  found  that 
the  mean  consumption  of  oxygen  during  24  hours,  by  a  man  weigliing 
70  kilos,  is  about  700  grms.,  or  490  litres.  The  quantity  of  oxygen  ab- 
sorbed increases  with  muscular  exercise,  and  falls  during  rest.  In  gen- 
eral terms  the  quantity  absorbed  varies  with  the  activity  of  the  metabolic 
jirocesses. 

4.  The  volume  of  air  is  diminished  (allowance  being  made  for  the  ex- 
pansion in  heating),  the  loss  being  due  to  the  fact  that  a  portion  of  the 
oxygen  absorbed  is  not  returned  in  the  form  of  carbon  dioxide.  Since 
the  oxygen  of  a  given  volume  of  carbon  dioxide  would  have  tiie  same 
volume  as  the  carbon  dioxide  itself  at  a  given  temperature  and  pressure, 
a  portion  of  the  oxygen  absorbed  must  be  used  for  other  purposes  than 
the  formation  of  carbon  dioxide.  In  fact,  some  of  it  is  used  in  the 
formation  of  urea,  some  in  the  formation  of  water,  etc.     The  oxygen  in 

i8 


274  HAKDBOOK    OF    PHTSIOLOGT. 

the  carbon  dioxide  exhaled,  divided  by  the  oxygen  absorbed,  gives  what 
is  known  as  the  respiratory  quotient ;  thus 

CO,  exhaled 
O2  absorbed 

Normally  in  man  on  a  mixed  diet  the  respiratory  quotient  is 

±^=  0.8-0.9. 

5 

But  it  is  subject  to  variation  through  several  causes;  for  example, 
through  variation  in  diet.  On  a  carbohydrate  diet  the  respiratory  quo- 
tient may  rise  above  0.9,  since  carbohydrates  contain  enough  oxygen  to 
oxidize  the  carbon  in  their  molecule.  On  a  diet  containing  much  fat  it 
is  lowest,  since  oxygen  is  needed  to  completely  oxidize  it.  And  the  same 
is  true,  but  to  a  less  degree,  in  the  case  of  j)roteids.  Muscular  exertion 
raises  the  respiratory  quotient,  because  in  its  performance  carbohydrates 
are  used  up. 

5.  The  watery  vapor  is  increased. — The  quantity  emitted  is,  as  a 
general  rule^  sufficient  to  saturate  the  expired  air,  or  very  nearly  so. 
Its  absolute  amount  is,  therefore,  influenced  by  the  following  circum- 
stances, (1),  by  the  quantity  of  air  respired;  for  the  greater  this  is,  the 
greater  also  will  be  the  quantity  of  moisture  exhaled;  (2),  by  the  quan- 
tity of  watery  vapor  contained  in  the  air  previous  to  its  being  inspired; 
because  the  greater  this  is,  the  less  will  be  the  amount  to  complete  the 
saturation  of  the  air;  (3),  by  the  temperature  of  the  expired  air;  for 
the  higher  this  is,  the  greater  will  be  the  quantity  of  watery  vapor  re- 
quired to  saturate  the  air;  (4),  by  the  length  of  time  which  each  volume 
of  inspired  air  is  allowed  to  remain  in  the  lungs;  for  although,  during 
ordinary  respiration,  the  expired  air  is  always  saturated  with  watery 
vapor,  yet  when  respiration  is  performed  very  rapidly  the  air  has  scarcely 
time  to  be  raised  to  the  highest  temperature,  or  be  fully  charged  with 
moisture  ere  it  is  expelled. 

The  quantity  of  water  exhaled  from  the  lungs  in  twenty-four  hours 
ranges  (according  to  the  various  modifying  circumstances  already  men- 
tioned) from  about  6  to  27  ounces,  the  ordinary  quantity  being  about  9 
or  10  ounces.  Some  of  this  is  probably  formed  by  the  chemical  com- 
bination of  oxygen  with  hydrogen  in  the  system;  but  the  far  larger 
proportion  of  it  is  water  which  has  been  absorbed,  as  such,  into  the 
blood  from  the  alimentary  canal,  and  which  is  exhaled  from  the  surface 
of  the  air-passages  and  cells,  as  it  is  from  the  free  surfaces  of  all  moist 
animal  membranes,  particularly  at  the  high  temperature  of  warm-blooded 
animals. 

6.  A  small  quantity  of  ammonia  is  added  to  the  ordinary  constitu- 
ents of  expired  air.      It  seeiiis  probable,  liowevcr,  botli  from  thefacttliat 


UESPIKATION.  275 

this  substance  cannot  be  always  detected,  and  from  its  minute  amount 
when  present,  that  the  whole  of  it  may  be  derived  from  decompos- 
ing particles  of  food  left  in  the  mouth,  or  from  carious  teeth  or  the 
like;  and  that  it  is,  therefore,  only  an  accidental  constituent  of  expired 
air. 

7.  The  quantihj  of  orgainc  matter  in  the  breath  is  increased.  It  was 
formerly  supposed  that  this  organic  matter  was  injurious  and  gave  rise 
to  the  unpleasant  symptoms  which  come  on  in  badly  ventilated  rooms. 
But  this  has  been  proved  erroneous. 

Method  of  Experiment.— The  experiments  are  conducted  in  such  a  manner  tliat 
comparative  analyses  may  be  made  between  the  air  inspired  and  that  expired. 
Generally  an  animal  is  placed  in  a  chamber,  called  the  respiratory  chamber,  having 
but  two  openings— one  for  the  entrance  of  the  inspired  air,  the  other  for  the  escape 
of  expired  air.  Some  form  of  pump  is  used  for  renewing  the  air  in  the  chamber. 
Both  the  inspired  and  expired  air  is  made  to  pass  through  agents  wliich  will  absorb 
the  contained  carbon  dioxide,  such  as  baryta  water  or  soda  lime,  and  in  turn  through 
agents  which  will  absorb  the  watery  vapor.  When  the  experiment  is  completed 
the  differences  between  the  two  are  determined.  The  difference  in  oxygen  has  to 
be  calculated,  and  is  open  to  error.  The  famous  respiratory  chamber  of  Petten- 
kofer  is  large  enough  to  perform  such  experiments  on  man,  and  is  of  very  elaborate 
construction. 

How  the  Changes  in  the  Air  are  effected. — The  method  by  which 
fresh  air  is  inhaled  and  expelled  from  the  lungs  has  been  explained. 
It  remains  to  consider  how  it  is  that  the  blood  absorbs  oxygen  from, 
and  gives  up  carbonic  acid  to,  the  air  of  the  alveoli.  In  the  first  place, 
it  must  be  remembered  that  the  tidal  air  only  amounts  to  about  25 — 30 
cubic  inches  (about  500  ccm.)  at  each  insjjiration,  and  that  this  is  of 
course  insufficient  to  fill  the  lungs,  but  it  mixes  with  the  stationary  air 
by  diffusion,  and  so  supplies  to  it  new  oxygen.  The  amount  of  oxygen 
in  expired  air,  which  may  be  taken  as  the  average  composition  of  the 
mixed  air  in  the  lungs,  is  about  16  to  17  per  cent;  in  the  pulmonary 
alveoli  it  may  be  rather  less  than  this.  From  this  air  the  venous  blood 
has  to  take  up  oxygen  in  the  proportion  of  8  to  12  vols,  per  cent  of 
blood,  as  the  difference  between  the  amount  of  oxygen  in  arterial  and 
venous  blood  is  no  less.  It  seems  therefore  somewhat  difficult  to  under- 
stand how  this  can  be  accomplished  at  the  low  partial  pressure  of  oxygen 
in  the  pulmonary  air.  But  as  Avas  pointed  out  in  a  previous  Chapter 
(V.),  the  oxygen  is  not  simply  dissolved  in  the  blood,  but  is  to  a  great 
extent  chemically  combined  with  the  haemoglobin  of  the  red  corpuscles; 
and  when  a  fluid  contains  a  body  which  enters  into  loose  chemical  com- 
bination in  this  way  with  a  gas,  the  tension  of  the  gas  in  the  fluid  is 
not  directly  proportional  to  the  total  quantity  of  the  gas  taken  up  by 
the  fluid,  but  to  the  excess  above  the  total  quantity  which  the  substance 
dissolved  in  the  fluid  is  capable  of  taking  up  (a  known  quantity  in  the 
case  of  haemoglobin,  viz.,   1.59  cm.  for  1  grm.  haemoglobin).     On  the 


276  HAXDBOOK    OF   PHYSIOLOGY. 

other  hand,  if  the  substance  be  not  saturated,  i.e.,  if  it  be  not  combined 
with  as  much  of  the  gas  as  it  is  capable  of  taking  up,  further  combina- 
tion leads  to  no  increase  of  its  tension.  However,  there  is  a  point  at 
which  the  haemoglobin  gives  up  its  oxygen  when  it  is  exposed  to  a 
low  partial  pressure  of  oxygen,  and  there  is  also  a  point  at  which  it 
neither  takes  up  nor  gives  out  oxygen;  in  the  case  of  arterial  blood  of 
the  dog,  this  is  found  to  be  when  the  oxygen  tension  of  the  atmosphere 
is  equal  to  3.9  per  cent  (or  29.G  mm.  of  mercury),  which  is  equivalent 
to  saying  that  the  oxygen  tension  of  arterial  blood  is  3.9  per  cent;  venous 
blood,  in  a  similar  manner,  has  been  found  to  have  an  oxygen  tension  of 
2.8  per  cent.  At  a  higher  temperature,  the  tension  is  raised,  as  there  is 
a  greater  tendency  at  a  high  temperature  for  the  chemical  compound  to 
undergo  dissociation.  It  is  therefore  easy  to  see  that  the  oxygen  tension 
of  the  air  of  the  pulmonary  alveoli  is  quite  sufficient,  even  supposing  it 
much  less  than  that  of  the  expired  air,  to  enable  the  venous  blood  to 
take  up  oxygen,  and  what  is  more,  it  will  take  it  up  until  the  haemo- 
globin is  very  nearly  saturated  with  the  gas. 

As  regards  the  elimination  of  carbon  dioxide  from  the  blood,  there 
is  evidence  to  show  that  it  is  given  up  by  a  process  of  simple  diffusion, 
the  only  condition  necessary  for  the  process  being  that  the  tension  of 
the  carbonic  acid  of  the  air  in  the  pulmonary  alveoli  should  be  less  than 
the  tension  of  the  carbonic  acid  in  venous  blood.  The  carbonic  acid 
tension  of  the  alveolar  air  probably  does  not  exceed  (in  the  dog)  3  or  4 
per  cent,  while  that  of  the  venous  blood  is  5.4  per  cent,  or  equal  to  41 
mm.  of  mercury. 

Respiratory  Changes  in  the  Blood. 

Circulation  of  Blood  in  the  Bcsjnratorjj  Organs. — To  be  exposed  to 
the  air  thus  alternately  moved  into  and  out  of  the  air-cells  and  minute 
bronchial  tubes,  the  blood  is  propelled  from  the  right  ventricle  through 
the  pulmonary  capillaries  in  steady  streams,  and  slowly  enough  to  per- 
mit every  minute  portion  of  it  to  be  for  a  few  seconds  exposed  to  the 
air,  with  only  the  thin  walls  of  the  capillary  vessels  and  the  air-cells 
intervening.  The  pulmonary  circulation  is  of  the  simplest  kind:  for 
the  pulmonary  artery  branches  regularly;  its  successive  branches  run  in 
straight  lines,  and  do  not  anastomose :  the  capillary  plexus  is  uniformly 
spread  over  the  air-cells  and  intercellular  passages;  and  the  veins  de- 
rived from  it  proceed  in  a  course  as  simple  and  uniform  as  that  of  the 
arteries,  their  branches  converging  but  not  anastomosing.  The  veins 
have  no  valves,  or  only  small  imperfect  ones  prolonged  from  their  angles 
of  junction,  and  incapable  of  closing  the  orifice  of  either  of  the  veins 
between  which  they  are  j)laced.  The  pulmonary  circulation  also  is  un- 
affected by  changes  of  atmospheric  pressure,  and  is  not  exposed  to  the 


RESPIRATTOX.  277 

influence  of  the  pressure  of  muscles:  the  force  by  which  it  is  accom- 
plished, and  the  course  of  the  Ijlood  are  alike  simple, 

Changcfi  in  the  Blood. — The  most  obvious  change  which  the  blood  of 
the  pulmonary  artery  undergoes  in  its  passage  through  the  lungs  is  \st, 
that  of  color,  the  dark  erimsoii  of  venous  blood  being  exchanged  for  the 
bright  scarlet  of  arterial  blood.  The  cause  of  this  has  been  already 
shown  to  be  that  the  arterial  blood  contains  a  greater  quantity  of  scarlet 
or  oxyha?moglobin;  '2d,  and  in  connection  with  the  preceding  change  it 
gains  oxifgen  ;  3d,  it  loses  carbon  dioxide.  It  was  incidentally  mentioned 
in  the  Chapter  on  the  Blood  that  the  carbon  dioxide  which  is  carried 
by  the  blood  to  be  eliminated  by  the  lungs  is  not  simply  dissolved  in 
the  plasma.  It  is  combined  with  some  substance  in  the  blood,  and 
when  it  is  carried  to  the  lungs  this  substance  must  undergo  decomposi- 
tion. What  is  the  nature  of  the  compound  it  forms  is  not  known,  but 
it  appears  most  likely  that  the  gas  is  combined  in  the  plasma  with  the 
sodium  car])onate  which  it  contains.  It  has  also  been  suggested  that  as 
the  carbon  dioxide  of  the  entire  blood  is  more  easily  given  up  to  the 
vacuum  of  a  mercurial  air-pump  than  is  the  gas  of  the  serum  correspond- 
ing to  the  blood  taken,  that  the  corpuscles  of  the  blood  exercise  some 
power  in  promoting  the  decomposition  of  the  substance  with  which  the 
gas  is  combined  in  the  plasma.  The  plasma  or  serum  will  not  give  up 
the  whole  of  its  carbon  dioxide  until  the  addition  of  an  acid,  when  the 
last  portion,  2  to  5  per  cent,  comes  off,  the  entire  blood  gives  up  the 
whole  of  its  carbon  dioxide  to  the  action  of  the  mercurial  pump,  and 
does  not  require  the  action  of  an  acid.  It  may  be  mentioned  that,  ac- 
cording to  some,  the  carbon  dioxide  is  combined  with  proteid,  tither  in 
the  plasma  or  in  the  red  blood-corpuscles;  4:th,  it  becomes  slightly 
cooler;  5fh,  it  coagulates  sooner  and  more  firmly,  apparently  containing 
more  fibrin.  The  oxygen  absorbed  into  the  blood  from  the  atmospheric 
air  in  the  lungs  is  combined  chemically  with  the  haemoglobin  of  the 
red  blood-corpuscles.  In  this  condition  it  is  carried  in  the  arterial  blood 
to  the  various  parts  of  the  body,  and  brought  into  near  relation  or  con- 
tact with,  the  tissues.  In  these  tissues,  a  certain  portion  of  the  oxygen,, 
which  the  arterial  blood  contains,  disappears,  and  a  proportionate  quan- 
tity of  carbon  dioxide  and  water  is  formed.  The  venous  blood,  contain- 
ing the  new-formed  carbon  dioxide,  returns  to  the  lungs,  where  a  portion 
of  the  carbon  dioxide  is  exhaled,  and  a  fresh  supply  of  oxygen  is  taken  in. 

In  what  way  these  changes  are  brought  about  will  be  next  discussed. 

Respiratory  Changes  in  the  Tissues. 

The  changes  which  occur  in  the  composition  of  the  blood  during  its 
circulation  are  believed  to  take  place  in  the  tissues,  and  particularly  in 
the  muscles.     The  changes  are,  as  we  have  Just  mentioned,  chiefly  the 


278  HANDBOOK    OF    PHYSIOLOGY, 

removal  of  oxygen  from  aud  the  addition  of  carbon  dioxide  to  the  blood. 
These  changes  are  sometimes  spoken  of  as  internal  respiration.  The 
oxygen  carried  by  the  corpuscles  of  the  blood  in  the  form  of  oxyhsemo- 
globin  is  given  np  to  the  tissues^  as  the  tension  of  the  gas  within  them 
is  very  small.  The  gas  thus  set  free  is  apparently  seized  upon  by  the 
protoplasm  of  the  tissues  and  built  up  into  its  molecule,  and  thus  assists 
in  the  process  of  anabolism,  possibly  uniting  with  some  compound 
somewhat  in  the  same  manner  but  more  firmly  than  it  does  with  hgemo- 
giobin.  The  low  oxygen  pressure  of  the  tissues  thus  allows  a  constant 
abstraction  of  the  gas  from  the  blood.  The  process  of  katabolism,  or 
breaking  down,  is  always  associated  with  the  evolution  of  carbon  diox- 
ide, so  that  as  the  blood  passes  through  the  tissues  containing  little  of 
this  gas,  the  high  tension  of  the  gas  in  the  tissues  permits  of  its  passage 
into  the  blood.  It  has  been  proved  that  the  process  of  the  evolution  of 
carbon  dioxide  from  living  muscle  will  go  on  for  a  time  in  the  absence 
of  a  supply  of  free  oxygen,  and  so  it  is  clear  that  the  former  gas  is  not 
derived  directly  from  the  combustion  of  the  carbon  in  the  presence  of 
the  latter  gas.  It  was  at  one  time  believed  that  the  carbon  dioxide  of 
venous  blood  resulted  from  the  oxidation  of  substances  in  the  blood 
itself.  It  has,  however,  been  shown  that  the  blood  itself  has  very  slight 
oxidizing  powers,  and  that  in  the  frog  the  whole  of  the  blood  may  be 
replaced  by  saline  solution  without  producing  any  marked  effect  upon 
the  metabolism  of  the  body.  It  is  obviously  unlikely  that  any  but  very 
slight  oxidation  could  go  on  in  such  a  medium.  It  has  moreover  been 
demonstrated  that  the  tension  of  carbon  dioxide  in  the  tissues  is  con- 
siderably greater  in  the  tissues  than  it  is  in  the  venous  blood. 

Special  Respiratory  Acts. 

It  will  be  well  here,  perhaps,  to  explain  certain  special  respiratory 
acts,  which  appear  at  first  sight  somewhat  complicated,  but  cease  to  be 
so  when  the  mechanism  by  which  they  are  performed  is  clearly  under- 
stood. The  diagram  (fig,  215)  shows  that  the  cavity  of  the  chest  is  sep- 
arated from  that  of  the  abdomen  by  the  diaphragm,  which,  when  acting, 
will  lessen  its  curve,  and  thus  descending,  will  push  dowmvard  and 
forward  the  abdominal  viscera;  while  the  abdominal  muscles  have  the 
opposite  efi'ect,  and  in  acting  will  push  the  viscera  upward  and  back- 
ward, and  with  them  the  diaphragm,  supposing  its  ascent  to  be  not 
from  any  cause  interfered  with.  It  will  also  be  seen  that  the  lungs 
communicate  with  the  exterior  of  the  body  through  the  trachea  aud 
larynx,  and  further  on  through  the  mouth  and  nostrils — through  either 
of  them  separately,  or  through  both  at  the  same  time,  according  to  the 
position  of  the  soft  palate.  The  stomach  communicates  with  the  ex- 
terior of  the  body  through  the  oesophagus,  pharynx,  and  mouth;  while 


TlESinitATION".  279 

below  tlie  rectum  opens  at  the  uiius,  and  the  bladder  through  the  ure- 
thra. All  these  openings,  through  which  the  hollow  viscera  communi- 
cate with  the  exterior  of  the  body,  are  guarded  by  muscles,  called 
sphincters,  which  can  act  independently  of  each  other. 

Si(j1iin(j. — In  sighing  there  is  a  somewhat  prolonged  inspiration;  the 
air  almost  noiselessly  passing  in  through  the  glottis,  and  by  the  elastic 
recoil  of  the  lungs  and  chest- walls,  and  probably  also  of  the  abdominal 
walls,  being  suddenly  expelled. 

In  the  first,  or  inspiratory  part  of  this  act,  the  descent  of  the  dia- 
phragm presses  the  abdominal  viscera  downward,  and  of  course  this 
pressure  tends  to  evacuate  the  contents  of  such  of  them  as  communicate 
with  the  exterior  of  the  body.  Inasmuch,  however,  as  their  various 
openings  are  guarded  by  sphincters,  in  a  state  of  constant  tonic  contrac- 
tion, there  is  no  escape  of  their  contents,  and  the  air  simply  enters  the 
lungs.  In  tlie  second,  or  expiratory  part  of  the  act,  pressure  is  also 
made  on  the  abdominal  viscera  in  the  opposite  direction,  by  the  recoil 
of  the  abdominal  walls;  but  the  pressure  is  relieved  by  the  escape  of  air 
through  the  open  glottis,  and  the  relaxed  diaphragm  is  pushed  up  again 
into  its  original  position.  The  sphincters  of  the  stomach,  rectum,  and 
bladder,  act  in  the  same  manner  as  before. 

Hicconyh  resembles  sighing  in  that  it  is  an  inspiratory  act:  but  the 
inspiration  is  sudden  instead  of  gradual,  the  diaphragm  acting  suddenly 
and  spasmodically;  and  tlie  air,  rusbing  through  the  unprepared  rima 
glottidis,  is  suddenly  arrested  and  produces  the  peculiar  sound. 

Cougliiny. — In  the  act  of  coughing  there  is  most  often  first  of  all  a 
deep  inspiration,  followed  by  an  expiration;  but  the  latter,  instead  of 
being  easy  and  uninterrupted,  as  in  normal  breathing,  is  obstructed,  the 
glottis  being  momentarily  closed  by  the  approximation  of  the  vocal 
cords.  The  abdominal  muscles,  then  strongly  acting,  push  up  the 
viscera  against  the  diaphragm,  and  thus  make  pressure  on  the  air  in  the 
lungs  until  its  tension  is  sufficient  to  noisily  open  the  vocal  cords  which 
oppose  its  outward  passage.  In  this  way  considerable  force  is  exercised, 
and  mucus  or  any  other  matter  that  may  need  expulsion  from  the  air- 
passages  is  quickly  and  sharply  expelled  by  the  outstreaming  current  of 
air.  It  will  be  evident  on  reference  to  fig.  215,  that  pressure  exercised 
by  the  abdominal  muscles  in  the  act  of  coughing,  acts  as  forcibly  on  the 
abdominal  viscera  as  on  the  lungs,  inasmuch  as  the  viscera  form  the 
medium  by  which  the  upward  pressure  on  the  diaphragm  is  made,  and 
there  is  of  necessity  quite  as  great  a  tendency  to  the  expulsion  of  their 
contents  as  of  the  air  in  the  lungs.  The  instinctive  and  if  necessary 
voluntarily  increased  contraction  of  the  sphincters,  however,  prevents 
any  escape  at  the  openings  guarded  by  them,  and  the  pressure  is  effec- 
tive at  one  part  only,  at  the  rima  glottidis. 


280 


HANDBOOK    OF   PHYSIOLOGY. 


Sneezing. — The  same  remarks  that  apply  to  coughing,  are  almost 
exactly  ai^plicable  to  the  act  of  sneezing;  but  in  this  instance  the  blast 
of  air,  on  escaj^ing  from  the  lungs,  is  directed,  by  an  instinctive  contrac- 
tion of  the  pillars  of  the  fauces,  and  descent  of  the  soft  palate,  chiefly 
through  the  nose,  and  any  offending  matter  is  thence  expelled. 

S'peaking. — In  speaking,  there  is  a  voluntary  expulsion  of  air  through 
the  glottis  bv  means  of  the  expiratory  muscles.     The  vocal  cords,  by  the 


Fitc.  215. 

muscles  of  the  larynx,  are  put  in  a  proper  position  and  state  of  tension 
for  vibrating  as  the  air  passes  over  them,  and  sound  is  produced.  The 
sound  is  moulded  into  articulate  speech  by  the  tongue,  teeth,  lips,  etc. 
— the  vocal  cords  producing  the  sound  only,  and  having  nothing  to  do 
with  articulation. 

Singing. — Singing  resembles  speaking  in  the  manner  of  its  produc- 
tion; the  laryngeal  muscles,  by  variously  altering  the  position  and  de- 
gree of  tension  of  the  vocal  cords,  producing  the  different  notes.  "Words 
used  in  the  act  of  singing  are  of  course  framed,  as  in  speaking,  by  the 
tongue,  teeth,  lips,  etc. 

Sniffing. — Sniffing  is  produced  by  a  rapidly  repeated  but  incomplete 


HESPIRATIOK.  281 

action  of  tlie  diaphragm  and  other  inspiratory  muscles.  The  mouth  is 
closed,  and  the  whole  stream  of  air  is  made  to  enter  the  air-passages 
through  the  nostrils.  Tlie  al^e  nasi  are  commonly  at  the  same  time 
instinctively  dilated. 

Hohbing. — Sobbing  consists  of  a  series  of  convulsive  inspirations,  at 
the  moment  of  which  the  glottis  is  usually  more  or  less  closed. 

Lat((jliin<j. — Laughing  is  made  u]>  of  a  series  of  short  and  rapid  expi- 
rations. 

YawniiKj. — Yawning  is  an  act  of  inspiration  ])ut  is  unlike  most  of 
the  preceding  actions  as  it  is  always  more  or  less  involuntary.  It  is 
attended  by  a  stretching  of  various  muscles  about  tbe  palate  and  lower 
jaw,  which  is  probably  analogous  to  the  stretching  of  the  muscles  of  the 
limbs  in  which  a  weary  man  finds  relief,  as  a  voluntary  .ict,  when  the^y 
have  been  some  time  out  of  action.  The  involuntary  and  reflex  charac- 
ter of  yawning  prol)ably  depends  on  the  fact  that  the  muscles  concerned 
are  themselves  at  all  times  more  or  less  used  involuntarily,  :vnd  require, 
therefore,  something  beyond  the  exercise  of  the  w^ill  to  set  them  in 
action.  For  the  same  reason,  yawni7ig,  like  sneezing,  cannot  be  well 
performed  voluntarily. 

Siiching. — Sucking  is  not  j^roperly  a  respiratory  act,  but  it  may  be 
most  conveniently  considered  in  this  place.  It  is  caused  chiefly  by  the 
depressor  muscles  of  the  os  hyoides.  These,  by  drawing  doAvnward  and 
backward  the  tongue  and  floor  of  the  mouth,  produce  a  partial  vacuum 
in  the  latter:  and  the  weight  of  the  atmosphere  then  acting  on  all  sides 
tends  to  produce  equilibrium  on  the  inside  and  outside  of  the  mouth  as 
best  it  may.  The  communication  between  the  mouth  and  pharynx  is 
completely  shut  oft'  by  the  contraction  of  the  pillars  of  the  soft  palate 
and  descent  of  the  latter  so  as  to  touch  the  back  of  the  tongue;  and  the 
equilibrium,  therefore,  can  be  restored  only  by  the  entrance  of  some- 
thing through  the  mouth.  The  action,  indeed,  of  the  tongue  and  floor 
of  the  mouth  in  sucking  may  be  compared  to  that  of  the  piston  in  a 
syringe,  and  the  muscles  which  pull  down  the  os  hyoides  and  tongue,  to 
the  power  wliich  draws  the  handle. 

The  Nervous  Apparatus  of  Respiration. 

Like  all  other  functions  of  the  body,  the  discharge  of  Avhich  is  nec- 
essary to  life,  respiration  is  essentially  an  involuntary  act.  Unless  these 
were  the  case,  life  would  be  in  constant  danger,  and  would  cease  on  the 
loss  of  consciousness  for  a  few  moments,  as  in  sleep.  It  is,  however, 
also  necessary  that  respiration  should  be  to  some  extent  under  the  con- 
trol of  the  will.  For  were  it  not  so,  it  would  be  impossible  to  perform 
those  respiratory  acts  Avhicli  have  been  just  discussed,  such  as  speaking, 
singing,  and  the  like. 


282  HANDBOOK   OP   PHYSIOLOGY. 

It  lias  been  known  for  centuries  that  there  exists  a  district  of  the 
central  nervons  system  on  the  destruction  of  which  both  respiration 
and  life  cease.  All  attempts  to  localize  this  district,  however,  before 
those  of  Flourens  were  unsuccessful.  Flourens,  after  many  series  of 
experiments  as  to  the  exact  position  of  what  he  called  the  "knot  of 
life"  (noeud  vital),  placed  it  in  the  fourth  ventricle,  at  the  point  of  the 
V  in  the  gray  matter  at  the  lower  end  of  the  calamus  scriptorius;  a  dis- 
trict of  considerable  size,  viz.,  5  mm.,  on  both  sides  of  the  middle  line. 
Observers  subsequent  to  Flourens  have  attempted  to  show  that  the  chief 
respiratory  centre  on  the  one  hand  is  situated  higher  up  in  the  nervous 
system,  e.g.,  in  the  floor  of  the  third  ventricle  (Christiani),  or  in  the 
corpora  quadrigemina  (Martin  and  Booker,  Christiani,  and  Stanier),  or 
on  the  other  hand,  lower  down  in  the  spinal  cord,  and  that  the  medullary 
centres,  if  they  exist,  are  either  accessory  or  subservient  to  such  centres. 
The  balance  of  experimental  evidence,  however,  is  to  prove  that  the  sole 
centres  for  respiration  is  a  limited  district  in  the  medulla  oblongata  in 
close  connection  with  the  vagus  nucleus  on  each  side,  with  which  they 
are  probably  identical.  The  destruction  of  this  district  stops  respira- 
tion forever;  whereas,  if  it  be  left  in  connection  with  the  muscles  of 
respiration  by  their  nerves,  although  the  remainder  of  the  central  nervous 
system  be  separated  from  it,  respiration  continues.  It  may  be  considered 
almost  certain  that  the  medullary  centre  is  the  only  true  respiratory 
centre,  and  that  the  observations  of  LangendorH,  that  in  newly-born 
animals  in  which  the  medulla  has  been  cut  immediately  or  a  few  milli- 
metres below  the  point  of  the  calamus  scriptorius  respiration  continues 
for  some  time  as  in  normal  animals  cannot  be  received.  We  are  indebted 
to  Marckwald  for  much  information  on  this  subject,  and  he  has  come  to 
the  conclusion  that  normal  respiration  does  not  occur  after  division  of 
the  bulb  from  the  cord,  and  that  the  so-called  respiratory  movements 
noticed  by  Langendorff  are  merely  tetanic  contractions  of  the  respirav 
tory  muscles  with  which  often  enough  other  muscles  take  part. 

The  action  of  the  medullary  centre  is  to  send  out  impulses  during 
inspiration,  which  cause  respiratory  movements  of  the  muscles — {a)  of 
the  nostrils,  and  jaws  through  the  facial  and  inferior  division  of  the 
fifth  nerves;  (5)  of  the  glottis,  chiefly  through  the  inferior  laryngeal 
branches  of  the  vagi;  (c)  of  the  intercostal  and  other  muscles  which 
produce  raising  of  the  ribs,  chiefly  through  the  intercostal  nerves,  and 
{d)  of  the  diaphragm  through  the  phrenic  nerves. 

If  any  one  of  these  sets  of  nerves  be  divided,  respiratory  movements 
of  the  corresponding  part  cease. 

Similarly  it  may  be  supposed  that  the  centre  sends  out  impulses  dur- 
ing expiration  to  certain  other  muscles.  It  has  been  suggested,  however, 
that  the  centre  consists  of  two  parts,  or  is  double,  and  that  it  is  made 
up  of  an  inspiratory  centre,  which  is  constantly  in  action,  and  of  an  ex- 


llESPIKATIOK.  3ft3 

piratory  centre,  which  acts  less  generally,  inasmuch  as  ordinary  tranquil 
expiration  is  seldom  more  than  an  elastic  recoil,  and  not  a  muscular  act 
to  any  marked  degree. 

Assuming  this  view  of  the  double  centres  to  be  correct,  of  their  exact 
mode  of  action  there  is  some  difference  of  opinion ;  it  is  now  thought  that 
they  may  act  automatically,  but  normally  are  influenced  by  att'ereut  im- 
pulses from  the  periphery,  as  well  as  by  impulses  passing  down  from 
the  cerebrum.  The  centre  is,  in  other  words,  both  automatic  and  re- 
flex.    It  will  be  simplest  to  discuss  its  reflex  function  first  of  all. 

Action  of  Afferent  Stimuli. — {a)  Action  of  ttie  vagi. — If  both  vagi 
be  divided  in  the  neck,  the  respirations  become  much  slower  and  deeper; 
this  may  be  the  case,  but  to  a  less  marked  degree,  if  one  of  the  nerves 
is  divided  instead  of  both.  If  the  central  end  of  the  divided  nerve  be 
stimulated  with  a  weak  interrupted  current,  the  most  constant  effect  is 
that  the  respirations  are  quickened,  and  if  the  stimuli  are  properly  reg- 
ulated, the  normal  rhythm  of  respiration  may  be  resumed.  If  the  stimuli 
be  repeated  with  sufficient  quickness,  after  a  wdiile  the  breathing  is 
brought  to  a  stand-still  at  the  height  of  inspiration  by  tetanus  of  the 
diaphragm.  Sometimes,  however,  stimulation  of  the  central  end  of  the 
divided  vagi  produces  still  greater  slowi7ig  than  that  which  follows 
the  division,  so  that  if  it  be  continued,  the  respirations  cease,  with  the 
diaphragm  in  a  condition  of  complete  relaxation.  Marckwald  considers 
that  the  differences  in  the  effects  of  vagus  stimulation  are  due  to  the 
stimulus  being  applied  to  the  nerve  at  different  periods  in  the  respira- 
tory cycle,  and  that  the  action  of  the  vagus  may  be  to  call  forth  either 
inspiration  or  expiration — the  impulses  passing  up  the  vagi  being  neces- 
sary to  the  production  of  the  normal  respiratory  rhythm.  The  fibres 
of  the  vagus  are  used  under  the  following  circumstances,  those  fibres 
which  tend  to  inhibit  expiration  and  to  stimulate  inspiration  are  stim- 
ulated at  their  distribution  in  the  lung  when  the  lung  is  empty  and  in 
a  condition  of  expiration,  and  the  fibres  which  tend  to  inhibit  inspira- 
tion and  to  jiromote  expiration  are  stimulated  when  the  lung  is  fully  ex- 
panded. The  afferent  impulses  are  the  results  of  mere  mechanical 
stimulation,  and  do  not  depend  upon  the  chemical  nature  of  the  gases 
within  the  pulmonary  alveoli.  The  vagus  always  acts  upon  the  centres 
as  a  stimulator  of  discliarge,  or  exciter  of  catabolism. 

{b)  Action  of  the  superior  laryngeal  nerves.— If  the  superior 
laryngeal  branch  of  the  vagus  be  divided,  which  usually  produces  no 
apparent  effect,  and  the  central  end  be  stimulated,  the  effect  is  very 
constant,  respirations  are  slowed,  but  there  is  a  tendency  toward  expi- 
ration, as  is  shown  by  the  contraction  of  the  abdominal  muscles.  Thus 
if  the  vagus  fibres  contain  fibres  which  stimulate  inspiration  and  inhibit 
expiration,  as  well  as  other  fibres  which  have  the  reverse  effect,  the  su- 
perior laryngeal  fibres  inhibit  inspiration  and  stimulate  expiration. 


HANDBOOK    OF    PHYSIOLOGY. 

The  superior  laryngeal  nerves  are  true  expiratory  nerves,  and  may 
oe  set  in  action  when  tlie  mucous  membrane  of  the  larynx  is  irritated. 
They  are  not  constantly  in  action  like  the  vagi. 

{(■)  Action  of  the  glosso-pharyngeal  nerves. — It  has  been  as- 
certained, chiefly  by  the  researches  of  Marckwald,  that  while  division  of 
the  glosso-pharyngeal  nerves  produces  no  effect  upon  respiration,  stim- 
ulation of  them  causes  inhibition  of  inspiration  for  a  short  period.  This 
action  accounts  for  the  very  necessary  cessation  of  breathing  during 
swallowing.  The  effect  of  the  stimulation  is  only  temporary,  and  is 
followed  by  normal  breathing  movements. 

(d)  Action  of  other  sensory  nerves. — The  respiratory  centres 
are  as  a  rule  stimulated  to  produce  respiration  by  imjoressions  conveyed 
by  sensory  nerves,  e.g.,  the  nerves  of  the  skin;  cold  water  applied  to 
the  surface  is  almost  invariably  followed  by  a  deep  inspiration.  Stimu- 
lation of  the  splanchnics  and  of  the  abdominal  branches  of  the  vagi 
produce  expiration.  The  fifth  nerves,  as  well  as  the  glosso-pharyngeal 
and  the  superior  laryngeal,  inhibit  inspiration,  but  they  tend  to  pi;oduce 
a  gradual  slowing  and  not  an  absolute  inliibition,  as  do  the  glosso- 
pharyngeal. 

It  must  be  remembered  that  although  many  sensory  nerves  may  on 
stimulation  be  made  to  j^roduce  an  effect  upon  the  resj)iratory  centres, 
there  is  no  evidence  to  show  that  any  one  of  them,  except  the  vagi,  is 
constantly  in  action.  The  vagi  indeed  are,  as  far  as  we  know,  the  only 
normal  regulators  of  respiration. 

Automatic  Ac  tion  of  the  Respiratory  Centres. — Although  it  has  been 
very  definitely  proved  that  the  respiratory  centres  may  be  affected  by 
afferent  stimuli,  and  |Darticularly  by  those  reaching  them  through  the 
vagi,  there  is  reason  for  believing  that  the  centres  are  capable  of  sending 
out  efferent  impulses  to  the  respiratory  muscles  without  the  action  of 
any  afferent  stimuli.  Thus,  if  the  brain  be  removed  above  the  bulb, 
respiration  continues.  If  the  spinal  cord  be  divided  below  the  bulb,  the 
facial  and  laryngeal  respiratory  movements  continue,  although  no  affer- 
ent impulses  can  reach  the  centres  except  through  the  cranial  sensory 
nerves,  and  these,  as  we  have  seen,  are  not  always  in  action,  and  indeed 
may  be  divided  without  producing  any  effect,  when  the  bulb  and  cord 
are  intact.  As  has  been  shown,  too,  respiration  continues  when  the  vagi 
are  divided.  All  of  these  experiments  render  it  highly  probable  that 
afferent  impulses  are  not  required  in  order  that  the  respiratory  centres 
should  send  out  efferent  impulses  of  some  kind  to  the  respiratory  mus- 
cles ;  these  centres,  then,  are  automatic.  How  they  act  in  the  absence 
of  afferent  stimuli  has  been  demonstrated  by  Marckwald.  He  has  shown 
—  {a)  firstly,  that  if  the  bulb  be  separated  from  the  brain,  and  the  vagi 
be  then  cut,  there  is  first  of  all  inspiratory  spasm  followed  by  irregular 
spasm  of  muscles  both   of  inspiration  and  expiration,  and  death;  {b) 


RESPIRATIOX.  285 

secondly,  that  if  the  vagi  are  divided,  the  respirations,  although  altered 
in  character,  are  regular,  but  that  if  then  the  brain  is  separated  from 
the  medulla,  the  same  respiratory  spasms  occur.  From  these  experiments 
it  is  concluded  that  the  automatic  action  of  the  centres  consists  in  the 
liberation  of  respiratory  spasms  only,  and  not  of  regular  rhythmic  move- 
ments; but  that  impressions  reaching  the  centres  either  from  the  cere- 
brum or  through  the  vagi,  prevent  the  gathering  tension  in  the  centres 
from  becoming  too  great,  and  convert  the  spasms  which  would  other- 
wise arise  into  regular  movements.  The  chief  difference  between  the 
action  of  the  vagi  and  of  the  cerebral  tracts,  is  that  the  former  are  always 
in  action,  whilst  the  latter  are  not.  When  the  vagi  are  in  action  and  the 
higher  centres  are  not,  periodic  respiration  takes  place,  that  is  to  say, 
respirations  occurring  in  groups,  each  such  grouj). being  followed  by  a 
pause;  a  type  of  respiration  known  as  Cheyne-StoJces  breathi)ir/, to v/hich 
we  shall  return  presently.  It  will  be  thus  seen  that  even  the  ordinary 
action  of  the  respiratory  centres  is  to  a  large  extent  reflex,  and  depend- 
ent upon  vagus  or  cerebral  stimulation. 

3Iethod  of  Stiimdation  of  the  Respiratory  Centres. — Apart  then  from 
afferent  impulses,  the  respiratory  centres  are  capable  of  working  auto- 
matically, and  this  fact  has  been  explained  by  the  supposition  that  thc}^ 
are  stimulated  to  action  by  the  condition  of  the  blood  circulating  through 
them,  since  when  the  blood  becomes  more  and  more  venous  the  action 
of  the  centres  becomes  more  and  more  energetic,  and  if  the  air  is  pre- 
vented from  entering  the  chest,  the  respiration  in  a  short  time  becomes 
very  labored.  Any  obstruction  to  the  entrance  of  air  indeed,  whether 
partial  or  complete,  is  followed  by  an  abnormal  rapidity  of  the  inspira- 
tory acts.  The  condition  caused  by  any  interference  Avith  the  free  ex- 
change of  gases  in  the  lungs,  or  by  any  circumstance  in  consequence  of 
which  the  oxygen  of  the  blood  is  used  up  in  an  abnormally  quick  man- 
ner, is  known  as  dyspncea.  If  the  aeration  of  the  blood  is  much  inter- 
fered with,  not  only  are  the  ordinary  respiratory  muscles  employed,  but 
also  those  muscles  of  extraordinary  inspiration  and  expiration  which 
have  been  previously  enumerated.  Thus  as  the  blood  becomes  more  and 
more  venous,  the  action  of  the  medullary  centres  becomes  more  and 
more  active.  The  question  has  been  much  debated  as  to  what  quality 
of  the  venous  blood  it  is  which  causes  this  increased  activity;  whether 
it  is  its  deficiency  of  oxygen  or  its  excess  of  carbonic  acid.  It  has  been 
answered  to  some  extent  by  the  experiments,  which  show  on  the  one 
hand  that  dyspnoea  occurs  when  there  is  no  obstruction  to  the  exit  of 
carbonic  acid  as  when  an  animal  is  placed  in  an  atmosphere  of  nitrogen, 
and  that  it  cannot  therefore  be  due  to  the  accumulation  of  carbonic 
acid ;  and  on  the  other,  that  if  jilenty  of  oxygen  is  supplied,  true  dyspnoea 
does  not  occur,  although  the  carbonic  acid  of  the  blood  is  in  excess.  It 
is  highly  probable,  therefore,  that  the  respiratory  centres  may  be  stimu- 


286  HAXDBOOK    OF   PHYSIOLOGY. 

lated  to  action  by  the  absence  of  sufficient  oxygen  in  the  blood  circulat- 
ing in  it,  and  not  by  the  presence  of  an  excess  of  carbonic  acid. 

But  this  is  not  all,  since  it  has  been  j)roved  by  Marckwald  that  the 
medullary  centres  are  capable  of  acting  for  some  time  in  the  absence 
of  any  circulation,  and  after  excessive  bleeding.  The  view  taken  by 
this  author  with  regard  to  the  action  of  the  centres  is  as  follows :  the 
respiratory  ceutres  are  set  to  act  by  the  condition  of  their  metabolism, 
much  in  the  same  way  as  the  heart  is  set  to  beat  rhythmically.  When 
anabolism  is  completed,  catabolism  or  discharge  occurs,  and  this  alter- 
nate but  crude  and  spasmodic  action  will  occur  without  a  definite  blood- 
supply,  as  long  as  the  centres  are  properly  nourished  and  stimulated  by 
their  own  intercellular  fluid.  The  afferent  impulses  brought  by  the  vagi, 
in  consequence  of  the  stimulation  of  their  terminal  fibres  in  the  lungs, 
have  a  tendency  to  bring  about  catabolism,  and  to  convert  crude  respi- 
ratory spasms  into  regular  and  rhythmic  discharges.  In  the  absence  of 
the  vagus  stimulation,  the  impulses  from  the  cerebrum  may  be  effectual 
for  the  same  purpose. 

It  is  unreasonable  to  think,  however,  that  the  respiratory  centres  are 
independent  of  the  character  of  the  blood-supply  either  as  regards  quan- 
tity or  quality.  This  must  have  a  great  influence  upon  their  irritability; 
it  is  certain,  for  example,  that  venous  blood  greatly  increases  the  respi- 
ratory movements,  first  of  all  both  of  inspiration  and  of  expiration,  and 
then  of  the  latter  to  a  greater  degree.  It  may  be  that  the  diminution 
of  oxygen  in  the  blood  acts  as  a  stimulator  of  catabolism,  in  both  in- 
spiratory and  expiratory  centres,  but  particularly  in  the  latter,  in  a 
manner  similar  to  but  not  identical  with,  that  of  the  vagus.  It  has  also 
been  shown  that  the  presence  of  the  products  of  great  muscular  metabo- 
lism in  the  blood  will  greatly  increase  the  irritability  of  the  respiratory 
centres,  even  if  the  blood  itself  be  not  particularly  venous  in  character. 

It  appears  that  the  inspiratory  and  expiratory  resj)iratory  centres  are 
bilateral,  and  that  each  pair  may  act  independently,  since  the  bulb  may 
be  divided  longitudinally,  and  then  if  one  vagus  be  divided,  the  respi- 
ratory rhythm  on  the  two  sides  of  the  body  becomes  unequal,  the  move- 
ments of  the  side  upon  which  the  vagus  is  divided  being  slower  than  on 
the  other  side,  while  stimulation  of  the  divided  nerve  acts  only  upon 
the  movements  of  its  own  side. 

Apncea. — When  we  take  several  deep  inspirations  in  rapid  succes- 
sion by  voluntary  effort,  we  find  that  we  can  do  without  breathing  for  a 
much  longer  time  than  usual;  in  other  words,  several  rapid  respirations 
seem  to  inhibit  for  a  time  normal  respiratory  movements.  It  was 
thought  that  the  reason  for  this  partial  cessatiDn  of  respiration,  which 
was  called  apncea,  is  that  by  taking  several  deep  breaths  we  overcharge 
our  blood  with  oxygen,  and  that  as  the  respiratory  centre  can  only  be 
stimulated  by  blood  in  which  the  standard  of  oxygen  is  below  a  certain 


RESPIRATION".  287 

level,  no  respiratory  impulses  can  occur  until  the  oxygen  tension  of  the 
blood  reach  that  level.  This  idea  must  now  be  modified,  if  not  given  up, 
in  face  of  the  experiments,  e.g.,  those  of  Hering,  on  cats'  blood  during 
apnroa,  which  have  shown  that  animals  in  a  condition  of  apncea  may 
have  less  and  not  more  oxygen  in  their  blood  than  in  a  normal  state, 
although  the  carbonic  anhydride  is  less.  One  view  now  taken  of  the 
cause  of  apnoea  is  that  by  rapid  inflations  of  the  lungs  impulses  pass  up 
by  the  vagi,  by  means  of  which  inspiration  is  after  a  while  inhibited; 
another  view  is  that  by  the  repeated  stimulation  of  the  centre  by  vagus 
impulses  which  result  in  rapid  respiratory  movements,  anabolism  is  at 
last  arrested.  Apnoea  is  with  difficulty  produced,  if  at  all,  when  the 
vagi  are  divided. 

Effects  of  Vitiated  Air. — Ventilation.— As  the  air  expired  from 
the  lungs  contains  a  large  proportion  of  carbon  dioxide  and  a  minute 
amount  of  organic  putrescible  matter,  it  is  obvious  that  if  the  same  air 
be  breathed  again  and  again,  the  proportion  of  carbonic  dioxide  and 
organic  matter  in  it  will  constantly  increase  till  it  becomes  unfit  to 
breathe;  long  before  this  point  is  reached  however,  uneasy  sensations 
occur,  such  as  headache,  languor,  and  a  sense  of  oppression.  It  is  a  re- 
markable fact,  however,  that  the  organism  after  a  time  adapts  itself  to 
a  very  vitiated  atmosphere,  and  that  a  jjerson  soon  comes  to  breathe, 
without  sensible  inconvenience,  an  atmosphere  which,  when  he  first  en- 
ters it,  feels  intolerable.  Such  an  adaptation,  however  can  only  take 
place  at  the  expense  of  a  depression  of  all  the  vital  functions,  which 
must  be  injurious  if  long  continued  or  often  repeated. 

This  power  of  adaptation  is  well  illustrated  by  the  experiments  of 
Claude  Bernard.  A  sparrow  is  jilaced  under  a  bell-glass  of  such  a  size 
that  it  Avill  live  for  three  hours.  If  now  at  the  end  of  the  second  hour 
(when  it  could  have  survived  another  hour)  it  be  taken  out  and  a  fresh 
healthy  sparrow  introduced,  the  latter  will  perish  instanth^ 

It  must  be  evident  that  provision  for  a  constant  and  plentiful  supply 
of  fresh  air,  and  the  removal  of  that  which  is  vitiated,  is  of  far  greater 
importance  than  the  actual  cubic  space  per  head  of  occupants.  Not 
less  than  2,000  cubic  feet  per  head  should  be  allowed  in  sleej)ing  apart- 
ments (barracks,  hospitals,  etc.),  and  with  this  allowance  the  air  can  only 
be  maintained  at  the  proper  standard  of  purity  by  such  a  system  of  ven- 
tilation as  provides  for  the  sujaply  of  1,500  to  2,000  cubic  feet  of  fresh 
air  per  head  per  hour.     (Parkes.) 

The  Effect  of  Respiration  on  the  Circulation. 

As  the  heart,  the  aorta,  and  pulmonary  vessels  are  situated  in  the 
air-tight  thorax,  they  are  exposed  to  a  certain  alteration  of  pressure 
when  the  capacity  of  the  latter  is  increased  in  inspiration ;  for  although 
the  expansion  of  the  lungs  tends  to  counter-balance  this  increase  of  area. 


288 


HAXDBOOK    OF    PHYSIOLOGY, 


it  neyer  does  so  entirely,  since  part  of  the  jaressure  of  the  air  which  is 
drawn  into  the  hmgs  through  the  trachea  is  expended  in  overcoming 
their  elasticity.  The  amount  thus  used  up  increases  as  the  lungs 
become  more  and  more  expanded,  so  that  the  pressure  inside-  the  thorax 
during  inspiration,  as  far  as  the  heart  and  great  vessels  are  concerned, 
never  quite  equals  that  outside,  and  at  the  conclusion  of  inspiration  is 
considerably  less  than  the  atmospheric  jjressure.  It  has  been  ascertained 
that  the  amount  of  the  pressure  used  up  in  the  way  above  described, 
varies  from  5  or  7  mm.  of  mercury  during  the  pause,  to  30  mm.  of 
mercury  when  the  lungs  are  expanded  at  the  end  of  a  deep  inspiration, 
so  that  it  will  be  understood  that  the  pressure  to  which  the  heart  aud 
great  vessels  are  subjected  diminishes  as  inspiration  progresses,  and  at 


Fig.  216.— Diagram  of  an  apparatus  illustranng  me  effect  of  inspiration  upon  the  heart  and 
great  vessels  within  the  thorax.  I,  the  thorax  at  res  ;  II,  during  inspiration  ;  d,  represents  the 
diaphragm  when  relaxed ;  d',  when  contracted  (it  must  be  i-emembered  that  this  position  is  a  mere 
diagrani),  i.e.,  when  the  capacity  of  the  thora"  is  enla.ged  ;  h.  the  heart;  v,  the  veins  entering  it, 
and  A,  the  aorta  ;  v.1,  l/,  the  riglit  and  left  lung  ;  t,  th  trachea:  m,  mercurial  manometer  in  con- 
nection with  pleura.  The  increase  in  the  capacity  of  the  box  representing  the  thorax  is  seen  to 
dilate  the  heart  as  well  as  the  lungs,  and  so  to  pump  in  blood  through  v.  whereas  the  valve  prevents 
reflex  through  a.  The  position  of  the  mercury  in  m  shows  also  the  suction  which  is  taking  place. 
(Landois.) 


its  minimum  is  less  by  30  mm.,  than  the  normal  pressure,  760  mm.  of 
mercury.  It  will  be  understood  from  the  accompanying  diagram  how, 
that  if  there  were  no  lungs  in  the  chest,  if  its  capacity  were  increased, 
the  efEect  of  the  increase  would  be  expended  in  pumping  blood  into  the 
heart  from  the  veins.  With  the  lungs  placed  as  they  are,  during  in- 
spiration the  iDressure  outside  the  heart  and  great  vessels  is  dimiuished, 
and  they  have  therefore  a  tendency  to  expand  and  to  diminish  the  intra- 
vascular pressure.  The  diminution  of  pressure  within  the  veins  passiug 
to  the  right  auricle  and  within  the  right  auricle  itself,  will  draw  the 
blood  into  the  thorax,  and  so  assist  the  circulation.  This  suction  action 
is  independent  of  the  suction  power  of  the  diastole  of  the  auricle  about 
which  we  have  previously  spoken.     The  efEect  of  sucking  more  blood 


RESPIRATIOX.  289 

into  the  right  auricle  will,  cmteris  paribus,  increase  the  amount  passing 
through  the  right  ventricle,  which  also  exerts  a  similar  suction  action, 
and  through  the  lungs  into  the  left  auricle  and  ventricle,  and  thus  into 
the  aorta.  This  all  tends  to  increase  the  blood-pressure.  The  effect  of 
the  diminished  pressur6  upon  the  pulmonary  vessels  will  also  help 
toward  the  same  end,  i.e.,  an  increased  flow  through  the  lungs,  so  that, 
as  far  as  the  heart  and  its  veins  are  concerned,  inspiration  increases  the 
blood-pressure  in  the  arteries.  The  effect  of  inspiration  upon  the  aorta 
and  its  branches  within  the  thorax  would  be,  however,  contrary;  for  as 
the  pressure  outside  is  diminished  the  vessels  would  tend  to  expand,  and 
thus  to  diminish  the  tension  of  the  blood  within  them,  but  inasmuch  as 
the  large  arteries  are  capable  of  little  exj^ansion  beyond  their  natural 
calibre,  the  diminution   of  the  arterial   tension   caused  by  this  means 


Fig.  S17.— Comparison  of  blood-pressure  curve  with  curve  of  intra-thoracie  pressure.  (To  be  reaci 
f rotu  left  to  ripht.)  a  is  the  curve  of  blood-pressure  with  its  respiratory  undulations,  the  slower 
beats  on  the  descent  being  very  marked;  b  is  the  curve  of  intra-thoracic  pressure  obtainctl  )iy  con- 
necting one  limb  of  a  manometer  with  the  plural  cavity.  Inspiration  begins  at  /  and  expiration  at 
c.  The  intra-thoracic  pressure  rises  very  rapidly  after  the  cessation  of  the  inspiratory  effort,  and 
then  slowly  falls  as  the  air  issues  from  the  ohe-st;  at  the  beginning  of  the  inspiratory  effort  the  fall 
becomes  more  rapid.     (M.  Foster.) 

would  be  insufficient  to  counteract  the  increase  of  blood-pressure  jn'o- 
duced  by  the  effect  of  inspiration  upon  the  veins  of  the  chest,  and  the 
balance  of  the  whole  action  would  be  in  favor  of  an  increase  of  blood- 
pressure  during  the  inspiratory  period.  But  if  a  blood-pressure  tracing 
be  taken  at  the  same  time  that  the  respiratory  movements  are  being 
recorded,  it  will  be  found  that,  although  speaking  generally,  the  arterial 
tension  is  increased  during  inspiration,  the  maximum  of  arterial  tension 
does  not  correspond  witii  the  acme  of  inspiration  (fig.  217).  In  fact,  at 
the  beginning  of  inspiration  the  pressure  continues  to  fall,  then  gradually 
rises  until  the  end  of  inspiration,  and  continues  to  do  so  for  some  time 
after  expiration  has  commenced. 

As  regards  the  effect  of  cxpira/imi,  the  capacity   of   the   chest   is 
diminished,  and  the  intra-thoracic  pressure  returns  to  the  normal,  which 
is  not  exactly  equal  to  the  atmospheric  pressure.     The  effect  of  this  on 
19 


290  HANDBOOK    OF    PHYSIOLOGY. 

the  veins  is  to  increase  their  extra-vascular  and  so  their  intra-vascular 
pressure,  and  to  diminish  tlie  flow  of  blood  into  the  left  side  of  the 
heart,  and  with  it  the  general  blood-pressure,  but  this  is  almost  exactly 
balanced  by  the  necessary  increase  of  arterial  tension  caused  by  the 
increase  of  the  extra- vascular  pressure  of  the  aorta  and  large  arteries,  so 
that  the  arterial  tension  is  not  much  affected  during  expiration  either 
way.  Thus,  ordinary  ex^iiration  does  not  produce  a  distinct  obstruction 
to  the  circulation,  as  even  when  the  expiration  is  at  an  end  the  intra- 
thoracic pressure  is  less  than  the  extra-thoracic. 

The  effect  of  violent  expiratory  efforts,  however,  has  a  distinct  action 
in  obstructing  the  current  of  blood  through  the  lungs,  as  seen  in  the 
blueness  of  the  face  from  congestion  in  straining,  this  condition  being 
produced  by  jaressure  on  the  small  pulmonary  vessels. 

We  may  summarize  this  mechanical  effect  of  respiration  on  the  blood- 
pressure  therefore,  and  say  that  inspiration  aids  the  circulation  and  so 
increases  the  arterial  tension,  and  that  although  expiration  does  not 
materially  aid  the  circulation,  yet  under  ordinary  conditions  neither  does 
it  obstruct  it.  Under  extraordinary  conditions,  however,  as  in  violent 
expiration,  the  circulation  is  decidedly  obstructed. 

We  have  seen,  however,  that  there  is  no  exact  correspondence  between 
the  point  of  highest  blood-pressure  and  the  end  of  inspiration,  and  we 
must  suppose  that  there  are  other  mechanical  factors,  such,  for  example, 
as  the  effect  of  the  abdominal  movements,  both  in  inspiration  and  in 
expiration,  upon  the  arteries  and  veins  within  the  abdomen  and  of  the 
lower  extremities,  and  the  influence  of  the  varying  intrathoracic  pres- 
sure upon  the  pulmonary  vessels,  both  of  which  ought  to  be  taken  into 
consideration.  As  regards  the  first  of  these,  the  effect  during  inspira- 
tion— as  the  cavity  of  the  abdomen  is  diminished  by  the  descent  of  the 
diaphragm — should  be  two-fold:  on  the  one  hand,  blood  would  be  sent 
upward  into  the  chest  by  compression  of  the  vena  cava  inferior;  on  the 
other  hand,  the  passage  of  blood  downward  from  the  chest  in  the 
abdominal  aorta,  and  upward  in  the  veins  of  the  lower  extremity,  would 
be  to  a  certain  extent  obstructed.  In  ordinary  expiration  all  this  would 
be  reversed,  but  if  the  abdominal  muscles  are  violently  contracted,  as  in 
extraordinary  expiration,  the  same  effect  would  be  produced  as  by  in- 
spiration. The  effect  of  the  varying  intrathoracic  pressure,  which  occurs 
during  inspiration  upon  the  pulmonary  vessels  is  to  produce  an  initial 
dilatation  of  both  artery  and  veins,  and  this  delays  for  a  short  time  the 
passage  of  blood  toward  the  left  side  of  the  heart,  and  the  arterial 
pressure  falls,  but  the  fall  of  blood-pressure  is  soon  followed  by  a  steady 
rise,  since  the  flow  is  increased  by  the  initial  dilatation  of  the  vessels : 
the  converse  is  the  case  with  expiration.  As,  however,  the  pulmonary 
veins  are  more  easily  dilatable  than  the  pulmonary  artery,  their  greater 
distensibility  increases  the  flow  of   blood  as  inspiration  proceeds,  while 


RESPIRATION.  291 

during  expiration,  except  at  its  beginning,  this  property  of  theirs  acts  in 
the  opposite  direction,  and  diminishes  the  flow.  Thus,  at  the  beginning 
of  inspiration  the  diminution  of  blood-pressure,  which  commenced  during 
expiration,  is  continued,  but  after  a  time  the  diminution  is  succeeded  by 
a  steady  rise;  the  reverse  is  the  case  with  expiration — at  first  a  rise  and 
then  a  fall. 

The  effect  of  the  nervous  system  in  producing  rhythmical  altera- 
tions quite  independent  of  the  mechanically  caused  undulations  of  the 


Fig.  aiH.— Traube-Hering-"s  curves.  (To  be  read  from  left  to  right. ^  The  curves  1.  ~.  3,  4.  and  5 
are  portions  selected  from  one  continuous  tracing  forming  the  record  of  a  prolonged  observation, 
so  that  the  several  curves  represent  successive  stages  of  the  same  experiment.  Each  curve  is  placed 
in  its  proper  position  relative  to  the  l)ase  line,  which  is  omitted  ;  the  blood-pressure  rises  in  stages 
from  1  to  2,  3,  and  4,  but  falls  again  in  stage  5.  Curve  1  is  taken  from  a  period  when  artificial  res- 
piration was  being  kept  up,  but  the  vagi  having  been  divided,  the  pulsations  on  the  ascent  and  de- 
scent of  the  undulations  do  not  differ;  when  artificial  respiration  ceased  these  undulations  for  a 
whiledisaiipcarcd,  and  the  blood-pressure  rose  steadily  while  the  heart-beats  became  slower.  Soon, 
as  at  '2.  new  undulations  appeared  ;  a  little  later,  the  blood-pressure  was  still  rising,  the  heart  beats 
still  slower,  but  the  undulations  still  more  obvious  (8);  still  later  (41,  tlie  pressure  was  still  higher, 
but  the  heart-beats  were  qiucker,  and  the  undulations  flatter,  the  pressure  then  began  to  fallrapidly 
(.")),  and  continued  to  fall  un.il  some  time  after  artificial  respiration  was  resumed.     (.M.  Foster.) 

blood-pressure  is  two-fold.  In  the  lirst  place  the  cardiu-inhibitory  ccnfrc 
is  stimulated  during  the  fall  of  blood-pressure,  and  produces  a  slower 
rate  of  heart-beat,  which  will  be  noticed  in  the  tracing  (fig.  218).  The 
undulations  during  the  decline  of  blood-pressure  are  therefore  longer 
but  less  frequent.  This  effect  disappears  when,  by  section  of  the  vagi, 
the  effect  of  the  centre  is  cut  off  from  the  heart.  In  the  second  place, 
the  raso-motor  mnlrt'  sends  out  rliythmical  impulses,  by  which  undula- 
tions of  blood-pressure  are  produced,  quite  independent  of  the  so-called 


292  HANDBOOK    OF   PHYSIOLOGY. 

respiratory  undulations.  The  action  of  this  centre  in  producing  such 
undulations  is  thus  demonstrated.  In  an  animal  under  the  influence 
of  urari,  a  record  of  whose  blood-pressure  is  being  taken,  and  where 
artificial  respiration  has  been  stopped,  and  both  vagi  cut,  the  blood- 
pressure  curve  rises  at  first  almost  in  a  straight  line,  but  after  a  time 
rhythmical  undulations  occur  (called  Trauhe's  or  Trauhe-Hei'ing's 
curves) ;  there  may  be  upward  of  ten  of  the  respiratory  undulations  in 
one  Traube-Hering  curve.  They  continue  as  long  as  the  blood-pressure 
continues  to  rise,  and  only  cease  when  the  vaso-motor  centre  and  the 
heart  are  exhausted,  when  the  pressure  falls.  The  undulations  cannot 
depend  upon  anything  but  the  vaso-motor  centre,  as  the  mechanical 
effects  of  respiration  have  been  eliminated  by  the  urari  and  by  the 
cessation  of  artificial  respiration,  .^nd  the  effect  of  the  cardio-inhibitory 
centre  has  been  removed,  by  the  division  of  the  vagi.  The  rhythmic 
rise  of  blood-iDressure  is  most  likely  due  to  a  rhythmic  constriction  of 
the  arterioles  followed  by  a  rhythmic  fall  of  pressure  and  relaxation, 
both  being  due  to  the  action  of  the  vaso-motor  centre.  The  vaso-motor 
centre,  therefore,  as  well  as  the  cardio-inhibitory,  is  capable  of  produc- 
ing rhythmical  undulations  of  blood-pressure. 

Clieync- Stokes'  hreaihing  is  a  rhythmical  irregularity  in  respirations 
which  has  been  observed  in  various  diseases,  and  is  especially  connected 
with  fatty  degeneration  of  the  heart.  Eespirations  occur  in  groups,  at 
the  beginning  of  each  group  the  inspirations  are  very  shallow,  but  each 
successive  breath  is  deeper  than  the  preceding,  until  a  climax  is  reached, 
after  which  the  inspirations  become  less  and  less  deep,  until  they  cease 
after  a  slight  pause  altogether.  This  phenomenon  appears  to  be  due  to 
the  want  of  action  of  some  of  the  usual  cerebral  influences  which  pass 
down  to  and  regulate  the  discharges  of  the  resj)iratory  centres. 

Whatever  is  the  exact  quality  of  the  venous  blood  which  excites  the 
respiratory  centre  to  produce  normal  respirations,  there  can  be  no  doubt 
that  as  the  blood  becomes  more  and  more  venous  from  obstruction  to 
the  entrance  of  air  into  the  lung,  or  from  the  blood  not  taking  up  from 
the  air  its  usual  supply  of  oxygen,  the  respiratory  centre  becomes  more 
active  and  excitable,  and  a  condition- ensues,  which  passes  rapidly  from 
Hyperpnma  (excessive  breathing)  to  the  state  of  Dyspnoea  (difficult 
breathing),  and  afterward  to  Aspliyjyia  ;  and  the  latter,  unless  relieved, 
quickly  ends  in  death. 

The  ways  by  which  this  condition  of  asphyxia  may  be  produced  are 
very  numerous: — As,  for  example,  by  the  prevention  of  the  due  entry 
of  oxygen  into  the  blood,  either  by  direct  obstruction  of  the  trachea  or 
other  part  of  the  respiratory  passages,  or  by  introducing  instead  of 
ordinary  air  a  gas  devoid  of  oxygen,  or,  by  interference  with  the  due  in- 
terchange of  gases  between  the  air  and  the  blood. 

The  symptoms  of  asphyxia  may  be  divided  into  three  groups,  which 


rtESPTiiATio>r.  293 

correspond  with  the  stages  of  tlie  coiulitioii  which  are  usually  recog- 
nized, these  are  (1),  the  stage  of  exaggerated  hreathing;  {2),  tlie  stage 
of  convulsions;  (3),  the  stage  of  exhaustion. 

In  the  first  staye  the  breathing  becomes  more  rapid  and  at  the  same 
time  more  deep  than  usual,  the  inspirations  at  first  being  especially  ex- 
aggerated and  prolonged.  The  muscles  of  extraordinary  insjjiration  are 
called  into  action,  and  the  effort  to  respire  is  labored  and  painful.  This 
is  soon  followed  by  a  similar  increase  in  the  expiratory  efforts,  which 
become  excessively  prolonged,  being  aided  by  all  the  muscles  of  extra- 
ordinary expiration.  During  this  stage,  which  lasts  a  varying  time, 
from  a  minute  upward,  according  as  the  deprivation  of  oxygen  is  sudden 
or  gradual,  the  lips  become  blue,  the  eyes  are  prominent,  and  the  ex- 
pression intensely  anxious.  The  prolonged  respirations  arc  accompanied 
by  a  distinctly  audible  sound;  the  muscles  attached  to  the  chest  stand 
out  as  distinct  cords.  This  stage  includes  the  two  conditions  hyperpnoea 
and  dyspnova  already  spoken  of.  It  is  due  to  the  increasingly  powerful 
stimulation  of  the  respiratory  centres  by  the  increasingly  venous  blood. 

In  the  seciiud  stage,  which  is  not  marked  out  by  any  distinct  line  of 
demarcation  from  the  first,  the  violent  expiratory  efforts  become  con- 
vulsive, and  then  give  way,  in  men  and  other  warm-blooded  animals  at 
any  rate,  to  general  convulsions,  which  arise  from  the  further  stimula- 
tion of  the  centres.  The  spasms  of  the  muscles  of  the  body  in  general 
occur,  and  not  of  the  respiratory  muscles  only.  The  convulsive  stage 
is  a  short  one,  and  lasts  far  less  than  a  minute. 

The  tliird  stage  or  stage  of  exhanstio)/.  In  it,  the  respirations  all  but 
cease,  the  spasms  give  way  to  flaccidity  of  the  muscles,  there  is  insensi- 
bility^ the  conjunctivae  ai-e  insensitive  and  the  pujiils  are  widely  dilated. 
Every  now  and  then  a  prolonged  sighing  inspiration  takes  place,  at 
longer  and  longer  intervals  until  they  cease  altogether,  and  death  en- 
sues. During  this  stage  the  pulse  is  scarcely  to  be  felt,  but  the  lieart 
may  beat  for  some  seconds  after  respirations  have  quite  ceased.  The 
condition  is  due  to  the  gradual  paralysis  of  the  respiratory  centre  by 
the  prolonged  action  of  the  increasingly  venous  blood. 

As  with  the  first  stage,  the  duration  of  the  second  and  third  stages 
depends  whether  the  manner  of  the  deprivation  of  oxygen  is  sudden  or 
gradual.  The  convulsive  stage  is  short,  lasting,  it  may  be,  only  one 
minute.     The  third  stage  may  last  three  minutes  and  upward. 

The  conditions  of  the  vascular  system  in  asphyxia  are: — (1)  More  or 
less  interference  with  the  passage  of  tlie  blood  through  the  systemic  and 
tbe  pulmonary  blood-vessels;  (2)  Accunmlation  of  blood  in  the  right  side 
of  the  heart  and  in  the  systemic  veins;  (3)  Circulation  of  impure  (nou- 
aerated)  blood  in  all  parts  of  the  body. 

After  death  from  asphyxia  it  is  found  in  the  great  majority  of  cases 
that  the  right  side  of  the  heart,  tlie  {lulmonary  arteries,  and  the  systemic 


294  HANDBOOK   OP  PHYSIOLOGY. 

veins  are  gorged  with  dark,  almost  black  blood,  and  the  left  side  of  the 
heart,  the  pulmonary  veins,  and  the  arteries  are  empty.  The  explana- 
tion of  these  ajjpearances  maybe  thus  summarized:  when  resjjiration 
is  stopped,  venous  blood  at  first  passes  freely  through  the  lungs  to  the 
left  heart,  and  so  to  the  great  arteries.  When  it  reaches  the  arterioles 
either  by  its  direct  action  upon  their  muscular  tissue,  or  more  probably 
through  the  medium  of  the  vaso-motor  centres,  the  arterioles  contract, 
particularly  those  of  the  splanchnic  area,  the  blood-pressure  rises  and 
the  left  side  of  the  heart  becomes  distended.  This  latter  effect  may  be 
from  the  extra  action  of  the  right  heart,  but  is  more  probably  due  to 
the  increased  peripheral  resistance,  and  its  slower  beat.  Although  the 
arterioles  are  contracted,  a  little  blood  is  allowed  to  pass  through  them, 
and  this  highly  venous  blood,  favored  by  the  labored  respiratory  move- 
ments, arrives  at  the  right  side  of  the  heart.  When  it  reaches  the  pul- 
monary arterioles  it  gives  rise  to  the  same  contraction  in  them  as  it  did 
in  the  systemic  vessels.  This  obstruction  to  the  circulation  through 
the  lungs  causes  a  distended  condition  of  the  right  heart  and  the  pul- 
monary artery,  and  on  the  other  hand,  produces  a  greatly  diminished 
blood-flow  through  the  pulmonary  veins  and  to  the  left  side  of  the  heart, 
resulting  after  a  time  in  practical  emptiness.  So  that  in  the  third  stage 
of  asphyxia  it  is  stated  by  some  observers  that  the  left  heart  gets  into 
the  condition  in  which  it  is  found  after  death.  Others  think  that  the 
empty  condition  of  the  left  heart  is  a  post-mortem  phenomenon.  In 
the  first  and  second  stages  of  the  condition  the  blood-pressure  continu- 
ously rises  until  it  reaches  a  point  far  above  the  normal.  The  veins  are 
greatly  engorged,  so  that  when  pricked  they  act  as  arteries,  inasmuch  as 
they  eject  the  blood  for  some  distance.  Both  sides  of  the  heart  and  the 
pulmonary  vessels  are  engorged  with  blood,  at  any  rate  during  the 
greater  portion  of  these  stages,  and  at  the  third  stage  blood-pressure 
falls  rapidly. 

Cause  of  death. — The  causes  of  these  conditions  and  the  manner  in 
Avhich  they  act,  so  as  to  be  incompatible  with  life,  may  be  here  briefly 
considered. 

(1)  The  obstruction  to  the  passage  of  blood  through  the  lungs  occurs 
chiefly  in  the  later  stages  of  asphyxia,  the  obstruction  being  chiefly  in 
the  arterioles,  which  contract  under  the  influence  of  the  vaso-motor 
centre,  or  possibly  of  a  special  part  of  it,  which  governs  the  action  of 
the  pulmonary  blood-vessels. 

(2)  Accumulation  of  blood,  with  consequent  distention  of  the  right 
side  of  the  heart  and  of  the  systemic  veins,  is  the  direct  result,  at  least 
in  part,  of  the  obstruction  to  the  pulmonary  circulation  just  referred  to. 
Other  causes,  however,  are  in  operation,  {a)  The  vaso-motor  centres 
stimulated  by  blood  deficient  in  oxygen,  cause  contraction  of  all  the 
small  arteries  with  increase  of  arterial  tension,  and  as  an  immediate 


UESPIHATION.  2'Jo 

consequence  the  filling  of  the  systemic  veins.  {!>)  The  increased  arterial 
tension  is  followed  by  inhibition  of  the  action  of  the  lieart,  and  the 
heart,  contracting  less  frequently,  and  also  gradually  enfeebled  by  defi- 
cient supply  of  oxygen,  becomes  over-distended  with  blood  which  it 
cannot  expel.  At  this  stage  the  left  as  well  as  the  right  cavities  are 
over-distended. 

The  ill  effects  of  these  conditions  are  to  be  looked  for  partly  in  the 
heart,  the  muscular  fibj-es  of  which,  like  those  of  the  urinary  bladder  or 
any  other  hollow  muscular  organ,  may  be  paralyzed  by  over-stretcbing; 
and  partly  in  the  venous  congestion,  and  consequent  interference  with 
the  function  of  the  higher  nerve-centres,  especially  the  medulla  ob- 
longata. 

(3)  The  passage  of  non-aerated  blood  through  the  lungs  and  its  dis- 
tribution over  the  body  are  events  incompatible  with  life  in  one  of  the 
higher  animals  for  more  than  a  few  minutes;  the  rapidity  with  which 
death  ensues  in  asphyxia  being  diie,  more  particularly,  to  the  effect  of 
non-oxygenized  blood  on  the  medulla  oblongata,  and,  through  the 
coronary  arteries,  on  the  muscular  substance  of  the  heart.  The  excita- 
bility of  both  nervous  and  muscular  tissue  is  dependent  on  a  constant 
and  large  supply  of  oxygen,  and,  Avhen  this  is  interfered  with,  excita- 
bility is  rapidly  lost. 

Effects  of  hreatliing  gases  other  than  the  atmosphere. — The  diminu- 
tion of  oxygen  has  a  more  direct  influence  in  the  production  of  the  usual 
symptoms  of  asphyxia  than  the  increased  amount  of  carbon  dioxide. 
Indeed,  the  fatal  effect  of  a  gradual  accumulation  of  carbon  dioxide 
in  the  blood,  when  a  due  supply  of  oxygen  is  maintained,  resembles 
rather  the  action  of  a  narcotic  poison  than  it  does  asphyxia. 

Then  again  we  must  carefully  distinguish  the  asphyxiating  effect  of 
an  insufficient  supply  of  oxygen  from  the  directly  poisonous  action  of 
sucn  gases  as  carbonic  oxide,  which  is  contained  to  a  considerable 
amount  in  common  coal-gas.  The  fatal  effects  often  produced  by  this 
gas  (as  in  accidents  from  burning  charcoal  stoves  in  small,  close  rooms) 
are  due  to  its  entering  into  combination  with  the  haemoglobin  of  the 
blood-corpuscles  and  thus  expelling  the  oxygen.  The  partial  pressure 
of  oxygen  in  the  atmosphere  may  be  considerably  increased  without 
much  effect.  Hydrogen  may  take  the  place  of  nitrogen  if  the  oxygen 
is  in  the  usual  proportion  with  no  marked  ill  effect.  Sulphuretted 
hydrogen  destroys  the  haemoglobin  of  blood.  Nitrous  oxide  acts 
directly  on  the  nervous  system  as  a  narcotic.  Certain  gases,  such  as 
carbon  dioxide  in  more  than  a  certain  proportion ;  sulphurous  and 
other  acid  gases,  ammonia,  and  chlorine  produce  spasmodic  closure 
of  the  glottis,  and  are  irrespirable. 

As  conditions  causing  asphyxia  in  addition  to  the  obstruction  to  the 
trachea  or  elsewhere,  and  the  prevention  uf  the  meeting  of  tlie  blood 


296  HA^TDBOOK   OF   PHYSIOLOGY. 

and  the  air  in  the  lung  tissue  by  the  blocking  of  one  or  more  branches 
of  the  pulmonary  artery,  may  be  mentioned  the  following : 

Alteration  in  the  atmosplieric  ijressure. — The  normal  condition  of 
breathing  is  that  the  oxygen  of  the  air  breathed  should  be  at  the  pres- 
sure of  \  of  the  atmosphere,  yiz.,  \  of  760  mm.  of  mercury,  or  152  mm., 
but  it  is  found  that  life  may  be  carried  on  by  gradual  diminution  of 
the  oyxgen  pressure  to  considerably  less  than  one  half  of  this,  viz.,  to 
76  mm.,  or  ^^  partial  pressure,  which  is  reached  at  an  altitude  above 
15,000  feet.*  Any  pressure  less  than  this  may  begin  to  produce  altera- 
tions in  the  relations  of  the  gases  in  the  blood,  and  if  an  animal  is  sub- 
jected suddenly  to  a  marked  decrease  of  barometric  pressure,  and  so  of 
oxygen  pressure  (below  7  j^er  cent),  it  is  thrown  into  convulsions,  and  it 
is  found  that  the  gases  are  set  free  in  the  blood-vessels,  no  doubt  carbon 
dioxide  and  oyxgen  as  well  as  nitrogen,  although  the  latter  is  the  only 
one  of  the  three  gases  the  presence  of  which  in  the  vessels  in  death 
from  this  condition  of  affairs  has  been  proved;  the  others  are  said  to 
be  reabsorbed.  Other  derangements  may  precede  this,  e.g.,  bleeding 
from  the  nose,  dyspnoea,  and  vascular  derangement.  On  the  other  hand, 
the  oygxen  may  be  gradually  increased  to  a  considerable  extent  without 
marked  effect,  even  to  the  extent  of  8  or  10  atmospheres,  but  when  the 
oxygen  pressure  is  increased  up  to  20  atmosjDheres  the  animals  ex^ieri- 
mented  upon  by  Paul  Bert  died  with  severe  tetanic  convulsions.  The 
alteration  of  jjressure  above  or  below  a  certain  average  affects  primarily 
the  gaseous  interchange  in  the  lungs,  and  then  that  in  the  tissues  gene- 
rally, but  signs  of  dyspnoea  may  be  produced  as  well  either  by  cutting 
off  the  supply  of  Itlood  to  the  medullary  centres,  or  by  loarming  the  hlood 
of  the  carotid  arteries  which  supply  them.  The  cause  in  the  foriner 
case  being  the  deprivation  of  oxygen  and  the  accumulation  of  the  car- 
bon dioxide,  and  of  the  latter,  the  increased  metabolism  of  the  centre 
set  up  by  the  warmed  blood. 

*  For  an  interesting  account  of  the  symptoms  produced  by  diminished  atmos- 
pheric pressure  in  those  mounting  to  very  high  altitudes,  Whymper's  "Travels 
amongst  the  Andes  of  the  Equator"  may  be  consulted. 


CHAPTER   Till. 

SECRETION. 

It  is  tlie  funotion  of  gland  cells  to  produce  by  the  metabolism  of  their 
protoplasm  certain  substances  called  secretions.  These  materials  are  of 
two  kinds;  viz.,  those  which  are  employed  for  the  purpose  of  serving 
some  ulterior  office  in  the  economy,  and  those  which  are  discharged  from 
the  body  as  useless  or  injurious.  In  the  former  case,  the  separated 
materials  are  termed  true  secretions;  in  the  latter  they  are  termed  excre- 
tions. 

The  secretioiis  as  a  rule  consist  of  substances  which  do  not  pre-exist 
in  the  same  form  in  the  blood,  but  require  si^ecial  cells  and  a  process 
of  elaboration  for  their  formation,  e.g.,  the  liver  cells  for  the  forma- 
tion of  bile,  the  mammary  gland-cells  for  the  formation  of  milk.  The 
excretions,  on  the  other  hand,  commonly  consist  of  substances  which 
exist  ready-formed  in  the  blood,  and  are  merely  abstracted  therefrom. 
If  from  any  cause,  such  as  extensive  disease  or  extirpation  of  an  excre- 
tory organ,  the  separation  of  an  excretion  is  prevented,  and  an  accumu- 
lation of  it  in  the  blood  ensues,  it  frequently  escapes  through  other 
organs,  and  may  be  detected  in  various  fluids  of  the  body.  But  this  is 
never  the  case  with  secretions;  at  least  with  those  that  are  most  elabo- 
rated; for  after  the  removal  of  the  special  organ  by  which  each  of  them 
is  manufactured,  the  secretion  is  no  longer  formed.  Cases  sometimes 
occur  in  which  the  secretion  continues  to  be  formed  by  the  natural 
organ,  but  not  being  able  to  escape  toward  the  exterior,  on  account  of 
some  obstruction,  is  re-absorbed  into  the  blood,  and  afterward  discharged 
from  it  by  exudation  in  other  ways;  but  these  are  not  instances  of  true 
vicarious  secretions,  and  must  not  be  so  regarded. 

The  circumstances  of  their  fornuxtion,  and  their  final  destination,  are, 
however,  the  only  particulars  in  which  secretions  and  excretions  can  be 
distinguished;  for,  in  general,  the  structure  of  the  i)arts  engaged  in 
eliminating  excretions  is  as  complex  as  that  of  the  parts  concerned  in  the 
formation  of  secretions.  And  since  the  differences  of  the  two  processes 
of  separation,  corresponding  with  those  in  the  several  purposes  and  des- 
tinations of  the  fluids,  are  not  yet  ascertained,  it  will  be  sufficient  to 
speak  in  general  terms  of  the  process. 

\ 


■wH»S  HANDBOOK    OF    PHYSIOLOGY. 

Every  secreting  apparatus  possesses,  as  essential  parts  of  its  structure, 
a  simple  and  almost  textureless  membrane,  named  the  jjrimary  or  hase- 
ment-meinhrane;  certain  cells;  and  blood-vessels.  These  three  structural 
elements  are  arranged  together  in  various  ways;  but  all  the  varieties  may 
be  classed  under  one  or  other  of  two  principal  divisions,  namely,  mem- 
Iranes  and  glands. 


Organs  and  Tissues  of  Secretion. 

The  principal  secreting  organs  are  the  following : —  (1)  the  serous  and 
synovial  membranes;  (2)  the  mucous  membranes  with  their  special 
glands,  e.g.,  the  buccal,  gastric,  and  intestinal  glands;  (3)  the  salivary 
glands  and  pancreas;  (4)  the  mammary  glands;  (5)  the  liver;  (6)  the 
lachrymal  gland;   (7)  the  kidney  and  skin;  and  (8)  the  testes. 

The  structure  and  functions  of  the  glands  secreting  materials  used  in 
digestion  will  be  considered  when  we  study  the  alimentary  tract.  The 
functions  of  the  kidney  and  skin  will  be  described  in  a  future  chapter. 

The  lachrymal  gland  will  be  considered  with  the  rest  of  the  optic 
apparatus  and  the  testes  in  the  Chapter  on  Generation.  There  remain, 
then,  the  serous  and  mucous  membranes  and  the  mammary  gland  to  be 
here  described. 

(1.)  Serous  and  Synovial  Membranes. — Serous  membranes  are  of 
two  principal  kinds:  1st.  Those  which  line  visceral  cavities, — the  arach- 
noid, pericardium,  pleurce,  peritoneum,  and  tunicce  vaginales.  2d.  The 
synovial  membranes  lining  the  joints,  and  the  sheaths  of  tendons 
and  ligaments,  with  which,  also,  are  usually  included  the  syiiovial  hursce, 
or  hursce  mucosce,  whether  these  be  subcutaneous,  or  situated  beneath 
tendons  and  glide  over  bones. 

The  serous  membranes  form  closed  sacs,  and  exist  wherever  the  free 
surfaces  of  viscera  come  into  contact  with  each  other  or  lie  in  cavities 
unattached  to  surrounding  parts.  The  viscera  invested  by  a  serous 
membrane  are,  as  it  were,  pressed  into  the  shut  sac  which  it  forms, 
carrying  before  them  a  portion  of  the  membrane,  which  serves  as  their 
investment.  To  the  law  that  serous  membranes  form  shut  sacs,  there 
is,  in  the  human  subject,  one  exception,  viz. :  the  opening  of  the  Fal- 
lopian tubes  into  the  abdominal  cavity, — an  arrangement  which  exists 
in  man  and  all  Vertebrata,  with  the  exception  of  a  few  fishes. 

The  serous  membranes  are  esjDecially  distinguished  by  the  characters 
of  the  endothelium  covering  their  free  surface :  it  always  consists  of  a 
single  layer  of  polygonal  cells.  The  ground  substance  of  most  serous 
membranes  consists  of  connective-tissue  corpuscles  of  various  forms 
lying  in  the  branching  spaces  which  constitute  the  lymph  canalicular 
system,  and  interwoven  with    bundles  of  white  fibrous  tissue,  and   nu- 


SECKETIOK. 


2r»9 


merous  delicate  elastic  fibrilla?,  together  'with  blood-vessels,  nerves,  and 
lymphatics.  In  relation  to  the  process  of  secretion,  the  layer  of  connec- 
tive tissue  serves  as  a  groundwork  for  the  ramification  of  blood-vessels, 
nerves,  and  lymphatics.  But  in  its  nsual  form  it  is  absent  in  some  in- 
stances, as  in  the  arachnoid  covering  the  dura  mater,  and  in  the  interior 
of  the  ventricles  of  the  brain.     The  primary  membrane  and  epithelium 


'^s^ 


Fig.  319.— Section  of  sj'novial  membrane,  a.  Endothelial  covering  of  the  elevations  of  the 
membrane;  6,  subserous  tissue  containing  fat  and  blood-ves.sels ;  o,  ligament  covered  by  the  sy- 
novial membrane.     (Cadiat.) 

are  always  present,  and  are  concerned  in  the  formation  of  the  flnid  by 
which  the  free  surface  of  the  membrane  is  moistened. 

Functions. — The  principal  purjDose  of  the  serous  and  synovial  mem- 
branes is  to  furnish  a  smooth,  moist  surface,  to  facilitate  the  movements 
of  the  invested  organ,  and  to  prevent  the  injurious  etfects  of  friction. 
This  purpose  is  especially  manifested  in  joints,  in  which  free  and  exten- 
sive movements  take  place;  and  in  the  stomach  and  intestines,  -which, 
from  the  varying  quantity  and  movements  of  their  contents,  are  in  al- 
most constant  motion  upon  one  another  and  the  walls  of  the  abdomen. 

Fluid. — The  fluid  secreted  from  the  free  surface  of  the  serous  mem- 
branes is,  in  health,  rarely  more  than  sufficient  to  ensure  the  mainte- 
nance of  their  moisture.  The  opposed  surfaces  of  each  serous  sac  are  at 
every  point  in  contact  with  each  other.  After  death,  a  larger  quantity  of 
fluid  is  usually  found  in  each  serous  sac ;  but  this,  if  not  the  product  of 
manifest  disease,  is  probably  such  as  has  transuded  after  death,  or  in 
the  last  hours  of  life.  An  excess  of  such  fluid  in  any  serous  sac  consti- 
tutes dropsy  of  the  sac. 


300  HANDBOOK    OF    PHYSIOLOGY. 

The  fliiid  naturally  secreted  by  the  serous  membranes  appears  to  be 
identical,  in  general  and  chemical  characters,  with  very  dilute  liquor 
sanguinis.  It  is  of  a  pale-yellow  or  straw-color,  slightly  viscid,  alkaline, 
and  on  account  of  the  presence  of  albumen,  coagulable  by  heat.  This 
similarity  of  the  serous  fluid  to  the  liquid  part  of  blood,  and  to  the  fluid 
"with  "which  most  animal  tissues  are  moistened,  formerly  led  to  the  belief 
that  it  "was  a  simple  transudation;  but  Heidenhain  has  concluded  from 
experiments  that  the  process  of  separation  is  one  of  secretion,  dependent 
upon  the  vital  activity  of  the  endothelial  cells.  There  is  reason  for  sup- 
jDOsing  that  the  fluids  of  the  cerebral  ventricles  and  of  the  arachnoid  sac 
are  likewise  secretions;  for  they  differ  from  the  Huids  of  the  other  serous 
sacs  not  only  in  being  pellucid,  colorless,  and  of  much  less  specific  grav- 
ity, but  in  that  they  seldom  receive  the  tinge  of  bile  when  present  in  the 
blood,  and  are  not  colored  by  madder,  or  other  similar  substances  intro- 
duced abundantly  into  the  blood. 

It  is  also  probable  that  the  formation  of  synovial  fluid  is  a  process 
of  genuine  and  elaborate  secretion,  by  means  of  tiie  epithelial  cells  on 
the  surface  of  the  membrane,  and  especially  of  those  which  are  accumu- 
lated on  the  edge  and  processes  of  the  synovial  fringes;  for,  in  its  pecu- 
liar density,  viscidity,  and  abundance  of  albumen,  synovia  differs  alike 
from  the  serum  of  blood  and  from  the  fluid  of  any  of  the  serous  cavities. 

(2.)  Mucous  Membranes. — The  mucons  memhrnies  line  all  those 
passages  by  which  internal  imi-ts,  communicate  with  the  exterior,  and 
by  which  either  matters  are  eliminated  from  the  body  or  foreign  sub- 
stances taken  into  it.  They  are  soft  and  velvety,  and  extremely  vascu- 
lar. The  external  surfaces  of  mucous  membranes  are  attached  to  various 
other  tissues ;  in  the  tongue,  for  example,  to  muscle ;  on  cartilaginous 
parts,  to  perichondrium;  in  the  cells  of  the  ethmoid  bone,  in  the 
frontal  and  sjDhenoidal  sinuses,  as  well  as  in  the  tympanum,  to  perios- 
teum ;  in  the  intestinal  canal,  it  is  connected  with  a  firm  submucous 
membrane,  w^hich  on  its  exterior  gives  attachment  to  the  fibres  of  the 
muscular  coat.  The  mucous  membranes  line  certain  principal  tracts — 
Gastro-pulinonary  and  Genito-iirinarij;  the  former  being  subdivided  into 
the  Digestive  and  Respiratory  tracts. 

1.  The  Digestive  tract  commences  in  the  cavity  of  the  mouth,  from 
which  prolongations  pass  into  the  ducts  of  the  salivary  glands.  From 
the  mouth  it  passes  through  the  fauces,  pharynx,  and  oesophagus,  to  the 
stomach,  and  is  thence  continued  along  the  whole  tract  of  the  intestinal 
canal  to  the  termination  of  the  rectum,  being  in  its  course  arranged  in 
the  various  folds  and  depressions  already  described,  and  prolonged  into 
the  ducts  of  the  intestinal  glands,  the  pancreas  and  liver,  and  into  the 
gall-bladder. 


SECRETIOif.  301 

2.  The  Eespiratory  tract  includes  the  mucous  membrane  lining  the 
cavity  of  the  nose,  and  the  various  sinuses  communicating  with  it,  the 
lachrymal  canal  and  sac,  the  conjunctiva  of  the  eye  and  eyelids,  and  the 
prolongation  which  passes  along  the  Eustachian  tubes  and  lines  the  tym- 
panum and  the  inner  surface  of  the  membrana  tympani.  Crossing  the 
pharynx,  and  lining  that  jmrt  of  it  which  is  above  the  soft  palate,  the 
respiratory  tract  leads  into  the  glottis,  whence  it  is  continued,  through 
the  larynx  and  trachea,  to  the  bronchi  and  their  divisions,  which  it 
lines  as  far  as  the  branches  of  about  -^  of  an  inch  (4-  mm.)  in  diameter, 
and  continuous  with  it  is  a  layer  of  delicate  epithelial  membrane  which 
extends  into  the  pulmotiary  cells. 

3.  The  Genito-urinary  tract,  which  lines  the  whole  of  the  urinary  pas- 
sages, from  their  external  orifice  to  the  termination  of  the  tubuli  uriniferi 
of  the  kidneys,  extends  also  into  the  organs  of  generation  in  both  sexes, 
and  into  the  ducts  of  the  glands  connected  with  them :  and  in  the  female 
becomes  continuous  with  the  serous  membrane  of  the  abdomen  at  the 
fimbriae  of  the  Fallopian  tubes. 

Structure. — These  mucous  tracts,  and  different  portions  of  each  of 
them,  present  certain  structural  peculiarities,  adapted  to  the  functions 
which  each  part  has  to  discharge ;  yet  in  some  essential  characters  the 
mucous  membrane  is  the  same,  from  whatever  part  it  is  obtained.  In 
all  the  principal  and  larger  parts  of  the  several  tracts,  it  presents,  as 
just  remarked,  an  external  layer  of  epithelium,  situated  upon  a  hascment 
membrane,  and  beneath  this,  a  stratum  of  vascular  tissue  of  variable 
thickness,  containing  lympluitic  vessels  and  nerves.  The  vascular 
stratum,  together  with  the  basement  membrane  and  ejnthelium,  in  differ- 
ent cases,  is  elevated  into  minute  papilhe  and  villi,  or  depressed  into 
involutions  in  the  form  of  glands.  But  in  the  prolongations  of  the 
tracts,  where  they  pass  into  gland-ducts,  these  constituents  are  reduced 
in  the  finest  branches  of  the  ducts  to  the  epithelium,  the  primary  or  base- 
ment-membrane, and  the  capillary  blood-vessels  spread  over  tlie  outer 
surface  of  the  latter  in  a  single  layer. 

The  primary  or  basement  membrane  is  a  thin  transparent  layer,  sim- 
ple, homogeneous,  or  composed  of  endothelial  cells.  In  the  minuter 
divisions  of  the  mucous  membranes,  and  in  the  ducts  of  glands,  it  is  the 
layer  continuous  and  correspondent  with  this  basement-membrane  that 
forms  the  proper  walls  of  the  tubes.  The  cells  also,  which,  lining  the 
larger  and  coarser  mucous  membranes,  constitute  their  epithelium,  are 
continuous  with  and  often  similar  to  those  which,  lining  the  gland-ducts, 
are  called  f/lnnd-cells.  No  certain  distinction  can  be  drawn  between  the 
epithelium-cells  of  mucous  membranes  and  gland-cells. 

Mucons  Fluid:  Mucus. — From  all  mucous  membranes  there  issecreted 
either  from  the  surface  or  from  certain  special  glands,  or  from  both,  a 


302  HANDBOOK    OF    PHYSIOLOGY. 

more  or  less  viscid,  grayish,  or  semi-transparent  fluid,  of  alkaline  reac- 
tion and  high  specific  gravity,  named  nmcus.  It  mixes  imperfectly 
with  water,  but,  rapidly  absorbing  liquid,  it  swells  considerably  when 
water  is  added.  Under  the  microscope  it  is  found  to  contain  epithelium 
and  leucocytes.  It  is  found  to  be  made  up,  chemically,  of  mucin, 
which  forms  its  chief  bulk,  of  a  little  albumen,  of  salts  chiefly  chlorides 
and  phosphates,  and  water  with  traces  of  fats  and  extractives. 

Secreting  Glands. 

The  secreting  glands  present,  amid  manifold  diversities  of  form  and 
composition,  a  general  plan  of  structure;  all  contain,  and  appear  con- 
structed with  particular  regard  to  the  arrangement  of  the  cells,  which,  as 
already  expressed,  both  line  their  tubes  or  cavities  as  an  epithelium,  and 
elaborate,  as  secreting  cells,  the  substances  to  be  discharged  from  them. 

Tyj^es  of  Secreting  Glands.— Secreting  gla,nds  may  be  classified  accord- 
ing to  certain  types,  which  are  the  following: — 1.  The  sin)ple  tvMdar 
gland  (a,  fig.  320),  examples  of  Avhich  are  furnished  by  the  follicles  of 
Lieberkiihn,  and  the  tubular  glands  of  the  stomach.  They  are  simple 
tubular  depressions  of  the  mucous  membrane,  the  wall  of  which  is  formed 
of  primary  membrane  and  is  lined  with  secreting  cells  arranged  as  an 
epithelium.  To  the  same  class  may  be  referred  the  elongated  and  tor- 
tuous sudoriferous  glands. 

2.  The  compound  tubular  glands  (d,  fig.  220)  form  another  division. 
These  consist  of  main  gland-tubes,  wbich  divide  and  subdivide.  Each 
gland  may  be  made  up  of  the  subdivisions  of  one  or  more  main  tubes. 
The  ultimate  subdivisions  of  the  tubes  are  generally  highly  convoluted. 
They  are  formed  of  a  basement-membrane,  lined  by  epithelium  of 
various  forms.  The  larger  tubes  may  have  an  outside  coating  of  fibrous, 
areolar,  or  muscular  tissue.  The  Icidney,  testes,  salivary  glands,  pan- 
creas, Brunner^s  glands,  with  the  lachrymal  and  mammai-y  glands,  and 
some  mucous  glands  are  examples  of  this  type  but  present  more  or  less 
marked  variations  among  themselves. 

3.  The  aggregate  ox  racemose  glands,  in  which  a  number  of  vesicles  or 
acini  are  arranged  in  groups  or  globules  (c,  fig.  220).  The  meibomian 
follicles  are  examples  of  this  kind  of  gland.  There  seem  to  be  glands  of 
mixed  character,  combining  some  of  the  characters  of  the  tubular  with 
others  of  the  racemose  type;  these  are  called  tubulo-racemose  or  tubulo- 
acinous  glands.  These  glands  differ  from  each  other  only  in  secondary 
points  of  structure:  such  as,  chiefly,  the  arrangement  of  their  excretory 
ducts,  the  grouping  of  the  acini  and  lobules,  their  connection  by  areolar 
tissue,  and  supply  of  blood-vessels.  The  acini  commonly  appear  to  be 
formed  by  a  kind  of  fusion  of  the  walls  of  several  vesicles,  which  thus 


SECRETION. 


303 


combine  to  form  one  cavity  lined  or  filled  with  secreting  cells  which  also 
occupy  recesses  from  the  main  cavity.  The  smallest  branches  of  the 
gland-ducts  sometimes  open  into  the  centres  of  these  cavities;  some- 
times the  acini  are  clustered  round  the  extremities,  or  by  the  sides  of 
the  ducts:  but,  whatever  secondary  arrangement  there  may  be,  all  have 
the  same  essential  character  of  rounded  groups  of  vesicles  containing 


Fip;.  2a0.— Plans  of  extension  of  secretin^  membranp  by  invprsinn  or  nn-cssion  in  form  of  cav- 
ities. A,  Simple  s'ands,  viz.,  r/,  straight  tube;  /i,  sac:  /,  coiled  tube.  n.  I\Iultilociilar  crypts;  k\ 
of  tubular  form  :  /,  saccular,  c,  FUicemose,  or  saccular  compound  pland ;  ?",  entire  gland,  show- 
ing branched  duct  and  lobular  structure;  n,  a  lobule,  detached  with  o,  branch  of  duct  proceed- 
ing from  it.     D,  C'onipouud  tubular  gland  (Sharpey). 

gland-cells,  and  opening  by  a  common  central  cavity  into  minute  ducts, 
which  ducts  in  the  large  glands  converge  and  unite  to  form  larger  and 
larger  branches,  and  at  length  by  one  common  trunk  open  on  a  free 
surface  of  membrane. 

Among  these  varieties  of  structure,  all  the  secreting  glands  are  alike 
in  some  essential  points,  besides  those  wliicli   they  have  in  common  with 


304  HANDBOOK    OF    PHYSIOLOGY. 

all  truly  secreting  structures.  They  agree  in  presenting  a  large  extent 
of  secreting  surface  within  a  comparatively  small  space;  in  the  circum- 
stance that  while  one  end  of  the  gland-duct  opens  on  a  free  surface,  the 
opposite  end  is  always  closed,  having  no  direct  communication  with 
blood-vessels,  or  any  other  canal;  and  in  a  uniform  arrangement  of 
capillary  blood-vessels,  ramifying  and  forming  a  network  around  the 
walls  and  in  the  interstices  of  the  ducts  and  acini. 

Process  of  Secretion. — It  is  generally  conceded  that  the  process  of  se- 
cretion is  dependent  upon  the  vital  activity  of  the  secreting  cells.  It  is 
possible,  however,  in  the  case  of  the  water  and  salts,  that  the  physical 
processes  of  filtration  and  dialysis  may  play  a  part. 

The  chemical  processes  constitute  the  process  of  secretion,  properly  so 
called,  as  distinguished  from  mere  transudation  spoken  of  above.  In 
the  chemical  process  of  secretion  various  materials  which  do  not  exist  as 
such  in  the  blood  are  manufactured  by  the  agency  of  the  gland-cells  from 
the  blood,  or  to  speak  more  accurately,  from  the  plasma  which  exudes 
from  the  blood-vessels  into  the  interstices  of  the  gland-textures. 

The  best  evidence  in  favor  of  this  view  is  :  1st.  That  cells  and  nuclei 
are  constituents  of  all  glands,  however  diverse  their  outer  forms  and  other 
characters,  and  tliat  they  are  in  all  glands  placed  on  the  surface  or  in 
the  cavity  whence  the  secretion  is  poured.  2cl.  That  certain  materials 
of  secretions  are  visible  with  the  microscope  in  the  gland  cells  before 
they  are  discharged.  Thus,  granules  probably  representing  the  fer- 
ments of  the  pancreas  may  be  discerned  in  the  cells  of  that  gland; 
spermatozoids  in  the  cells  of  the  tubules  of  the  testicles;  granules  of 
uric  acid  in  those  of  the  kidneys  (of  fish);  fatty  particles,  like  those  of 
milk,  in  the  cells  of  the  mammary  gland. 

Secreting  cells,  like  the  cells  of  other  organs,  appear  to  develop,  grow, 
and  attain  their  individual  perfection  by  apin-opriating  nutriment  from 
the  fluid  exuded  by  adjacent  blood-vessels  and  building  it  up,  so  that 
it  shall  form  part  of  their  own  substance.  In  this  perfected  state  the 
cells  subsist  for  some  brief  time,  and  when  that  period  is  over  they 
appear  to  dissolve,  wholly  or  in  part,  and  yield  their  contents  to  the 
peculiar  material  of  the  secretion.  And  this  appears  to  be  the  case  in 
every  part  of  the  gland  that  contains  the  apj^ropriate gland-cells;  there- 
fore not  in  the  extremities  of  the  ducts  or  in  the  acini  alone,  but  in  great 
part  of  their  length. 

"We  will  describe  elsewhere  the  changes  which  have  been  noticed  from 
actual  experiment  in  the  cells  of  the  salivary  glands,  pancreas,  and  peptic 
glands. 

Discharrjc  of  secretions  from  glands  may  either  take  place  as  soon  as 
they   are  formed;    or  the  secretion  may  be  long  retained  within  the 


SECRETION.  305 

gland  or  its  ducts.  The  former  is  the  case  with  the  sweat  glands.  But 
the  secretions  of  those  glands  whose  activity  of  function  is  only  occa- 
sional are  usually  retained  in  the  cells  in  an  undeveloped  form  during 
the  periods  of  the  gland's  inaction.  And  there  are  glands  which  are 
like  both  these  classes,  such  as  the  lachrymal,  which  constantly  secrete 
small  portions  of  fluid,  and  on  occasions  of  greater  excitement  discharge 
it  more  abundantly. 

When  discharged  into  the  ducts,  the  further  course  of  secretions  is 
affected  (1)  partly  by  the  pressure  from  behind;  the  fresh  quantities  of 
secretion  propelling  those  that  were  formed  before.  In  the  larger  ducts, 
its  propulsion  is  (2)  assisted  by  the  contraction  of  their  walls.  All  the 
larger  ducts,  such  as  the  ureter  and  common  bile-duct,  possess  in  their 
coats  plain  muscular  fibres;  they  contract  when  irritated,  and  sometimes 
manifest  peristaltic  movements.  Ehythmic  contractions  in  the  pancreatic 
and  bile-ducts  have  been  observed,  and  also  in  the  ureters  and  vasa 
deferentia.  It  is  probable  that  the  contractile  power  extends  along  the 
ducts  to  a  considerable  distance  within  the  substance  of  the  glands  whose 
secretions  can  be  rapidly  expelled.  Saliva  and  milk,  for  instance,  are 
sometimes  ejected  with  much  force. 

Circumstances  hifiuencing  Secretion. — The  principal  conditions  which 
influence  secretion  are  (1)  variations  in  the  quantity  of  blood,  (2)  varia- 
tions in  the  quantity  of  the  peculiar  materials  for  any  secretion  that  the 
blood  may  contain,  and  (3)  variations  in  the  condition  of  the  nerves  of 
the  glands. 

(1.)  An  increase  in  the  quantity  of  Mood  traversing  a.  gland,  as  in 
nearly  all  the  instances  before  quoted,  coincides  generally  with  an  aug- 
mentation of  its  secretion.  Thus  the  mucous  membrane  of  the  stomach 
becomes  florid  when,  on  the  introduction  of  food,  its  glands  begin  to 
secrete ;  the  mammary  gland  becomes  much  more  vascular  during  lacta- 
tion ;  and  all  circumstances  which  give  rise  to  an  increase  in  the  quan- 
tity of  material  secreted  by  an  organ  produce,  coincidently,  an  increased 
supply  of  blood;  but  w,e  have  seen  that  a  discharge  of  saliva  may  occur 
under  extraordinary  circumstances,  without  increase  of  blood-supply, 
and  so  it  may  be  inferred  that  this  condition  of  increased  blood-supply 
is  not  absolutely  essential. 

(2.)  An  increase  in  tlie  amount  of  the  materials  which  the  glands  are 
designed  to  separate  or  elaborate,  contained  in  the  blood  supplied  to  them, 
increases  the  amount  of  any  secretion.  Thus,  when  an  excess  of  nitro- 
genous waste  is  in  the  blood,  from  destruction  of  one  kidney  or  whatever 
cause,  a  healthy  kidney  will  excrete  more  urea  than  it  did  before. 

(3.)  Influence  of  the  Nervous  System  on  Secretion. — The  process  of 
secretion  is  largely  influenced  by  the  condition  of  the  Dervoua  system. 

20 


306  HANDBOOK    OF    PHYSIOLOGY. 

The  exact  mode  in  which  the  influence  is  exhibited  must  still  be  re- 
garded as  somewhat  obscure.  In  part,  it  exerts  its  influence  by  increasing 
or  diminishing  the  quantity  of  blood  supplied  to  the  secreting  gland, 
in  virtue  of  the  power  which  it  exercises  over  the  contractility  of  the 
smaller  blood-vessels;  while  it  also  has  a  more  direct  influence,  as  is 
described  at  length  in  the  case  of  the  submaxillary  gland,  upon  the 
secreting  cells  themselves;  this  may  be  called  trophic  influence.  Its 
influence  over  secretion,  as  well  as  over  other  functions  of  the  body, 
may  be  excited  by  causes  acting  directly  upon  the  nervous  centres,  upon 
the  nerves  going  to  the  secreting  organ,  or  upon  the  nerves  of  other 
parts.  In  the  latter  case,  a  reflex  action  is  produced :  thus  the  impres- 
sion produced  upon  the  nervous  centres  by  the  contact  of  food  in  the 
mouth  is  reflected  upon  the  nerves  supplying  the  salivary  glands,  and 
produces,  through  these,  a  more  abundant  secretion  of  the  saliva. 

Through  the  nerves,  various  conditions  of  the  brain  also  influence  the 
secretions.  Thus,  the  thought  of  food  may  be  sufficient  to  excite  an 
abundant  flow  of  saliva.  And,  probably,  it  is  the  mental  state  which 
excites  the  abundant  secretion  of  urine  in  hysterical  paroxysms,  as  well 
as  the  perspirations,  and  occasionally  diarrhoea,  which  ensue  under  the 
influence  of  terror,  and  the  tears  excited  by  sorrow  or  excess  of  joy. 
The  quality  of  a  secretion  may  also  be  affected  by  mental  conditions,  as 
in  the  cases  in  which,  through  grief  or  passion,  the  secretion  of  milk  is 
altered,  and  is  sometimes  so  changed  as  to  produce  irritation  in  the 
alimentary  canal  of  the  child,  or  even  death. 

Relations  letiDeen  the  Secretions. — The  secretions  of  some  of  the  glands 
seem  to  bear  a  certain  relation  or  antagonism  to  each  other,  by  which 
an  increased  activity  of  one  is  usually  followed  by  diminished  activity  of 
one  or  more  of  the  others;  and  a  deranged  condition  of  one  is  apt  to 
entail  a  disordered  state  in  the  others.  Such  relations  appear  to  exist 
among  the  various  mucous  membranes;  and  the  close  relation  between 
the  secretion  of  the  kidney  and  that  of  the  skin  is  a  subject  of  constant 
observation. 

The  Mammary  Glands. 

Structure. — The  mammary  glands  are  composed  of  large  divisions  or 
lobes,  and  these  are  again  divisible  into  lobules — the  lobules  being  com- 
posed of  the  convoluted  and  dilated  subdivisions  of  the  main  ducts 
(alveoli)  held  together  by  connective  tissue.  The  lobes  and  lobules  too 
are  bound  together  by  areolar  tissue;  penetrating  between  the  lobes  and 
covering  the  general  surface  of  the  gland,  with  the  exception  of  the 
nipple,  is  a  considerable  quantity  of  yellow  fat,  itself  lobulated  by 
sheaths  and  processes  of  tough  areolar  tissue  (fig.  221)  connected  both 
with  the  skin  in  front  and  the  gland  behind ;  the  same  bond  of  connec- 


SECRETION.  .'jO? 

tion  extending  also  from  the  under  surface  of  the  gland  to  the  sheathing 
connective  tissue  of  the  great  pectoral  muscle  on  which  it  lies.  The 
main  ducts  of  the  gland,  fifteen  to  twenty  in  number,  called  the  lactif- 
erous or  galactop1i07'Ous  ducts,  are  formed  by  the  union  of  the  smaller 
(lobular)  ducts,  and  open  by  small  separate  orifices  through  the  nipple. 
At  the  points  of  junction  of  lobular  ducts  to  form  lactiferous  ducts,  and 
just  before  these  enter  the  base  of  the  nipple,  the  ducts  are  dilated  (fig. 


Fig.  S21.  —Dissection  of  the  lower  half  of  the  female  mamma,  during  the  period  of  lactation. 
%.— In  the  left-hand  side  of  the  dissected  part  the  glandular  lobes  are  exposed  and  partially  un- 
ravelled ;  and  on  the  right-hand  side,  the  glandular  substance  has  been  removed  to  show  the 
reticular  loculi  of  the  connective  tissue  in  which  the  glandular  lobules  are  placed:  1,  Upper  part 
of  the  mamilla  or  nipple;  2,  areola;  3,  subcutaneous  masses  of  fat;  4,  reticular  loculi  of  the 
connective  tissue  which  support  the  glandular  substance  and  contain  the  fatty  masses;  5,  one  of 
three  lactiferous  ducts  shown  passing  toward  the  mamilla  where  they  open;  6,  one  of  the  sinus 
lactei  or  reservoirs;  7,  some  of  the  glandular  lobules  which  have  been  unravelled;  7',  others 
massed  together  (Luschka). 

221);  and,  during  lactation,  the  period  of  active  secretion  by  the  gland, 
the  dilatations  form  reservoirs  for  the  milk,  which  collects  in  and  dis- 
tends them.  The  walls  of  the  gland -ducts  are  formed  of  areolar  with  some 
unstriped  muscular  tissue,  and  are  lined  internally  by  short  columnar 
and  near  the  nipple  by  squamous  epithelium.  The  alveoli  consist  of  a 
membrana  propria  of  flattened  endothelial  cells  lined  by  low  columnar 
epithelium,  and  are  filled  with  fat  globules. 

The  nipple,  which  contains  the  terminations  of  the  lactiferous  ducts, 
is  composed  also  of  areolar  tissue,  and  contains  unstriped  muscular  fibres. 
Blood-vessels  are  also  freely  supplied  to  it,  so  as  to  give  it  a  species  of 
erectile  structure.     On  its  surface  are  very  sensitive  papillae;  and  around 


308  HANDBOOK    OF    PHYSIOLOGY. 

it  is  a  small  area  or  areola  of  pink  or  dark-tinted  skin,  on  which  are  to 
be  seen  small  projections  formed  by  minute  secreting  glands. 

Blood-vessels,  nerves,  and  lymphatics  are  plentifully  supplied  to  the 
mammary  glands ;  the  calibre  of  the  blood-vessels,  as  Avell  as  the  size  of 
the  glands,  var34ng  very  greatly  under  certain  conditions,  especially 
those  of  pregnancy  and  lactation. 

The  alveoli  of  the  glands  during  the  secreting  periods  are  found  to  be 
lined  with  very  short  columnar  cells,  with  nuclei  situated  toward  the 


Fig.  222.— Section  of  mammary  gland  of  bitch,  showing  acini,  lined  with  epithelial  cells  of  a 
polyhedral  or  short  columnar  form.     X  200.     (V.  D.  Hai'ris. ) 

centre.  The  edges  of  the  cells  toward  the  lumen  may  be  irregular  and 
jagged,  and  the  remainder  of  the  alveolus  is  filled  up  with  the  materials 
of  the  milk.  During  the  intervals  between  the  acts  of  discharge,  the 
cells  of  the  alveoli  elongate  toward  the  lumen,  their  nuclei  divide,  and 
in  the  part  of  the  cells  toward  the  lumen  a  collection  of  oil  globules  and 
probably  of  other  materials  takes  place. 

The  next  stage  is  that  the  cells  divide  and  the  part  of  each  toward  the 
lumen  containing  a  nucleus  and  the  materials  of  the  secretion  is,  as  it 
were,  broken  off  from  the  outer  part  and  goes  to  form  the  solid  part  of 
the  milk.  The  cells  also  secrete,  from  the  blood  supplied  to  them,  the 
water,  salts,  and  probably  sugar.  In  addition  to  the  actual  casting  off 
parts  of  the  cells  containing  fat  and  the  other  materials,  oil  globules 
appear  to  pass  out  from  the  cells  with  the  other  materials  into  the  lumen 
of  the  alveoli.  The  cast-off  parts  of  the  cells  disintegrate  or  break  down, 
undergoing  a  kind  of  solution  in  the  more  fluid  j^art  of  the  secretion. 

In  the  earlier  days  of  lactation,  epithelial  cells  partially  transformed 
are  discharged  in  the  secretion :  these  are  termed  colostrum  corpuscles, 
but  later  on  the  cells  are  completely  transformed  into  fat  before  the 
secretion  is  discharged. 

After  the  end  of  lactation,  the  mamma  gradually  returns  to  its  original 
size  {involution).  The  acini,  in  the  early  stages  of  involution,  are  lined 
with  cells  in  all  degrees  of  vacuolatinn.  As  involution  proceeds  the 
acini  diminish  considerably  in  size,  and  at  length,  instead  of  a  mosaic 


SECKETION.  300 

of  lining  epithelial  cells  (twenty  to  thirty  in  each  acinus),  we  have  five 
or  six  nuclei  (some  with  no  surrounding  protoplasm)  lying  in  an  irregu- 
lar heap  within  the  acinus.  During  the  later  stages  of  involution,  large 
yellow  granular  cells  are  to  be  seen.  As  the  acini  diminish  in  size,  the 
connective  tissue  and  fatty  matter  between  them  increase,  and  in  some 
animals,  when  the  gland  is  completely  inactive,  it  is  found  to  consist  of 
a  thin  film  of  glandular  tissue  overlying  a  thick  cushion  of  fat.  Many 
of  the  products  of  waste  are  carried  off  by  the  lymphatics. 

During  pregnancy  the  mammary  glands  undergo  changes  {evolution) 
which  are  readily  observable.  They  enlarge,  become  harder  and  more 
distinctly  lobulated :  the  veins  on  the  surface  become  more  prominent. 
The  areola  becomes  enlarged  and  dusky,  with  projecting  papillae;  the 
nipple  too  becomes  more  prominent,  and  milk  can  be  squeezed  from  the 
orifices  of  the  ducts.  This  is  a  very  gradual  process,  which  commences 
about  the  time  of  conception,  and  progresses  steadily  during  the  whole 
period  of  gestation.  In  the  gland  itself  solid  columns  of  cells  bud  off 
from  the  old  alveoli  to  form  new  alveoli.  But  these  solid  columns  after 
a  while  are  converted  into  tubes  by  the  central  cells  becoming  fatty  and 
being  discharged  as  the  colostrum  corpuscles  above  mentioned. 

Milk. 

The  mammary  secretion,  or  milk,  is  a  bluish- white,  opaque  fluid  with 
a  pleasant,  sweet  taste,  of  specific  gravity  of  1028-1034.     It  is  a  true 

/^^         °§       ^R      Q.1    '"^ 


h       V--.     ll-f^    Oy 


Fig.  22:i.— Globules  and  molecules  of  cow's  milk,     x  400. 

emulsion.  Under  the  microscope,  it  is  found  to  contain  a  number  of 
globules  of  various  sizes  (fig.  223),  the  majority  about  Y¥FU"Tr  o^  ^^  i^^h 
(.25//-)  in  diameter.  They  are  composed  of  oily  matter,  and  are  called 
milk-globules,  but  the  old  view  that  they  had  an  investing  membrane  of 
albuminous  material  is  now  generally  discarded.  Accompanying  these 
are  numerous  minute  particles,  both  oily  and  albuminous,  which  exhibit 
ordiuarv  molecular  nioveiiiL'iits.     The  milk  which  is  secreted  in  the  first 


310  HANDBOOK    OF    PHYSIOLOGY. 

few  dajs  after  parturition  is  called  the  colostrum.  This  contains  the 
granular  colostrum  corpuscles,  which  are  four  or  five  times  the  size  of 
milk  globules,  and  difEers  from  ordinary  milk  in  containing  a  larger 
quantity  of  solid  matter,  and  in  being  deep  yellow,  less  sweet,  but  far 
more  alkaline,  and  in  having  a  specific  gravity  of  1040-1046. 

CoiiPosiTiON  OF  Colostrum  (Pfeiffer). 

Proteids 5.71 

Fat 2.04 

Sugar 3.74 

Salts 0.38 

Water 88.23 


4.00 

4 

2 

10 

1.50 

4 

2.5 

10 

7 

43 

5 

3.5 

.20 

.7 

.5 

.5 

100.00 
Chemical  Composition  of  Milk. — In  addition  to  the  oil  existing  in 
numberless  little  globules  floating  in  a  large  quantity  of  water,  milk 
contains  certain  proteids,  milk-sugar  (lactose),  and  several  varieties  of 
salts.  Its  percentage  composition  has  been  already  mentioned,  but  may 
be  here  repeated.     Its  reaction  is  slightly  alkaline. 

Chemical  Composition  of  Milk.     (After  Foster,  Harrington,  et  al. ) 

Human.       Cow.        Mare.        Bitch. 

Water 87.30        87  90  76 

Solids 12.70        13  10  24 

Fats                  .         . 
Proteids        .... 
Sugar      .... 
Salts 

Constituents  of  Milk. 

(1.)  Water. — The  amount  of  water  varies  in  difl:erent  animals,  and 
in  the  same  animal  from  time  to  time.  This  is  seen  from  the  varying 
specific  gravity;  that  of  cow's  milk,  on  the  average,  varies  from  1028  to 
1034  in  unskimmed  milk,  and  from  1033  to  1037  in  skimmed  milk. 
The  amount  secreted  by  a  woman  is  from  10  to  16  oz.  at  the  end  of  the 
first  week  of  lactation,  and  increases  to  from  30  to  40  oz.  by  the  eighth 
or  ninth  month.  A  cow  under  favorable  circumstances  secretes  at  least 
ten  pints  a  day. 

(2.)  Proteids. — These  are  of  two  kinds  at  least,  viz.,  caseinogen  and 
lact-albumin.  Caseinogen  may  be  obtained  from  milk  either  by  the 
addition  of  an  acid,  e.g.,  acetic,  or  by  saturation  with  crystallized  mag- 
nesium sulphate  or  sodium  chloride  in  the  way  already  indicated  (p. 
119).  Caseinogen,  as  already  pointed  out,  belongs  to  the  class  of 
nucleo-albumins  (^^ee  p.  119). 

Coagulation  of  Milk. — The  clotting  of  caseinogen  is  seen  when  the 
gastric  ferment  rennin,  or  when  similar  ferments  from  the  pancreas  or 
intestinal  juice  are  added   to  milk;  it  \vill  take  place  when  the  milk  is 


SECRETION. 


311 


neutral  or  alkaline.  By  the  clotting,  caseinogen  is  converted  into  a 
coagulated  proteid,  casein^  and  a  proteid  residue  called  whey-proteid. 
Casein  carries  down  with  it  the  fat,  and  the  two  materials  form  cheese. 
As  in  the  case  of  blood,  coagulation  cannot  occur  except  in  the  presence 
of  calcium  salts.  AVhen  caseinogen  is  acted  on  by  renniu,  it  is  split  by 
hydrolytic  cleavage  into  two  parts,  paracasein  and  whey-proteid.  Para- 
casein combines  with  the  calcium  salts  to  form  the  insoluble  compound 
casein;  the  whey-proteid  remains  behind  in  solution  in  the  whey.  By 
reference  to  the  coagulation  of  the  blood,  the  similarity  of  the  two  proc- 
esses will  be  seen.  Caseinogen  is  also  precipitated  from  milk  in  the 
presence  of  an  excess  of  acid.  When  milk  curdles  after  "souring,"  it  is 
due  to  the  formation  of  lactic  acid  from  the  milk-sugar  by  micro- 
organisms. 

Lad-albumin  differs  in  some  of  its  reactions  from  serum-albumin  (p. 
115);  it  coagulates  when  milk  is  boiled,  but  this  scum  is  also  partly  due 
to  the  drying  up  of  the  caseinogen  on  the  surface  of  the  milk. 

Lactoglohulin^  another  proteid  of  milk,  is  similar  to  the  paraglobuliu 
of  the  blood. 

(3.)  Fats. — The  fats  of  milk  are  those  usually  found  in  animal  tis- 
sues, viz.,  oleiu,  stearin,  and  palmatin  (p.  132).  There  are  also  others, 
especially  that  of  butyric  acid  in  combination  with  glycerin.  Lecithin 
and  cholesterin  and  a  lipochrome  may  also  be  j^resent.  The  fat,  split 
up  into  minute  particles,  which  are  lighter  than  the  remainder  of  the 
constituents,  rises  to  the  surface  when  the  milk  stands,  forming  cream; 
and  cream,  when  its  fatty  molecules  have  run  together,  forms  butter. 

(4.)  Lactose. — This  sugar,  the  reactions  of  which  are  mentioned  at 
p.  12-4,  is  apt  to  undergo  lactic-acid  fermentation  if  the  milk  be  exposed 
to  the  air,  from  the  action  of  the  organized  ferment,  the  bacterium 
lactis.  When  this  occurs  milk  becomes  sour  and  the  caseinogen  is 
thrown  down. 

(5.)  Salts. — The  chief  salt  of  milk  is  calcium  phosphate.  Without 
its  presence  caseinogen  cannot  form  casein.  The  gases  are  carbon 
dioxide  and  nitrogen. 

Salts  ix  Woman's  jMilk  (Rotch). 

Calcium  phosphate 

Calcium  silicate 

Calcium  sulpliate   .... 

Calcium  carbonate 

.Mas'iu'sium  carbonate     . 

Potassium  carbonate  . 

Potassium  sulphate 

Potassium  chloride 

Sodium  chloride      .         .         .         , 

Iron  oxide  and  alumina 

100.00 


.       23.87 

1.37 

2.25 

2.85 

8.77 

23.47 

8.33 

12.05 

.       21.77 

0.37 

312  HANDBOOK    OF    PHYSIOLOGY. 

The  Ductless  Glands 
AND  Ikteknal  Secretions. 

The  discovery  of  the  remarkable  and  sometimes  fatal  effects  of  the 
removal  of  certain  of  the  ductless  glands  has  given  a  marked  impetus  to 
the  study  of  these  organs,  so  that  at  the  present  time  tliey  occupy  a  place 
of  importance  in  physiology  formerly  unthought  of.  The  converse  ef- 
fects of  removing  certain  of  these  glands  and  of  injections  of  extracts 
(aqneons  and  others)  of  them  into  healthy  animals  or  those  operated  upon, 
have  led  to  the  belief  that  they  elaborate  in  the  course  of  their  metabolic 
activity  some  substance  or  substances  which  are  of  use  to  the  body. 
Since  the  parenchyma  cells  of  these  glands  belong  morphologically  to 
the  secretory  type,  and  since  active  constituents  may  be  extracted  from 
the  glands,  it  is  assumed  that  they  produce  a  secretion.  But  this  secre- 
tion, -whatever  its  quantity  may  be,  passes  either  into  the  blood  stream 
directly  (supra-renal)  or  indirectly  by  way  of  the  lymphatics  (thyroid), 
instead  of  discharging  through  a  duct  upon  a  free  surface,  as  in  the 
case  of  the  salivary  glands  and  others.  Hence  the  term  internal  secretion 
has  come  into  popular  use  by  way  of  distinction. 

It  must  be  borne  in  mind,  however,  that  both  anabolic  and  katabolic 
products  are  formed  by  all  tissues  and  are  absorbed  to  a  greater  or  less 
extent  into  the  circulation.  But  the  term  internal  secretion  does  not 
apply  to  these.  It  is  confined  to  such  products  as  are  formed  by  organs 
of  a  distinctly  glandular  type. 

The  glands  whicli  are  known  certainly  to  form  internal  secretions  are 
the  thyroid,  the  supra-renal  capsules,  the  pancreas,  and  possibly  the  pitu- 
itary body.  And  Howell  has  called  attention  to  the  fact  that  to  be 
consistent  the  glycogen  formed  by  the  liver  from  dextrose  (and  proteid) 
should  be  regarded  as  an  internal  secretion.  Thus  the  liver  forms  both 
an  internal  and  external  secretion,  as  in  the  case  of  the  pancreas. 

The  spleen  has  been  included  in  this  chapter  for  convenience.  It 
has  not  been  proved  to  form  an  internal  secretion. 

The  Thyroid. — The  thyroid  gland  is  situated  in  the  neck.  It  con- 
sists of  two  lobes,  one  on  each  side  of  the  trachea,  extending  upward  to 
the  thyroid  cartilage,  covering  its  inferior  cornu  and  part  of  its  body; 
these  lobes  are  connected  across  the  middle  line  by  a  middle  lobe  or 
isthmus.  The  thyroid  is  covered  by  tlie  muscles  of  the  neck.  It  is 
highly  vascular,  and  varies  in  size  in  diUerent  individuals. 

Structures. — The  gland  is  encased  in  a  thin  transparent  layer  of  dense 
areolar  tissue,  free  from  fat,  containing  elastic  fibres.  This  capsule  sends 
in  strong  fibrous  trabeculse,  which  inclose  the  thyroid  vmt'/es — which  are 
rounded  or  oblong  irregular  sacs,  consisting  of  a  wall  of  thin  hyaline 


SECRETlOiS' . 


3ia 


membrane  lined  by  a  single  layer  of  short  cylindrical  or  cubical  cells. 
These  vesicles  are  filled  with  transparent  nucleo-albuminous  colloid 
material.  The  colloid  substance  increases  with  age,  and  the  cavities 
appear  to  coalesce.  In  the  interstitial  connective  tissue  is  a  round 
meshed  capillary  plexus,  and  a  large  number  of  lymphatics.  The  nerves 
adhere  closely  to  the  vessels. 


Fig.  234.— Part  of  a  section  of  the  human  thyroid,  a.  Fibrous  capsule ;  b,  thyroid  vesicles  filled 
with,  e,  colloid  substance;  c,  supporting  fibrous  tissue;  d,  short  columnar  cells  lining  vesicles; /, 
arteries;  g,  veins  filled  with  blood;  /i,  lymphatic  vessel  filled  with  colloid  substance.  X  (S.  K. 
.\lcock.) 

In  the  vesicles  there  are  in  addition  to  the  yellowish  glassy  colloid 
material,  epithelium  cells,  colorless  blood-corpuscles,  and  also  colored 
corpuscles  undergoing  disintegration. 

Accessor^/  Thyroids. — These  are  small  bodies  possessing  the  structure 
of  the  thyroid  and  apparently  performing  the  same  function.  They  are 
found  in  the  neck  and  in  the  mediastinum  as  far  as  the  heart.  The  ac- 
cessory thyroids  undergo  hypertrophy  when  the  thyroid  has  been  removed. 

Parathyroids. — In  addition  to  the  accessory  thyroids,  parathyroids 
are  found  in  the  neck,  lying  behind  or  to  the  side  of  the  thyroid,  or 
even  within  its  substance  (in  the  rat).  They  are  small  bodies,  differing 
from  the  thyroid  in  structure  in  that  they  consist  of  solid  columns  of 
cells,  not  of  acini;  yet  they  seem  capable  of  performing  the  function  of 


314  HAXDBOOK    OF    PHYSIOLOGY. 

the  thjroid  when  that  body  is  removed.  They  frequently  exist  in 
pairs,  but  there  may  be  more  than  two,  lying  along  the  carotid  in  the 
region  of  the  thyroid.  The  parathyroids  are  thought  fo  be  immature 
thyroids. 

Functions  of  the  Tliyroid. — The  colloid  material  which  is  formed 
within  the  thyroid  vesicles,  and  is  believed  to  be  their  secretion,  finally 
ruptures  through  their  walls  into  the  lymph  channels  and  thus  gains  en- 
trance to  the  circulation.  The  secretion  of  the  thyroid  falls  into  the 
class  known  as  internal  secretions,  and  exerts  a  profound  influence  upon 
the  metabolic  processes  of  the  body,  probably  through  the  agency  of  the 
central  nervous  system.  Complete  extirpation  of  the  thyroid,  at  least  in 
some  animals,  produces  death,  preceded  by  a  group  of  characteristic 
symptoms.  In  man  and  the  monkey,  the  symptoms  after  removal  come 
on  slowly  and  resemble  the  disease  known  in  man  as  myxcedema. 

This  disease  is  known  definitely  to  be  due  to  disease  of  the  thyroid, 
whereby  its  function  is  interfered  with.  Moreover,  if  a  piece  of  thyroid 
of  sufficient  size  be  grafted  into  an  animal  from  which  the  glands  have 
been  removed,  and  the  graft  takes,  the  symptoms  of  thyroid  removal  are 
lessened  in  intensity  or  disappear  altogether.  And,  likewise,  thyroid 
feeding  or  the  administration  of  thyroid  extracts  relieves  the  symptoms 
of  the  disease  myxcedema. 

The  above  facts  show  that  the  thyroid  gland  must  perform  some  im- 
portant function  in  the  animal  economy,  and  it  is  believed  that  this  is 
accomplished  by  virtue  of  its  internal  secretion.  The  colloid  material 
of  the  gland  has  been  submitted  to  much  chemical  study,  and  a  substance 
called  ioclothyrin  has  been  isolated  as  its  active  principle.  Baumann  and 
EoGS  state  that  iodothyrin  exists  in  the  gland  in  combination  with  pro- 
teid  bodies.  Iodothyrin  relieves  the  symptoms  of  thyroid  removal  much 
to  the  same  extent  as  thyroid  feeding.  It  is  a  very  resistant  substance, 
and  is  not  injured  by  the  action  of  the  gastric  juice  or  by  boiling  with 
10  per  cent  sulphuric  acid  for  a  long  time. 

The  Supra-renal  Capsules  or  Adrenals. — These  are  two  flat- 
tened, more  or  less  triangular  or  cocked-hat  shaped  bodies,  resting  by 
their  lower  border  upon  the  upper  border  of  the  kidneys. 

Structure. — The  gland  is  surrounded  by  an  outer  sheath  of  connective 
tissue,  which  sometimes  consists  of  two  layers,  sending  in  exceedingly 
fine  prolongations  forming  the  framework  of  the  gland.  The  gland 
tissue  proper  consists  of  an  outside  firmer  cortical  portion,  and  an  inside 
soft  dark  medullary  portion. 

The  finer  structure  of  the  supra-renal  capsules  is  incompletely  known. 

(1.)  The  cortical  ^Jortion  is  divided  into  (fig.  225)  an  external  narrow 
layer  of  small  rounded  or  oval  spaces,  the  zo7ia  glomerulosa,  made  by  the 
fibrous  trabeculae,  containing  polyhedral  cells  (b).  The  second  layer  of 
cells  is  arranged  in  columns  radiating  from  the  medulla,  the  zonafascic- 


SECRETION.  316 

ulata  (c),  and  separated  from  each  other  by  fibrous  septa.  The  tliird 
layer,  that  next  the  medulla,  is  called  from  its  arrangement  the  zona 
reticularis  (not  shown  in  fig.  225).  The  individual  cells  are  polyhedral 
in  shape,  each  possessing  a  well-defined  nucleus.  In  man  the  proto- 
plasm of  the  cells  is  especially  rich  in  fat  globules,  and  oftentimes  con- 
tains in  addition  larger  or  smaller  granules  of  a  yellowish  pigment.  The 
blood-vessels  are  confined  to  the  septa,  and  do  not  penetrate  into  the  cell 
grouj)s. 

(2.)  The  medullary  substance  consists  of  a  coarse  rounded  or  irregular 
meshwork  of  fibrous  tissue,  in  the  alveoli  of  which  are  masses  of  multi- 
nucleated protoplasm  (fig.  226);  numerous  blood-vessels;  and  an  abun- 
dance of  nervous  elements.  The  celk  are  very  irregular  in  shape  and 
size,  poor  in  fat,  aud  occasionally  branched;  the  nerves  run  through  the 
cortical  substance,  and  anastomose  over  the  medullary  portion. 

Nerves. — The  adrenals  are  very  abundantly  supjjlied  with  nerves, 
chiefly  composed  of  meduUated  fibres.  These  fibres  are  derived  from 
the  solar  and  renal  plexuses,  vagi  and  phrenics.  Nerve-cells  are  also 
numerous  in  connection  with  these  fibres.  The  fibres  enter  the  hilum  of 
the  gland,  but  the  method  of  their  termination  is  unknown. 


Fig.  825.— Vertical  section  through  part  ot  the  cortical  portion  of  supra-renal  of  guinea-pig. 
o.  Capsule ;  6,  zona  glomei-ulosa ;  c,  zona  f  asciculata ;  d,  connective  tissue  supporting  the  columns 
or  the  cells  of  the  latter,  and  also  indicating  the  positions  of  the  blood-vessels,    x    (S.  K.  Alcock.) 

Composition. — In  addition  to  the  ordinary  extractives,  benzoic  acid, 
hippuric  acid,  and  tauriu  have  been  found,  and  also  inosite,  as  well  as  a 
peculiar  pigmentary  substance,  soluble  in  water,  becoming  red   on  ex- 


316 


HANDBOOK    OF    PHYSIOLOGY. 


posure  to  light,  and  giving  with  ferric  chloride  a  green  or  blue  color. 
Haeniochromogen  has  been  found  by  McMunn.  Neurin,  apparently 
from  the  nervous  elements,  has  also  been  shown. 

Function. — Though  formerly  unknown,  a  vast  amount  of  light  has 
been  thrown  upon  the  function  of  the  supra-renal  capsules  within  the  last 
few  years  by  the  researches  of  Schafer  and  Oliver,  Zjboulski,  Abel,  and 
others.  Brown-Sequard,  it  is  true,  showed  by  experiment  as  early  as 
1856  that  removal  of  the  supra-renal  capsules  is  followed  by  the  death  of 
the  animal,  but  his  experiments  were  repeated  by  others  who  did  not 
obtain  the  same  results;  and  it  was  concluded  that  the  supra-renal  cap- 
sules had  no  function,  or  at  least  that  their  function  was  not  known. 
Death  was  preceded  in  the  case  of  Brown-Sequard 's  animals  by  symptoms 


Fig.  326.— Section  through  a  portion  of  the  medullary  part  of  the  supra-renal  of  guinea-pi^. 
The  vessels  are  very  numerous,  and  the  fibrous  stroma  more  distinct  than  in  the  cortex,  and  is 
moreover  reticulated.  The  cells  are  irregular  and  larger,  clean,  and  free  from  oil  globules.  X 
(S.  K.  Alcock.) 

somewhat  analogous  to  those  of  the  disease  of  man  known  as  Addison's 
disease.  The  failures  to  produce  symptoms  after  attempted  removal  of 
the  glands  have  probably  resulted  from  iucomjDlete  removal  or  the  pres- 
ence of  accessory  bodies.  Accessory  supra-renal  capsules  are  commonly 
present  in  some  animals  and  are  sometimes  found  in  man.  Further,  if 
one  gland  is  removed,  the  other  hypertrophies.  The  experiments  of  all 
recent  observers  confirm  the  original  experiments  of  Brown-Sequard. 
The  presence  of  the  supra-renal  capsules  is  essential  to  life.  Thus  the 
supra-renal  capsules  are  proved  to  have  a  very  important  function,  and 
they  perform  this  function  through  the  agency  of  an  internal  secretion. 

Schafer  and  Oliver  found  that  injections  of  supra-renal  extract  pro- 
duced marked  effects  upon  the  muscular  layer  of  the  arteries,  the  mus- 
cular tissue  of  the  heart,  and  the  skeletal  muscles.  The  muscular  layer 
of  the  arteries  is  markedly  contracted,  causing  a  rise  of  blood-pressure. 


SECRETION.  31 T 

When  the  heart  is  freed  from  nervous  control  its  contractions  are  in- 
creased both  in  force  and  frequency,  still  further  raising  blood-pressure. 
The  contraction  of  the  skeletal  muscles  in  response  to  a  single  stimulus 
is  much  prolonged. 

Very  small  doses  of  supra-renal  extract  are  sufficient  to  produce 
marked  effects.  Thus  Schafer  states  that  less  than  ■^sijo'u  gramme  (-g-^ 
grain)  of  the  desiccated  gland  is  sufficient  to  produce  an  effect  upon  tlie 
heart  and  arteries  of  an  adult  man. 

It  is  a  curious  fact  that  only  extracts  of  the  medullary  portion  of  the 
gland  are  active. 

Abel  has  succeeded  in  separating  the  blood-pressure-raising  constitu- 
ent of  the  extract,  and  calls  it  epinephrin.  By  nature  it  is  related  to 
the  alkaloid  group. 

Destruction  of  the  supra-renal  capsules  through  disease  in  man  re- 
sults in  the  production  of  a  group  of  symptoms  known  as  Addison's  dis- 
ease. The  administration  of  supra-renal  extract  to  these  cases  sometimes 
results  beneficially,  but  not  so  uniformly  as  thyroid  feeding  does  in  myx- 
cedema.  Yet  Langlois  states  that  if  one-sixth  of  the  supra-renal  capsule 
by  "Weight  be  left  in  the  dog,  the  animal  survives  the  operation  of  re- 
moval. 

On  the  whole,  the  assumption  that  the  supra-renal  capsules  produce 
an  internal  secretion  which  is  essential  to  life  is  warranted. 

The  Pituitary  Body. — This  body  is  a  small  reddish-gray  mass, 
occupying  the  sella  turcica  of  the  sphenoid  bone. 

Structure. — It  consists  of  two  lobes — a  small  posterior  one,  consist- 
ing of  nervous  tissue;  an  anterior  larger  one,  resembling  the  thyroid  in 
structure.  A  canal  lined  with  flattened  or  with  ciliated  epithelium 
passes  through  the  anterior  lobe;  it  is  connected  with  the  infundib- 
ulum.  The  gland  spaces  are  oval,  nearly  round  at  the  periphery, 
spherical  toward  the  centre  of  the  organ ;  they  are  filled  with  nucleated 
cells  of  various  sizes  and  shapes  not  unlike  ganglion  cells,  collected  to- 
gether into  rounded  masses,  filling  the  vesicles,  and  contained  in  a  semi- 
fluid granular  substance.  The  vesicles  are  inclosed  by  connective  tissue 
rich  in  capillaries. 

Function. — The  function  of  the  pituitary  body  has  not  yet  been  es- 
tablished. Some  observers  have  found  that  its  removal  causes  death, 
preceded  by  symptoms  resembling  those  of  thyroid  removal.  Hence  it 
has  been  supposed  that  the  pituitary  body  has  a  function  identical  with 
or  analogous  to  that  of  the  thyroid.  On  the  other  hand,  tumors  or 
other  disease  of  the  pituitary  body  have  been  found  after  death  in  asso- 
ciation with  a  disease  known  as  acromegaly,  in  which  the  bones  and  soft 
parts  undergo  great  hypertrophy.  In  tiiis  connection  it  must  be  remem- 
bered that  the  two  lubes  of  the  pituitary  body  are  morphologically  and 
embryologically  distinct. 


318  HANDBOOK    OF    PHYSIOLOGY. 

I 

Internal  Secretion  of  the  Pancreas. 

Minkowski  and  von  Mering  have  shown  that  total  extirpation  of  the 
pancreas  is  followed  in  all  cases  in  the  course  of  a  few  hours  by  the  ap- 
pearance of  sugar  in  the  urine.  The  amount  of  sugar  which  appears  is 
considerable — from  5-10  per  cent.  This  experimental  disease  (diabetes 
mellitus)  is  accompanied  by  an  increase  in  the  quantity  of  urine  and  by 
abnormal  thirst  and  appetite,  and  proves  fatal  in  15  days  or  less.  These 
results  are  obtained  only  when  the  entire  gland  or  more  than  nine-tenths 
of  it  have  been  removed.  If  one-tenth  of  the  gland  be  left  behind, 
sugar  appears  in  the  urine  when  carbohydrates  are  eaten,  but  not  other- 
wise. Nor  is  it  necessary  that  the  remaining  portion  of  tlae  gland  be  in 
its  normal  situation.  Successful  grafts  under  the  skin  of  the  abdomen 
or  elsewhere  will  prevent  the  appearance  of  sugar  in  the  urine  and  the 
other  symptoms.  If,  however,  the  graft  be  subsequently  removed,  the 
sugar  in  the  urine  and  the  other  symptoms  reappear,  and  the  experi- 
mental disease  proceeds  to  a  rajDidly  fatal  issue. 

The  symptoms  produced  by  total  extirpation  of  the  pancreas  do  not 
depend  upon  the  loss  of  the  pancreatic  juice  proper  to  the  organism. 
This  secretion  may  be  diverted  from  the  intestine  through  a  pancreatic 
fistula  without  the  production  of  diabetes.  Moreover,  Hedon  and  Thiro- 
loix  have  rendered  the  acini  of  the  gland  functionally  inactive,  and  ul- 
timately destroyed  them,  by  the  injection  of  paraffin  or  other  substances 
into  the  duct  of  Wirsung,  without  the  supervention  of  diabetes.  These 
experiments  have  led  to  the  conviction  that  the  little  groups  of  epithelial- 
like  cells  situated  in  the  connective-tissue  stroma  of  the  pancreas  secrete 
something  which  is  absorbed  into  the  circulation  and  constitutes  its 
internal  secretion.  Lepine  and  Boulud  have  recently  extracted  from  the 
urine  of  patients  suffering  from  diabetes  or  pneumonia  a  crystalline  sub- 
stance which  produces  glycosuria  when  injected  under  the  skin  or  into 
the  jugular  vein  of  animals.  This  substance  loses  its  power  if  passed  in 
the  blood  through  the  vessels  of  a  living  pancreas.  They  conclude, 
therefore,  that  the  pancreas,  possibly  through  its  internal  secretion,  has 
an  antitoxic  function  and  favors  glycolysis  in  the  tissues  by  destroying 
the  substance  which  inhibits  the  conversion  of  glucose  into  glycogen  or 
fat. 

Internal  Secretion  of  the  Liver. 

This  subject  will  be  considered  at  length  when  we  come  to  study  the 
formation  of  glycogen  (see  p.  435). 

The  Spleen  is  the  largest  of  these  so-called  vascular  glands;  it  is 
situated  to  the  left  of  the  stomach,  between  it  and  the  diaphragm.      It 


SECRETION. 


319 


is  of  a  deep  red  color,  of  a  variable  shape,  generally  oval,  somewhat 
concavo-convex.  Vessels  enter  and  leave  the  gland  at  the  inner  side  or 
hiliis. 

Structure. — The  spleen  is  covered  externally  almost  completely  by  a 
serous  coat  derived  from  the  peritoneum,  while  within  this  is  the  proper 
fibrous  coat  or  capsule  of  the  organ.  The  latter,  composed  of  connective 
tissue,  with  a  large  preponderance  of  elastic  fibres,  and  a  certain  propor- 
tion of  unstriated  muscular  tissue,  forms  the  immediate  investment  of 
the  spleen.  Prolonged  from  its  inner  surface  are  fibrous  processes  or 
traheculce,  containing  much  unstriated  muscle,  which  enter  the  interior 
of  the  organ,  and,  dividing  and  anastomosing  in  all  parts,  form  a  kind 
of  supporting  framework  or  stroma,  in  the  interstices  of  which  the 
proper  substance  of  the  spleen  {spleen-indp)  is  contained  (fig.  228).  At 
the  hilus  of  the  spleen,  the  blood-vessels,  nerves,  and  lymphatics  enter, 
and  the  fibrous  coat  is  prolonged  into  the  spleen-substance  in  the  form 

ir 


Fig.  227.— Section  of  injected  dog's  spleen;  e,  capsule;  <»-,  trabeoilse;  m,  two  ^lalpighiao 
bodies  with  numerous  small  arteries  and  capillaries  ;  u,  artery  ;  i,  lymphoid  tissue,  consisting  of 
closely-packed  lyuiplioid  cells  supported  by  very  delicate  retiform  tissue  ;  a  lightspace  unoccupied 
by  cf lis  is  seen  all  round  the  trabeculae,  whicn  corresponds  to  the  "lymph  path"  in  lymp"iatic 
glands.     (Schofield.) 


of  investing  sheaths  for  the  arteries  and  veins,  which  sheaths  again  are 
continuous  with  the  trabecule  before  referred  to. 


320  HANDBOOK    OF    PHYSIOLOGY. 

Mall  has  recently  described  the  spleen  as  consisting  of  lobules, 
formed  by  the  trabeculae  and  contained  masses  of  spleen-pulp. 

The  splee7t-pul2J,  which  is  of  a  dark  red  or  reddish-brown  color,  is 
composed  chiefly  of  cells,  imbedded  in  a  matrix  of  fibres  formed  of  the 
branching  of  large  flattened  nucleated  endothelioid  cells.  The  spaces  of 
the  network  only  partially  occupied  by  cells  form  a  freely  communicat- 
ing system.  Of  the  cells  some  are  granular  corpuscles  resembling  the 
lymph-corpuscles,  more  or  less  connected  with  the  cells  of  themeshwork, 
both   in    general   appearance   and   in  being  able  to   perform    amoeboid 


Fig.  SS8.  —Reticulum  of  the  spleen  of  a  cat,  shown  by  injection  with  gelatine.    (Cadiat. ) 

movements;  others  are  red  blood-corpuscles  of  normal  appearance  or 
variously  changed ;  while  there  are  also  large  cells  containing  either  a 
pigment  allied  to  the  coloring  matter  of  the  blood,  or  rounded  corpuscles 
like  red  corpuscles. 

The  splenic  artery,  after  entering  the  spleen  by  its  concave  surface, 
divides  and  subdivides,  with  but  little  anastomosis  between  its  branches; 
at  the  same  time  its  branches  are  sheathed  by  the  prolongations  of  the 
fibrous  coat,  which  they,  so  to  speak,  carry  into  the  spleen  with  them. 
The  arteries  then  pass  into  the  spleen-pulp,  their  fibrous  coat  being  re- 
placed by  lymphoid  tissue,  and  end  in  capillaries,  which  communi- 
cate with  the  lacunar  spaces  in  the  spleen-pulp,  from  which  veins  arise. 

The  walls  of  the  smaller  veins  are  more  or  less  incomplete,  and  read- 
ily allow  lymphoid  corpuscles  to  be  swept  into  the  blood-current.  The 
blood  from  the  arterial  capillaries  is  emptied  into  a  system  of  interme- 
diate passages,  which  are  directly  bounded  by  the  cells  and  fibres  of  the 
network  of  the  pulp,  and  from  which  the  smallest  venous  radicles  with 
uheir  cribriform  walls  take  origin.  The  veins  are  largo  and  distensible: 
"uhe  whole  tissue  of  the  spleen  is  highly  vascular  and  becomes  readily 
engorged  with  blood:  the  amount  of  distention  is,  however,  limited  by 
the  fibrous  and  muscular  tissue  of  its  capsuleand  trabeculae,  which  forms 
an  investment  and  support  for  the  pulpy  mass  within. 

On  the  face  of  a  section  of  the  spleen  can  be  usually  seen  readily  with 
the  naked  eye,  minute,  scattered  rounded  or  oval  whitish  spots,  mostly 
from  -^7  to  ^V  ^Dch  (|  to -f  j/^w.)  in  diameter.     These  are  the  Malpi- 


SECRETION. 


321 


ghian  corpuscles  of  the  spleen,  and  are  situated  on  the  sheaths  of  the 
minute  splenic  arteries,  of  which,  indeed,  they  may  be  said  to  be  out- 
growths (fig.  229).  For  while  the  sheaths  of  the  larger  arteries  are  con- 
structed of  ordinary  connective  tissue,  this  has  become  modified  where 
it  forms  an  investment  for  the  smaller  vessels,  so  as  to  be  composed  of 
adenoid  tissue,  with  abundance  of  corpuscles,  like  lymph-corpuscles, 
contained  in  its  meshes,  and  the  Malpighian  corpuscles  are  but  small 
outgrowths  of  this  cytogenous  or  cell-bearing  connective  tissue.  They 
are  composed  of  cylindrical  masses  of  corpuscles,  intersected  in  all  parts 
by  a  delicate  fibrillar  tissue,  which,  thougli  it  invests  the  Malpighian 
bodies,  does  not  form  a  complete  capsule.  Blood-capillaries  traverse  the 
Malpighian  corpuscles  and  form  a  plexus  in  their  interior.     The  struc- 


i^^si^*^. 


'  ■  ■  '•    -  ■••v'i^p<ci?'i**?Si.   •••  • 


.;•:«  ^- i;- -^^i:^v 


'i;-.-i'1v.-  ■fiiyiSiY':'- 


a 


---a 


-^b' 


—  c 


Fig.  229.— Section  of  spleen  of  cat.     a,  o',  Malpighian  corpuscles,  in  case  of  a',  in  connection 
.with  small  artery,  h;  b,  b',  small  arteries;  c,  section  of  trabeculse. 


ture  of  a  Malpighian  corj)uscle  of  the  spleen  is,  therefore,  very  similar  to 
that  of  lymphatic-gland  substance. 

Functions. — With  respect  to  the  office  of  the  spleen,  we  have  the  fol- 
lowing data:  (1.)  The  large  size  which  it  gradually  acquires  toward 
the  termination  of  the  digestive  process,  and  the  great  increase  observed 
about  this  period  in  the  amount  of  the  finely-granular  albuminous 
plasma  within  its  parenchyma,  and  the  subsequent  gradual  decrease  of 

21 


322  HANDBOOK    OF    PHYSIOLOGY. 

this  material,  seem  to  indicate  that  this  organ  is  concerned  in  storing  up 
some  of  the  changed  and  absorbed  proteid  food,  to  be  gradually  intro- 
duced into  the  blood  according  to  the  demands  of  the  general  system. 

(2.)  It  seems  probable  that  the  spleen,  like  the  lymphatic  glands,  is 
engaged  in  the  formation  of  Mood-corpuscles.  For  it  is  quite  certain 
that  the  blood  of  the  splenic  vein  contains  an  unusually  large  amount  of 
white  corpuscles;  and  in  the  disease  termed  leucocythajmia,  in  which 
the  pale  corpuscles  of  the  blood  are  remarkably  increased  in  number, 
there  is  almost  always  found  an  hypertrophied  state  of  the  spleen  or  of 
the  lymphatic  glands.  In  Kolliker's  opinion,  the  development  of  color- 
less and  also  colored  corpuscles  of  the  blood  is  one  of  the  essential  func- 
tions of  the  spleen,  into  the  veins  of  which  the  new-formed  corpuscles 
pass,  and  are  thus  conveyed  into  the  general  current  of  the  circulation. 

(3.)  The  formation  of  red  corpuscles.  The  spleen  is  concerned  in  the 
formation  of  red  corpuscles  during  foetal  life  and  shortly  after  birth,  and 
in  some  animals  during  their  whole  existence.  For,  if  the  spleen  be 
removed  from  such  animals,  the  red  marrow  undergoes  hypertrophy. 
Moreover,  in  these  animals  the  cells  previously  described  as  hsematoblasts 
may  be  found  in  the  spleen. 

It  was  formerly  believed  that  the  spleen  exercised  the  function  of  de- 
stroying red  corpuscles  that  had  lived  out  their  allotted  time.  The  evi- 
dence of  this,  however,  is  not  convincing,  and  the  theory  has  been 
practically  abandoned.  It  rested  chiefly  upon  the  fact  that  large  nu- 
cleated cells  were  found  in  the  spleen,  Avith  whole  or  partially  disinte- 
grated red  cells  in  their  interior.  But  the  phenomenon  is  probably  of 
post-mortem  occurrence.  When  the  circulation  ceases,  the  red  cells 
come  to  rest,  and,  lying  alongside  these  large  cells,  are  probably  then 
ingested. 

(4.)  From  the  almost  constant  presence  of  uric  acid,  in  larger  quan- 
tities than  in  other  organs,  as  well  as  of  the  nitrogenous  bodies,  xanthin, 
hypoxanthin,  and  leucin,  in  the  spleen,  some  special  nitrogenous  meta- 
bolism  may  be  fairly  inferred  to  occur  in  it.  One  of  the  features  of  the 
chemical  composition  of  the  spleen  is  the  presence  of  a  special  proteid, 
of  the  nature  of  alkali-albumin,  containing  iron.  The  salts  of  the 
spleen  consist  chiefly  of  sodium  phosphates. 

(5.)  Besides  these,  its  supposed  direct  offices,  the  spleen  is  believed  to 
fulfil  some  purpose  in  regard  to  the  portal  circulation,  with  which  it  is 
in  close  connection.  From  the  readiness  with  which  it  admits  of  being 
distended,  and  from  the  fact  that  it  is  generally  small  while  gastric 
digestion  is  going  on,  and  enlarges  when  that  act  is  concluded,  it  is  sup- 
posed, to  act  as  a  kind  of  vascular  reservoir,  or  diverticulum  to  the  portal 
system,  or  more  particularly  to  the  vessels  of  the  stomach.  That  it  may 
serve  such  a  purpose  is  also  made  probable  by  the  enlargement  which  it 


SECKETION. 


323 


undergoes  in  certain  affections  of  the  heart  and  liver,  attended  with  ob- 
struction to  the  passage  of  blood  through  the  latter  organ,  and  by  its 
diminution  when  the  congestion  of  the  portal  system  is  relieved  by 
discharges  from  the  bowels,  or  by  the  effusion  of  blood  into  the  stomach. 
This  mechanical  influence  on  the  circulation,  however,  can  hardly  be 
supposed  to  be  more  than  a  very  subordinate  function. 

The  spleen  may  be  removed  witliout  any  obvious  ill  effect. 

Influence  of  Qe  Nervous  SystSm  upon  the  Spleen. — '"When  the  sjDleen  is 
enlarged  after  digestion,  its  enlargement  is  probably  due  to  two  causes, 
(1)  a  relaxation  of  the  muscular  tissue  which  forms  so  large  a  part  of 


Fig.  230. 


Fig.   231. 


Fig.  230.— Transverse  section  of  a  lobule  of  an  injected  infantile  thymus  gland,  a,  Capsule 
of  connective-tissue  surrounding  the  lobule;  6,  membrane  of  the  glandular  vesicles;  c,  cavity  of 
the  lobule,  from  which  the  larger  blood-vessels  are  seen  to  extend  toward  and  ramify  in  the 
spheroidal  masses  of  the  lobule,     x  30.     (Kdlliker.) 

Fig.  231,— Tliymus  of  a  calf,  a.  Cortex  of  follicle;  b,  medulla;  c,  interfollicular  tissue, 
magnified  about  twelve  times.     (Watney.) 

its  framework ;  (2)  a  dilatation  of  the  vessels.  Both  these  phenomena 
are  doubtless  under  control  of  the  nervous  system.  It  has  been  found 
by  experiment  that  when  the  splenic  nerves  are  cut  the  spleen  enlarges, 
and  that  contraction  can  be  brought  about  (1)  by  stimulation  of  the 
spinal  cord  (or  of  the  divided  nerves);  (2)  refle.xly  by  stimulation  of  the 
central  stumps  of  certain  divided  nerves,  e.g.,  vagus  and  sciatic;  (3)  by 
local  stimulation  by  an  electric  current;  (4)  the  exhibition  ofquim'ne  and 
some  other  drugs.  It  has  been  shown  by  the  oncometer  of  Eoy  (fig.  307), 
that  the  spleen  undergoes  rhythmical  contractions  and  dilatations,  due 
no  doubt  to  the  contraction  and  relaxation  of  the  muscular  tissue  in  its 
capsule  and  trabeculae.  It  also  shows  the  rhythmical  alteration  of  the 
general  blood  pressure,  but  to  a  less  extent  than  the  kidney. 


32-1  HANDBOOK    OF    PHYSIOLOGY. 

The  Thymus. — This  gland  must  be  looked  upon  as  a  temporary 
organ,  as  it  attains  its  greatest  size  early  after  birth,  and  after  the 
second  year  gradually  diminishes,  until  in  adult  life  hardly  a  vestige 
remains.  At  its  greatest  development  it  is  a  long,  narrow  body,  situated 
in  the  front  of  the  chest  behind  the  sternum  and  partly  in  the  lower  part 
of  the  neck.     It  is  of  a  reddish  or  grayish  color,  distinctly  lobulated. 

Structure. — The  gland  is  surrounded  by  a  fibrous  capsule,  which  sends 
in  processes,  forming  trabecule,  which  divide  the  glands  into  lobes,  and 
carry  the  blood  and  lymph-vessels.  The  large  trabecule  branch  into 
small  ones,  which  divide  the  lobes  into  lobules.     The  lobules  are  further 


Fig.  S32.  Fig.  233. 

Fig.  232.— From  a  horizontal  section  through  superficial  part  of  the  thymus  of  a  calf ,  slightly 
raagnifled.  Showing  in  the  centre  a  follicle  of  polygonal  shape  with  similarly  shaped  follicles 
round  it.     (Klein  and  Noble  Smith.) 

Fig.  233.— The  reticulum  of  the  Thymus,  a,  Epithelial  elements;  b,  corpuscles  of  Hassall. 
(Cadiat. ) 

subdivided  into  follicles  by  fine  connective  tissue.  A  follicle  (fig.  232) 
is  seen  on  section  to  be  more  or  less  polyhedral  in  shape,  and  consists  of 
cortical  and  medullary  portions,  both  of  which  are  composed  of  adenoid 
tissue,  but  in  the  medullary  portion  the  matrix  is  coarser,  and  is  not  so 
filled  up  with  lymphoid  corpuscles  as  in  the  cortex.  The  adenoid  tissue 
of  the  cortex,  and  to  a  less  marked  extent  that  of  the  medulla,  consists 
of  the  two  elements,  one  with  small  meshes  formed  of  fine  fibres  with 
thickened  nodal  points,  and  the  other  enclosed  within  the  first,  com- 
posed of  branched  connective-tissue  corpuscles  (Watney).  Scattered  in 
the  adenoid  tissue  of  the  medulla  are  the  concentric  corpuscles  of  HasscdJ, 
which  are  protoplasmic  masses  of  various  sizes,  consisting  of  a  nucleated 
granular  centre,  surrounded  by  flattened  nucleated  epithelial  cells. 
In  the  reticulum,  especially  of  the  medulla,  are  large  transparent  giant 
cells.  In  the  thymus  of  the  dog  and  of  other  animals  are  to  be  found 
cysts,  probably  derived  from  the  concentric  corpuscles,  some  of  which 
are  lined  with  ciliated  ei)ithelium,  and  others  with  short  columnar  cells. 
The  arteries  radiate  from  the  centre  of  the  gland.  Lymph  sinuses  may 
be  seen  occasionally  surrounding  a  greater  or  smaller  portion  of  the 
periphery  of  the  follicles  (Klein).      The  nerves  are  vpry  minute. 


SECKETION.  325 

From  the  thymus  various  substances  may  be  extracted,  many  of  them 
similar  to  those  obtained  from  tlie  spleen,  e.g.^  xanthin,  hypoxanthiu, 
and  leucin,  as  well  as  certain  proteids,  especially  nucleo-proteid  (found 
in  all  protoplasm),  which  on  injection  into  the  veins  of  an  animal  pro- 
duces intra-vascular  clotting. 

Function. — Beard  has  recently  concluded  from  some  experiments  on 
the  smooth  skate  that  the  important  function  of  the  thymus  is  the  forma- 
tion of  tlie  colorless  corpuscles — that  the  thymus,  in  fact,  is  the  parent 
source  from  which  all  the  colorless  corpuscles  are  derived.  The  first  are 
developed  from  the  thymus  cells,  and  from  them  all  the  others  arise. 

Ecspecting  the  thymus  gland  in  the  hybernating  animals,  in  which  it 
exists  throughout  life,  as  each  successive  period  of  hybernation  approaches, 
the  thymus  greatly  enlarges  and  becomesladen  with  fat,  which  accumulates 
in  it  and  in  fat  glands  connected  with  it,  in  even  larger  proportions  than 
it  does  in  the  ordinary  seats  of  adipose  tissue.  Hence  it  appears  to 
serve  for  the  storing  ujd  of  materials  which,  being  re-absorbed  in  inactivity 
of  the  hybernating  period,  may  maintain  the  respiration  and  the  tem- 
perature of  the  body  in  the  reduced  state  to  which  they  fall  during  that 
time.  It  is  also  believed  to  be  a  source  of  the  red  blood-corpuscles,  at 
any  rate  in  early  life. 

The  Pineal  Gland. — This  gland,  which  is  a  small  reddish  body,  is 
placed  beneath  the  back  part  of  the  corpus  callosum,  and  rests  upon  the 
corpora  quadrigemina. 

Structure. — It  contains  a  central  cavity  lined  with  ciliated  epithelium. 
The  gland  substance  proper  is  divisible  into — (1.)  An  outer  cortical 
layer,  analogous  in  structure  to  the  anterior  lobe  of  the  pituitary  body; 
and  (2.)  An  inner  central  layer,  wholly  nervous.  The  cortical  layer 
consists  of  a  number  of  close  follicles,  containing  {a)  cells  of  variable 
shape,  rounded,  elongated,  or  stellate;  {h)  fusiform  cells.  There  is  also 
present  a  gritty  matter  (acerviihis  cerebri) ,  consisting  of  round  particles 
aggregated  into  small  masses.  The  central  substance  co^jsists  of  white 
and  gray  matter.  The  blood-vessels  are  small,  and  form  a  very  delicate 
capillary  plexus. 

The  pineal  gland  is  a  vestigial  structure,  being  the  atrophied  third 
eye  which  was  situated  in  the  median  line.  It  is  found  in  a  better  de- 
veloped condition  in  certain  lizards,  though  it  is  functionless. 

The  Coccyg-eal  and  Carotid  Glands. — These  so-called  glands  are 
situated,  the  one  in  front  of  the  tip  of  the  coccyx,  and  the  other  at  the 
point  of  bifurcation  of  the  common  carotid  artery  on  each  side.  They 
are  made  up  of  a  plexus  of  small  arteries,  are  inclosed  and  supported  by 
a  capsule  of  fibrous  tissue,  which  contains  connective-tissue  corpuscles. 
The  blood-vessels  are  surrounded  by  one  or  more  layers  of  cells  like 
secreting  cells,  which  are  said  to  he  modified  plasma  cells  of  the  connec- 
tive tissue.     The  function  of  these  bodies  is  unknown. 


OHAPTEE  IX. 

FOOD  AND  DIGESTION. 

The  object  of  digestion  is  to  bring  the  materials  of  the  food  into 
such  a  condition  that  they  may  be  taken  up  by  the  blood  and  lymphatic 
vessels,  and  so  rendered  available  for  the  wants  of  the  system.  It  makes 
the  foods  soluble  and  diffusible,  and  also  converts  bodies  already  soluble 
and  diffusible  into  forms  which  can  be  utilized,  e.g.,  cane  sugar,  al- 
though soluble  and  diffusible,  cannot  be  used  by  tbe  body  until  it  has 
been  split  into  two  molecules  of  monosaccharide.  Very  few  of  these 
materials  are  fit  for  this  purpose  when  taken  into  the  body,  and  the 
majority  would  therefore  be  to  all  intents  and  purposes  quite  useless 
unless  digested. 

It  is  unnecessary  to  mention  all  the  various  substances  which  may 
have  been  used  as  food  at  some  time  or  another,  and  we  shall  confine  our 
attention,  therefore,  to  the  chief  and  most  familiar  articles  of  diet. 

We  find,  then,  that  foods  may  be  divided  into  classes  corresponding 
closely  to  those  employed  to  describe  the  chief  substances  of  which  the 
animal  body  consists.  This  classification  may  be  recapitulated  as  fol- 
lows : — 

ORGANIC. 

I.  Foods  primarily  containing  Nitrogenous  substances,  consisting  of  Pro- 
teids,  e. (/., albumen,  casein,  mj^osin,  gluten,  legumin  and  their  allies; 
and  Albuminoids,  e.g.,  gelatin,  elastin,  and  chondrin. 
II.  Food  primarily  containing  Non-Nitrogenous  substances,  comprising : 
(1.)  Amyloid  or  saccharine   bodies,    chemically  known  as  carbo-hydrates; 

e.g.,  starches  and  sugars. 
(2.)   Oils  and  fats. — These  substances  contain  carbon,  hydrogen,  and  oxy- 
gen, but  the  oxygen  is  less  in  amount  than   in  the  amyloids  and 
saccharine  bodies. 

INORGANIC. 

I.  Foods  which  supply  Mineral  and  saline  matter. 
II.   Liquid  food  containing  chiefly  Water. 

Man  requires  that  the  chief  part  of  his  food  should  be  cooked.  Very 
few  organic  substances  can  be  properly  digested  without  previous  ex- 
posure to  heat  and  to  other  manipulations  which  constitute  the  process 
of  cooking. 

Organic  nitrogenous  foods. 

a. — The  Flesh  of  Animals,  e.g.,  of  the  ox  (beef,  veal),  sheep  (mutton, 
lamb),  pig  (pork,  bacon,  ham). 

Of  these,  beef  is  richest  in  nitrogenous  matters,  containing  about  20 
per  cent,  whereas  mutton  contains  about   18  per  cent,   veal  16.5,  and 

326 


FOOD   AKD    DIGESTION",  32? 

pork,  10;  beef  is  also  firmer,  more  satisfying,  and  is  supposed  to  be 
more  strengthening  than  mutton,  whereas  the  latter  is  more  digestible. 
The  flesh  of  young  animals,  such  as  lamb  and  veal,  is  less  digestible  and 
less  nutritious.  Pork  is  comparatively  indigestible,  and  contains  a 
large  amount  of  fat. 

Flesh  contains: — (1)  Nitrogenous  bodies;  chiefly  myosin,  and  one  or 
more  globulim;  serum-albumin,  gelatin  (from  the  interstitial  fibrous 
connective  tissue);  elastin  (from  the  elastic  tissue),  as  well  as  liwmo- 
glohin.  (2)  Fatty  matters,  including  lecithin  and  cholesterin.  (3)  Ex- 
tractive matters,  some  of  which  are  agreeable  to  the  j^alate,  e.g.  osmazome, 
and  others,  which  are  weakly  stimulating,  e.g.,  creatin.  Besides,  there 
are  sarcolactic  and  inositic  acids,  taurin,  xantliin,  and  others.  (4)  Salts, 
chiefly  of  potassium,  calcium,  and  magnesium.  (5)  Water,  the  amount 
of  which  varies  from  15  per  cent  in  dried  bacon  to  39  in  pork,  51  to  53 
in  fat  beef  and  mutton,  to  72  per  cent  in  lean  beef  and  mutton.  (6)  A 
certain  amount  of  carbo-hydrate  material  is  found  in  the  flesh  of  some 
animals,  in  the  form  of  inosite,  dextrin,  grape  sugar,  and  (in  young 
animals)  glycogen. 

Table  of  Percentage  Composition  of  Beef,  Mutton,    Pork,    and  Veal. — 

(Letheby.  ) 

Beef. — Lean     . 

Fat  . 
Mutton. — Lean 

Fat      . 
Veal         .... 
Pork.— Fat 

Together  with  the  flesh  of  the  above-mentioned  animals,  that  of  the 
deer,  hare,  rabbit.,  and  birds,  constituting  venison,  game,  and  poultry, 
should  be  added  as  taking  part  in  the  supply  of  nitrogenous  substances, 
and  also_^,s7/ — salmon,  eels,  etc.,  and  shell-fish,  e.g.,  lobster,  crab,  mussels, 
oysters,  shrimps,  scollops,  cockles,  etc. 

T.a.BLE  OF  Percentage  Composition  of  Polt^try  and  Fish.  —  (Letheby.) 

Water.         Proteid.  Fats.  Salts. 

Poultry 74  21  3.8  1.2 

(Singularly  devoid  of  fat,  and  is  therefore  generally  eaten  with  bacon 
or  pork.) 


Iter. 

Proteid. 

Fats. 

Salts. 

72 

19.3 

3.6 

5.1 

51 

14.8 

29.8 

4.4 

72 

18.3 

4  9 

4.8 

53 

12.4 

31.1 

3.5 

63 

16.5 

15.8 

4.7 

39 

9.8 

48.9 

2.3 

Water. 

Proteid. 

Fats. 

Salts. 

"White  Fish      . 

78 

18.1 

2.9 

1. 

Salmon        .         .         .        . 

77 

16.1 

5.5 

1.4 

Eels  (verj-  rich  in  fat)     . 

75 

9.9 

13.8 

1.3 

Oysters        .         .         .         . 

75.74 

11.72 

2.42 

2.73 

(7.39  consist  of  non-nitrogenous  matter  and  loss.)     (Payen.) 
Even  now  the  list  of  fleshy  foods  is  not  complete,  as  the  flesh  of 
nearly  all  animals  has  been  occasionally  eaten,  and   we  may  ])resume 


328  HANDBOOK    OF    PHYSIOLOGY. 

that  except  for  difference  of  flavor,  etc.,  the  average   composition    is 
nearly  the  same  in  every  case. 

h.  Milk* — Is  intended  as  the  entire  food  of  young  animals,  and  as 
such  contains,  when  pure,  all  the  elements  of  a  typical  diet.  (1)  Albu- 
minous substances  in  the  form  of  caseinogen,  and  serum  or  lact-albumin. 
(2)  Fats  in  the  cream.  (3)  Carbo-hydrates  in  the  form  of  lactose  or  milk 
sugar.  (4)  Salts,  chiefly  calcium  phosphate ;  and  (5)  Water.  From  it  we 
obtain  (a)  cheese,  which  is  the  clotted  caseinogen  or  casein  precipitated 
with  more  or  less  of  fat  according  as  the  cheese  is  made  of  skim  milk 
(skim  cheese),  of  fresh  milk  with  its  cream  (Cheddar  and  Cheshire),  or  of 
fresh  milk  plus  cream  (Stilton  and  double  Gloucester).  The  precipi- 
tated casein  is  allowed  to  ripen,  by  which  process  some  of  the  al- 
bumin is  further  split  up,  with  formation  of  fat.  (/?)  Cream,  consists  of 
the  fatty  globules  encased  in  caseinogen  and  serum-albumin,  and  which 
being  of  low  specific  gravity  float  to  the  surface,  {y)  Butter,  or  the 
fatty  matter  deprived  of  its  proteid  envelope  by  the  process  of  churning. 
{d)  Buttermilk,  or  the  fluid  obtained  from  cream  after  butter  has  been 
formed ;  very  rich  therefore  in  nitrogen,  (e)  Whey,  or  the  fluid  which 
remains  after  the  precipitation  of  casein;  it  contains  sugar,  salt,  and  a 
small  quantity  of  albumin. 

Table  of  Composition  of  Milk,  Butter- milk,  Cream,  and  Cheese. — (Letheby 


AND 

Pa  YEN.) 

Nitrogenous  matters, 

.  Fats. 

Lactose.        Salts. 

Water. 

Milk  {Cow) 

4.1 

3.9 

5.3             .8 

86 

Buttermilk 

^          , 

4.1 

.7 

6.4            .8 

88 

Cream 

3.7 

26.7 

3.8          1.8 

66 

Cheese.  — Skim 

. 

44.8 

6.3 

—            4.9 

44 

Cheese. — Cheddar    . 

• 

38.4 

31.1 

—            4.5 

Non-nitrogenous 
matter  and  loss. 

36 

Cheese.— Neufchatel  (Fresh).  8.  40.71        36.58  .51      36.58 

c.  Bggs. — The  yolk  and  albumen  of  eggs  are  in  the  same  relation  as 
food  for  the  embryos  of  oviparous  animals  that  milk  is  to  the  young  of 
mammalia,  and  afford  another  example  of  the  natural  admixture  of 
the  various  alimentary  principles.  The  proteids  of  eggs  are  egg-alMimin 
and  globulins,  of  which  the  vitellin  of  the  yolk  is  most  important; 
nuclein  in  combination  with  iron  is  also  found.  In  addition  to  the 
three  common  fats  there  is  a  yellow  fat,  lutein  (lipochome),  a  small 
quantity  of  grape  sugar;  lecithin,  and  cholesterin  and  inorganic  salts, 
chiefly  potassium  chloride  and  phosphates. 

Table  of  the  Percentage  Composition  op  Fowls'  Eggs. 

Nitrogenous  substances.       Fats.         Salts.        Water. 

Wtdte 30.4  —  1.6  78 

Yolk  ....  16.  80.7         1.3  53 

*The  details  of  the  composition  of  milk  liave  been  discussed  in  the  Chapter  on 
Secretion. 


Carbo- 

hydi-ates. 

51. 

Fats. 
1.6 

Salts. 
2.S 

Water. 
37 

70.85 

2. 

1.7 

15 

FOOD    AND    DIGESTION.  329 

d.  Leguminous  fruits  are  used  by  vegetarians,  as  the  chief  source  of 
the  nitrogen  of  the  food.  Those  chiefly  used  are  ^;ea5,  beans,  lentils, 
etc.,  they  contain  a  nitrogenous  substance  called  legumin,  allied  to 
albumen.  They  contain  about  25.30  per  cent  of  this  nitrogenous  body, 
and  twice  as  much  nitrogen  as  wheat. 

Organic  non-nitrogenous  foods. 

I.  Carbo-hydrates. — a.  Bread,  made  from  the  ground  grain  obtained 
from  various  so-called  cereals,  viz.,  wheat,  rye,  maize,  barley,  rice,  oats, 
etc.,  is  the  direct  form  in  which  the  carbo-hydrate  is  supplied  in  an 
ordinary  diet.  It  contains  starch,  dextrin,  and  a  little  sugar.  It  also, 
besides  these,  contains  gluten,  composed  of  several  vegetable  proteids, 
and  a  small  amount  of  fat. 

Table  of  Percentage  Composition  of  Bread  and  Flour. 

Nitrogenous 
matters. 

Bread      .        .        .        .       '     8.1 
Flour  ....  10.8 

Various  articles  of  course  besides  bread  are  made  from  flour,  e.g., 
sago,  macaroni,  biscuits,  etc.  There  is  dextrine  and  a  small  amount  of 
dextrose  in  bread,  particularly  in  the  crust. 

b.  Vegetables,  especially  potatoes.  They  contain  starch  and  sugar. 
In  cabbage,  turnips,  etc.,  the  salts  of  potassium  are  abundant. 

c.  Fruits  contain  sugar,  and  organic  acids,  tartaric,  malic,  citric, 
and  others. 

d.  Sugar,  chiefly  saccharose,  used  pure  or  in  various  sweetmeats. 

II.  Oils  and  fats. — The  substances  supplying  the  oils  and  fats  of  the 
food  are  chiefly  butter,  bacon  and  lard  (pig's  fat),  suet  (beef  and  mutton 
fat),  and  vegetable  oils.  These  contain  olein,  stearin,  and  palmitin. 
Butter  contains  others  in  addition,  while  vegetable  oils,  as  a  rule,  con- 
tain no  stearin. 

Mineral  or  Inorganic  Foods. 

The  salts  of  the  food. — Nearly  all  the  foregoing  substances  in  the 
preceding  classes,  contain  a  greater  or  less  amount  of  the  salts  required 
in  food,  but  green  vegetables  and  fruit  supply  certain  salts,  chiefly 
potassium,  without  which  the  normal  health  of  the  body  cannot  be 
maintained. 

Sodium  chloride  is  an  essential  food;  it  is  contained  in  nearly  all 
solids,  but  so  much  is  required  that  it  has  also  to  be  taken  as  a  condi- 
ment. Potassium  salts  are  supplied  in  muscle,  nerve,  in  meats  generally, 
and  in  potatoes.  Calcium  salts  are  supplied  in  eggs,  blood  of  meat,  wheat 
and  vegetables.     Iron  is  contained  in  haemoglobin,  in  milk,  eggs,  and 


330  HANDBOOK    OF    PHYSIOLOGY. 

vegetables.  It  is  derived  in  all  cases,  so  it  is  supposed,  by  organic 
compounds,  into  which  it  is  built  up  during  plant  life,  or  during  the  life 
of  other  animals  (haematogens). 

Liquid  Foods. 

Water  is  consumed  alone,  or  together  with  certain  other  substances 
used  to  flavor  it,  e.g.,  tea,  coffee,  etc.  Tea  in  moderation  is  a  stimulant, 
and  contains  an  aromatic  oil  to  which  it  owes  its  peculiar  aroma,  an 
astringent  of  the  nature  of  tannin,  and  an  alkaloid,  tJieine.  The  composi- 
tion of  coffee  is  very  nearly  similar  to  that  of  tea.  Cocoa,  in  addition 
to  similar  substances  contained  in  tea  and  coffee,  contains  fat,  albumin- 
ous matter  and  starch,  and  must  be  looked  upon  more  as  a  food. 

Beer,  in  various  forms,  is  an  infusion  of  malt  (barley  which  has 
sprouted,  and  in  which  its  starch  is  converted  in  great  part  into  sugar), 
boiled  with  hops  and  allowed  to  ferment.  Beer  contains  from  1.2  to  8.8 
per  cent  of  alcohol. 

Cider  and  Perry,  the  fermented  juice  of  the  apple  and  pear. 

Wine,  the  fermented  juice  of  the  grape,  contains  from  6  or  7  (Ehine 
wines,  and  white  and  red  Bordeaux)  to  24-25  (ports  and  sherries)  per 
cent  of  alcohol. 

Spirits,  obtained  from  the  distillation  of  fermented  liquors.  They 
contain  upward  of  40-70  per  cent  of  absolute  alcohol. 

The  effect  of  cooking. — In  general  terms  this  may  be  said  to  make 
the  food  more  easily  digestible;  this  usually  implies  two  alterations, — 
food  is  made  more  agreeable  to  the  palate  and  also  more  pleasing  to  the 
eye.  Cooking  consists  in  exposing  the  food  to  various  degrees  of  heat, 
either  to  the  direct  heat  of  the  fire,  as  in  roasting,  or  to  the  indirect 
heat  of  the  fire,  as  in  broiling,  baking,  or  frying,  or  to  hot  water,  as  in 
boiling  or  stewing.  The  effect  of  heat  upon  {a)  flesh  is  to  coagulate  the 
albumin  and  coloring  matter,  to  solidify  fibrin,  and  to  gelatinize  ten- 
dons and  fibrous  connective  tissue.  Previous  beating  or  bruising  (as 
with  steaks  and  chops)  or  keeping  (as  in  the  case  of  game),  renders  the 
meat  more  tender.  Prolonged  exposure  to  heat  also  develops  on  the  sur- 
face certain  empyreumatic  bodies,  which  are  agreeable  both  to  the  taste 
and  smell.  By  placing  meat  in  hot  water,  the  external  coating  of  albu- 
min is  coagulated,  and  very  little,  if  any,  of  the  constituents  of  the 
meat  are  lost  afterward  if  boiling  be  prolonged;  but  if  the  constituents 
of  the  meat  are  to  be  extracted,  it  should  be  exposed  to  prolonged  sim- 
mering at  a  much  lower  temperature, and  the  "broth"  will  then  contain 
the  gelatin  and  extractive  matters  of  the  meat,  as  well  as  a  certain 
amount  of  albumin.     The  addition  of  salt  will  help  to  extract  myosin. 

The  effect  of  boiling  (5)  an  Qgg  is  to  coagulate  the  albumen,  which 
helps  to  render  it  more  easily  digestible.     Upon  (c)  milk,  the  effect  of 


FOOD    AND    DIGESTION.  331 

heat  is  to  produce  a  scuin  composed  of  albumen  and  a  little  caseinogen 
(the  greater  part  of  the  caseinogen  being  uncoagulated)  with  some  fat. 
Upon  {d )  vegetables,  the  cooking  produces  the  necessary  effect  of  render- 
ing them  softer,  so  that  they  can  be  more  readily  broken  up  in  the  mouth ; 
it  also  causes  the  starch  grains  to  swell  up  and  burst,  and  so  aids  the 
digestive  fluids  in  penetrating  into  their  substance.  The  albuminous 
matters  are  coagulated,  and  the  gummy,  saccharme  and  saline  matters 
are  removed.  The  conversion  of  flour  into  dough  is  effected  by  mixing  it 
with  water,  and  adding  a  little  salt  and  a  certain  amount  of  yeast.  Yeast 
consists  of  the  cells  of  an  organized  ferment  {Torula  cerevisia'),  and  it  is 
by  the  growth  of  this  plant,  changing  by  ferment  action  the  sugar  pro- 
duced from  the  starch  of  the  flour,  that  a  quantity  of  carbonic  acid  gas 
and  alcohol  is  formed.  By  means  of  the  former  the  dough  rises.  An- 
other method  of  making  dough  consists  in  mixing  the  flour  with  water 
containing  a  large  quantity  of  carbonic  acid  gas  in  solution. 

By  the  action  of  heat  during  baking  {cl )  the  dough  continues  to  ex- 
pand, and  the  gluten  being  coagulated,  the  bread  sets  as  a  permanently 
vesiculated  mass. 

Dig-estion. 

The  Enzymes,  or  unorganized  ferments,  are  the  essential  factors 
in  digestion,  and  their  predominant  action  is  one  of  hydrolytic  cleavage ; 
that  is,  the  substance  acted  upon  takes  up  water  and  then  splits  into  two 
different  substances,  usually  of  the  same  class.  Their  chemical  nature 
is  as  yet  undetermined  because  of  the  inability  of  getting  absolutely  pure 
specimens,  but  it  is  generally  admitted  that  they  contain  nitrogen,  and 
they  are  usually  classed  as  proteids.  Practically  all  are  secreted  in  the 
glands  as  zi/mogcns,  which  bear  the  same  relation  to  enzymes  as  fibrinogen 
does  to  fibrin  ;  they  are  transformed  to  enzymes  by  the  proper  stimulus  but 
never  exist  as  such  in  the  glands.  Some  of  them  pass  into  the  urine,  but 
most  are  excreted  Avith  the  faeces. 

Each  enzyme  has  a  special  point  of  temperature  at  which  it  acts  best, 
and  any  change  in  the  temperature  retards  its  action ;  the  action  is  sus- 
pended at  a  definite  point  of  low  temperature,  but  the  enzyme  is  not  de- 
stroyed by  cold ;  the  action  is  also  suspended  at  higher  temperatures,  and 
at  a  still  higher  point  the  enzyme  is  destroyed.  Some  enzymes  act  only 
in  an  alkaline  medium,  being  destroyed  in  an  acid  medium,  and  vice  versa; 
others  act  in  either  alkaline,  neutral  or  acid  media.  Enzymes  are  hin- 
dered in  their  action  by  the  accumulation  of  the  products  of  their  activity. 
Most  of  them  cease  acting  altogether  when  these  products  reach  a  certain 
concentration,  but  will  begin  acting  again  on  the  removal  of  these  prod- 
ucts or  if  the  mixture  be  simply  diluted. 


332  handbooe;  of  physiology. 

The  quantity  of  the  enzyme  determines  the  rapidity  of  the  action  but 
not  the  amount ;  a  small  quantity  will  digest  as  much  as  a  large  quantity 
but  will  take  longer.  The  enzymes  are  not  used  up  in  the  course  of  their 
activity,  as  far  as  can  be  seen,  and  do  not  seem  to  undergo  any  change  in 
their  composition.  They  are  classified  either  according  to  the  chemical 
nature  of  their  action,  or  according  to  the  class  of  substances  on  which 
they  act ;  the  former  classification  is  more  logical,  but  the  latter  is  more 
convenient  and  more  generally  used. 

The  food  is  first  of  all  received  into  the  mouth,  and  is  subjected  to  the 
action  of  the  teeth  and  tongue,  being  at  the  same  time  mixed  with  the  first 
of  the  digestive  juices  — the  saliva.  It  is  then  swallowed,  and,  passing 
through  the  pharynx  and  oesophagus  into  the  stoTnach,  is  subjected  to  the 
action  of  the  gastric  juice — the  second  digestive  juice.  Thence  it  passes 
into  the  intestines,  where  it  meets  with  the  bile,  the  pancreatic  juice,  and 
the  intestinal  juices,  all  of  which  exercise  an  influence  upon  the  portion 
of  the  food  not  already  absorbed  from  the  stomach.  By  this  time  most 
of  the  food  is  digested,  and  the  residue  of  undigested  matter  leaves  the 
body  in  the  form  ol  faeces  by  the  external  opening  of  the  bowel. 

The  Mouth  is  the  cavity  contained  between  the  jaws  and  inclosed 
by  the  cheeks  laterally,  the  lips  anteriorly;  behind,  it  opens  into  the 
pharynx  by  the  fauces,  and  is  separated  from  the  nasal  cavity  above,  by 
the  hard  palate  in  front,  and  the  soft  palate  behind,  which  forms  its  roof. 
The  tongue  forms  the  lower  part  or  floor.  In  the  jaws  are  contained  the 
teeth,  and  when  the  mouth  is  closed  these  form  its  anterior  boundaries. 
The  whole  of  the  cavity  of  the  mouth  is  lined  with  stratified  epithelium, 
of  which  the  superficial  layers  are  squamous.  This  epithelium  is  contin- 
uous at  the  lips  with  that  of  the  skin  anteriorly,  and  posteriorly  with 
that  of  the  pharynx.  The  mucous  membrane  itself,  varying  in  thickness 
in  various  parts,  and  consisting  of  a  fine  areolar  connective,  in  which  is 
found  adenoid  tissue  in  considerable  amount,  is  provided  with  numerous 
small  tubular  glands  lined  with  columnar  epithelium,  and  resembling  in 
structure  the  mucous  salivary  glands,  to  be  presently  described.  Into 
the  buccal  cavity  open  the  ducts  of  the  salivary  glands,  which  are  three 
in  number  on  either  side. 

In  the  mouth,  then,  the  food  is  subjected  to  the  action  of  the  teeth, 
or  is  masticated,  and  is  mixed  with  saliva.  These  processes  of  mastica- 
tion and  insalivation  must  be  considered  more  in  detail. 

Mastication. — The  act  of  chewing,  or  mastication,  is  performed  by 
the  biting  and  grinding  movement  of  the  lower  range  of  teeth  against  the 
upper.  The  simultaneous  movements  of  the  tongue  and  cheeks  assist 
partly  by  crushing  the  softer  portions  of  the  food  against  the  hard  palate 
and  gums,  and  thus  supplementing  the  action  of  the  teeth,  and  partly  by 
returning  the  morsels  of  food  to  the  action  of  the  teeth,  again  and  again, 


FOOD    AXD    DIGESTION.  333 

as  they  are  .s(i^ueezed  out  from  between  them,  until  they  have  been  suffi- 
ciently chewed. 

Muscles. — The  simple  up  and  down,  or  biting  movements  of  the  lower 
jaw,  are  performed  by  the  temporal,  masseter,  and  internal  pterygoid  mus- 
cles, the  action  of  which  in  closing  the  jaws  alternates  with  that  of  the 
digastric  and  other  muscles  passing  from  the  os  hyoides  to  the  lower  jaw, 
which  open  them.  The  grinding  or  side  to  side  movements  of  the  lower 
jaw  are  performed  mainly  by  the  external  pterygoid  muscles,  the  muscle 
of  one  side  acting  alternately  with  the  other.  "^Tien  both  external 
pterygoids  act  together,  the  lower  jaw  is  pulled  directly  forward,  so  that 
the  lower  incisor  teeth  are  brought  in  front  of  the  level  of  the  upper. 

Temporo-m axillary  Fibro-cartilage. — The  function  of  the  inter-articu- 
lo-fibro-cartilage  of  the  temporo-m  axillary  joint  in  mastication  is  to  serve : 
— (1)  As  an  elastic  pad  to  distribute  the  pressure  caused  by  the  exceed- 
ingly powerful  action  of  the  masticatory  muscles.  (2)  As  a  joint-surface 
or  socket  for  the  condyle  of  the  lower  jaw  when  the  latter  has  been  par- 
tially drawn  forward  out  of  the  glenoid  cavity  of  the  temporal  bone  by 
the  external  pterygoid  muscle,  some  of  the  fibres  of  the  latter  being  at- 
tached to  its  front  surface,  and  consequently  drawing  it  forward  with  the 
condyle  which  moves  on  it. 

Nervous  Mechanism. — The  act  of  mastication  is  partly  voluntary  and 
partly  reflex  and  involuntary.  The  consideration  of  such  nervous  actions 
will  come  hereafter.  It  will  suffice  here  to  state  that  the  afferent  nerves 
chiefly  concerned  are  the  sensory  branches  of  the  fifth  and  the  tenth  or 
glosso-pharyngeal,  and  the  efferent  are  the  motor  branches  of  the  fifth  and 
the  twelfth  (hypoglossal)  cerebral  nerves.  The  nerve-centre  through 
which  the  reflex  action  occurs,  and  by  which  the  movements  of  the  vari- 
ous muscles  are  harmonized,  is  situated  in  the  medulla  oblongata.  In  so 
far  as  mastication  is  voluntary  or  mentally  perceived,  it  is  under  the  in- 
fluence of  the  cerebral  hemispheres. 

Insalivation. — The  act  of  mastication  is  much  assisted  by  the  saliva 
A\hich  is  secreted  by  the  salivary  glands  in  largely  increased  amount  dur- 
ing the  process,  and  the  intimate  incorporation  of  which  with  the  food, 
as  it  is  being  chewed,  is  termed  insalivation. 

The  Salivary  Glands. 

The  glands  which  secrete  the  saliva  in  the  human  subject  are  the  sal- 
ivary glands  proper,  viz.,  i\\Q parotid,  the  sub-maxillary,  and  the  sub-lin- 
gual, and  numerous  smaller  bodies  of  similar  structure,  and  with  sepa- 
rate ducts,  which  are  scattered  thickly  beneath  the  mucous  membrane  of 
the  lips,  cheeks,  soft  palate,  and  root  of  the  tongue. 

Structure. — The  salivary  glands  are  compound  tubular  or  tubnln-race- 


334 


HANDBOOK    OF    PHYSIOLOGY. 


mose  glands.  They  are  made  up  of  lobules.  Each  lobule  consists  of  the 
branchings  of  a  subdivision  of  the  main  duct  of  the  gland,  which  is  gen- 
erally more  or  less  convoluted  toward  its  extremities,  and  sometimes,  ac- 
cording to  some  observers,  sacculated  or  pouched.  The  convoluted  or 
pouched  portions  form  the  alveoli,  or  proper  secreting  parts  of  the  gland. 
The  alveoli  are  composed  of  a  basement  membrane  of-  flattened  cells 
joined  together  by  processes  to  produce  a  fenestrated  membrane,  the 
spaces  of  which  are  occupied  by  a  homogeneous  ground-substance.  With- 
in, upon  this  membrane,  which  forms  the  tube,  the  nucleated  salivary 
secreting  cells,  of  cubical  or  columnar  form,  are  arranged  parallel  to  one 
another  enclosing  a  central  canal.  The  granular  appearance  frequently 
seen  in  the  salivary  cells  is  due  to  the  numerous  zymogen  granules  which 
they  contain.  When  isolated,  the  cells  not  infrequently  are  found  to  be 
branched.     Connecting  the  alveoli  into  lobules  is  a  considerable  amount 


Fig.  234. 


-Section  of  sub-inaxillary  slaud  of  dog.     ShowiiiK  gland  cells,  b,  and  a  duct,  a,  in  section. 

(KoUiker.) 


of  fibrous  connective  tissue,  which  contains  both  flattened  and  granular 
protoj)lasniic  cells,  lymph  corpuscles,  and  in  some  cases  fat  cells.  The 
lobules  are  connected  to  form  larger  lobules  (lobes),  in  a  similar  manner. 
The  alveoli  pass  into  the  intralobular  ducts  by  a  narrowed  portion  (inter- 
calary), lined  with  flattened  epithelium  with  elongated  nuclei.  The  in- 
tercalary ducts  pass  into  the  intralobular  ducts  by  a  narrowed  neck,  lined 
with  cubical  cells  with  small  nuclei.  The  intralobular  duct  is  larger  in 
size,  and  is  lined  with  large  columnar  nucleated  cells,  the  parts  of  which, 
toward  the  lumen  of  the  tube,  present  a  fine  longtitudinal  striation,  due 
to  the  arrangement  of  the  cell  network.  It  is  most  marked  in  the  sub- 
maxillary gland.  The  intralobular  ducts  pass  into  the  larger  ducts,  and 
these  into  the  main  duct  of  the  gland.  As  these  ducts  become  larger 
they  acquire  an  outside  coating  of  connective  tissue,  and  later  on  some 
unstriped  muscular  fibres.  The  lining  of  the  larger  ducts  consist  of  one 
or  more  layers  of  columnar  epithelium,  the  cells  of  which  contain  an 
intracellular  network  of  fibres  arranged  longitudinally. 


FOOD    AND    DIGESTION. 


335 


Varieties. — Certain  differences  in  tlie  structure  of  salivary  glands  may 
be  observed  according  as  the  glands  secrete  pure  saliva,  or  saliva  mixed 
■with  mucus,  or  pure  mucus,  and  tlierefore  the  glands  have  been  classified 
as: — 

(1)  I'nfji  salivorij  glands  (called  most  unfortunately  by  some,  serous 
glands),  e.(j.,  the  parotid  of  man  and  other  animals,  and  the  submaxil- 
lary of  the  rabbit  and  guinea-pig  (fig.  235).  In  this  kind  the  alveolar 
lumen  is  small,  and  the  cells  lining  the  tubule  are  short  granular  colum- 
nar cells,  with  nuclei  presenting  the  intranuclear  network.  During  rest 
the  cells  become  larger,  highly  granular,  with  obscured  nuclei,  and  the 
lumen  becomes  smaller.  During  activity,  and  after  stimulation  of  the 
sympathetic,  the  cells  become  smaller  and  their  contents  more  opaque; 
the  granules  first  of  all  disappearing  from  the  outer  part  of  the  cells,  and 


Fig.  235.— Fromasectionthroughatruesalivary  gland,     cr.  The  gland  alveoli,  lined  with  albumin- 
ous "salivary  cells;"  6,  intralobular  duct  cut  transversely.     (Klein  and  Noble  Smith.) 


then  ])eing  found  only  at  the  extreme  inner  part  and  contiguous  border 
of  the  cell.     The  nuclei  reappear,  as  does  also  the  lumen. 

(2)  In  the  true  mucvs- secreting  glands,  as  the  sublingual  of  man  and 
other  animals,  and  in  the  submaxillary  of  the  dog,  the  tubes  are  larger, 
contain  a  larger  lumen,  and  also  have  larger  cells  lining  them.  The  cells 
are  of  two  kinds,  [a)  nn/roas  or  central  cells,  which  are  transparent 
columnar  cells  with  irregular  or  flattened  nuclei  near  the  basement  mem- 
brane. The  cell  substance  is  made  up  of  a  fine  network,  which  in  the 
resting  state  contains  a  transparent  substance  called  niucigen,  during 
which  tlie  cell  does  not  stain  well  witli  logwood  (fig.  236).  When  the 
gland  is  secreting,  as  well  as  on  stimulation  of  the  nerve,  niucigen  is  con- 
verted into  mucin,  and  the  cells  swell  u]),  appear  more  transparent,  and 
stain  deeply  in  logwood  (fig.  237).  After  stimulation,  the  cells  become 
smaller,  more  granular,  and  more  easily  stained,  from  having  discharged 
their  contents.  The  nuclei  appear  more  distinct.  (J>)  Crescents  of  Gia- 
nuzzi,  sometimes  called  the  Semilunes  of  Heidenhain  (fig.  236),  which 
are  erescentic  masses  of  granular  parietal  cells  found  here  and  there  be- 


336 


HANDBOOK    OF    PHYSIOLOGY. 


tween  the  basement  meuibrane  and  the  central  cells.  The  cells  compos- 
ing the  mass  are  small,  and  have  a  very  dense  reticulum,  the  nuclei  are 
spherical,  and  increase  in  size  during  secretion.  In  the  mucous  gland 
there  are  some  large  tubes,  lined  with  large  transparent  central  cells,  and 
having  besides  a  few  granular  parietal  cells ;  other  small  tubes  are  lined 
with  small  granular  parietal  cells  alone ;  and  a  third  variety  are  lined 
equally  with  each  kind  of  cell. 

(3)  In  the  nmco-salivary  or  mixed  glands,  as  the  human  submaxillary 


Fig.  236. 


Fig.  237 


Fig.  236.  —Section  of  the  submaxillary  gland  of  a  dog,  during  rest.  Most  of  the  alveolar  cells 
are  large  and  clear,  being  filled  with  the  material  for  secretion  (in  this  case,  mucigen)  which 
obscures  their  protoplasm  ;  some  of  the  crlls,  however,  are  small  and  protoplasmic,  forming  the 
crescents  seen  in  most  of  tlie  alveoli.     (Banvier.) 

Fig.  237.— Section  of  a  similar  gland  after  a  period  of  activity.  The  mucigen  has  been  dis- 
charged from  the  mucin-secreting  cells,  which  consequently  appear  shrunken  and  less  clear. 
Both  the  cells  and  the  alveoli  are  much  smaller,  and  the  protoplasm  of  the  cells  is  more  apparent. 
The  crescents  of  Gianuzzi  are  enlarged.     (Ranvier.) 

c.  Crescent  cells;  g,  mucus-secreting  cells;  i,  lumen  of  alveolus. 


gland,  part  of  the  gland  presents  the  structure  of  the  mucous  gland, 
while  the  remainder  has  that  of  the  salivary  glands  proper. 

Nerves  and  Blood-vessels. — Nerves  of  large  size  are  found  in  the  sali- 
vary glands;  they  are  principally  contained  in  the  connective  tissue  of 
the  alveoli,  and  in  certain  glands,  especially  in  the  dog,  are  provided 
with  ganglia.  Some  nerves  have  special  endings  in  Pacinian  corpuscles, 
some  supply  the  blood-vessels,  and  others  penetrate  the  basement  mem- 
brane of  the  alveoli  and  end  upon,  but  not  in,  the  salivary  cells. 

The  blood-vessels  form  a  dense  capillary  network  around  the  ducts  of 
the  alveoli,  being  carried  in  by  the  fibrous  trabeculse  between  the  alveoli, 
ill  which  also  begin  the  lymphatics  by  lacunar  sj^aces. 

The  so-called  mucous  glands  of  the  mouth  and  tongue  present  in  some 
cases  the  structures  of  mucous,  in  others  of  serous  glands. 


FOOD    AND    DIGESTION.  337 


Saliva. 


Saliva,  as  it  commonly  flows  from  the  mouth,  is  the  mixed  secretion 
of  the  salivary  glands  proper  and  of  the  glands  of  the  buccal  mucous 
membrane  and  tongue ;  it  is  often  mixed  with  air,  which,  being  retained 
by  its  viscidity,  makes  it  frothy.  When  obtained  from  the  parotid  ducts, 
and  free  from  mucus,  saliva  is  a  transparent  watery  fluid,  the  specific 
gravity  of  which  varies  from  1004  to  1008,  and  in  which,  when  examined 
with  the  microscope,  are  found  floating  a  number  of  minute  particles, 
derived  from  the  secreting  ducts  and  vesicles  of  the  glands.  In  the  im- 
pure or  mixed  saliva  are  found,  besides  these  particles,  numerous  epithe- 
lial scales  separated  from  the  surface  of  the  mucous  membrane  of  the 
mouth  and  tongue,  and  the  so-called  salivary  corpuscles,  discharged 
probably  from  the  mucous  glands  of  the  mouth  and  the  tonsils,  which, 
when  the  saliva  is  collected  in  a  deep  vessel,  and  left  at  rest,  subside 
in  the  form  of  a  white  opaque  matter,  leaving  the  supernatant  salivary 
fluid  transparent  and  colorless,  or  with  a  pale  bluish-ray  tint.  It  also 
contains  various  kinds  of  micro-organisms  (bacteria).  In  reaction,  the 
saliva,  when  first  secreted,  appears  to  be  always  alkaline :  the  alkalinity 
is  about  equal  to  .08  or  .10  per  cent  of  sodium  carbonate  and  is  due  to  the 
presence  of  disodium  hydrogen  phosphate  ]Sra,^HPO^.  During  fasting,  the 
saliva,  although  secreted  alkaline,  shortly  becomes  neutral ;  especially 
when  it  is  secreted  slowly  and  is  allowed  to  mix  with  the  acid  mucus  of 
the  mouth,  by  which  its  alkaline  reaction  is  neutralized. 

Chemical  Composition  of  Human  Saliva.  (Hammerbacher). 

In  1,000  parts. 

Water 994.2 

Solids 5.8 

Mucus  and  epithelium 2.2 

Soluble  organic  matter  (ptyalin) 1.4 

Potassium  sulpho-cyanide      .  0.04 

Salts 2.20 

The  mucm  is  the  largest  representative  of  the  organic  nitrogenous 
class  of  bodies  in  the  saliva ;  it  may  be  thrown  down  by  addition  of  ace- 
tic acid,  if  sodium  chloride  be  absent.  It  gives  the  three  chief  proteid 
reactions,  and  may  easily  be  split  up  by  the  action  of  a  dilute  mineral  acid 
into  globulin  and  a  carbohydrate  whose  exact  character  has  not  yet  been 
established,  though  it  resembles  a  sugar  in  reducing  copper  sulphate  solu- 
tions. 

The  presence  of  potassium  sulphocyanide  (CNKS)  in  saliva,  may  be 
shown  by  the  blood-red  coloration  which  the  fluid  gives  with  a  solution 
of  ferric  chloride  (Fe^ClJ,  and  which  is  bleached  on  the  addition  of  a 
solution  of  mercuric  chloride  fHgClJ,  but  not  by  hydrochloric  acid. 

22 


338  HANDBOOK    OF    PHYSIOLOGY. 

Rate  of  Secretion  and  Quantity. — The  rate  at  which  saliva  is  secreted 
is  subject  to  considerable  variation.  When  the  tongue  aiid  muscles  con- 
cerned in  mastication  are  at  rest,  and  the  nerves  of  the  mouth  are  subject 
to  no  unusual  stimulus,  the  quantity  secreted  is  not  more  than  sufficient, 
with  the  mucus,  to  keep  the  mouth  moist.  During  actual  secretion  the 
flow  is  much  accelerated. 

The  quantity  secreted  in  twenty-four  hours  varies,  but  is  at  least  2 
pints  (1  litre). 

Uses  of  Saliva. — The  purposes  served  by  saliva  are  (a)  mechanical 
and  (h)  chemical. 

(a).  Mechanical. — (1)  It  keeps  the  mouth  in  a  due  condition  of  mois- 
ture, facilitating  the  movements  of  the  tongue  in  speaking,  and  the  mas- 
tication of  food.  (2)  It  serves  also  in  dissolving  sapid  substances,  and 
rendering  them  capable  of  exciting  the  nerves  of  taste.  But  the  principal 
mechanical  purpose  of  the  saliva  is,  (3)  that  by  mixing  with  the  food 
during  mastication,  it  makes  it  a  soft  pulpy  mass,  such  as  may  be  easily 
swallowed.  To  this  purpose  the  saliva  is  adapted  both  by  quantity  and 
quality.  For,  speaking  generally,  the  quantity  secreted  during  feeding 
is  in  direct  proportion  to  the  dryness  and  hardness  of  the  food.  The 
quality  of  saliva  is  equally  adapted  to  this  end.  It  is  easy  to  see  how 
much  more  readily  it  mixes  with  most  kinds  of  food  than  water  alone 
does ;  and  the  saliva  from  the  jDarotid,  labial,  and  other  small  glands, 
being  more  aqueous  than  the  rest,  is  that  which  is  chiefly  braided  and 
mixed  with  the  food  in  mastication ;  while  the  more  viscid  mucous  secre- 
tion of  the  submaxillary,  palatine,  and  tonsillitic  glands  is  spread  over 
the  surface  of  the  softened  mass,  to  enable  it  to  slide  more  easily  through 
the  fauces  and  oesophagus. 

(V)  Chemical. — The  chemical  action  which  the  saliva  exerts  upon  the 
food  in  the  mouth  is  to  convert  the  starchy  materials  which  it  contains  into 
soluble  starch  and  then,  partially,  into  sugar.  This  power  the  saliva 
owes  to  one  of  its  constituents,  i:>tyalin,  which  is  one  of  the  enzymes,  or 
unorganized  ferments.  Certain  investigators  have  of  late  asserted  that 
saliva  contains  another  enzyme,  known  as  glucase,  which  has  the  power 
of  splitting  the  disaccharides  into  monosaccharides,  or  maltose  into  dex- 
trose. The  action  of  this  ferment  is  certainly  very  limited.  The  conver- 
sion of  the  starch  under  the  influence  of  the  ferment  into  sugar  takes 
place  in  several  stages,  and  in  order  to  understand  it,  a  knoAvledge  of  the 
structure  and  composition  of  starch  granules  is  necessary.  A  starch 
granule  consists  of  two  parts :  an  envelope  of  cellulose,  which  does  not 
give  a  blue  color  with  iodine  except  on  addition  of  sulphuric  acid,  and  of 
yramdose,  which  is  contained  within,  and  which  gives  a  blue  with  iodine 
alone.  Brilcke  states  that  a  third  body  is  contained  in  the  granule,  which 
gives  a  red  with  iodine,  viz.,  erythro-granulose.  On  boiling,  the  granu- 
l«se  swells  up,  bursts  the  envelope,  and  the  whole  granule  is  more  or  less 


FOOT)    AND    DIGf:ST10X.  339 

completely  eonverled  into  a  paste  or  gruel,  which  i.s  (;alUMl  m'hitiiiuu.s 
starch. 

When  ptyalin  acts  upon  boiled  starch,  it  first  changes  the  latter  (by 
hydrolysis)  into  soluble  starch,  or  am idi/li/i :  this  is  more  limpid  and  more 
like  a  true  solution,  though  it  still  gives  the  blue  coloration  on  the  addi- 
tion of  iodine.  This  stage  is  very  brief,  only  thirty  seconds  ])eing  some- 
times recpiircd  in  laboratory  experiments,  to  render  a  stiff  starch  paste 
completely  fluid  when  a  few  drops  of  saliva  are  added  at  body  temper- 
ature. This  ra])idity  of  action  is  of  great  importance,  as  under  proper 
conditions  of  mastication  ])ractically  all  the  boiled  starch  of  the  food 
ought  to  enter  the  stomach  as  soluble  starch.  When  the  starch  has  not 
been  previously  boiled,  the  envelope  of  cellulose  retards  the  action  of  the 
ptyalin  to  a  very  marked  degree. 

The  further  stages  of  hydrolytic  cleavage  result  in  the  formation  of  a 
variable  mixture  of  maltose  and  iso-maltose  with  dextrins,  but  never  re- 
sult (in  laboratory  experiments)  in  the  complete  conversion  of  the  dex- 
trins into  sugars.  Gradually,  as  the  starch  is  converted,  the  blue  color- 
ation with  iodine  is  replaced  by  a  purplish-red  and  finally  by  a  distinctly 
red  color :  the  latter  color  is  produced  by  en^thro-dextrin  (so-called  from 
the  color),  a  hypothetical  substance  which  has  never  been  isolated.  In 
the  later  stages  no  coloration  is  obtained  with  iodine,  and  for  this  reason 
the  dextrins  formed  are  known  as  achroo-dextrins  ;  there  are  probably 
several  of  these,  but  they  have  not  yet  been  sufficiently  isolated.  As 
sugar  appears  very  early  in  the  process,  even  at  the  stage  of  erythro-dex- 
trin,  and  gradually  increases  in  amount,  it  is  generally  concluded  that 
maltose  is  formed  early  in  the  decomposition  of  the  starch  molecule :  the 
process  is  usually  represented  schematically  as  follows : 

Starch. 
Sohible  starch. 


Ervtlnii  dextrin.  Maltose  and  iso-nialtose. 


.Xflii'oo dextrins.  Maltose  and  iso maltose. 

The  sugars  formed  are  maltose  (C|.,H.,.,0,,)  and  a  closely  allied  sugar 
known  as  iso-maltose.  A  small  percentage  of  dextrose  has  been  found  by 
some  observers,  and  this  may  be  due  to  the  action  of  glucose.  Maltose  is 
allied  to  saccharose  or  cane-sugar  more  nearly  than  to  glucose ;  it  is  crys- 
talline;  its  solution  has  the  property  of  polarizing  light  to  the  right  to  a 
greater  degree  than  solutions  of  glucose  (3  to  1) ;  it  is  not  so  sweet,  and 
reduces  coppei-  sulphate  less  easily.  It  can  be  converted  into  glucose  by 
boiling  with  dilute  acids. 


340  HAS^DBOOK    OF    PHYSIOLOGY. 

According  to  Brown  and  Heron  the  reactions  may  be  represented  thus: — 
(Jne  molecule  of  gelatinous  starch  is  converted  by  the  action  of  an  amylolytic  fer- 
ment into  11  molecules  of  soluble  starch. 
One  molecule  of  soluble  starch  =  10  (Ci2H2oO]o) +  8  (H2O),  which  is  further  con- 
verted by  the  ferment  into 

1.  Erythro-dextrin  (giving  red  with  iodine)  -|-    Maltose. 
9  (C12H20O10)  (C12H22O11) 

then  into  2.    Erythro-dextrin   (giving  yellow  with  iodine)    -|-    Maltose. 

8  (C12H20O10)  3  (Ci3H220ii) 

next  into   3.    Achroo-dextrin        -|-        Maltose. 

7(C,2H2oOio)  3(C:2H220„) 

And  so  on  ;  the  resultant  being : — 

10    (Cl2H2oO:o)    +    8    (H2O)    =    8    (Ca2H220„)  +    2   (Cl2H2oO,o) 

Soluble  starch        Water  Maltose        Achroo-dextrin. 

Many  observers,  however,  deny  that  the  maltose  simultaneously  pres- 
ent with  erythro-dextrin  is  actually  split  off  from  the  starch  molecule  in 
the  formation  of  erythro-dextrin ;  they  claim  that  it  is  rather  the  product 
of  more  advanced  hydrolysis  in  other  starch  molecules,  and  point  out  that 
in  such  a  chemical  reaction  of  considerable  time  duration,  it  is  improbable 
that  all  the  starch  molecules  are  attacked  at  the  same  rate  or  are,  at  any 
given  moment,  equally  advanced  in  cleavage.  Their  theory  is  that  a 
series  of  more  and  more  simple  dextrins  are  formed  which  give  rise  finally 
to  the  disaccharides. 

Test  f 01'  Sugar. — In  such  an  experiment  the  presence  of  sugar  is  at 
once  discovered  by  the  application  of  Trommer's  test,  which  consists  in 
the  addition  of  a  drop  or  two  of  a  solution  of  copper  sulphate,  followed 
hj  a  larger  quantity  of  caustic  potash.  When  the  liquid  is  boiled,  an 
orange-red  precipitate  of  copper  suboxide  indicates  the  presence  of  sugar. 

The  action  of  saliva  on  starch  is  facilitated  by :  (a)  Moderate  heat, 
about  37.8°  C.  (100°  F.).  {b)  A  neutral  medium,  (c)  Removal  of  the 
changed  material  from  time  to  time.  Its  action ^s  retarded  by :  (a)  Cold; 
a  temperature  of  0°  C.  (32°  F.)  stops  it  for  a  time,  but  does  not  destroy  it, 
whereas  a  high  temperature  above  60°  C.  (140°  F.)  destroys  it.  {b)  Acids 
or  strong  alkalies  either  delay  or  stop  the  action  altogether;  the  action 
in  a  faintly  alkaline  medium  is  nearly  as  vigorous  as  in  a  neutral  medium, 
(c)  Presence  of  too  great  a  percentage  of  the  changed  material.  Ptyalin, 
in  that  it  converts  starch  into  sugar,  is  an  amylolytic  or  diastasic  ferment. 

Starch  appears  to  be  the  only  principle  of  food  upon  which  saliva  acts 
chemically :  the  secretion  has  no  apparent  influence  on  any  of  the  other 
ternary  principles,  such  as  sugar,  gum,  cellulose,  or  on  fat,  and  seems  to 
be  equally  destitute  of  power  over  albuminous  and  gelatinous  substances. 

Saliva  from  the  parotid  is  less  viscid ;  less  alkaline,  the  first  few  drops 
discharged  in  secretion  being  even  acid  in  reaction  ;  clearer,  although  it 
may  become  cloudy  on  standing  from  the  precipitation  of  calcium  carbon- 
ate from  escape  of  carbon  dioxide ;  and  more  watery  than  that  from  the 
submaxillary.  It  has  moreover  a  less  powerful  action  on  starch.  Sub- 
lingual saliva  is  the  most  viscid,  and  contains  more  solids  than  either  of 
the  other  two,  but  has  little  diastasic  action. 


FOOD    AND    DIGESTION.  341 

'  The  salivajy  glands  of  children  do  not  become  functionally  active  till 
the  age  of  4  to  6  months,  and  hence  the  bad  etfect  of  feeding  them  before 
this  age  on  starchy  food,  corn-flour,  etc.,  which  they  are  unable  to  render 
soluble  and  capable  of  absorption.  The  salivas  of  the  dog,  cat,  bear,  and 
pig  are  almost  inactive,  whereas  that  of  monkeys,  rabbits,  mice,  squirrels, 
and  guinea-pigs,  are  strongly  diastasic. 

Salirary  Digestion  in  the  Stomach. — Under  proper  conditions  salivary 
digestion  may  continue  for  some  time  after  the  food  has  entered  the  stom- 
ach. In  laboratory  experiments  it  is  found  that  while  the  addition  of 
even  .05  per  cent,  of  hydrochloric  acid  will  inhibit  the  action  of  ptyalin  on 
a  solution  of  starch,  if  any  proteids  be  present  in  the  solution,  much 
more  acid  must  be  added  before  the  action  of  the  ptyalin  is  stopped. 
The  exi^lanation  of  the  latter  fact  is  that  the  acid  unites  with  the  proteids 
in  some  loose  chemical  combination,  forming  " combined  acid"  which  has 
little  effect,  comparatively,  on  ptyalin.  This  " combined  acid"  gives  a 
red  color  with  litmus,  but  is  distinguished  from  free  acid  by  giving  a 
brownish  instead  of  a  bluish  color  with  Congo  red. 

AVlien  food  enters  an  empty  stomach,  as  happens  at  the  beginning  of 
a  meal,  the  acid  first  secreted  combines  Avith  the  proteid  food-stuffs  and 
so  does  not  affect  the  ptyalin.  It  usually  requires  at  least  15  to  20  min- 
utes before  the  acid  is  secreted  in  sufficient  quantity  to  be  in  excess,  as 
free  acid,  of  the  amount  which  can  combine  with  the  proteids,  and  during 
this  time  salivary  digestion  may  continue.  Of  course  the  action  of  pty- 
alin on  food  taken  later  in  a  meal  is  promptly  stopped  when  it  reaches  the 
stomach  because  of  the  presence  of  free  acid. 

The  Nervous  Mechanism  of  the  Secretion  of  Saliva. 

The  secretion  of  saliv^a  is  under  the  control  of  the  nervous  system.  It 
is  a  reflex  action.  Under  ordinary  conditions  it  is  excited  by  the  stimu- 
lation of  the  peripheral  branches  of  two  nerves,  viz.,  the  giintatori/  or 
Ungual  branch  of  the  inferior  maxillarj'"  division  of  the  fifth  nerve,  and 
the  gloHso-pharyngeal  part  of  the  eighth  pair  of  nerves,  which  are  distrib- 
uted to  the  mucous  membrane  of  the  tongue  and  pharynx  conjointly. 
The  stimulation  occurs  on  the  introduction  of  sapid  substances  into  the 
mouth,  and  the  secretion  is  brought  about  in  the  following  way:  From 
the  terminations  of  the  above-mentioned  sensory  nerves  distributed  in  the 
mucous  membrane  an  impression  is  conveyed  upward  (afferent)  to  the 
special  nerve  centre  situated  in  the  medulla-oblongata  which  controls 
the  process,  and  by  it  is  reflected  to  certain  nerves  supplied  to  the 
salivary  glands,  which  will  be  presently  indicated.  In  other  words, 
the  centre,  stimulated  to  action  by  the  sensory  impressions  carried 
to  it,  sends  out  impulses  along  efferent  or  secretory  nerves  supplifd 
to  the  salivary  glands,  which  cause  the  saliva  to  be  secreted  by  and  dis- 


34:2  HAXDBOOK    OF    PHYSIOLOGY. 

charged  from  the  gland  cells.  Other  stunuli,  however,  besides  that  of 
the  food,  and  other  sensory  nerves  besides  those  mentioned,  may  pro- 
duce refiexly  the  same  effects.  For  example,  saliva  may  be  caused  to 
flow  by  irritation  of  the  mucous  membrane  of  the  mouth  with  mechani- 
cal, chemical,  electrical,  or  thermal  stimuli,  also  by  the  irritation  of  the 
mucous  membrane  of  the  stomach  in  some  way,  as  in  nausea,  which 
precedes  vomiting,  when  some  of  the  peripheral  fibres  of  the  vagi  are 
irritated.  Stimulation  of  the  olfactory  nerves  by  smell  of  food,  of  the 
ojjtic  nerves  by  the  sight  of  it,  and  of  the  auditory  nerves  by  the  sounds 
which  are  known  by  experience  to  accompany  the  preparation  of  a  meal, 
may  also,  in  the  hungry,  stimulate  the  nerve  centre  to  action.  In  addi- 
tion to  these,  as  a  secretion  of  saliva  follows  the  movement  of  the  mus- 
cles of  mastication,  it  may  be  assumed  that  this  movement  stimulates  the 
secreting  nerve  fibres  of  the  gland,  direct  or  refiexly.  From  the  fact 
that  the  flow  of  saliva  may  be  increased  or  diminished  by  mental  emo- 
tions, it  is  evident  that  impressions  from  the  cerebrum  also  are  capable 
of  stimulating  the  centre  to  action  or  of  inhibiting  its  action. 

Salivary  secretion  may  also  be  excited  by  direct  stimulation  of  the 
centre  in  the  medulla. 

On  the  Submaxillai^y  Gland. — The  submaxillary  gland  has  been  the 
gland  chiefly  employed  for  the  purpose  of  experimentally  demonstrating 
the  influence  of  the  nervous  system  upon  the  secretion  of  saliva,  because 
of  the  comparative  facility  with  which,  with  its  blood-vessels  and  nerves, 
it  may  be  exposed  to  view  in  the  dog,  rabbit,  and  other  animals.  The 
chief  nerves  supplied  to  the  gland  are  (1)  the  cliorda  tympani,  a  branch 
given  off  from  the  facial  (or  -portio  dura  of  the  seventh  pair  of  nerves), 
in  the  canal  through  which  it  passes  in  the  temporal  bone,  in  its  passage 
from  the  interior  of  the  skull  to  the  face;  and  (2)  branches  of  the  sym- 
pathetic nerve  from  the  plexus  around  the  facial  artery  and  its  branches 
to  the  gland.  The  chorda  (fig.  238,  ch.  t.),  after  quitting  the  temporal 
bone,  passes  downward  and  forward,  under  cover  of  the  external  ptery- 
goid muscle,  and  joins  at  an  acute  angle  the  lingual  or  gustatory  nerve, 
proceeds  with  it  for  a  short  distance,  and  then  passes  along  the  submax- 
illary gland  duct  (fig.  238,  sm.  d.),  to  which  it  is  distributed,  giving 
branches  to  the  submaxillary  ganglion  (fig.  2S8,sm..  _(//.), and  sending  others 
to  terminate  in  the  superficial  muscles  of  the  tongue.  It  consists  of  fine 
medullated  fibres  which  lose  their  medulla  in  the  gland.  If  this  nerve 
be  exposed  and  divided  anywhere  in  its  course  from  its  exit  from  the  skull 
to  the  gland,  no  immediate  result  will  follow,  nor  will  stimulation 
either  of  the  lingual  or  of  the  glosso-pharyngeal  produce  a  flow  of  saliva. 
But  if  tlie  peripheral  end  of  the  divided  nerve  be  stimulated,  an  abundant 
secretion  of  saliva  ensues,  and  the  blood  supply  is  enormously  increased, 
the  arteries  being  dilated.  The  veins  even  pulsate,  and  the  blood  con- 
tained within  them  is  more  arterial  than  venous  in  character. 


FOOD    AND    DIGESTION". 


34^ 


When,  on  the  other  hand,  the  stimukis  is  applied  to  the  sympathetic 
filaments  (mere  division  producing  no  apparent  effect),  the  arteries  con- 
tract, and  the  blood  stream  is  in  consequence  much  diminished;  and 
from  the  veins,  when  opened,  there  escapes  only  a  sluggish  stream  of 
dark  blood.  The  saliva,  instead  of  being  abundant  and  watery,  becomes 
scanty  and  tenacious.  If  both  chorda  tympani  and  sympathetic  branches 
be  divided,  the  gland,  released  from  nervous  control,  may  secrete  con- 
tinuously and  abundantly  (  paralytic  secretion). 

The  abundant  secretion  of  saliva,  which  follows  stimulation  of  tho 
chorda  tympani,  is  not  merely  the  result  of  a  filtration  of  fluid  from 


Fig.  238.— Diagrammatic  representation  of  the  sub-maxillary  gland  of  the  clog  with  its  nei-ves  and 
blood-vessels.  (This  is  not  intended  to  illustrate  the  exact  anatomical  relations  of  the  several  struc- 
tures.) sm.  gld.,  the  suh-niaxillary  gland  into  the  duct  (itm.  d.)  of  which  a  canula  has  been  tied. 
The  subungual  gland  and  duct  are  not  shown,  n.  ?.,  n.  I'.,  the  lingual  or  gustatory  nerve  ;  c/(.  t., 
ch.  t'.,  the  chorda  tympani  proceeding  from  the  facial  nerve,  becoming  conjoined  with  the  lingual 
at  »i.  i'.,  and  afterward  diverging  and  passing  to  the  gland  along  the  duct ;  sm.  gl.,  sub-maxillary 
ganglion  with  its  roots;  n,  i.,  the  lingual  nerve  proceeding  to  the  tongue  ;  a.  rar.,  the  carotid  arterj-, 
two  branches  of  which,  a.  sm.  a.  and  r.  sm.  p.,  pass  to  the  anterior  and  posterior  parts  of  the  gland  ; 
V.  sm.,  the  anterior  and  posterior  veins  from  the  gland  ending  in  v.  J.,  the  jugular  vein  ;  v.  sijm.,  the 
conjoined  vagus  and  sympathetic  trunks  ;  c/l.  cer.s..  the  superior-cervical  ganglion,  two  branches 
of  which  forming  a  plexus,  a.f..  over  the  facial  artery  are  distributed  (ji.  .tym.  sm.}  along  the  two 
glandular  arteries  to  the  anterior  and  posterior  portion  of  the  gland.  The  arrows  indicate  the 
direction  taken  by  the  nervous  impulses  ;  during  reflex  stimulations  of  the  gland  they  ascend  to  the 
brain  by  the  lingual  and  descend  by  the  chorda  tympani.    Ql.  Foster.) 

the  blood-vessels,  in  consequence  of  the  largely  increased  circulation 
through  them.  This  is  proved  by  the  fact  that,  when  the  main  duct  is 
obstructed,  tlie  pressure  within  may  considerably  exceed  the  blood-pres- 
sure in  the  arteries,  and  also  that  when  into  the  veins  of  the  animal 
experimented  upon  some  atropin  has  been  previously  injected,  stimula- 
tion of  the  peripheral  end  of  the  divided  chorda  produces  all  the  vascu- 
lar effects  as  before,  without  any  secretion  of  saliva  accompanying  them. 
Again,  if  an  animal's  head  be  cut  off,  and  the  chorda  be  rapidly  exposed 
and  stimulated  with  an  interrupted  current,  a  secretion  of  saliva  ensues  for 
a  short  time,  although  the  blood  supply  is  necessarily  absent.     These 


344  HANDBOOK   OF   PHTSIOLOGT. 

experiments  serve  to  prove  that  the  chorda  contains  two  sets  of  nerve 
fibres,  one  set  {vaso-dilato7')  which,  when  stimulated,  act  upon  a  local 
vaso-motor  centre  for  regulating  the  blood  supply,  inhibiting  its  action, 
and  causing  the  vessels  to  dilate,  and  so  producing  an  increased  supply  of 
blood  to  the  gland;  while  another  set,  which  are  paralyzed  by  injection 
of  atropin,  directly  stimulate  the  cells  themselves  to  activity,  whereby 
they  secrete  and  discharge  the  constituents  of  the  saliva  which  they 
produce.  These  latter  fibres  very  possibly  terminate  on  the  salivary  cells 
themselves.  If,  on  the  other  hand,  the  sympathetic  fibres  be  divided, 
stimulation  of  the  tongue  by  sapid  substances,  or  of  the  trunk  of  the 
lingual,  or  of  the  glosso-pharyugeal,  continues  to  produce  a  flow  of  saliva. 
From  these  experiments  it  is  evident  that  the  chorda  tympani  nerve  is 
the  principal  nerve  through  which  efferent  impulses  proceed  from  the 
centre  to  excite  the  secretion  of  this  gland. 

The  sympathetic  nerve  also  contains  two  sets  of  fibres,  vaso-constrictor 
and  secretory.  But  the  flow  of  saliva,  upon  stimulating  the  sympathetic, 
is  scanty,  and  the  saliva  itself  viscid.  At  the  same  time  the  vessels  of 
the  gland  are  constricted.  The  secretory  fibres  may  be  paralyzed  by  the 
administration  of  atropine. 

On  the  Parotid  Gland. — The  nerves  which  influence  secretion  in  the 
parotid  gland  are  branches  of  the  facial  (lesser  superficial  petrosal)  and 
of  the  sympathetic.  The  former  nerve,  after  passing  through  the  otic 
ganglion,  joins  the  auriculo-temporal  branch  of  the  fifth  cerebral  nerve, 
and,  with  it,  is  distributed  to  the  gland.  The  nerves  by  which  the 
stimulus  ordinarily  exciting  secretion  is  conveyed  to  the  medulla  ob- 
longata, are,  as  in  the  case  of  the  submaxillary  gland,  the  fifth,  and  the 
glosso-pharyngeal.  The  pneumogastric  nerves  convey  a  further  stimu- 
lus to  the  secretion  of  saliva,  when  food  has  entered  the  stomach;  the 
nerve  centre  is  the  same  as  in  the  case  of  the  submaxillary  gland. 

Changes  in  the  Gland  Cells. — The  method  by  which  the  salivary  cells 
produce  the  secretion  of  saliva  appears  to  be  divided  into  two  stages, 
which  differ  somewhat  according  to  the  class  to  which  the  gland  belongs, 
viz.,  whether  to  (1)  the  true  salivary,  or  (2)  to  the  mucous  type.  In  the 
former  case,  it  has  been  noticed,  as  has  been  already  described,  that 
during  the  rest  which  follows  an  active  secretion  the  lumen  of  the  alveo- 
lus becomes  smaller,  the  gland  cells  larger  and  very  granular.  During 
secretion  the  alveoli  and  their  cells  become  smaller,  and  the  granular 
appearance  in  the  latter  to  a  considerable  extent  disappears,  and  at  the 
end  of  secretion  the  granules  are  confined  to  the  inner  part  of  the  cell 
nearest  to  the  lumen,  which  is  now  quite  distinct  (fig.  239). 

It  is  supposed  from  these  appearances  that  the  first  stage  in  the  act 
of  secretion  consists  in  the  protoplasm  of  the  salivary  cell  taking  up 
from  the  lymph  certain  materials  from  which  it  manufactures  the  ele- 


FOOD    AXD    DIGESTION. 


345 


ments  of  its  own  secretion,  and  which  are  stored  up  in  the  form  of 
granules  in  the  cell  during  rest,  the  second  stage  consisting  of  the  actual 
discharge  of  these  granules,  with  or  without  previous  cliange.  The 
granules  are  zymogen  granules,  and  represent  the  chief  substance  of  the 
salivary  secretion,  i.e.,  ptyalin.  In  the  case  of  the  submaxillary  gland  of 
the  dog,  at  any  rate,  the  sympathetic  nerve-fibres  appear  to  have  to  do 
with  the  first  stage  of  the  process,  and  when  stimulated  the  protoplasm  is 
extremely  active  in  manufacturing  the  granules,  whereas  the  chorda 
tympani  is  concerned  in  the  production  of  the  second  act,  the  actual  dis- 
charge of  the  materials  of  secretion,  together  with  a  considerable  amount 
of  fluid,  the  latter  being  an  actual  secretion  by  the  protoplasm,  as  it 
ceases  to  occur  when  atropin  has  been  subcutaneously  injected. 

In  the  mucus-secreting  gland,  the  changes  in  the  cells  during  secre- 
tion have  been  already  spoken  of.     They  consist  in  the  gradual  secre- 


Fig.  239.— Alveoli  of  true  salivary  gland.    A,  at  rest;  B,  in  the  first  stage  of  secretion  ;  C.  after  pro- 
longed secretion.    (Langley.) 


tion  by  the  protoplasm  of  the  cell  of  a  substance  called  mucigen,  which 
is  converted  into  mucin,  and  discharged  on  secretion  into  the  canal  of 
the  alveoli.  The  mucigen  is,  for  the  most  part,  collected  into  the  inner 
part  of  the  cells  during  rest,  pressing  the  nucleus  and  the  small  portion 
of  the  protoplasm  which  remains,  against  the  limiting  membrane  of  the 
alveoli. 

The  process  of  secretion  in  the  salivary  glands  is  identical  with  that 
of  glands  in  general;  the  cells  which  line  the  ultimate  branches  of  the 
ducts  being  the  agents  by  which  the  special  constituents  of  the  saliva 
are  formed.  The  materials  which  they  have  incorporated  with  them- 
selves are  almost  at  once  given  up  again,  in  the  form  of  a  fluid  (secre- 
tion), which  escapes  from  the  ducts  of  the  gland;  and  the  cells,  them- 
selves, undergo  disintegration — again  to  be  renewed,  in  the  intervals  of 
the  active  exercise  of  the  functions.  The  source  whence  the  cells  obtain 
the  materials  of  their  secretion  is  the  blood,  or,  to  speak  more  accu- 
rately, the  plasma,  which  is  filtered  off  from  the  circulating  blood  into 
the  interstices  of  the  glands  as  of  all  living  textures. 


J46 


HANDBOOK    OP    PHYSIOLOGY. 


The  Tongue. 

Structure. — The  tongue  is  a  muscular  organ  covered  by  mucous 
membrane.  The  muscles,  which  form  the  greater  part  of  the  substance 
of  the  tongue  {intrinsic  muscles)  are  termed  linguales;  and  by  these. 


Fig.  840.— Papillar  surface  of  the  tongue,  with  the  fauces  and  tonsils.  1,  1,  clrcumvallate  pa 
pillae,  in  front  of  3,  the  foramen  csecum;  3,  fungiform  papillae  ;  4,  filiform  and  conical  papillse  ;  5, 
transverse  and  oblique  rugae  ;  C,  mucous  glandsatthebaseof  the  tongueand  in  the  fauces;  7,  tonsils; 
8,  part  of  the  epiglottis  ;  9^  median  glosso-epiglottidean  fold  (frsenum  epiglottidis).  (From  Sappey.) 

which  are  attached  to  the  mucous  membrane  chiefly,  its  smaller  and 
more  delicate  movements  are  chiefly  performed. 

By  other  muscles  {extrinsic  muscles),  as  the  genio-hyoglossus,  the 
styloglossus,  etc.,  the  tongue  is  fixed  to  surrounding  parts,  and  by  this 
group  of  muscles  its  larger  movements  are  performed. 

The  mucous  membrane  of  the  tongue  resembles  other  mucous  mem- 


FOOD   AXD    DIGESTIOif. 


347 


braues  in  essential  points  of  structure,  but  contains  papillce,  more  or 
less  peculiar  to  itself;  peculiar,  however,  in  details  of  structure  and  ar- 
rangement, not  in  their  nature.  The  tongue  is  beset  with  numerous 
mucous  follicles  and  glands. 

The  larger  2)a2nllcB  of  the  tongue  are  thickly  set  over  the  anterior 
two-thirds  of  its  uj^per  surface,  or  dorsum  (fig.  240),  and  give  to  it  its 
characteristic  roughness.  In  carnivorous  animals,  especially  those  of 
the  cat  tribe,  the  papillae  attain  a  large  size,  and  are  developed  into 

sharp  recurved  horny  spines.  Such  papillae 
cannot  be  regarded  as  sensitive,  but  they  en- 
able the  tongue  to  play  the  part  of  a  most 
efficient  rasp,  as  in  scraping  bones,  or  of  a 
comb  in  cleaning  fur.  Their  greater  prom- 
inence than  those  of  the  skin  is  due  to  their 
interspaces  not  being  filled  up  with  epithe- 
lium, as  the  interspaces  of  the  papillae  of 
the  skin  are.  The  papillae  of  the  tongue 
present    several    diversities    of    form;    but 


Fig.  241. 


Fig.  24-3. 


Fig.  241.— Section  of  a  mucovis  gland  from  the  tongue.  A,  opening  of  the  duct  on  the  free  sur- 
face; V,  basement  membrane  with  nuclei;  B,  flattened  epithelial  cells  lining  duct  Theduct  divides 
into  several  branches,  which  are  convoluted  and  end  blmdly,  being  lined  throughout  by  columnar 
epithelium.     D,  lumen  of  one  of  the  tuhuli  of  the  gland,     x  90.     (Klein  and  Noble  Smitli.) 

Fig.  542. — Vertical  section  of  a  circumvallate  papilla  of  the  calf.  1  and  S.  epitheUal  layers 
covering  it ;  2,  taste  goblets  ;  4  and  4',  ductof  serous  gland  opening  out  into  the  pit  in  which  papilia 
Is  situated;  5  and  G,  nen-es  ramifying  within  the  papilla.    (.Engelmann.) 


three  principal  varieties,  differing  both  in  seat  and  general  characters, 
may  usually  be  distinguished,  namely,  the  (1)  circumvallaie,  the  (2) 
fungiform,  and  the  (3)  Jiliform  papilla?.  Essentially  these  have  all  of 
them  the  same  structure,  that  is  to  say,  they  are  all  formed  by  a  projec- 
tion of  the  mucous  membrane,  and  contain  special  branches  of  blood- 
vessels and  nerves.  In  details  of  structure,  however,  they  differ  consid- 
erably one  from  another. 

The  surface  of  each  kind  is  studded  by  minute  conical  processes  of 
mucous  membrane,  which  thus  form  secondary  papilla. 

(1.)  CircumvaUate. — These  papillse  (fig.  242),  eight  or  ten  in  num- 


348 


HANDBOOK    OF    PHYSIOLOGY. 


"ber,  are  situate  in  two  V-shaped  lines  at  the  base  of  the  tongue  (1,  1, 
fig.  240).  They  are  circular  elevations  from  ^^^h  to  y^th  of  an  inch 
wide,  (1  to  2  mm.),  each  with  a  central  depression,  and  surrounded  by 
a  circular  fissure,  at  the  outside  of  which  again  is  a  slightly  elevated 
ring,  both  the  central  elevation  and  tbe  ring  being  formed  of  close-set 
simple  papillae. 

(2.)  Fungiform. — The  fungiform  papillae  (3,  fig.  240)  are  scattered 
chiefly  over  the  sides  and  tip,  and  sparingly  over  the  middle  of  the  dor- 
sum, of  the  tongue;  their  name  is  derived  from  their  being  usually  nar- 
rower at  their  base  than  at  their  summit.  They  also  consist  of  groups 
of  simple  papillae  (A.  fig,  243),  each  of  which  contains  in  its  interior  a 
loop  of  capillary  blood-vessels  (B.),  and  a  nerve-fibre. 

(3.)  Conical  or  Filiform. — These,  which  are  the  most  abundant  pa- 
pillse,  are  scattered  over  the  whole  surface  of  the  tongue,  but  especially 


Fig.  243.— Surface  and  section  of  the  fungiform  papillas.  A,  the  surface  of  a  fungiform  papilla, 
partially  denuded  of  its  epithelium;  p,  secondary  papillas;  e,  epithelium.  B,  section  of  a  fungiform 
papilla  with  the  blood-vessels  injected  ;  ci,  artery  ;  v,  vein ;  c,  capillary  loops  of  similar  papilla  in 
the  neighboring  structure  of  the  tongue;  d,  capillary  loops  of  the  secondary  papillge;  e,  epithelium. 
(From  Kolliker,  after  Todd  and  Bowman.) 


over  tbe  middle  of  the  dorsum.  They  vary  in  shape  somewhat,  but  for 
the  most  part  are  conical  or  filiform,  and  covered  by  a  thick  layer  of 
epidermis,  which  is  arranged  over  them,  either  in  an  imbricated  manner, 
or  is  prolonged  from  their  surface  in  the  form  of  fine  stiff  projections, 
hair-like  in  appearance,  and  in  some  instances  in  structure  also  (fig. 
244).  From  their  peculiar  structure,  it  seems  likely  that  these  papillae 
have  a  mechanical  function,  or  one  allied  to  that  of  touch  rather  than 
of  taste;  the  latter  sense  being  probably  seated  especially  in  the  other 
"  two  varieties  of  papillae,  the  circumvallate  and  the  fungiform. 

The  e^ntUelium  of  the  tongue  is  stratified  with  the  upper  layers  of 
the  squamous  kind.  It  covers  every  part  of  the  surface;  but  over  the 
fungiform  papillae  forms  a  thinner  layer  than  elsewhere.  The  epithelium 
covering  the  filiform  papillse  is  extremely  dense  and  thick,  and,  as  before 
mentioned,  projects  from  their  sides  and  summits  in  the  form  of  long, 
stiff,  hair-like  processes  (fig.  244).  Many  of  these  processes  bear  a  close 
resemblance  to  hairs.     Blood-vessels  and  nerves  are  supplied  freely  to 


FOOD    AND    DIGESTION. 


349 


the  papillae.  The  nerves  in  the  fungiform  and  circumvallate  papillaa 
form  a  kind  of  plexus,  spreading  out  brushwise  (fig.  244),  but  the  exact 
mode  of  termination  of  the  nerve-filaments  is  not  certainly  known. 

In  the  circumvallate  papillae  of  the  tongue  of  man  peculiar  struc- 
tures known  as  gustatory  buds  or  taste  goblets,  have  been  discovered. 
They  are  of  an  oval  shape,  and  consist  of  a  number  of  closely  packed, 

very  narrow  and  fusiform,  cells 
(gustatory  cells).  This  central 
core  of  gustatory  cells  is  in- 
closed in  a  single  layer  of 
broader  fusiform  cells  [incas- 
ing  cells).  The  gustatory  cells 
terminate  in  fine  spikes  not 
unlike  cilia,  which  jDroject  on 
the  free  surface  (fig.  245  a). 

These  bodies  also  occur  side 
bv  side  in  considerable   num- 


Fig.  244. 


Fig.  345. 


Kig.  244.  —Two  filiform  papillse,  one  with  epithelium,  the  other  without,  ^.—d,  the  substance  of 
the  papillae  dividing  at  their  upper  extremities  into  secondary  papillaj ;  a,  artery,  and  v,  vein, 
dividing  into  capillary  loops  ;  e,  epithelial  covering,  laminated  between  the  papillEe.  but  extended 
into  hair-like  processes,  /,  from  the  extremities  of  the  secondary  papillae.  (From  Kolliker,  after 
Todd  and  Bowman.) 

Fig.  245 Taste-goblet  from  dog's  epiglottis  Oaryngeal  surface  near  the  base),  precisely  similar 

in  structure  to  those  found  in  the  tongue,  a,  depression  in  epithelium  over  goblet;  beluw  the  letter 
are  seen  the  fine  hair-like  processes  in  which  the  cells  terminate  :  c,  two  nuclei  of  the  axial  (gusta- 
tory) cells.  The  more  supei-ficial  nuclei  belong  to  the  supei-ficial  (incasing)  cells  ;  the  converging 
lines  indicate  the  fusiform  shape  of  the  incasing  cells.    X  400.    (Schofield.) 

bers  in  the  epithelium  of  the  papilla  foliata,  which  is  situated  near  the 
root  of  the  tongue  in  the  rabbit,  and  also  in  man.  Similar  taste-goblets 
have  been  observed  on  the  posterior  (laryngeal)  surface  of  the  epiglottis. 


The  Pharynx. 

The  portion  of  the  alimentary  canal  which  intervenes  between  the 
mouth  and  the  oesophagus  is  termed  the  Pharynx.  It  will  suffice  here 
to  mention  that  it  is  constructed  of  a  series  of  three  muscles  with  stri- 


350 


HANDBOOK   OF   PHYSIOLOGY. 


ated  fibres  {constrictors),  which  are  covered  by  a  thin  fascia  externally, 
and  are  lined  internally  by  a  strong  fascia  (pharyngeal  aponeurosis),  on 
the  inner  aspect  of  which  is  areolar  (submucous)  tissue  and  mucous 
membrane,  continuous  with  that  of  the  mouth,  and,  as  regards  the  part 
concerned  in  swallowing,  is  identical  with  it  in  general  structure.  The 
epithelium  of  this  part  of  the  pharynx,  like  that  of  the  mouth,  is  strati- 
fied and  squamous. 

The  pharynx  is  well  supplied  with  mucous  glands  (fig.  241). 

Between  the  anterior  and  posterior  arches  of  the  soft  palate  are  sit- 
uated the  Tonsils,  one  on  each  side.  A  tonsil  consists  of  an  elevation 
of  the  mucous  membrane  representing  32  to  15  orifices,  which  lead  into 


Fig.  216. 


Fig.  247. 


Fig.  246. — Lingual  follicle  or  crypt,  o,  involution  of  mucous  membrane  with  its  papillae;  b, 
lymphoid  tissues,  with  several  lymphoid  sacs.     (Frey.) 

Fig.  247. —Vertical  section  through  a  crypt  of  the  human  tonsil.  1,  entrance  to  the  crypt ;  2  and 
3,  the  frame worli  or  adenoid  tissue;  4,  the  inclosing  fibrous  tissue  ;  a  and  6,  lymphatic  follicles;  5 
and  6,  blood-vessels.     (Stohr.) 


crypts  or  recesses,  in  the  walls  of  which  arc  placed  nodules  of  adenoid 
or  lymphoid  tissue  (fig.  247).  These  nodules  are  enveloped  in  a  less 
dense  adenoid  tissue  which  reaches  the  mucous  surface.  The  surface 
is  covered  with  stratified  squamous  epithelium,  and  the  subepithelial  or 
mucous  membrane  proper  may  present  rudimentary  papillae  formed  of 
adenoid  tissue.  The  tonsil  is  bounded  by  a  fibrous  capsule  (fig.  247,  4). 
Into  the  crypts  open  the  ducts  of  numerous  mucous  glands. 

The  viscid  secretion  which  exudes  from  the  tonsils  serves  to  lubri- 
cate the  bolus  of  food  as  it  passes  them  in  the  second  part  of  the  act  of 
deglutition. 


FOOD    AND    DIGESTION.  351 


The  (Esophagus  or  Gullet. 

The  (Esophagus  or  Gullet^  the  narrowest  portion  of  the  alimentary 
canal,  is  a  muscular  and  mucous  tube,  nine  or  ten  inches  in  length,  which 
extends  from  the  lower  end  of  the  pharynx  to  the  cardiac  orifice  of  the 
stomach. 

Structure. — The  oesophagus  is  made  up  of  three  coats — viz.,  the 
outer,  muscular;  the  middle,  submucous;  and  the  inner,  mucous.  The 
muscular  coat  is  covered  externally  by  a  varying  amount  of  loose  fibrous 


4=P 


<^  r-9\^ 


<:£f3?^J?: 


Figr.  248.— Transverse  section  of  the  human  oesophagus,  a.  Fibrous  covering;  6.  longitudinal 
mirticular  fibres;  c,  transverse  muscular  fibres;  d,  areolor  or  submucous  coat;  e,  niuscularis 
mucosae;  A  nmcous  membrane,  with  part  of  a  lymphoid  nodule;  gr,  stratified  epithelial  lining:  A, 
mucous  gland;  t,  gland  duct;  7?i',  striated  muscle  fibres.    (V.  Horsley. ) 

tissue.  It  is  composed  of  two  layers  of  fibres,  the  outer  being  arranged 
longitudinally,  and  the  inner  circularly.  At  the  upper  part  of  the  oesoph- 
agus this  coat  is  made  up  principally  of  striated  muscle  fibres,  as  they 
are  continuous  with  the  constrictor  muscles  of  the  jaharynx;  but  lower 
down  the  unstriated  fibres  become  m.ore  and  more  numerous,  and  toward 
the  end  of  the  tube  form  the  entire  coat.  The  muscular  coat  is  con- 
nected with  the  mucous  coat  by  a  more  or  less  developed  layer  of  areolar 
tissue,  which  forms  the  submucous  coat  (fig.  248,/),  in  which  is  con- 
tained in  the  lower  half  or  third  of  the  tube  many  mucous  glands,  the 
ducts  of  which,  passing  through  the  mucous  membrane,  open  on  its  sur- 
face.    Separating  this  coat  from  the  mucous  membrane  proper  is  a  well- 


352  HANDBOOK   OF    PHYSIOLOGY. 

developed  layer  of  longitudinal^  unstriated  muscle,  called  the  miiscularis 
mucosce.  The  mucous  membrane  is  composed  of  a  closely  felted  mesh- 
work  of  fine  connective  tissue,  which,  toward  the  surface,  is  elevated  into 
rudimentary  papillte.  It  is  covered  with  a  stratified  epithelium,  of 
which  the  most  superficial  layers  are  squamous.  The  epithelium  is  ar- 
ranged upon  a  basement  membrane. 

In  newly-born  children  the  mucous  membrane  exhibits,  in  many 
parts,  the  structure  of  lymphoid  tissue  (Klein). 

Blood-  and  lymph-vessels,  and  nerves,  are  distributed  in  the  walls  of 
the  oesophagus.  Between  the  outer  and  inner  layers  of  the  muscular 
coat,  nerve-ganglia  of  Auerbach  are  also  found  (fig.  254). 

Deglutition. 

When  properly  masticated,  the  food  is  transmitted  in  successive  por- 
tions to  the  stomach  by  the  act  of  deglutition  or  swallowing.  The  fol- 
lowing account  of  deglutition  is  based  upon  the  researches  of  Kronecker 
and  Meltzer,  whose  experiments  seem  to  disprove  the  earlier  theory  of 
Magendie: 

The  mouth  is  closed,  and  the  food  is  rolled  after  thorough  mixing 
with  the  saliva  into  a  bolus  on  the  dorsum  of  the  tongue.  The  tip  of 
the  tongue  is  pressed  upward  and  forward  against  the  hard  palate,  thus 
shutting  off  the  anterior  part  of  the  mouth  cavity.  The  mylo-hyoid 
muscles  then  suddenly  contract,  the  bolus  of  food  is  put  under  great 
pressure,  and  shot  backward  and  downward  through  the  pharynx  and 
oesophagus  to  the  cardiac  orifice  of  the  stomach.  Coincidently  with  the 
contraction  of  the  mylo-hyoid  muscles,  the  hyoglossi  are  thrown  into 
action,  drawing  the  tongue  backward  and  downward,  not  only  increasing 
the  pressure  upon  the  food,  but  forcing  the  epiglottis  over  the  glottis 
and  thus  closing  the  larynx.  The  interval  of  time  between  the  com- 
mencement of  the  act  of  deglutition  and  the  arrival  of  the  food  at  the 
cardiac  orifice  of  the  stomach  is  not  more  than  0.1  second.  Usually  the 
food  remains  at  the  cardiac  orifice  without  entering  the  stomach  until 
the  first  pare  of  the  act  of  swallowing  is  reinforced  by  the  subsequent 
contraction  of  the  constrictors  of  the  pharynx  and  the  passage  of  a  peri- 
staltic wave  down  the  oesophagus.  This  wave,  reaching  the  cardiac  ori- 
fice about  6  seconds  after  the  commencement  of  the  act  of  deglutition, 
forces  the  food  into  the  stomach,  the  sphincter  having  previously  re- 
laxed. In  some  cases,  however,  the  food  is  not  stopped  at  the  cardiac 
orifice,  but  is  sent  through  the  relaxed  sphincter  by  the  original  force  of 
the  mylo-hyoid  contraction. 

In  man  the  oesophagus  contracts  in  three  separate  segments — the 
first  segment  lying  in  the  neck  and  being  about  6  centimetres  long,  the 


FOOD    AND    DIGESTION.  353 

second  being  the  next  10  centimetres  of  the  tube,  and  the  third  the  re- 
maining portion  to  the  stomach. 

The  act  of  swallowing  consists,  then,  of  the  contraction  in  sequence 
of  five  muscle-segments:  the  mylo-hyoids,  the  constrictors  of  the  phar- 
ynx, and  the  three  segments  of  the  oesophagus.  The  computed  time  of 
contraction  is  as  follows: 

Seconds. 
Contraction  of  niylo-hyoids  and  constrictors  of  tlie  pharynx         ....  0.3 

Contraction  of  tlie  first  part  of  the  oesophagus  .         .         .         .         .         .         .0.9 

Contraction  of  the  second  part  of  the  oesophagus  .......  1.8 

Contraction  of  the  third  part  of  the  oesophagus  ......        3.0 

6.0 

If  a  second  attempt  at  swallowing  be  made  before  the  first  has  been 
completed  (that  is,  before  6  seconds  have  elapsed),  the  remaining  portion 
of  the  first  act  is  inhibited,  and  the  contraction  wave  reaches  the  stomach 
6  seconds  after  the  commencement  of  the  second  act. 

In  addition  to  the  above,  the  following  facts  must  be  noted: 

During  the  act  of  deglutition  the  posterior  nares  are  closed  through 
the  action  of  the  levator  palati  and  tensor  palati  muscles,  which  raise 
the  velum;  the  palato-pharyngei,  drawing  the  posterior  pillars  of  the 
fauces  together;  and  the  azygos  uvulte,  which  raises  the  uvula — thus 
forming  a  complete  curtain.  Otherwise  the  food  would  pass  into  the 
nose,  as  happens  in  the  case  of  cleft  palate.  At  the  same  time  the  lar- 
ynx is  closed  by  the  adductor  muscles  of  the  vocal  cords  and  the  descent 
of  the  epiglottis,  the  larynx  being  drawn  upward  as  a  whole  through  the 
action  of  the  mylo-hyoid,  gonio-hyoid,  thyro-hyoid,  and  digastric  mus- 
cles. The  presence  of  the  epiglottis  is  not  necessary  for  the  completion 
of  the  act  of  deglutition. 

A'ervuus  Mechanism. — The  nerves  engaged  in  the  reflex  act  of  deglu- 
tition are : — sensory,  branches  of  the  fifth  cerebral  supplying  the  soft  pal- 
ate; glosso-phuryngeal,  supplying  the  tongue  and  pharynx;  the  superior 
laryngeal  branch  of  the  vagus,  supplying  the  epiglottis  and  the  glottis; 
while  the  mutor  fibres  concerned  are : — branches  of  the  fifth,  supplying 
part  of  the  digastric  and  mylo-hyoid  muscles,  and  the  muscles  of  masti- 
cation; the  facial,  supplying  the  levator  palati;  the  glosso-pharyngeal, 
supplying  the  muscles  of  the  pharynx;  the  vagus,  supplying  the  muscles 
of  the  larynx  through  the  inferior  laryngeal  branch,  and  the  hypoglos- 
sal, the  muscles  of  the  tongue.  The  nerve-centre  by  which  the  muscles 
are  harmonized  in  their  action,  is  situate  in  the  medulla  oblongata.  In 
the  movements  of  the  oesophagus,  the  ganglia  contained  in  its  walls, 
with  the  pneumo-gastrics,  are  the  nerve-structures  chiefly  concerned. 

It  is  important  to  note  that  the  SAvallowing  both  of  food  and  drink  is 
a  muscular  act,  and  can,  therefore,  take  place  in  opposition  to  the  force 
of  gravity.     Thus,  horses  and  many  other  animals  habitually  drink  up- 
hill, and  the  same  feat  can  be  performed  by  jugglers. 
23 


354 


HANDBOOK   OF   PHYSIOLOGY. 


The  STOMA.CH. 

In  man  and  those  Mammalia  which  are  proYided  with  a  single  stom- 
ach, it  consists  of  a  dilatation  of  the  alimentary  canal  placed  between 
and  continuous  with  the  oesophagus, 
which  enters  its  larger  or  cardiac 
end  on  the  one  hand,  and  the  small 
intestine,  which  commences  at  its 
narrowed  end  or  pylorus,  on  the 
other.  It  varies  in  shape  and  size 
according  to  its  state  of  distention. 

Structure. — The  stomach  is  com- 
posed of  four  coats,  called  respec- 
tively— (1)  an  external  or  peritoneal, 
(2)  muscular,  (3)  submucous,  and 
(4)  mucous  coat;  with  blood-vessels, 
lymphatics,  and  nerves  distributed 
in  and  between  them. 

(1)  The  peritoneal  coat  has  the 
structure  of  serous  membranes  in 
general,  as  has  been  described.  (3) 
The  muscular  coat  consists  of  three 
separate  layers  or  sets  of  fibre,  which, 
according  to  their  several  directions, 
are  named  the  longitudinal,  circular, 
and  oblique.  The  longitudi7ial  set 
are  the  most  superficial :  they  are 
continuous  with  the  longitudinal 
fibres  of  the  cesophagus  and  spread 
out  in  a  diverging  manner  over  the 
cardiac  end  and  sides  of  the  stom- 
ach. They  extend  as  far  as  the  py- 
lorus, being  especially  distinct  at 
the  lesser  or  upper  curvature  of  the 
stomach,  along  which  they  pass  in 
several  strong  bands.  The  next  set 
are  the  circular  or  transverse  fibres, 
which  more  or  less  completely  en- 
circle all  parts  of  the  stomach  ;  they 

are  most  abundant  at  the  middle  and  in  the  pyloric  portion  of  the  or- 
gan, and  form  the  chief  part  of  the  thick  projecting  ring  of  the  pylorus. 
These  fibres  are  not  simple  circles,  but  form  double  or  figure-of-8  loops, 
the  fibres   intersecting  very  obliquely.       The   next,   and    consequently 


Fig.  249.— From  a  vertical  section  through 
the  mucous  membrane  of  the  cardiac  end  of 
stomach.  Two  peptic  glands  are  shown  with  a 
duct  common  to  both,  one  gland  only  in  part, 
a,  duct  with  columnar  epithelium  becoming 
shorter  as  the  cells  are  traced  downward ;  n, 
neck  of  gland  tubes,  with  central  and  parietal 
or  so-called  peptic  cells ;  6,  fundus  with  curved 
csecal  extremity— the  parietal  cells  are  not  so 
numerous  here.  X  400.  (Klein  and  Noble 
Smith.) 


FOOD   AND    DIGESTION.  355 

deepest  set  of  fibres,  are  the  oUique,  continuotis  with  the  circular  mus- 
cular fibres  of  the  oesophagus,  and  having  the  same  double-looped  ar- 
rangement that  prevails  in  the  preceding  layer:  they  are  comparatively 
few  in  number,  and  are  placed  only  at  the  cardiac  orifice  and  portion  of 
the  stomach,  over  both  surfaces  of  which  they  are  spread,  some  passing 
obliquely  from  left  to  right,  others  from  right  to  left,  around  the  cardiac 
orifice,  to  which,  by  their  interlacing,  they  form  a  kind  of  sphincter, 
continuous  with  that  around  the  lower  end  of  the  oesophagus.  The 
muscular  fibres  of  the  stomach  and  of  the  intestinal  canal  are  unsiriated, 
being  composed  of  elongated,  spindle-shaped  fibre-cells. 

(3)  and  (4)  The  7nucous  menibrane  of  the  stomach,  which  rests  upon 
a  layer  of  loose  cellular  membrane,  or  submucous  tissue,  is  smooth, 
level,  soft,  and  velvety;  of  a  pale  pink  color  during  life,  and  in  the  con- 
tracted state  thrown  into  numerous,  chiefiy  longitudinal,  folds  or  rugae, 
which  disappear  when  the  organ  is  distended. 

The  basis  of  the  mucous  membrane  is  a  fine  connective  tissue,  which 


Fig.  250.— Transverse  section  through  lower  part  of  peptic  glands  of  a  cat.    a,  peptic  ceUs;  6,  small 
spheroidal  or  cubical  cells;  c,  transverse  section  of  capillaries.    (Frey.) 

approaches  closely  in  structure  to  adenoid  tissue;  this  tissue  supports 
the  tubular  glands  of  which  the  superficial  and  chief  part  of  the  mucous 
membrane  is  composed,  and  passing  up  between  them  assists  in  binding 
them  together.  Here  and  there  are  to  be  found  in  this  coat,  immedi- 
ately underneath  the  glands,  masses  of  adenoid  tissue  sufficiently 
marked  to  be  termed  by  some  lymphoid  follicles.  The  glands  are  sepa- 
rated from  the  rest  of  the  mucous  membrane  by  a  very  fine  homogene- 
ous basement  membrane. 

At  the  deepest  part  of  the  mucous  membrane  are  two  layers  (circu- 
lar and  longitudinal)  of  unstriped  muscular  fibres,  called  the  muscularis 
mucosm,  which  separate  the  mucous  membrane  from  the  scanty  sub- 
mucous tissue. 

When  oxaniined  with  a  lens,  the  internal  or  free  surface  of  the  stom- 
ach presents  a  peculiar  honeycomb  appearance,  produced  by  shallow 
polygonal  depressions,  the  diameter  of  which  varies  generally  from -j^th 
to  -g^tli  of  an  inch  (about  125,^)  ;  but  near  the  pylorus  is  as  much  as 
Yj-Q-th  of  an  inch  (250;/).  They  are  separated  by  slightly  elevated 
ridges,  which  sometimes,  especially  in  certain  morbid  states  of  the  stom- 
ach, bear  minute,  narrow  vascular  processes,  which  look  like  villi,  and 


35G 


HANDBOOK    OF   PHYSIOLOGY. 


have  given  rise  to  the  erroneous  supposition  that  the  stomach  has 
absorbing  villi,  like  those  of  the  small  intestines.  In  the  bottom  of 
these  little  pits,  and  to  some  extent  between  them,  minute  openings  are 
visible,  which  are  the  orifices  of  the  ducts  of  perpendicularly  arranged 
tubular  glands  (fig.  249),  imbedded  side  by  side  in  sets  or  bundles,  on 
the  surface  of  the  mucous  membrane,  and  composing  nearly  the  whole 
structure. 

The  glands  of  the  mucous  membrane  are  of  two  varieties,  (a)  Cardiac, 
(b)  Pyloric. 

(a)   Cardiac  glands  are  found  throughout  the  whole  of  the  cardiac 
VxTmBTA  ®^*^  ^^  *^^®  stomach.      They  are  arranged 

in  groups  of  four  or  five,  which  are  sep- 
arated by  a  fine  connective  tissue.  Two 
or  three  tubes  often  open   into  one  duct, 


Fig.  851.  Fig.  252. 

Fig.  251.— Section  showing  the  pyloric  glands,  s,  free  surface;  d,  ducts  of  pyloric  glands;  n, 
necli  of  same;  m,  the  gland  alveoli;  mm,  muscularis  mucosse.    (Klein  and  Noble  Smith.) 

Fig.  252.  —Plan  of  the  blood-vessels  of  the  stomach,  as  they  would  be  seen  in  a  vertical  section. 
a,  arteries,  passing  up  from  the  vessels  of  submucous  coat;  6,  capillaries  branching  between  and 
around,  the  tubes;  c,  superficial  plexus  of  capillaries  occupying  the  ridges  of  the  mucows  membrane; 
d,  vein  formed  by  the  union  of  veins  which,  having  collected  the  blood  of  the  superficial  capillary 
plexus,  are  seen  passing  down  between  the  tubes.    (Brinton.) 

which  forms  about  a  third  of  the  whole  length  of  the  tube  and  opens  on 
the  surface.  The  ducts  are  lined  with  columnar  epithelium.  Of  the 
gland  tube  proper,  i.e.,  the  part  of  the  gland  below  the  duct,  the  upper 
third  is  the  neck  and  the  rest  the  body.  The  neck  is  narrower  than  the 
body,  and  is  lined  with  granular  cubical  cells  which  are  continuous  with 
the  columnar  cells  of  the  duct.  Between  these  cells  and  the  membrana 
propria  of  the  tubes,  are  large  oval  or  spherical  cells,  opaque  or  granular 
in  appearance,  with  clear  oval  nuclei,  bulging  out  the  membrana  pro- 
pria; these  cells  are  called  oxyntic  or  parieUd  cells.  They  do  not  form 
a  continuous  layer.     The  body,  which  is  broader  than  the  neck  and  ter- 


¥in)U   ANlJ    DIGESTION.  IIS 7 

niinates  iu  a  blind  extremity  or  fundus  near  the  niuscularis  mucosa?,  is 
lined  by  cells  continuous  T\ith  the  cubical  or  central  cells  of  the  neck, 
but  longer,  more  columnar  and  more  transparent.  In  this  part  are  a 
few  parietal  cells  of  the  same  kind  as  in  the  neck  (fig.  249). 

As  the  pylorus  is  approached  the  gland  ducts  become  longer  and 
the  tube  proper  becomes  shorter,  and  ocfasionally  branched  at  the 
fundus. 

(J)  Pyloric  GlaiuJs. — These  glands  (fig.  251)  have  much  longer  ducts 
than  the  peptic  glands.  Into  each  duct  two  or  three  tubes  open  by 
very  short  and  narrow  necks,  and  the  body  of  each  tube  is  branched, 
wavy,  and  convoluted.  The  lumen  is  very  large.  The  ducts  are  lined 
with  columnar  epithelium,  and  the  neck  and  body  with  shorter  and 
more  granular  cubical  cells,  wdiich  correspond  with  the  central  cells  of 
the  cardiac  glands.  During  secretion  the  cells  become,  as  in  the  case  of 
the  cardiac  glands,  larger  and  the  granules  restricted  to  the  inner  zone 
of  the  cell.  As  they  ajiproach  the  duodenum  the  pyloric  glands  become 
larger,  more  convoluted  and  more  deeply  situated.  They  are  directly 
continuous  Avith  Brunner's  glands  in  the  duodenum.      (Watney.) 

Changes  in  the  gland  cells  during  secretion. — The  chief  or  cubical 
cells  of  the  cardiac  glands,  and  the  corresponding  cells  of  the  pyloric 
glands  during  the  early  stage  of  digestion,  if  hardened  in  alcohol,  appear 
swollen  and  granular,  and  stain  readily.  At  a  later  stage  the  cells  be- 
come smaller  and  less  granular,  and  stain  even  more  readily.  The 
parietal  cells  swell  up,  but  are  otherwise  not  altered  during  digestion. 
The  granules,  however,  in  the  alcohol-hardened  specimen,  are  believed 
not  to  exist  in  the  living  cells,  but  to  have  been  precipitated  by  the 
hardening  reagent;  for  if  examined  during  life  they  appear  to  be  con- 
fined to  the  inner  zone  of  the  cells,  and  the  outer  zone  is  free  from 
granules,  whereas  during  rest  the  cell  is  granular  throughout.  These 
granules  are  thought  to  be  pepsin,  or  the  substance  from  which  pepsin 
is  iormed,  2}epsi  no  gen,  which  is  during  rest  stored  chiefly  in  the  inner 
zone  of  the  cells  and  discharged  into  the  lumen  of  the  tube  during 
secretion.     (Langley.) 

Lymph((iirs. — Lymphatic  vessels  surround  the  gland  tubes  to  a 
greater  or  less  extent.  Toward  the  fundus  of  the  peptic  glands  are 
found  masses  of  lymphoid  tissue  which  may  appear  as  distinct  follicles, 
somewhat  like  the  solitary  glands  of  the  small  intestine. 

Blood-vessels. — The  blood-vessels  of  the  stomach,  which  first  break 
up  in  the  sub-mucous  tissue,  send  branches  upward  between  the  closely 
packed  glandular  tubes,  anastomosing  around  them  by  means  of  a  fine 
capillary  network,  with  oblong  meshes.  Continuous  with  this  deeper 
plexus,  or  prolonged  upward  from  it,  so  to  speak,  is  a  more  superficial 
network  of  larger  capillaries,  which  branch  densely  around  the  orifices 
of  the  tubes,  and  form  the  framework  on  which  are  moulded  the  small 


358  HANDBOOK    OF    PHTSIOLOGT. 

elevated  ridges  of  mucous  membrane  bounding  the  minute,  polygonal  pits 
before  referred  to.  From  this  superficial  network  the  veins  chiefly  take 
their  origin.  Thence  passing  down  between  the  tubes,  with  no  very  free 
connection  with  the  deeper  inter-tubular  capillary  plexus,  they  open 
finally  into  the  venous  network  in  the  submucous  tissue. 

Nerves. — The  nerves  of  the  stomach  are  derived  from  the  pueumogas- 
trie  and  sympathetic,  and  form  a  plexus  in  the  sub-mucous  and  muscular 
coats  containing  many  ganglia  (Remak,  Meissner) . 

Gastric  Juice. 

The  functions  of  the  stomach  are,  (;i)  to  afford  storage  for  the  food 
until  it  can  be  taken  up  for  digestion  and  absorption  by  the  intestines ;  {b) 
to  secrete  a  digestive  fluid,  the  gastric  juice,  to  the  action  of  which  the 
food  is  subjected  after  it  has  entered  the  cavity  of  the  stomach  from  the 
oesophagus ;  (c)  to  thoroughly  incorporate  the  fluid  with  the  food  by 
means  of  its  muscular  movements ;  and  (d)  to  absorb  such  substances  as 
are  ready  for  absorption.  It  is  not  essential  to  life  as  has  been  shown  by 
successful  removal  of  the  stomach  ;  but  in  such  cases  food  has  to  be  given 
in  small  quantities  frequently  until  a  secondary  dilatation  of  the  intestine 
has  formed  and  can  act  as  a  place  of  storage.  Wliile  the  stomach  con- 
tains no  food,  and  is  inactive,  no  gastric  fluid  is  secreted ;  and  mucus, 
which  is  either  neutral  or  slightly  alkaline,  covers  its  surface.  But  im- 
mediately on  the  introduction  of  food  or  other  substance,  the  mucous 
membrane,  previously  quite  pale,  becomes  slightly  turgid  and  reddened 
with  the  influx  of  a  larger  quantity  of  blood ;  the  gastric  glands  com- 
mence secreting  actively,  and  an  acid  fluid  is  poured  out  in  minute  drops, 
which  gradually  run  together  and  flow  down  the  walls  of  the  stomach,  or 
soak  into  the  substances  within  it. 

Chemical  Composition. — The  first  accurate  analysis  of  gastric  juice 
was  made  by  Prout :  but  it  does  not  appear  to  have  been  collected  in  any 
large  quantity,  or  pure  and  separate  from  food,  until  the  time  when  Beau- 
mont Avas  enabled,  by  a  fortunate  circumstance,  to  obtain  it  from  the  stom- 
ach of  a  man  named  St.  Martin,  in  whom  there  existed,  as  the  result  of 
a  gunshot  wound,  an  opening  leading  directly  into  the  stomach,  near  the 
u^jper  extremity  of  the  great  curvature,  and  three  inches  from  the  cardiac 
orifice.  The  introduction  of  any  mechanical  irritant,  such  as  the  bulb  of 
a  thermometer,  into  the  stomach,  through  this  artificial  opening,  excited 
at  once  the  secretion  of  gastric  fluid.  This  was  drawn  off,  and  was  often 
obtained  to  the  extent  of  nearly  an  ounce.  The  introduction  of  alimen- 
tary substances  caused  a  much  more  rapid  and  abundant  secretion  than 
did  other  mechanical  irritants.     No  increase  of  temperature  could  be  de- 


FOOD    AND    DIGESTION.  359 

tected  during  the  most  active  secretion ;  the  thermometer  introduced  into 
the  stomach  always  stood  at  37.8°  C.  (100°  F.)  except  during  muscular 
exertion,  when  the  temperature  of  the  stomach,  like  that  of  other  parts 
of  the  body,  rose  one  or  two  degrees  higher. 

The  chemical  composition  of  human  gastric  juice  has  been  also  inves- 
tigated by  Schmidt.  The  fluid  in  this  case  was  obtained  by  means  of  an 
accidental  gastric  fistula,  Avhich  existed  for  several  years  below  the  left 
mammary  region  of  a  patient  between  the  cartilages  of  the  ninth  and  tenth 
ribs.  The  mucous  membrane  was  excited  to  action  by  the  introduction  of 
some  hard  matter,  such  as  dry  peas,  and  the  secretion  was  removed  by 
means  of  an  elastic  tube.  The  fluid  thus  obtained  was  found  to  be  acid, 
limpid,  odorless,  with  a  mawkish  taste — with  a  specific  gravity  of  1002 
to  1010.  It  contained  a  few  cells,  seen  with  the  microscope,  and  some 
fine  granular  matter.  The  analysis  of  the  fluid  obtained  in  this  way  is 
given  below.  Essentially  it  is  a  weakly  acid  fluid  containing  hydro- 
chloric acid  and  two  enzymes,  pepsin  and  rennin,  with  possibly  a  third 
(glucase) .  The  gastric  juice  of  dogs  and  other  animals  obtained  by  the 
introduction  into  the  stomach  of  a  clean  sponge  through  an  artificially 
made  gastric  fistula,  shows  a  decided  difference  in  composition,  but  pos- 
sibly this  is  due,  at  least  in  part,  to  admixture  with  food. 

CHEMICAL   COMPOSITION   OP   GASTRIC   JUICE. 

Dogs.  Human. 

Water 971.17        994.4 

Solids 28.82  5.6U 


Solids- 
Ferment— Pepsin    17.5  3.19 

Hydrochloric  acid  (free) 2.7  .2 

Salts- 
Calcium,    sodium,    and   potassium,    cblorides;    and 
calcium,  magnesium,  and  iron,  phosphates   .        .         8.57  2.19 

The  quantity  of  gastric  juice  secreted  daily  has  been  variously  esti- 
mated ;  but  the  average  for  a  healthy  adult  may  be  assumed  to  range 
from  ten  to  twenty  pints  in  the  twenty-four  hours.  The  aciditj^  of  the 
fluid  is  due  to  free  hi/drochloric  acid,  although  other  acids,  e.f/.,  lactic, 
acetic,  butyric,  are  not  infrequently  to  be  found  therein  as  products  of 
gastric  digestion  or  abnormal  fermentation.  In  healthy  gastric  juice  the 
amount  of  free  hydrochloric  acid  is  usually  about  0.2  per  cent,  but  may 
be  as  much  as  0.3  per  cent.  In  pathological  conditions  it  may  be  en- 
tirely absent,  or  may  amount  to  0.5  per  cent,  or  even  more. 

There  is  but  little  doubt  that  hydrochloric  acid  is  the  proper  acid  of 
healthy  gastric  juice,  and  various  tests  have  been  used  to  prove  this; 
most  of  these  depend  upon  changes  produced  in  aniline  colors  by  the 


360  HANDBOOK    OF    PHYSIOLOGY. 

action  of  liydrochloric  acid,  even  in  miuate  traces,  whereas  lactic  aud 
other  organic  acids  have  no  such  action.  Pepsin  will  act  with  phos- 
phoric, lactic,  and  oxalic  acids,  as  proven  by  laboratory  experiments,  but 
the  best  results  are  obtained  with  hydrochloric  acid.  Of  these  tests  the 
following  may  be  mentioned. 

An  aqueous  alkaline  solution  of  00  tropceolin,  a  bright  yellow  dye,  is 
turned  red  on  the  addition  of  a  minute  trace  of  hydrochloric  acid;  and 
aqueous  solutions  of  methyl  violet  and  gentian  violet  are  turned  blue  un- 
der the  same  circumstances.  The  lactic  acid  sometimes  present  in  the 
contents  of  the  stomach  is  derived  partly  from  the  sarcolactic  acid  of 
muscle,  and  partly  from  lactic  acid  fermentation  of  carbohydrates.  Lactic 
acid  (CjHjOg),  if  present,  gives  the  following  test.  A  solution  of  10  cc. 
of  a  4  per  cent  aqueous  solution  of  carbolic  acid,  20  cc.  of  water,  and  one 
drop  of  liquor  ferri  perchloridi  is  made,  forming  a  blue-colored  mixture ; 
a  mere  trace  of  free  lactic  acid  added  to  such  a  solution  causes  it  to 
become  yellow,  whereas  hydrochloric  acid  even  tn  large  amount  only 
bleaches  it. 

The  proteid  matter  in  the  food  combines  with  part  of  the  hydro- 
chloric acid,  which  is  then  known  as  combined  acid  and  does  not  redden 
litmus  paper.  As  this  combination  is  immediate,  it  follows  that  no  free 
acid  is  found  in  the  gastric  contents  until  the  amount  secreted  is  more 
than  enough  to  saturate  the  various  albuminous  affinities.  It  is  for  this 
reason  that,  as  already  mentioned,  salivary  digestion  may  continue  in 
the  stomach  for  some  time  after  the  commencement  of  gastric  digestion. 
According  to  Ehrlich  the  amount  necessary  to  saturate  the  affinities  of 
100  grammes  of  various  articles  of  diet  is  as  follows : 


Beef  (boiled)      . 
Mutton  (boiled)     . 
Veal  (boiled)     . 
Pork  (boiled) 
Ham  (boiled) 
Sweatbread  (boiled) 
Wheat  bread 
Rye  bread     . 
Swiss  cheese 


2.0  i>rammes  of  pure  HCl. 

1.9"      " 

2.2 

1.6 

1.8 

0.9 

0.3 

0.5 

2.6 


Milk  (100  cc.)        ....         0.32-0.42"  "  " 

As  regards  the  formation  of  pepsin  and  acid,  the  former  is  ])roduced 
by  the  central  or  chief  cells  of  the  cardiac  glands,  and  also  most  likely 
by  the  similar  cells  in  the  pyloric  glands ;  the  acid  is  chiefly  found  at  the 
surface  of  the  mucous  membrane,  but  is  in  all  probability  formed  by  the 
parietal  cells  of  the  cardiac  glands,  hence  called  oxyntic,  as  no  acid  is 
formed  by  the  pyloric  glands  in  which  this  variety  of  cell  is  absent. 

Tlie  acid  is  probably  formed  from  materials  in  the  blood  and  results 
from    a  comlnnation    of   common    salt  with    monosodic    orthophosphate 


KOOD    AXD    mGESTlON.  3H] 

(NaH„PO,  +  NaCl  =  Na^HPO^  +  HCl) ;  the  disodic  orthophospJiate  is 
then  reconverted  by  the  action  of  carbonic  acid  and  water  (Xa.HPO^  + 
CO^  +  H^O  =  NaH^PO^  +  XaHCO  J  :  all  these  salts  are  found  in  the  blood. 

The  ferment  Pepsin  can  be  procured  by  digesting  portions  of  the  mucous  mem- 
brane of  the  stomach  in  cold  water,  after  they  have  been  macerated  for  some  time 
in  water  at  a  temperature  27°— 37.8°  C.  (80°— 100°  F.).  The  warm  water  dissolves 
various  substances  as  well  as  some  of  the  pepsin,  but  the  cold  water  takes  up  little 
else  than  pepsin,  which  is  contained  in  a  grayish-brown  viscid  fluid,  on  evaporating 
the  cold  solution.  The  addition  of  alcohol  throws  down  the  pepsin  in  grayish-white 
flocculi.  Glycerine  also  has  the  property  of  dissolving  out  the  ferment;  and  if  the 
mucous  membrane  be  finely  minced,  and  dehj'diated  by  absolute  alcohol,  a  power- 
ful extract  may  he  obtained  by  macerating  it  in  glycerine. 

Functions. — The  chief  function  of  gastric  juice  is  such  alteration  of 
proteid  food-stuffs  as  will  lead  to  their  ready  absorption  and  such  moditi- 
cation  as  Avill  favor  their  further  digestion  (as  far  as  necessary)  in  the 
intestines;  gastric  digestion  is  thus  both  a  complete  and  a  j)reliminary 
process.  Less  important  functions  are  the  antiseptic  action,  coagulation 
of  milk,  and  inversion  of  disaccharides  into  monosaccharides.  The  chief 
digestive  poAver  of  the  gastric  juice  depends  on  the  pepsin  and  acid  con- 
tained in  it,  both  of  Avhich  are,  under  ordinary  circumstances,  necessary 
for  the  process. 

The  general  effect  of  digestion  in  the  stomach  is  the  conversion  of  the 
food  into  cliyme,  a  substance  of  varying  composition  according  to  the 
nature  of  the  food,  yet  always  presenting  a  characteristic  thick,  pulta- 
ceous,  grumous  consistence,  with  the  undigested  portions  of  the  food 
mixed  in  a  more  fluid  substance,  and  a  strong,  disagreeable  acid  odor  and 
taste. 

This  action  on  proteids  may  be  shown  by  adding  a  little  gastric  juice 
(natural  or  artificial)  to  some  diluted  egg-albiTmin ,  and  keeping  the  mix- 
ture at  a  temperature  of  about  37,8°  C.  (100°  F.);  it  is  soon  found  that 
the  albumin  cannot  be  precipitated  on  boiling,  btit  that  if  the  sokition  be 
neutralized  with  an  alkali,  a  precii:>itate  of  acid-albumin  is  thrown  down. 
After  a  while  the  acid-albumin  disapjiears,  so  that  no  precipitate  results 
on  neutralization,  and  proper  analysis  will  show  that  all  the  albumin  has 
been  converted  into  other  proteid  substances,  viz.,  2^>'ot<ioses  and  jjejjtones. 
I'he  process,  as  is  the  case  in  salivarj'  digestion,  is  never  complete  and 
the  final  result  is  always  a  mixture  of  peptones  with  proteoses  Avhich  can- 
not be  further  peptonized :  the  relative  proportions,  of  course,  depend  on 
the  duration  of  the  process.  A  side  product  is  found  (as  an  insoluble 
residue)  in  artificial  gastric  digestion  which  gives  practically  all  the  pro- 
teid reactions  and  is  soluble  in  dilute  alkali,  though  insoluble  in  water, 
sodium  chloride,  or  dilute  acid.     This  is  known  as  anti-nJhum'ul  and  may 


362  HANDBOOK    OP    PHYSIOLOGY. 

be  changed  into  peptone  by  prolonged  digestion ;  it  does  not  occur  in 
physiological  gastric  digestion.  The  commonest  proteose  is  the  one 
formed  from  albumin  and  is  known  as  albumose :  the  class  name,  how- 
ever, is  proteose,  and  this  name  is  used  in  the  subsequent  descriptions  of 
the  digestive  processes. 

Characteristics  of  Fejjtojies. — Peptones  have  a  certain  characteristic 
which  distinguishes  them  from  other  proteids.  They  are  diffusible,  i.e., 
they  possess  the  property  of  passing  through  animal  membranes. 

In  their  ditt'usibility  peptones  differ  remarkably  from  egg-albumin,  and 
on  this  diffusibility  depends  one  of  their  chief  uses.  Egg-albumin  as 
such,  even  in  a  state  of  solution,  would  be  of  little  service  as  food,  inas- 
much as  its  in  diffusibility  would  effectually  prevent  its  passmg  by  absorp- 
tion into  the  blood-vessels  of  the  stomach  and  intestinal  canal.  When 
completely  changed  by  the  action  of  the  gastric  juice  into  peptones,  albu- 
minous matters  diffuse  readily,  and  are  thus  quickly  absorbed. 

After  entering  the  blood  the  peptones  are  very  soon  again  modified, 
so  as  to  reassume  the  chemical  characters-  of  albumin,  a  change  as  neces- 
sary for  preventing  their  diffusing  out  of  the  blood-vessels,  as  the  pre- 
vious change  was  for  enabling  them  to  pass  in.  This  is  effected,  prob- 
ably, in  great  part  by  their  passage  through  the  vascular  walls. 

Products  of  Gastric  Digestion.— Th.Q  proteid  is  first  changed  into  syn- 
tonin,  or  acid  proteid,  by  the  combined  action  of  the  pepsin  and  acid. 
Though  the  acid  alone  is  capable  of  accomplishing  this,  the  fact  that  it 
does  not  do  so  physiologically  is  proven  by  the  great  length  of  time  re- 
quired, in  laboratory  experiments,  for  the  change.  The  next  change  is 
the  conversion  of  the  syntonin  into  proteoses  which,  according  to  IsTeu- 
meister,  occurs  in  two  successive  stages.  The  first  of  these  stages  is  the 
conversion  of  syntonin  into  the  primary  proteoses,  i.  e. ,  proto-proteose  and 
hetero-proteose ;  the  second  is  the  conversion  of  both  proto-proteose  and 
hetero-proteose  into  the  secondary  proteoses,  i.e.,  deutero-proteose. 
The  last  change  is  the  conversion  of  the  deutero-proteose  into  peptone ; 
this  change  does  not  occur  to  any  great  extent  physiologically  and  the 
proteoses  always  predommate.  Schematically  the  changes  in  the  proteids 
may  be  represented  as  follows : 

Proteid. 

I 
Syntonin  (acid  proteid). 


I  „  I 

Proto-proteose.  Hetero-proteose. 

I  ^  I 

Deutero-proteose.  Deutero-proteose, 

Peptone.  Peptone. 


FOOD    AND    DIGESTION.  363 

The  action  of  pepsin  is  one  of  hydrolysis  and  the  products  are  hydrated 
forms  of  proteid.  The  acid  is  not  only  essential  to  the  action  of  pepsin, 
but  it  also  aids  digestion  by  causing  the  proteids  to  swell.  That  this  ac- 
tion is  important  is  proven,  in  laboratory  experiments,  by  the  increased 
length  of  time  required  for  digestion  when  fibrin  has  been  wrapped  with 
tliread  and  thus  prevented  from  SAvelling. 

Reactions  of  Proteoses. — The  proteoses  cannot  be  coagulated  by  heat. 
All  are  soluble  in  salt  solution.  All  are  precipitated  by  picric  acid  or  by 
saturation  (after  neutralizing)  with  ammonium  sulphate.  All  give  the 
Biuret  test,  copper  sulphate  producing  a  precipitate  Avhich  redissolves  on 
the  addition  of  caustic  potash  and  forms  a  rose  red  solution.  The  pri- 
mary proteoses  are  precipitated  by  strong  nitric  acid,  also  by  acetic  acid 
and  potassium  ferrocyanide,  and  by  saturation  with  sodium  chloride  and 
magnesium  sulphate.  The  secondary  proteoses  are  not  precipitated  by 
these  reactions  just  mentioned  but  are  characterized  by  the  fact  that  their 
precipitates,  when  formed,  disappear  on  warmmg  and  reappear  on  cool- 
ing. Proto-proteose  is  distinguished  by  being  soluble  in  water  while 
hetero-proteose  is  not. 

Peptone  reacts  to  the  same  test  as  deutero-proteose,  biit  is  not  precipi- 
tated on  saturation  with  ammonium  sulphate. 

Chxumstances  favoring  Gastric  Digestion. — 1.  A  temperature  of  about 
37.8°  C.  (100°  F.);  at  0°  C.  (32°  F.)  it  is  delayed,  and  by  boiling  is  al- 
together stopped.  2.  An  acid  medium  is  necessary.  Hydrochloric  is  the 
best  acid  for  the  purpose.  Excess  of  acid  or  neutralization  stops  the  proc- 
ess. 3.  The  removal  of  the  products  of  digestion.  Excess  of  peptone 
delays  the  action. 

a.  Fibrin  is  first  dissolved,  forming  a  solution  of  globulins.  The  in- 
termediate products  of  the  digestion  of  globulins  are  called  globuloses ; 
of  vitellin,  vitelloses;  of  casein,  caseinoses;  of  myosin,  myosinoses. 
These  are  practically  the  same  as  albumoses,  and  are  included  under  the 
term  proteoses. 

h.  Proteids. — All  proteids  are  converted  by  the  gastric  juice  into  pro- 
teoses and  peptones,  and,  therefore,  whether  they  be  taken  into  the  body 
in  meat^  eggs,  milk,  bread,  or  other  foods,  proteoses  and  peptone  are  still 
the  resultant. 

c.  Milk  is  curdled,  the  casein  being  precipitated,  and  then  dissolved. 
The  curdling  is  due  to  a  special  ferment  of  the  gastric  juice,  and  is  not 
due  to  the  action  of  the  free  acid  only.  The  effect  of  reniiet,  which  is  a 
decoction  of  the  fourth  stomach  of  a  calf  in  brine  (rennet),  has  long  been 
known,  as  it  is  used  extensively  to  cause  precipitation  of  casein  in  cheese 
manufacture.  The  ferment  which  produces  this  curdling  action  is  dis- 
tinct from  pepsin,  and  is  called  rennin. 


util  HANDBOOK    OF    PHYSIOLOGY. 

d.  Upon  pure  oZeap'uiowspriuciplesthe  gastric  juice  has  no  action.  In 
the  case  of  adipose  tissue,  its  effect  is  to  dissolve  the  areolar  tissue,  albu- 
minous cell-walls,  etc.,  which  enter  into  its  composition,  by  which  means 
the  fat  is  able  to  mingle  more  uniformly  with  the  other  constituents  of 
the  chyme. 

The  gastric  fluid  acts  as  a  general  solvent  for  some  of  the  saline  con- 
stituents of  the  food,  as,  for  example,  particles  of  common  salt,  which 
may  happen  to  have  escajDed  solution  in  the  saliva ;  while  its  acid  may 
enable  it  to  dissolve  some  other  salts  which  are  insoluble  in  the  latter  or 
in  water. 

e.  Upon  starches  the  gastric  juice  has  no  action,  but  by  the  aid  of  its 
hydrochloric  acid  it  inverts  the  disaccharides  into  monosaccharides  to  a 
certain  extent,  changing  cane  sugar  into  dextrose ;  the  ferment  glucose  (if 
existent)  may  have  a  similar,  though  unimportant  and  slight,  action. 

g.  The  action  of  the  gastric  juice  in  preventmg  and  checking  putre- 
faction has  been  often  directly  demonstrated.  Indeed,  that  the  secretion 
which  the  food  meets  with  in  the  stomach  is  antisejitiG  in  its  action,  is 
what  might  be  anticipated  from  the  proneness  to  decomposition  of  organic 
matters,  such  as  those  used  as  food,  especially  under  the  influence  of 
warmth  and  moisture.  It  is  due  to  the  antiseptic  action  of  the  gastric 
juice  that  disease-germs  are  often  destroyed  in  the  stomach,  and  the  per- 
son is  saved  from  an  attack  of  illness. 

Time  occupied  in  Gastric  Digestion. — Under  ordinary  conditions,  from 
three  to  four  hours  may  be  taken  as  the  average  time  occupied  by  the 
digestion  of  a  meal  in  the  stomach.  But  many  circumstances  will  modify 
the  rate  of  gastric  digestion.  The  chief  are  :  the  natvre  of  the  food  taken 
and  its  quantity  (the  stomach  should  be  fairly  filled — not  distended)  ;  the 
time  that  has  elapsed  since  the  last  meal,  which  should  be  at  least  enough 
for  the  stomach  to  be  quite  clear  of  food ;  the  amount  of  exercise  previous 
and  subsequent  to  a  meal  (gentle  exercise  being  favorable,  over-exertion 
injurious  to  digestion) ;  the  state  of  mind  (tranquillity  of  temper  being 
essential,  in  most  cases,  to  a  quick  and  due  digestion),  and  the  bodily 
health. 

Movements  of  the  Stomach. — The  gastric  fluid  is  assisted  in  accom- 
plishing its  share  in  digestion  by  the  movements  of  the  stomach.  In 
granivorous  birds,  for  example,  the  contraction  of  the  strong  muscular 
gizzard  affords  a  necessary  aid  to  digestion,  by  grinding  and  triturating 
the  hard  seeds  which  constitute  part  of  the  food.  But  in  the  stomachs  of 
man  and  other  Mammalia,  the  movements  of  the  muscular  coat  are  too 
feeble  to  exercise  any  such  mechanical  force  on  the  food;  neither  are 
they  needed,  for  mastication  has  already  done  the  mechanical  work 
of  a  gizzard;   and  oxporiraents  have  demonstrated  that  substances  are 


l-'OOD    AND    DIGESTION,  o(J5 

digested  even  inclosed  in  perforated  tnbes,  and  consequently  protected 
from  mechanical  influence. 

The  normal  actions  of  the  muscular  fibres  of  the  human  stomach 
appear  to  have  a  three-fold  purpose:  (1)  to  adajot  the  stomach  to  the 
quantity  of  food  in  it,  so  tliat  its  walls  may  be  in  contact  with  tlic  food 
on  all  sides,  and,  at  the  same  time,  may  exercise  a  certain  amount  of 
compression  upon  it;  (2)  to  keep  the  orifices  of  the  stomach  closed  until 
the  food  is  digested ;  and  (3)  to  jjerform  certain  jieristaltic  movements, 
whereby  the  food,  as  it  becomes  chymified,  is  gradually  propelled  toward, 
and  ultimately  through,  the  pylorus.  In  accomplishing  this  latter  end, 
the  movements  without  doubt  materially  contribute  toward  effecting  a 
thorough  intermingling  of  the  food  and  the  gastric  fluid. 

When  digestion  is  not  going  on,  the  stomach  is  uniformly  contracted, 
its  orifices  not  more  firmly  than  the  rest  of  its  walls;  but,  if  examined 
shortly  after  the  introduction  of  food,  it  is  found  closely  encircling  its 
contents,  and  its  orifices  are  firmly  closed  like  sphincters.  The  cardiac 
orifice,  every  time  food  is  swallowed,  opens  to  admit  its  passage  to  the 
stomach,  and  immediately  again  closes.  The  pyloric  orifice,  during  the 
first  part  of  gastric  digestion,  is  usually  so  comi^letely  closed,  that  even 
when  the  stomach  is  separated  from  the  intestines,  none  of  its  contents 
escape.  But  toward  the  termination  of  the  digestive  process,  the  pylorus 
seems  to  offer  less  resistance  to  the  passage  of  substances  from  the  stom- 
ach; first  it  yields  to  allow  the  successively  digested  portions  go  through 
it;  and  then  it  allows  the  transit  of  even  undigested  substances.  It  ap- 
pears that  food,  so  soon  as  it  enters  the  stomach,  is  subjected  to  a  kind 
of  peristaltic  action  of  the  muscular  coat,  whereby  the  digested  portions 
are  gradually  moved  toward  the  pylorus.  The  movements  were  observed 
to  increase  in  rapidity  as  the  i^rocess  of  chymification  advanced,  and  were 
continued  until  it  was  completed. 

The  contraction  of  the  fibres  situated  toward  the  pyloric  end  of  the 
stomach  seems  to  be  more  energetic  and  more  decidedly  peristaltic  than 
those  of  the  cardiac  portion.  Thus,  it  was  found  in  the  case  of  St.  Mar- 
tin, that  when  the  bulb  of  the  thermometer  was  placed  about  three  inches 
from  the  pylorus,  through  the  gastric  fistula,  it  was  tightly  embraced 
from  time  to  time,  and  drawn  toward  the  pyloric  orifice  for  a  distance  of 
three  or  four  inches.  The  object  of  this  movement  appears  to  be,  as 
just  said,  to  carry  the  food  toward  the  pylorus  as  fast  as  it  is  formed  into 
chyme,  and  to  propel  the  chyme  into  the  duodenum:  the  undigested 
portions  of  food  being  kept  back  until  they  are  also  reduced  into  chyme, 
or  until  all  that  is  digestible  has  passed  out.  The  action  of  these  fibres 
is  often  seen  in  the  contracted  state  of  the  pyloric  portion  of  the  stom- 
ach after  death,  when  it  alone  is  contracted  and  firm,  while  the  cardiac 
portion  forms  a  dilated  sac.  Sometimes,  by  a  predominant  action  of 
strong  circular  fibres  placed  between  the  cardia  and  pylorus,  tlie  two  por- 


366 


HANDBOOK    OF    PHYSIOLOGY. 


tiona,  or  ends  as  they  are  called,  of  the  stomach,  are  partially  separated 
from  each  other  by  a  kind  of  hour-glass  contraction.  By  means  of  the 
peristaltic  action  of  the  muscular  coats  of  the  stomach,  not  merely  is 
chymified  food  gradually  propelled  through  the  pylorus,  but  a  kind  of 
double  current  is  continually  kept  up  among  the  contents  of  the  stomacli, 
the  circumferential  parts  of  the  mass  being  gradually  moved  onward 
toward  the  pylorus  by  the  contraction  of  the  muscular  fibres,  while  the 
central  portions  are  propelled  in  the  opposite  direction,  namely  toward 
the  cardiac  orifice;  in  this  way  is  kept  up  a  constant  circulation  of  the 
contents  of  the  viscus,  highly  conducive  to  their  free  mixture  with  the 
gastric  fluid  and  to  their  ready  digestion. 

Influence  of  the  Nervous  System. — The  normal  movements  of 
the  stomach  during  gastric  digestion  do  not  appear  to  be  so  closely  con- 


Fig.  253.— Very  diagrammatic  representation  of  the  nerves  of  the  alimentary  canal.  Oe  to  Ret, 
the  various  parts  of  the  alimentary  canal  from  oesophag:us  to  rectum;  L.  V,  left  vagus,  ending  on 
front  of  stomach;  rl,  recurrent  laryngeal  nerve,  supplying  upper  part  of  oesophagus;  R.V,  right 
vagus,  joining  left  vagus  in  oesophageal  plexus;  oe.pl,  supplying  the  posterior  part  of  stomach,  and 
continues  as  R'V  to  join  the  solar  plexus,  here  represented  by  a  single  ganglion,  and  connected  with 
the  inferior  mesenteric  ganglion  m.gl.;  a,  branches  from  the  solar  plexus  to  stomach  and  small 
intestine,  and  from  the  mesenteric  ganglia  to  the  large  intestine;  Spl.maj.,  large  splanchnic  nerve, 
arising  from  the  thoracic  ganglia  and  rami  communicantes;  r.c,  belonging  to  dorsal  nerves  from 
the  6th  to  the  9th  (or  10th);  Spl.min.,  small  splanchnic  nerve  similarly  from  the  10th  and  llth  dorsal 
nerves.  The.se  both  join  the  solar  plexus,  and  thence  make  their  way  to  the  alimentary  canal;  c.r., 
nerves  from  the  ganglia,  etc.,  belonging  to  llth  and  12th  dorsal  and  1st  and  2d  lumbar  nerves, 
proceeding  to  the  inferior  mesenteric  ganglia  (or  plexus),  m.gl.,  and  thence  by  the  hypogastric 
nerve,  n.hyp.,  and  the  hypogastric  nerve,  n.hyp.,  and  the  hypogastric  plexus,  pi. hyp.,  to  the  circular 
muscles  of  the  rectum  ;  l.r.,  nerves  from  the  2d  and  3d  sacral  nerves,  S.2,  S.3  (nervi  erigentes) 
proceeding  by  the  hypogastric  plexus  to  the  longitudinal  muscles  of  the  rectum.    (M.  Foster^ 


nected  with  the  plexuses  of  nerves  and  ganglia  contained  in  its  walls  as 
was  formerly  supposed.  The  action,  however,  appears  to  be  set  up  by 
the  presence  of  food  within  it.  The  stomach  is,  moreover,  directly  con- 
nected with  the  higher  nerve-centres  by  means  of  branches  of  the  vagi 
and  of  the  splanchnic  nerves  through  the  solar  plexus. 


FOOD    AST)    DIGESTION.  367 

First  as  to  the  function  of  the  vagi  in  connection  with  the  gastric 
movements.  Irritation  of  these  nerves  produces  contraction  of  the  stom- 
ach, including  the  sphincter  pylori.  The  vagi,  then,  are  the  motor 
nerves  to  the  stomach. 

Secondly  as  to  the  other  nerve-fibres,  which  reach  the  stomach  and 
intestines  through  the  solar  plexus.  These  fibres  pass  from  the  spinal 
cord  in  the  anterior  roots  of  the  nerves  from  the  sixth  to  the  twelfth 
dorsal,  passing  in  the  splanchnic  nerves  to  the  solar  plexus,  and  thence 
to  the  stomach.  Stimulation  of  the  splauchuics  causes  sto]Dpage  of  the 
muscular  movements  as  well  as  relaxation  of  the  sphincter  pylori. 

It  seems  probable  that  automatic  peristaltic  contraction  is  inherent 
in  the  muscular  coat  of  the  stomach,  and  that  the  central  nervous  system 
is  only  employed  to  regulate  it  by  impulses  passing  down  by  the  vagi  or 
splanchnic  nerves. 

Next  as  to  the  influence  of  the  nerves  on  the  secretion  of  the  gastric 
juice.  It  has  been  known  for  a  long  time  that  the  secretion  of  gastric 
juice  could  be  reflexly  stimulated.  For  example.  Bidder  and  Schmidt 
observed  in  a  dog  with  a  gastric  fistula  that  the  mere  sight  of  food  was 
sufficient  to  cause  a  flow  of  gastric  juice.  Quite  recently,  Pawlow  has 
proved  that  secretory  fibres  are  carried  to  the  gastric  glands  in  the  vagus 
trunk.  His  experiment  consisted  in  establishing  a  gastric  fistula,  and 
some  days  later  in  dividing  the  oesophagus  in  the  neck  in  such  a  manner 
that  any  food  swallowed  would  be  diverted  to  the  exterior  through  the 
cut  end.  "  Fictitious  meals  "  could  then  be  given  to  the  animal,  and  the 
effect  upon  the  stomach  noted.  As  loug  as  the  vagi  were  intact,  certain 
foods  (meats)  caused  a  flow  of  gastric  juice,  though  none  of  the  food 
reached  the  stomach.  When  the  vagi  had  been  cut,  no  secretion  oc- 
curred. Moreover,  he  found  that  direct  stimulation  of  the  vagus  pro- 
duced a  flow  of  gastric  juice. 

The  subject  has  been  still  further  elucidated  by  some  experiments  of 
Heidenhain,  relative  to  the  normal  mechanism  of  secretion.  He  cut 
out  a  portion  of  the  fundic  end  of  the  stomach,  converting  it  into  a 
blind  pouch  opening  to  the  exterior,  while  the  continuity  of  the  stomach 
itself  was  established  by  sutures.  Food  given  to  the  animal  caused  a 
secretion  in  the  cul-de-sac  as  well  as  in  the  stomach.  From  the  experi- 
ments he  concludes  that  normally  there  occur  a  primary  secretion  due  to 
the  mechanical  stimulation  of  the  mucous  membrane  and  confined  to 
isolated  spots,  and  a  secondary  secretion  due  to  the  absorption  of  the 
products  of  digestion,  which  comes  from  the  whole  mucous  membrane. 

Khigine  has  carried  these  experiments  still  further  and  obtained  very 
complete  results.  He  has  investigated  the  effects  of  various  chemical 
substances  upon  the  flow  of  secretion,  and  has  found  that  peptone  is  the 


308  HANDBOOK    OF    PHYSIOLOGY. 

best  of  all  stimuli.  How  it  acts  is  unknown.  Khigine  believes  that  it 
acts  upon  the  afferent  nerve-filaments  in  the  stomach,  and  that  the  effect 
is  reflex. 

The  influence  of  the  higher  nerve-centres  on  gastric  digestion,  as  in 
the  case  of  mental  emotion,  is  too  well  known  to  need  more  than  a  ref- 
erence. 

Digestion  of  the  Stomach  after  Death. — If  an  animal  die  during  the  pro- 
cess of  gastric  digestion,  and  when,  therefore,  a  quantity  of  gastric  juice 
is  present  in  the  interior  of  the  stomach,  the  walls  of  this  organ  itself  are 
frequently  themselves  acted  on  by  their  own  secretion,  and  to  such  an 
extent  that  a  perforation  of  considerable  size  may  be  produced,  and  the 


Fig.  254.— Auerbach's  nerve-plexus  in  small  intestine.  The  plexus  consists  of  fibrillated  sub- 
stance, and  is  made  up  of  trabecule  of  various  thicknesses.  Nucleus-like  elements  and  ganglion- 
cells  are  imbedded  in  the  plexus,  the  whole  of  which  is  inclosed  in  a  nucleated  sheath.    (Klein. ) 

contents  of  the  stomach  may  in  part  escape  into  the  cavity  of  the  abdo- 
men. This  phenomenon  is  not  infrequently  observed  in  post-mortem  ex- 
aminations of  the  human  body.  If  a  rabbit  be  killed  during  a  period 
of  digestion,  and  afterward  exposed  to  artificial  warmth  to  prevent  its 
temperature,  from  falling,  not  only  the  stomach,  but  many  of  the  sur- 
rounding parts  will  be  found  to  have  been  dissolved  (Pavy). 

From  these  facts,  it  becomes  an  interesting  question  why,  during 
life,  the  stomach  is  free  from  liability  to  injury  from  a  secretion,  which, 
after  death,  is  capable  of  such  destructive  effects. 

It  is  only  necessary  to  refer  to  the  idea  of  Bernard,  that  the  living 
stomach  linds  protection  from  its  secretion  in  the  presence  of  epithelium 
and  mucus,  which  are  constantly  renewed  in  the  same  degree  that  they 
are  constantly  dissolved,  in  order  to  remark  that  although  the  gastric 
mucus  is  probably  protective,  this  theory,  so  far  as  the  eyitheliiim  is 


FOOD    AS  I)    DIGESTION.  369 

concerned,  has  been  disproved  by  experiments  of  Pavy's,  in  -which  the 

mucous  membrane  of  the  stomachs  of  dogs  was  dissected  off  for  a  small 
space,  and,  on  killing  the  animals  some  days  afterward,  no  sign  of  diges- 
tion of  the  stomach  was  visible.  "Upon  one  occasion,  after  removing 
the  mucous  membrane,  and  exposing  the  muscular  fibres  over  a  space 
of  about  an  inch  and  a  half  in  diameter,  the  animal  was  allowed  to  live 
for  ten  days.  It  ate  food  every  day,  and  seemed  scarcely  aifected  by 
the  operation.  Life  was  destroyed  while  digestion  was  being  curried  on, 
and  the  lesion  in  the  stomach  was  found  very  nearly  repaired ;  new  mat- 
ter had  been  deposited  in  the  place  of  what  had  been  removed,  and  the 
denuded  spot  had  contracted  to  much  less  than  its  original  dimensions." 
Pavy  believes  that  the  natural  alkalinity  of  the  blood,  which  circu- 
lates so  freely  during  life  in  the  walls  of  the  stomach,  is  sufficient  to 
neutralize  tbe  acidity  of  the  gastric  juice;  and  as  may  be  gathered  from 
what  has  buen  previously  said,  the  neutralization  of  the  acidity  of  the 
gastric  secretion  is  quite  sufificient  to  destroy  its  digestive  powers;  but 
the  experiments  adduced  in  favor  of  this  theory  are  open  to  many  objec- 
tions, and  afford  only  a  negative  support  to  the  conclusions  they  are  in- 
tended to  prove.  Again,  the  pancreatic  secretion  acts  best  on  proteids 
in  an  alkaline  medium;  but  it  has  no  digestive  action  on  the  living  in- 
testine. No  satisfactory  theory  of  the  reason  why  the  stomach  does  not 
digest  itself  has  yet  been  suggested. 

VOMITIXG. 

The  expulsion  of  the  contents  of  the  stomach  in  vomiting,  like  that 
of  mucus  or  other  matter  from  the  lungs  in  coughing,  is  preceded  by 
an  inspiration ;  the  glottis  is  then  closed,  and  immediately  afterward  the 
abdominal  muscles  strongly  act;  but  here  occurs  the  difference  in  the 
two  actions.  Instead  of  the  vocal  cords  yielding  to  the  action  of  the  ab- 
dominal muscles,  they  remain  tightly  closed.  Thus  the  diaphragm  being 
unable  to  go  up,  forms  an  unyielding  surface  against  which  the  stomach 
can  be  pressed.  In  this  Avay,  as  well  as  by  its  own  contraction,  the  dia- 
phragm is  Jixed,  to  use  a  technical  ])hrase.  At  the  same  time  the  cardiac 
sphincter-muscle  being  relaxed,  and  the  orifice  which  it  naturally  guards 
being  actively  dilated,  while  the  pi/Ioras  is  closed,  and  the  stomach  itself 
also  contracting,  the  action  of  the  abdominal  muscles,  by  these  means 
assisted,  expels  the  contents  of  the  organ  through  the  oesophagus, 
pharynx,  and  mouth.  The  reversed  peristaltic  action  of  the  oisophagus 
probably  increases  the  effect. 

It  has  been  frequently  stated  that  the  stomach  itself  is  quite  passive 
during  vomiting,  and  that  the  expulsion  of  its  couteuts  is  effected  solely 
by  the  pressure  exerted  upon  it  when  the  capacity  of  the  abdomen  is  di- 
minished by  the  contraction  of  the  di  i2)hragm,  and  subsequently  of  the 
abdominal  muscles.  The  experiments  and  observations,  however,  which 
-4 


370  HANDBOOK    OF    PHYSIOLOGY. 

are  supposed  to  confirm  this  statement,  only  show  that  the  contraction 

of  the  abdominal  muscles  alone  is  sufficient  to  expel  matters  from  an 
unresisting  bag  through  the  oesophagus;  and  that,  under  very  abnormal 
circumstances,  the  stomach,  by  itself,  cannot  expel  its  contents.  They 
by  no  means  show  that  in  ordinary  vomiting  the  stomach  is  passive; 
and,  on  the  other  hand,  there  are  good  reasons  for  believing  the  contrary. 

It  is  true  that  facts  are  wanting  to  demonstrate  with  certainty  this 
action  of  the  stomach  in  vomiting;  but  some  of  the  cases  of  fistulous 
opening  into  the  organ  appear  to  support  the  belief  that  it  does  take 
place;  and  the  analogy  of  the  case  of  the  stomach  with  that  of  the  other 
hollow  viscera,  as  the  rectum  and  bladder,  may  be  also  cited  in  confirm- 
ation. 

The  muscles  concerned  in  the  act  of  vomiting,  are  chiefly  and  pri- 
marily tliose  of  the  abdomen;  the  diaphragm  also  acts,  but  usually  not  as 
the  muscles  of  the  abdominal  walls  do.  They  contract  and  compress 
the  stomach  more  and  more  toward  the  diaphragm;  and  the  diaphragm 
(which  is  usually  drawn  down  in  the  deep  inspiration  that  precedes  each 
act  of  vomiting)  is  fixed,  and  presents  an  unyielding  surface  against 
which  the  stomach  may  be  pressed.  The  diaphragm  is,  therefore,  as  a 
rule  passive,  during  the  actual  expulsion  of  the  contents  of  the  stomach. 
But  there  are  grounds  for  believing  that  sometimes  this  muscle  actively 
contracts,  so  that  the  stomach  is,  so  to  speak,  squeezed  between  the  de- 
scending diaphragm  and  the  retracting  abdominal  walls. 

Some  persons  possess  the  power  of  vomiting  at  will,  without  applying 
any  undue  irritation  to  the  stomach,  but  simply  by  a  voluntary  eifort. 
It  seems  also  that  this  power  may  be  acquired  by  those  who  do  not  nat- 
urally possess  it,  and  by  continual  practice  may  become  a  habit.  There 
are  cases  also  of  rare  occurrence  in  which  persons  habitually  swallow 
their  food  hastily,  and  nearly  unmasticated,  and  then  at  their  leisure  re- 
gurgitate it,  piece  by  piece,  into  their  mouth,  remasticate,  and  again 
swallow  it,  like  members  of  the  ruminant  order  of  Mammalia. 

The  various  nerve-actions  concerned  in  vomiting  are  governed  by  a 
nerve-centre  situated  in  the  medulla  oblongata. 

The  sensory  nerves  are  the  fifth,  glosso-pharyngeal  and  vagus  prin- 
cipally; but,  as  well,  vomiting  may  occur  from  stimulation  of  sensory 
nerves  from  many  organs,  e.g.,  kidney,  testicle,  etc.  The  centre  may 
also  be  stimulated  by  impressions  from  the  cerebrum  and  cerebellum, 
so-called  central  vomiting  occurring  in  disease  of  those  parts.  The 
efferent  impulses  are  carried  by  the  phrenics  and  other  spinal  nerves. 

The  Intestines. 

The  Intestinal  canal  is  divided  into  two  chief  portions,  named  from 
their  differences  in  diameter,  the  small  and  large  intestine  (fig.  215). 


FOOD    AND    DIGESTIOX. 


371 


These  are  continuous  \vitli  eacli  other,  and  communicate  by  means  of 
an  opening  guarded  by  ;i  vulve,  the  ihocmcal  valve,  which  allows  the 
passage  of  the  products  of  digestion  from  the  small  into  the  large  bowel, 
but  not,  under  ordinary  circumstances,  in  the  opposite  direction. 

The  Small  Intestine. — The  Small  Intestine,  the  average  length 
of  which  in  an  adult  is  about  twenty  feet,  has  been  divided,  for  conven- 
ience of  description,  into  three  portions,  viz.,  the  duodemim,  which  ex- 
tends for  eight  or  ten  inches  beyond  the  pylorus;  the  jejunum,  which 
forms  two-fifths,  and  the  ileum,  which  forms  three-fifths  of  the  rest  of 
the  canal. 

Striicture. — The  small  intestine,  like  the  stomach,  is  constructed  of 
four  j)rinci2')dl  coats,  viz.,  the  serous,  muscular,  sub-mucous,  and  mucous. 


Fig.  255. 


Fig.  255. 


Fig.  255,— Horizontal  section  of  a  small  fragrnient  of  the  mucous  membrane,  includinR  one 
entire  cryot  of  Lieberkiihu  and  parts  of  several  others. 

Fig.  256.— Piece  of  small  intestine  (previously  distended  and  hardened  by  alcohol),  laid  open  to 
show  tne  normal  position  of  the  valvulse  conuiventtjs. 


(1.)  The  serous  coat  is  formed  by  the  visceral  layer  of  the  perito- 
neum, and  has  the  structure  of  serous  membranes  in  general. 

(2.)  The  muscular  coats  consist  of  an  internal  circular  and  an  ex- 
ternal longitudinal  layer:  the  former  is  usually  considerably  the  thicker. 
Both  alike  consist  of  bundles  of  unstriped  muscle  supported  by  con- 
nective tissue.  They  are  well  provided  with  lymph  itic  vessels,  which 
form  a  set  distinct  from  those  of  the  mucous  membrane. 

Between  the  two  muscular  coats  is  a  nerve  plexus  (Auerbach's 
plexus)  (fig.  254),  similar  in  structure  to  Meissner's  (in  the  submucous 
tissue),  but  with  more  numerous  ganglia. 

(3.)  Between  the  mucous  and  muscular  coats  is  the  submucous  coat, 
which  consists  of  connective  tissue,  in  which  numerous  blood-vessels 
and  lymphatics  ramify.     A  fine  plexus,  consisting  mainly  of  non-medul- 


373 


ha:n'dbook  of  physiology. 


lated  nerve-fibres,  Meissner''s  plexus^  with  ganglion  cells  at  its  nodes, 
occurs  in  the  submucous  tissue  from  the  stomach  to  the  anus. 

(4.)  The  tmccous  memh'ane  is  the  most  important  coat  in  relation  to 
the  fun'.tion  of  digestion.  The  following  structures,  which  enter  into 
its  composition,  may  now  be  successively  described : — the  valvulm  conni- 
ventes  ;  the  villi;  and  the  glands.  The  general  structure  of  the  mucous 
membrane  of  the  intestines  resembles  that  of  the  stomach  (p.  347),  and, 
like  it,  is  lined  on  its  inner  surface  by  columnar  epithelium.  Adenoid 
tissue  (fig.  255)  enters  largely  into  its  construction;  and  on  its  deep 
surface  is  the  muscularis  mucoscB  {mm,  fig.  360),  the  fibres  of  which  are 
arranged  in  two  layers :  the  outer  longitudinal  and  the  inner  circular. 

Valvuhe  Conniventes. — The  valvulge  conniventes  (fig.  256)  commence 
in  the  duodenum,  about  one  or  two  inches  beyond  the  pylorus,  and 


Fig.  257.  Fig.  So8. 

Fig.  257.  — Transverse  section  through  four  crypts  of  Lieberkiihn  from  the  large  intestine  of  the 
pig.  They  are  Mued  by  columnar  epithelial  cells,  the  iiucli-i  being  placed  in  the  outer  part  of  the 
cells.  The  divisions  between  the  cells  are  seen  as  lines  radiating  from  l,  the  lumen  of  the  crypt;  g, 
epitheli.ij  i-ells,  wliich  have  become  transformed  into  goblet  cells,     x  350.    (Klein  and  Noble  Hmith.) 

Fig.  268.— A  gland  of  Lieberkiihn  in  longitudinal  section.    (Brinton.) 

becoming  larger  and  more  numerous  immediately  beyond  the  entrance 
of  the  bile  duct,  continue  thickly  arranged  and  well  developed  through- 
out the  jejunum;  then,  gradually  diminishing  in  size  and  number,  they 
cease  near  the  middle  of  the  ileum.  They  are  formed  by  a  doubling 
inward  of  the  mucous  membrane;  the  crescentic,  nearly  circular,  folds 
thus  formed  being  arranged  transversely  to  the  axis  of  the  intestine,  and 
each  individual  fold  seldom  extending  around  more  than  ^  or  f  of  the 
bowel's  circumference.  Unlike  the  rugae  in  the  oesopnagus  and  stom- 
ach, they  do  not  disappear  on  distention  of  the  canal.  Only  an  imper- 
fect notion  of  their  natural  position  and  function  can  be  obtained  by 
looking  at  them  after  the  intestine  has  been  laid  open  in  the  usual 
manner.  To  understand  them  aright,  a  piece  of  gut  should  be  distended 
either  with  air  or  alcohol,  and  not  opened  until  the  tissues  have  become 
hardened.     On  then  making  a  section  it  will  be  seen  that,  instead  of 


FOOD    AND    DIGESTION.  373 

disappearing,  they  stand  out  at  right  angles  to  the  general  surface  of 
the  mucous  membrane  (fig.  256),  Their  functions  are  (1)  to  afford  a 
largely  increased  surface  for  secretion  and  absorption,  and  (2)  to  prevent 
the  too  rapid  passage  of  the  very  liquid  products  of  gastric  digestion, 
immediately  after  their  escape  from  the  stomach,  and  (3)  to  assist  in 
the  more  perfect  mingling  of  the  latter  with  the  secretions  poured  out 
to  act  on  them,  by  their  projection,  and  consequent  interference  with 
an  uniform  and  untroubled  current  of  the  intestinal  contents. 

Glands. — The  glands  are  of  three  principal  kinds: — viz.,  those  of  (1) 
Lieberkiihn,  (3)  Brunner,  and  (3)  Peyer. 

(1.)  The  glands  or  crypts  of  Lieherkiihn  are  simple  tubular  depres- 


Fig.  259.— Transverse  section  of  injected  Peyer's  Rlands  (from  KSlliker).  The  drawing  was 
taken  from  a  preparation  made  by  Frey:  it  represents  the  fine  eapillar>--looped  network  spre-xding 
from  the  surromiding  blood-vessels  into  the  interior  of  three  of  Peyer's "capsules  from  the  intestine 
of  the  rabbit. 

sions  of  the  intestinal  mucous  membrane,  thickly  distributed  over  the 
whole  surface  both  of  the  large  and  small  intestines.  In  the  small  in- 
testine they  are  visible  only  with  the  aid  of  a  lens;  and  tlieir  orifices 
appear  as  minute  dots  scattered  between  the  villi.  Tliey  are  larger  in 
the  large  intestine,  and  increase  in  size  the  nearer  they  approach  the 
anal  end  of  the  intestinal  tube;  and  in  the  rectum  tlieir  orifices  may  be 
visible  to  the  naked  eye.  In  length  they  vary  from  -j^  to  ^  of  an 
inch.  Each  tubule  (fig.  258)  is  constructed  of  the  same  essential  part  as 
the  intestinal  mucous  membrane,  viz.,  of  a  fine  memhrana  propria,  or 
basement  membrane,  a  layer  of  columnar  epithelium  lining  it,  many  of 
which  are  goblet  cells,  and  capillary  blood-vessels  covering  its  exterior, 
the  free  surface  of  the  columnar  cells  presenting  a  striated  appearance. 


574 


HANDBOOK    OF    PHYSIOLOGY. 


li 
m 


(2.) — Brunner'' s  glands  (fig.  260)  are  confined  to  the  duodenum;  they 
are  most  abundant  and  thickly  set  at  its  commencement,  diminish  grad- 
ually as  the  duodenum  advances.  They  are  situated  beneath  the  mus- 
cularis  mucosse,  imbedded  in  the  submucous  tissue;  each  gland  is  a 
branched  and  convoluted  tube,  lined  with  columnar  epithelium.  As 
before  said,  in  structure  they  are  very  similar  to  the  pyloric  glands  of 
the  stomach,  and  their  epithelium  undergoes  a  similar  change  during 
secretion;  but  they  are  more  branched  and 
convoluted  r.nd  their  ducts  are  longer. 
(Watney.)  The  duct  of  each  gland  passes 
through  the  muscularis  mucosse,  and  opens 
on  the  surface  of  the  mucous  membrane. 

(3.)  The  glands  of  Peyer  ^ficcnr  chiefly 
but  not  exclusively  in  the  small  intestine. 
They  are  found  in  greatest  abundance  in 
the  lower  part  of  the  ileum  near  to  the 
ileo-caecal  valve.  They  are  met  with  in 
two  conditions,  viz.,  either  scattered  sin- 
gly, in  which  case  they  are  termed  glandules 
solitarice,  or  aggregated  in  groups  varying 
from  one  to  three  inches  in  length,  and 
about  half-an-inch  in  width,  chiefly  of  an 
oval  form,  their  long  axis  parallel  with  that 
of  the  intestine.  In  this  state,  they  are 
named  glandulce  agminaim^  the  groups  be- 
ing commonly  called  Peyefs  ]}atclies  (fig. 
261),  and  almost  always  placed  opposite 
the  attachment  of  the  mesentery.  In 
structure,  and  in  function,  there  is  no 
essential  difference  between  the  solitary 
glands  and  the  individual  bodies  of  which 
each  group  or  patch  is  made  up.  They 
are  really  single  or  aggregated  masses  of 
adenoid  tissue  forming  lymph-follicles.     In 

the  condition  in  which  they  have  been  most  commonly  examined,  each 
gland  appears  as  a  circular  opaque-white  rounded  body,  from  -^-^  to  -^^  inch 
(1  to  2  mm.)  in  diameter,  according  to  the  degree  in  which  it  is  devel- 
oped. They  are  principally  contained  in  the  submucous  coat,  but  some- 
times project  through  the  muscularis  mucosas  into  the  mucous  mem- 
brane. In  the  agminate  glands,  each  follicle  reaches  the  free  surface  of 
the  intestine,  and  is  covered  with  columnar  epithelium.  Each  gland  is 
surrounded  by  the  openings  of  Lieberktihn's  follicles. 

The  adjacent  glands  of  a  Peyer's  patch  are  connected  together  by 
areolar  tissue.     Sometimes  the  lymphoid  tissue  reaches  the  free  surface, 


Figr.  260.— Vertical  section  of  du- 
odenum, showing  a,  villi ;  6,  crypts 
of    Lieberkiihn,    and    c,    Brunner's 

f lands  in  the  submucosa  s,  wiLh 
ucts,  d  ;  muscularis  mucosae,  m, ; 
and  circular  muscular  coat,  /. 
(SchofieldO 


FOOD    AND    DIGESTIOJf.  375 

replacing  the  epithelium,  as  is  also  the  case  with  acme  of  the  lymphoid 
follicles  of  the  tousil. 

Peyer's  glands  are  surrouuded  by  lymphatic  sinuses  which  do  not 
penetrate  into  their  interior;  the  interior  is,  however,  traversed  by  a 
very  rich  blood  capillary  plexus.  If  the  vermiform  appendix  of  a  rab- 
bit, which  consists  largely  of  Peyer's  glands,  be  injected  with  blue  by 
pressing  the  point  of  a  fine  syringe  into  one  of  the  lymphatic  sinuses, 
the  Peyer's  glands  will  appear  as  grayish  white  spacer  surrounded  by 
blue;  if  now  the  arteries  of  the  same  be  injected  with  red,  the  grayish 
patches  will  change  to  red,  thus  proving  that  they  are  surrounded  by 
lymphatic  spaces  but  penetrated  by  blood-vessels.  The  lacteals  passing 
out  of  the  villi  communicate  with  the  lymph  sinuses  round  Peyer's 
glands.  It  is  to  be  noted  that  Peyer's  patches  are  largest  and  most 
prominent  in  children  and  young  persons. 

Villi.— The  Villi  (figs.  260,  262,  and  263)  are  confined  exclusively  to 
the  mucous  membrane  of  the  small  intestine.  They  are  minute  vascu- 
lar processes,  from  a  line  -^^  to  -g-  of  an  inch  (.5  to  3  mm.)  in  length, 
covering  the  surface  of  the  mucous  membrane,  and  giving  it  a  peculiar 
velvety,  fleecy  appearance.  Krause  estimates  them  at  fifty  to  ninety 
in  number  in  a  square  line  at  the  upper  part  of  the  small  intestine,  and 


Fie:.  261. — Agminate  follicles,  or  Peyer's  patch,  in  the  state  of  distention,     x  •">.    (Boehm.) 

at  forty  to  seventy  in  the  same  area  at  the  lower  part.  They  vary  in 
form  even  in  the  same  animal,  and  differ  according  as  the  lymphatic 
vessels  or  lacteals  which  they  contain  are  empty  or  full;  being  usually, 
in  the  former  case,  flat  and  pointed  at  their  summits,  in  the  latter  cyliu- 
drical  or  clavate. 

Each  villus  consists  of  a  small  projection  of  mucous  membrane;  its 
interior  is  supported  throughout  by  fine  adenoid  tissue,  which  forms 
the  framework  or  stroma  in  which  the  other  constituents  are  contained. 

The  surface  of  the  villus  is  clothed  by  columnar  epithelium,  whic^h 
rests  on  a  fine  basement  membrane;  wlnle  within  this  are  found,  reck- 
oning from  without  inward,  blood-vessels,  fibres  of  the  inKscalan's  mu- 


376 


HANDBOOK    OF    PHYSIOLOGY. 


cos(B,  and  a  single  lymphatic  or  lacteal  vessel  rarely  looped  or  branched 
(fig.  263). 

The  epithelium  is  continuous  with  that  lining  the  other  parts  of  the 
mucous  membrane.  The  cells  are  arranged  with  their  long  axis  radiat- 
ing from  the  surface  of  the  villus  (fig. 260),  and  their  smaller  ends 
resting  on  the  basement  membrane.  The  free  surface  of  the  epithelial 
cells  of  the  villi,  like  that  of  the  cells  which  cover  the  general  surface 
of  the  mucous  membrane,  is  covered  by  a  fine  border  which  exhibits  very 
delicate  striations,  whence  it  derives  its  name,  striated  basilar  border. 

Beneath  the  basement  or  limiting  membrane  there  is  a  rich  supply  of 
blood-vessels.  Two  or  more  minute  arteries  are  distributed  within  each 
villus;  and  from  their  capillaries,  which  form  a  dense  network,  proceed 
one  or  two  small  veins,  which  pass  out  at  the  base  of  the  villus. 

The  layer  of  the  muscularis  mucosce  in  the  villus  forms  a  kind  of 

b 


Fig.  262.  — Vertical  section  of  a  villus  of  the  small  intestine  of  a  cat.  a,  striated  basilar  border 
of  tlieepahelium;  b,  columnar  epithelium;  c,  goblet  cells;  d,  central  lymph-vessel;  e,  smooth  mus- 
cular fibres;  /,  adenoid  stroma  of  the  villus  in  which  lymph  corpuscles  he.    (Klein.) 

thin  hollow  cone  immediately  around  the  central  lacteal,  and  is,  there- 
fore, situated  beneath  the  blood-vessels.  It  is  without  doubt  instru- 
mental in  the  propulsion  of  chyle  along  the  lacteal. 

The  lacteal  vessel  in  each  villus  is  the  form  of  commencement  of  the 
lymphatic  system  of  vessels  *  in  the  intestines.  It  begins  almost  at  the 
tip  of  the  villus  commonly  by  a  dilated  extremity.  In  the  larger  villi 
there  may  be  two  small  lacteal  vessels  which  join  on  (fig.  263),  or  the 
lacteals  may  form  a  kind  of  network  in  the  villus.  The  last  method 
is  rarely  or  never  seen  in  the  human  subject,  although  common  in  some 
of  the  lower  animals  (a,  fig.  263). 

The  Large  Intestine. — The  Large  Intestine,  which  in  an  adult 
is  from  about  4  to  6  feet  long,  is  subdivided  for  descriptive  purposes 
into  three  portions,  viz.: — the  ccecum,  a  short  wide  pouch,  communi- 
cating with  the  lower  end  of  the  small  intestine  through  an  opening, 
guarded  by  the  ileo-ccecal  valve;  the  colon,  continuous  with  the  caecum, 

*For  an  account  of  the  Lymphatic  System,  see  Chapter  IX. 


FOOD    AJTD    DlfiESTION. 


377 


which  forms  the  principul  part  of  the  large  intestine,  and  is  divided 
into  ascending,  transverse,  and  descending  portions;  and  the  nctum, 
which,  after  dilating  at  its  lower  part,  again  contracts,  and  immedi- 
ately afterward  opens  externally  through  the  amis.  Attached  to  the 
caecum  is  the  small  appendix  vermiformis. 

Structure. — Like  the  small  intestine,  the  large  intestine  is  con- 
structed of  four  principal  coats,  viz.,  the  serous,  muscular,  sub-mucous 
and  mucous.  The  serous  coat  need  not  be  here  particularly  described. 
Connected  with  it  are  the  small  processes  of  i^eritoneum  containing 
fat,  called  appendices  epiploiccp.  The  fibres  of  the  muscular  coat,  like  those 
of  the  small  intestine,  are  arranged  in  two  layers — the  outer  longitudinal, 
the  inner  circular.  In  the  ca?cumand  colon,  the  longitudinal  fibres,  be- 
sides being,  as  in  the  small  intestine,  thinly  disposed  in  all  parts  of  the  wall 
of  the  bowel,  are  collected,  for  the  most  part,  into  three  strong  bands, 
which,  being  shorter,  from  end  to  end,  than  the  other  coats  of  the  in- 
testine, hold  the  canal  in  folds,  bounding  intermediate  sacculi.  On  the 
division  of  these  bands,  the  intestine  can  be  drawn  out  to  its  full  length. 


Fi.^.  2()3.— A.   Villus  of -ihcfj).     B.   Villi  of  man.     (^Slislitly  altered  from  Teichmann.) 

and  it  then  assumes,  of  course,  an  uniformly  cylindrical  forni.  In  the 
rectum,  the  fasciculi  of  these  longitudinal  bands  spread  out  and  mingle 
with  the  other  longitudinal  fibres,  forming  with  them  a  thicker  layer  of 
fibres  than  exists  on  any  other  part  of  the  intestinal  canal.  The  circu- 
lar muscular  fibres  are  spread  over  the  whole  surface  of  the  bowel,  but 


378  HANDBOOK    OF    PHYSIOLOGY, 

are  somewhat  more  marked  in  the  intervals  between  the  sacculi.  Toward 
the  lower  end  of  the  rectum  they  become  more  numerous,  and  at  the 
anus  they  form  a  strong  band  called  the  interned  sphincier  muscle. 

The  mucous  mernbrane  of  the  large,  like  that  of  the  small  intestine, 
is  lined  throughout  by  columnar  epithelium,  but,  unlike  it,  is  quite  des- 
titute of  villi,  and  is  not  projected  in  the  form  of  valvulce  conniventes. 
Its  general  microscopic  structure  resembles  that  of  the  small  intestine: 
and  it  is  bounded  below  by  the   muscularis  mucosa;. 

The  general  arrangement  of  ganglia  and  nerve-fibres  in  the  large 
intestine  resembles  that  in  the  small. 

Olands. — The  glands  with  which  the  large  intestine  is  provided  are 
of  two  kinds,  (1)  the  tubidar  and  (2)  the  lymplioid. 

(1.)  The  tulidar  glands,  or  glands  of  Lieberkiihn,  resemble  those 
of  the  small  intestine,  but  are  somewhat  larger  and  more  numerous. 
They  also  contain  many  goblet  cells. 

(2.)  Follicles  of  adenoid  or  lymphoid  tissue  are  most  numerous  in 
the  caecum  and  vermiform  appendix.  They  resemble  in  shape  and 
structure,  almost  exactly,  the  solitary  glands  of  the  small  intestine. 
Peyer's  patches  are  not  found  in  the  large  intestine. 

lleo-ccecal  Valve. — The  ileo-cffical  valve  is  situate  at  the  place  of 
junction  of  the  small  with  the  large  intestine,  and  guards  against  any 
reflux  of  the  contents  of  the  latter  into  the  ileum.  It  is  composed  of 
two  semilunar  folds  of  mucous  membrane.  Each  fold  is  formed  by  a 
doubling  inward  of  the  mucous  membrane,  and  is  strengthened  on  the 
outside  by  some  of  the  circular  muscular  fibres  of  the  intestine,  which 
are  contained  between  the  outer  surfaces  of  the  two  layers  of  which  each 
fold  is  composed.  While  the  circular  muscular  fibres,  however,  of  the 
bowel  at  the  junction  of  the  ileum  with  the  csecum  are  contained  be- 
tween the  outer  opposed  surfaces  of  the  folds  of  mucous  membrane 
which  form  the  valve,  the  longitudinal  muscular  fibres  and  the  peri- 
toi^eum  of  the  small  and  large  intestine  respectively  are  continuous 
with  each  other,  without  dipping  in  to  follow  the  circular  fibres  and  the 
mucous  membrane.  In  this  manner,  therefore,  the  folding  inward  of 
these  two  last-named  structures  is  jireserved,  while  on  the  other  hand, 
by  dividing  the  longitudinal  muscular  fibres  and  the  peritoneum,  the 
valve  can  be  made  to  disappear,  just  as  the  constrictions  between  the 
sacculi  of  the  large  intestine  can  be  made  to  disajopear  by  performing  a 
similar  operation.  The  inner  surface  of  the  folds  is  smooth;  the 
mucous  membrane  of  the  ileum  being  continuous  with  that  of  the  caecum. 
That  surface  of  each  fold  which  looks  toward  the  small  intestine  is 
covered  with  villi,  while  that  which  looks  to  the  cEscum  has  none. 
When  the  caecum  is  distended,  the  margin  of  the  folds  are  stretched, 
and  thus  are  brought  into  firm  apposition  one  with  the  other. 


HANDBOOK   OF    PHYSIOLOGY. 


679 


Digestion  in  the  Intestines. 

After  the  food  has  been  duly  acted  upon  by  the  gastric  juice,  such  of 
it  as  has  not  been  absorbed  passes  into  the  duodenum,  and  is  there 
subjected  to  the  action  of  the  secretions  of  the  pancreas  and  liver  which 
enter  that  portion  of  the  small  intestine,  as  well  as  to  the  secretion 
(succus  entericus)  which  is  poured  out  into  the  intestines  from  the  glands 
lining  them.  Mixed  with  products  of  gastric  digestion  is  found  a 
certain  amount  of  proteid  matter  which  has  not  been  acted  upon 
at  all:  the  fats  are  also  included  and  such  carbohydrates  as  have  not 
been  acted  upon  by  salivary  digestion  together  with  products  of  this 
digestion. 


FiK-  264.  —Section  of  the  pancreas  of  a  dog:  during  digestion,  a,  alveoli  lined  with  cells,  the 
outer  zoue  of  which  is  well  stained  with  hceinatoxyliu;  d,  intermediary  duct  lined  with  squamous 
epithehnm.     X  350.     (Klein  and  Noble  Smith.) 

The  Pancreas,  and  its  Secretion. 

The  Pancreas  is  situated  within  the  curve  formed  by  the  duo- 
denum; and  its  main  duct  opens  into  that  part  of  the  small  intestine, 
through  a  .small  opening,  or  through  a  duct  common  to  it  and  to  the 
liver,  about  two  and  a  halt  inches  from  the  pylorus. 

Structure. — In  structure  the  pancreas  bears  some  resemblance  to  the 
salivary  glands.  Its  capsule  and  septa,  as  well  as  the  blood-vessels  and 
lymphatics,  are  simihirly  distributed.  It  is,  however,  looser  and  softer, 
the  lobes  and  lobules  being  less  compactly  arranged.  The  main  duct 
divides  into  branches  (lobar  ducts),  one  for  each  lobe,  and  these  branches 
subdivide  into  intra-lobular  ducts,  and  these  again  by  their  division 
and  branching  form  the  gland  tissue  proper.  The  intralobar  ducts 
correspond  to  a  lobule,  while  between  them  and  the  secreting  tubes  or 


380  HANDBOOK    OF    PHYSIOLOGY. 

alveoli  are  longer  or  shorter  intermediary  ducts.  The  larger  ducts 
possess  a  very  distinct  lumea  and  a  niembrana  propria  lined  with 
columnar  epithelium,  the  cells  of  which  are  longitudinally  striated,  but 
are  shorter  than  those  found  in  the  ducts  of  the  salivary  glands.  In  the 
intralobular  ducts  the  epithelium  is  short  and  the  lumen  is  smaller. 
The  intermediary  ducts  opening  into  the  alveoli  jDossess  a  distinct  lumen, 
with  a  membrana  propria  lined  with  a  single  layer  of  flattened  elongated 
cells.  The  alveoli  are  branched  and  convoluted  tubes,  Avith  a  membrana 
propria  lined  with  a  single  layer  of  columnar  cells.  They  have  a 
distinct  lumen,  though  spindle-shaped  cells  are  often  seen  in  the 
centre  of  the  acini.  Heidenhain  has  observed  that  the  alveolar 
cells  in  the  pancreas  of  a  fasting  dog  consist  of  two  zones,  an  inner  or 
central  zone  which  is   finely  granular,  and  which  stains  feebly,  and  a 


Fig.  265.— Section  of  the  pancreas  of  armadillo,  showing  the  two  kinds  of  gland-structure.    (V.  D. 

Harris.) 

smaller  parietal  zone  of  finely  striated  protoplasm  which  stains  easily. 
The  nucleus  is  partly  in  one,  partly  in  the  other  zone.  During  digestion, 
it  is  found  that  the  outer  zone  increases  in  size,  and  the  central  zone 
diminishes;  the  cell  itself  becoming  smaller  from  the  discharge  of  the 
secretion.  At  the  end  of  digestion  the  first  condition  again  appears,  the 
inner  zone  enlarging  at  the  expense  of  the  outer.  It  appears  that  the 
granules  are  formed  by  and  stored  up  in  the  protoplasm  of  the  cells,  from 
material  supplied  to  it  by  the  blood.  The  granules  are  thought  to 
consist  of  material  from  which,  under  certain  conditions,  the  ferments 
of  the  gland  are  developed,  and  which  is  therefore  called  Zymogen.  In 
addition  to  the  ordinary  alveoli  of  the  pancreas  there  are  found  distri- 
buted irregularly  in  the  gland  other  collections  of  cells  of  a  di£ferent 
character.  They  are  considerably  smaller,  their  protoplasm  is  more 
granular,  and  is  less  easily  stained  with  haematoxylin,  and  their  nuclei 
are  small  and  deeply  staining,  being  situated  also  more  toward  the 
centre  of  the  cells.     The  collections  of  cells  vary  in  size  and  shape,  and 


FOOD    AXD    DIGESTION.  381 

sometimes  seem  to  be  mere  masses  of  proto^^lasm  with  nuclei  imdifferen- 
tiated  into  cells.  Tliese  iiests  of  cells  are  sometimes  seen  to  consist  of 
distinct  columns  of  cells.  No  distinct  basement  membrane,  however, 
can  be  made  out  as  bounding  these  columns.  The  special  form  of  nerve 
terminations,  called  Parinian  corjmsclcs,  are  often  found  in  the  pancreas. 
The  Pancreatic  Juice. — The  secretion  of  the  pancreas  has  been 
obtained  for  purposes  of  experiment  from  the  lower  animals,  especially 
the  dog,  by  opening  the  abdomen  and  exposing  the  duct  of  the  gland, 
which  is  then  made  to  communicate  with  the  exterior.  A  pancreatic 
fistula  is  thus  established. 

An  extract  of  pancreas  made  from  the  gland  which  has  been  removed 
from  an  animal  killed  during  digestion  possesses  the  active  properties  of 
pancreatic  secretion.  It  is  made  by  first  dehydrating  the  gland,  cut  up 
into  small  j)ieces,  by  keeping  it  for  some  days  in  absolute  alcohol,  and 
then,  after  the  entire  removal  of  the  alcohol,  by  pounding  up  these 
pieces  into  a  pulpy  mass  and  placing  it  in  strong  glycerin.  A  glycerin 
extract  is  thus  obtained.  It  is  a  remarkable  fact,  however,  that  the 
amount  of  the  ferment  trypsin  greatly  increases  if  the  gland  be  exposed 
to  the  air  for  twenty-four  hours  before  placing  in  alcohol;  indeed,  a 
glycerin  extract  made  from  the  gland  immediately  upon  the  removal 
from  the  body  often  appears  to  contain  none  of  the  ferments.  This 
seems  to  indicate  that  the  conversion  of  zymogen  in  the  gland  into  the 
ferment  only  takes  place  during  the  act  of  secretion,  and  that  the  gland, 
although  it  always  contains  in  its  cells  the  materials  (trypsinogen)  out 
of  which  trypsin  is  formed,  yet  the  conversion  of  the  one  into  the 
other  only  takes  place  by  degrees.  Dilute  acid  appears  to  assist  and 
accelerate  the  conversion,  and  if  a  recent  pancreas  be  rubbed  up  with 
dilute  acid  before  dehydration,  a  glycerin  extract  made  afterward,  even 
though  the  gland  may  have  been  only  recently  removed  from  the  body, 
is  very  active. 

Many  other  vehicles  may  be  employed  instead  of  glycerin,  e.g.,  brine, 
chloroform,  water,  dilute  methylated  spirit  acidulated  Avith  acetic  acid. 

ProjJerties. — Pancreatic  juice  is  colorless,  transparent,  and  slightly 
viscid,  alkaline  in  reaction.  It  varies  in  specific  gravity  from  1010  to 
1030,  according  as  it  is  obtained  from  a  permanent  fistula — then  more 
watery — or  from  a  newly-opened  duct.  The  solids  vary  in  a  temporary 
fistula  from  80  to  100  parts  per  thousand,  and  in  a  permanent  one  from 
IG  to  50  per  thousand.  It  is  characterized  by  having  three  distinct  and 
important  enzymes  known  as  trypsin,  amylopsin,  and  stnapsin,  whose 
action  is,  respectively,  proteolytic,  amylolytic,  and  lipolytic  (fat-split- 
ting); there  is  also  a  fourth  distinct,  though  less  important,  one  known 
as  glucase,  which  inverts  the  disaccharides. 


382  HANDBOOK    OF    PHYSIOLOGY. 

Chemical  Composition  op  Pancreatic  Juice  (C.  Schmidt). 

From  a  dog.  Recent  fistula.       Permanent  fistula. 

^Yate^ 900.76  980.45 

Solids 99.24  19.55 

Organic  substances 90.44  12.71 

Ash 8.80  6.84 

Sodium  carbonate 0.58  3.31 

Sodium  chloride 7.35  2.50 

Calcium,  magnesium,  and  sodium  phosphates     0.53  0.08 

Functions. — (!.)  By  the  aid  of  its  proteolytic  or  proteid-splitting 
enzyme,  trypsin,  it  conv  evts  pj'oteids  into  2J'>'Gteoses  and  peptones,  but  the 
process  is  both  more  rapid  and  more  complete  than  in  gastric  digestion, 
so  that,  in  tlie  final  result,  the  peptones  are  greatly  in  excess  of  the  pro- 
teoses. The  proteids  pass  through  the  same  preliminary  stages  as  in 
gastric  digestion,  being  split  at  first  into  alkali-albumin,  then  into 
primary  proteoses,  both  proto-proteose  and  hetero-proteose,  and  then 
into  deutero-proteose;  but  the  first  stages  are  so  transient  that  it  is 
difficult  to  detect  either  the  alkali-albumin  or  primary  proteose.  For 
this  reason  some  investigators  deny  the  existence  of  either  alkali-albumin 
or  primary  proteose  in  pancreatic  digestion.  The  deutero-albumoses 
are  easily  demonstrated  in  the  earlier  stages,  but  become  very  scanty 
later.  Anti-albumid  is  found  as  a  side  product  in  artificial  digestion, 
but  is  not  present  in  normal  digestion.  Trypsin  also  has  the  power  of 
splitting  a  certain  proportion  of  peptones  into  simpler  bodies,  such  as 
leiicin,  or  amido-caproic  acid,  tyrosin  or  paroxyphenyl-amido-propionic 
acid,  lysin,  lysatinin,  tryptophan,  and  some  other  bodies.  Leucin  and 
tyrosin  have  been  found  in  the  intestinal  contents,  so  that  this  destruc- 
tion of  hemipeptone  must  take  place  to  a  certain  extent  within  the  body 
as  well  as  in  artificial  tryptic  digestion. 

In  laboratory  experiments  only  about  one-half  of  the  peptones  can 
be  changed  in  this  way.  The  more  stable  portion  which  cannot  be 
changed  is  usually  known  as  antipeptone,  though  it  is  as  yet  undecided 
whether  this  term  represents  a  single  chemical  substance  or  a  complex  of 
various  bodies;  recent  experiments,  however,  tend  to  show  that  it  repre- 
sents a  mixture  of  much  simpler  substances  than  peptone.  There  are 
several  theories  as  to  the  reason  or  use  of  this  change  into  leucin,  tyrosin, 
etc.  One  of  the  most  plausible  is  that  it  saves  the  body  from  needless 
work  when  too  much  proteid  food  has  been  taken;  the  breaking  down  in 
the  intestine  of  bodies  only  slightly  removed  from  urea  relieves  the  liver 
and  other  glandular  organs  from  the  strain  of  converting  an  excess  of  ab- 
sorbed proteid  material  into  a  form  in  which  it  can  be  excreted.  Another 
theory  is  that  leucin,  tyrosin,  etc.,  are  essential  for  the  physiological 


FOOD    AND    DIGESTION.  383 

working  of  tlie  body,  in  soiiiu  uukijowu  way,  just  as  the  products  of  the 
thyroid  ghiiid  are. 

The  formation  of  the  decomposition  products  indol  and  skatol  is 
caused  by  the  action  of  bacteria  on  proteids,  and  will  bespoken  of  under 
another  heading. 

The  albuminous  or  prpteid  substances  which  liave  not  been  converted 
into  peptone  and  absorbed  in  the  stomach,  and  the  partially  changed 
substances,  i.e.,  the  proteoses,  are  converted  into  peptone  by  the  pan- 
creatic juice,  and  then  in  part  into  leucin  and  tyrosin. 

The  ferment  trypsin  acts  best  in  an  alkaline  medium,  but  will  act 
also  in  a  neutral  medium,  or  in  the  presence  of  a  small  amount  of  com- 
bined acid;  it  will  not  work  in  the  presence  of  free  acid.  It  therefore 
differs  from  pepsin  in  being  able  to  act  without  the  aid  of  any  other 
substance  than  water.  In  the  process  of  tryptic  digestion,  proteid  mat- 
ter does  not  swell  up  at  first  but  seems  to  be  corroded. 

(2.)  Starch  is  converted  into  maltose  in  an  exactly  similar  manner  to 
that  which  happens  with  saliva,  erythro-dextrine  and  one  or  more  achroo- 
dextrines  being  the  intermediate  products.  The  amylolytic  enzyme  of 
the  pancreatic  juice,  which  cannot  be  distinguished  from  ptyalin,  is 
called  amylopsin.  The  maltose  thus  formed  is  converted  to  dextrose 
either  just  before  or  during  its  absorption,  in  which  form  it  jiasses  into 
the  blood.  This  conversion  is  in  part  due  to  the  action  of  the  enzyme 
glucase. 

(3.)  Pancreatic  juice  possesses  the  property  of  curdling  milk,  contain- 
ing a  special  (rennet)  ferment  for  tliat  purpose.  The  ferment  is  distinct 
from  trypsin,  and  will  act  in  the  presence  of  an  acid  (W.  Eoberts).  It  is 
best  extracted  by  brine.  The  milk-ciirdling  ferment  of  the  pancreas  is, 
in  some  pancreatic  extracts,  extremely  powerful,  insomuch  that  1  cc.  of 
a  brine  extract  will  coagulate  50  cc.  of  milk  in  a  minute  or  two. 

(4.)  Oils  and  fats  are  emulsified  and  saponified  hy  Yiaucrentic  secre- 
tion. The  terms  emulsification  and  saponification  may  need  a  little  ex- 
planation. The  former  is  used  to  signify  an  important  mechanical 
change  in  oils  or  fats,  whereby  they  are  made  into  an  emulsion,  or  in 
other  words  aie  minutely  subdivided  into  small  particles.  If  a  small 
drop  cf  on  emulsion  bo  looked  at  under  the  microscope  it  will  be  seen 
to  bo  made  up  of  an  immense  number  of  minute  rounded  particles  of 
oil  cr  fat,  cf  varying  sizes.  The  more  complete  the  emulsion  the  snuiller 
are  these  particles.  An  emulsion  is  formed  at  once  if  oil  or  fat,  which 
when  old  is  slightly  acid  from  the  presence  cf  free  fatty  acid,  is  mixed 
with  an  alkaline  solution.  Saponification  signifies  a  distinct  chemical 
change  in  the  composition  of  oils  and  fats.  An  oil  cr  a  fat  being  made 
up  chemically  of  (jhjccrin,  a  triatomic  alcohol,  and  one  or  more  fatty 
acid  radicles,  when   an  alkali  is  added   to  it,  and  heat  is  applied,  two 


384  HANDBOOK    OF    PHYSIOLOGY. 

changes  take  place:  firstly,  the  oil  or  fat  is  split  up  into  glycerin,  and 
its  corresponding  fatty  acid;  secondly,  the  fatty  acid  combines  with  the 
alkali,  to  form  a  soap  which  is  chemically  known  as  stearate,  cleate,  or 
palmitate  of  j^otassium  or  sodium.  Thus  saponification  means  a  chem- 
ical splitting  up  of  oils  or  fats  into  ]:iew  compounds,  and  emulsification 
means  merely  a  mechanical  splitting  of  them  up  into  minute  particles. 
The  pancreatic  juice  has  been  for  many  years  credited  with  the  posses- 
sion of  a  special  ferment,  Avhich  was  called  by  Claude  Bernard  steapsin^ 
and  which  is  a  lipolytic  or  fat-splitting  ferment.  This  ferment  has  not 
been  isolated,  but  its  presence  may  be  demonstrated  by  adding  portions 
of  the  fresh  pancreas  to  butter  or  other  fat  and  maintaining  the  proper 
temperature.  Its  action  is  made  manifest  by  the  liberation  of  butyric 
acid,  which  smells  like  rancid  butter. 

The  generally  accepted  theory  is  that  only  a  small  portion  of  the 
fat  which  is  eaten  is  thus  changed  into  soap,  and  that  the  function  of  the 
saponified  fat  is  to  assist  in  the  emulsification  of  the  major  part,  a  proc- 
ess which  is  favorably  infiuenced  by  the  bile.  The  proper  emulsifica- 
tion of  fat  is  a  necessary  preliminary  to  its  absorption,  for  whei  in 
disease  the  entrance  of  the  pancreatic  juice  or  the  bile  to  the  intestine 
is  interfered  with,  the  faeces  contains  a  great  excess  of  fat. 

Some  recent  experiments,  liowever,  tend  to  invalidate  the  emulsion  theory  and 
to  prove  that  the  entire  fat  of  the  food  is  changed  in  the  intestine  into  fatty  acids 
and  glycerine;  that  the  fatty  acids  are  entirely,  or  in  part,  changed  to  soaps;  and 
that  these  soaps,  or  the  mixture  of  soaps  and  free  fatty  acids,  are  absorbed  in  solu- 
tion. The  chief  facts  favoring  this  view  are  that:  (1)  The  action  of  steapsin  is  suf- 
ficiently rapid  to  allow  the  saponilication  of  a  full  fatty  meal  within  the  ordinarj^ 
period  of  digestion ;  (2)  histological  examination  has  never  shown  that  fat  particles 
can  pass  into  a  columnar  cell,  and  none  have  ever  been  found  in  tL'c  broad  striated 
border  of  the  cell;  (3)  the  fat  globules  found  in  columnar  cells  after  a  fatty  meal 
grow  steadily  larger  as  the  period  of  absorption  progresses,  indicating  that  they  are 
deposited  from  solution;  (4)  the  fatt.y  acids  are  easily  soluble  in  bile  solutions,  and 
the  solubility  of  the  soaps  is  greatly  increased  by  the  presence  of  bile.  The  fat  con- 
stituents, according  to  this  theory,  are  recombined  in  the  colunmar  cells  to  form 
neutral  fats. 

Conditions  favorahU  to  the  Action. — These  are  almost  precisely  sim- 
ilar to  those  which  have  been  mentioned  as  favorable  to  the  action  of 
the  saliva,  and  the  reverse.  The  secretion  of  the  pancreatic  juice  ap- 
pears to  be,  at  any  rate  in  some  animals,  e.g..,  the  rabbit  and  dog,  almost 
continuous;  the  flow,  however,  is  not  uniform,  the  amount  increases 
immediately  after  taking  food,  and  the  maximum  is  reached  in  from 
one  to  one  and  a  half  hours,  then  the  amount  falls  to  about  one-half, 
after  which  a  conspicuous  rise  occurs,  and  this  is  followed  by  a  gradual 
fall  to  the  base  line.  The  nervous  mechanism  of  the  pancreatic  secretion 
has  only  recently  "oeen  discovered  by  Pawlow.  Increased  flow  of  secretion 
will  occur  on  stimulation  of  the  spinal  bulb  or  cord,  or  of  the  gland  it- 


FOOD    ANJJ    J>IGESTION.  385 

self,  even  after  division  of  the  vagus.  By  special  methods  of  investiga- 
tion Pavvlow  has  found  tliat  tlie  innervation  of  the  pancreas  is  somewhat 
similar  to  that  of  the  salivary  glands.  Stimulation  of  both  the  vagus 
and  sympathetic  nerves,  under  proper  conditions,  "will  cause  a  flow  of 
secretion,  but  the  secretion  is  more  abundant  in  the  case  of  the  vagns. 
Both  nerves  appear  to  contain  secretory  fibres;  they  are  more  numerous, 
however,  in  the  vagus,  Avhile  troi^hio  fibres  or  those  which  cause  a  build- 
ing up  of  the  secretion  materials  in  the  gland  cells  are  more  abundant 
in  the  sympathetic.  In  function  the  nerves  are  analogous  to  the  chorda 
tymjiaui  and  sympathetic  of  the  submaxillary  gland.  The  gland  will 
continue  to  secrete  after  the  section  of  all  of  its  nerves,  and  in  this  re- 
spect is  said  to  differ  from  the  salivary  glands.  The  secretion  ap- 
pears to  be  called  forth  on  the  introduction  of  food  into  the  stomach, 
when  the  blood-vessels  of  the  gland  become  much  dilated,  and  the  se- 
cretion continues,  as  we  have  seen,  for  many  hours  after  a  meal;  'indeed, 
may  be  continuous.  The  pressure  of  the  secretion  is  not  so  great  as  in 
the  case  of  the  salivary  glands;  the  maximum  pressure  in  the  duct  is 
said  not  to  exceed  17  mm.  of  mercury. 

The  amount  of  secretion  per  diem  is  not  definitely  known  but  is  ap- 
proximately estimated  to  be  about  half  a  litre. 


The  Liver. 

The  Liver,  the  largest  gland  in  the  body,  situated  in  the  abdomen 
on  the  right  side  chiefly,  is  an  extremely  vascular  organ,  and  receives 
its  supply  of  blood  from  two  distinct  sources,  viz.,  from  the  porial  vein 
and  from  the  hepatic  artery,  while  the  blood  is  returned  from  it  into  the 
vena  cava  inferior  by  the  hepatic  veins.  Its  secretion,  the  tile,  is  con- 
veyed from  it  by  the  hepatic  duct,  either  directly  into  the  intestine,  or, 
when  digestion  is  not  going  on,  into  the  cystic  duct,  and  thence  into 
the  gall-bladder,  where  it  accumulates  until  required.  The  portal  vein, 
hepatic  artery,  and  hepatic  duct  branch  together  throughout  the  liver, 
while  the  hepatic  veins  and  their  tributaries  run  by  themselves. 

On  the  outside,  the  liver  has  an  incomplete  covering  of  peritoneum, 
and  beneath  this  is  a  very  fine  coat  of  areolar  tissue,  continuous  over 
the  whole  surface  of  the  organ.  It  is  thickest  wdiere  the  peritoneum  is 
absent,  and  is  continuous  on  the  general  surface  of  the  liver  with  the 
fine  and,  in  the  human  subject,  almost  imperceptible  areolar  tissue  in- 
vesting the  lobules.  At  the  transverse  fissure  it  is  merged  in  the  areolar 
investment  called  Glisson's  capsule,  which,  surrounding  the  portal  vein, 
hepatic  artery,  and  hepatic  duct,  as  they  enter  at  this  part,  accompanies 
them  in  their  branches  through  the  substance  of  the  liver. 

iStructure. — The  liver  is  made  ui)  of  small  roundish  or  oval  portions 
25 


386 


HANDBOOK    OF    PHYSIOLOGY. 


called  lobules,  each  of  which  is  about  ^^  of  an  inch  (about  1  mm.)  in 
diameter,  and  composed  of  the  minute  branches  of  the  portal  vein,  he- 
patic artery,  hepatic  duct,  and  hepatic  vein;  while  the  interstices  of  these 


Fig.  266.— The  liver  from  below  and  behind.  L.S.,  Spigelian  lobe;  L.C.,  caudate  lobe;  L.Q., 
quadrate  lobe:  R.L.,  right  lobe;  L.L.,  left  lobe;  g.bl.,  gall-bladder;  v.c.i.,  inferior  vena  cava. 
u.f.,  umbilical  fissure; /.d. v.,  fissure  of  the  ductus  venosus;  p,  portal  fissure  with  portal  veiu, 
hepatic  artery  and  bile-duct.     (Wesley,  from  a  His  model.) 

vessels  are  filled  by  the  liver  cells.     The  hepatic  cells  (fig.  254),  which 

form  the  glandular  or  secreting  part  of  the  liver,  are  of  a  spheroidal 

form,  somewhat  polygonal  from  mutual  pressure  about  -^  to  -poVo^  inch 

(about  ^3  to  ^V  mm.)  in  diameter,  possessing  one,  sometimes  two  nuclei. 

The  cell-substance  contains  numerous  fattj  molecules,  and  possibly  some 

granules  of  bile-pigment,  as  well 

as  a  variable  amount  of  glycogen. 

The  cells  sometimes  exhibit  slow 

amoeboid  movements.     They  are 

held  together  by  a  very  delicate 

sustentacular    tissue,    continuous 

with  the  interlobular  connective 

tissue. 


Fig.  267.  Fig.  268. 

Fig.  267.— A.  Liver-cells.    B.  Ditto,  containing  various-sized  particles  of  fat. 

Fig.  268.— Longitudinal  section  of  a  portal  canal,  containing  a  portal  vein,  hepatic  artery  and 
hepatic  duct,  from  the  pig.  p,  branch  of  vena  portse,  situate  in  a  portal  canal  formed  among  the 
lobules  of  the  liver.  I,  I,  and  giving  oflf  vaginal  branches;  there  are  also  seen  within  the  large  portal 
vein  numerous  orifices  of  the  smallest  mterlobular  veins  arising  directly  from  it;  a,  hepatic 
artery ;  d,  hepatic  duct.    X  5.     (Kiernan). 


FOOD   AND   DIGESTION.  387 

To  understand  the  distribution  of  the  blood-vessels  in  the  liver,  it 
will  be  well  to  trace,  first,  the  two  blood-vessels  and  the  duct  which  enter 
the  organ  on  the  under  surface  at  the  transverse  fissure,  viz.,  the  portal 
vein,  hepatic  artery,  and  hepatic  duct.  As  before  remarked,  all  three 
run  in  company,  and  their  appearance  on  longitudinal  section  is  shown 
in  fig.  268.  Running  together  through  the  substance  of  the  liver,  they 
are  contained  in  small  channels  called  portal  canals,  their  immediate  in- 
vestment being  a  sheath  of  areolar  tissue  continuous  with  Glisson's  cap- 
sule. 

To  take  the  distribution  of  the  portal  vein  first : — In  its  course  through 
the  liver  this  vessel  gives  otf  small  branches  which  divide  and  subdivide 
between  the  lobules  surrounding  them  and  limiting  them,  and  from  this 
circumstance  called  inter-lohular  veins.  From  these  small  vessels  a 
dense  capillary  network  is  prolonged  into  the  substance  of  the  lobule, 

h 


p  I' 

Fig.  269  — Capillaiy  network  of  the  lobules  of  the  rabl)it".s  liver.  The  figrure  is  taken  from  a  very 
successful  injection  of  the  hepatic  veins,  made  by  Harting:  it  shows  nearly  the  whole  of  two  lo- 
bules, and  parts  of  tliree  others  ;  p.  portal  branches  running  in  the  interlobular  spaces;  h,  hepatic 
veins  penetrating  and  radiating  from  the  centre  of  the  lobules,     x  45.    (Kolliker.) 

and  this  network  gradually  gathering  itself  up,  so  to  speak,  into  larger 
vessels,  converges  finally  to  a  single  small  vein,  occupying  the  centre  of 
the  lobule,  and  hence  called  intr a-lohixlar.  This  arrangement  is  well 
seen  in  tig.  269,  which  represents  a  transverse  section  of  a  lobule. 

The  small  iM//Y/-lobular  veins  discharge  their  contents  into  veins 
called  6"«<Wobular  {h  h  h,  fig.  270),  while  these  again,  by  their  union, 
form  the  main  branches  of  the  hepatic  veins,  which  leave  the  posterior 
border  of  the  liver  to  end  by  two  or  three  principal  trunks  in  the  infe- 
rior vena  cava,  just  before  its  passage  through  the  diaphragm.  The 
SM^-lobular  and  hepatic  veins,  unlike  the  portal  vein  and  its  companions, 
have  little  or  no  areolar  tissue  around  them,  and  their  coats  being  very 
thin,  they  form  little  more  than  mere  channels  in  the  liver  substance 
which  closely  surrounds  them. 

The  manner  in  which  the  lobules  are  connected  with  the  sublobular 


J88 


HANDBOOK   OF   PHYSIOLOGY. 


veins  by  nieaus  of  the  small  i7iiralohuIar  veins  has  been  likened  to  a  twig 
having  leaves  without  footstalks — the  lobules  representing  the  leaves, 
and  the  suUohular  vein  the  small  branch  from  which  it  springs. 


Fig.  270  Fig.  271. 

Fig.  270  —Section  of  a  portion  of  liver  passing  longitudinally  through  a  considerable  hepatic 
vein,  from  the  pig.  h,  hepatic  venous  trunk,  against  which  the  sides  of  the  lobules  (/)  are  apphed; 
h,  h,  h,  sublobular  hepatic  veins,  on  which  the  bases  of  the  lobules  rest,  and  through  the  coats  of 
which  they  are  seen  as  polygonal  figures;  i,  mouth  of  the  intralobular  veins,  opening  into  the  sub- 
lobular veins;  i\  intralobular  veins  shown  passing  up  the  centre  of  some  divided  lobules;  I,  I,  cut 
surface  of  the  liver;  c,  c,  walls  of  the  hepatic  venous  canal,  formed  by  the  polygonal  bases  of  the 
lobules.     X  5.     (Kieman.) 

Fig.  271  —Portion  of  a  lobule  of  liver,  a,  bile  capillaries  between  Uver-cells,  the  network  in 
which  is  well  seen;  b,  blood  capillaries.     X  850.    (Klein  and  Noble  Smith.) 

The  hepatic  artery,  the  chief  function  of  which  is  to  distribute  blood 
for  nutrition  to  Glisson's  capsule,  the  walls  of  the  ducts  and  blood-ves- 
sels, and  other  parts  of  the  liver,  is  distributed  in  a  very  similar  manner 

■  vp .  V  p 


Fig.  272  —Hepatic  cells  and  bile  capillaries,  from  the  liver  of  a  child  three  months'  old.  Both 
figures  represent  fragments  of  a  section  carri(;d  through  the  periphery  of  a  lobule.  The  red  cor- 
puscles of  the  blood  are  recognized  by  their  circular  contour;  vp,  corresponds  to  an  interlobular 
vein  in  immediate  proximity  with  which  are  the  epithelial  cells  of  the  biliary  ducts,  to  which,  at  the 
lower  part  of  the  figures,  the  much  larger  hepatic  cells  suddenly  succeed.    (E.  Hering.) 


to  the  portal  vein,  its  blood  being  returned  by  small  branches  either 


FOOD   AND   DIGESTION.  389 

into  tlie  ramifications  of  the  portal  vein,  or  into  the  capillar}'  plexus  of 
the  lobules  which  connect  the  inter-  and  m^ra-lobular  veins. 

The  hepatic  duct  divides  and  subdivides  in  a  manner  very  like  that 
of  the  portal  vein  and  hepatic  artery,  the  larger  branches  being  lined 
by  cylindrical,  and  the  smaller  by  small  polygonal  epithelium. 

The  bile-caj^illaries  commence  between  the  hepatic  cells,  and  are 
bounded  by  a  delicate  membranous  wall  of  their  own.  They  appear  to 
be  always  bounded  by  heiDatic  cells  on  all  sides,  and  are  thus  separated 
from  the  nearest  blood-capillary  by  at  least  the  breadth  of  one  cell  (figs. 
271  and  272). 

The  Gall-bladder. 

The  Gall-bladder  (ff-ln.  fig.  2GG)  is  a  pyriform  bag,  attached  to  the 
under  surface  of  the  liver,  and  supported  also  by  the  peritoneum,  which 
passes  below  it.  The  larger  end,  or  fundus,  projects  beyond  the  front 
margin  of  the  liver;  while  the  smaller  end  contracts  into  the  cystic  duct. 

Structure. — The  walls  of  the  gall-bladder  are  constructed  of  three 
principal  coats.  (1)  Externally  (excepting  that  part  which  is  in  contact 
with  the  liver)  is  the  serous  coat,  which  has  the  same  structure  as  the 
peritoneum,  with  which  it  is  continuous.  Within  this  is  (2)  the /iro?/5 
or  areolar  coat,  constructed  of  tough  fibrous  and  elastic  tissue,  with 
which  is  mingled  a  considerable  number  of  plain  muscular  fibres,  both 
longitudinal  and  circular.  (3)  Internally  the  gall-bladder  is  lined  by 
mucous  membrane,  and  a  layer  of  columnar  epithelium.  The  surface 
of  the  mucous  membrane  presents  to  the  naked  eye  a  minutely  honey- 
combed appearance  from  a  number  of  tiny  polygonal  depressions  with 
intervening  ridges,  by  which  its  surface  is  mapped  out.  In  the  cystic 
duct  the  mucous  membrane  is  raised  up  in  the  form  of  crescentic  folds, 
which  together  appear  like  a  spiral  valve,  and  which  minister  to  the 
function  of  the  gall-bladder  in  retaining  the  bile  during  the  interval  of 
digestion. 

The  gall-bladder  and  all  the  main  biliary  ducts  are  provided  with 
mucous  glands,  which  open  on  the  internal  surface. 

Functions  of  the  Liver. 

The  function  of  the  liver  in  connection  with  digestion  is  to  secrete 
the  bile,  and  may  be  now  considered.  The  other  functions  in  connec- 
tion with  the  general  metabolism  of  the  body,  and  particularly  its  gly- 
cogenic function,  will  be  discussed  later  on.  First  of  all  it  will  be  as 
well  to  take  the  composition  and  functions  of  the  bile,  and  afterward  to 
discuss  its  mode  of  secretion. 


390  HANDBOOK   OF   PHYSIOLOGY. 


The  Bile. 

Properties. — The  bile  is  a  somewhat  viscid  fluid,  of  a  yellow,  reddish- 
yellow  or  green  color,  a  strongly  bitter  taste,  and,  when  fresh,  with  a 
scarcely  perceptible  odor :  it  has  a  neutral  or  slightly  alkaline  reaction, 
and  its  specific  gravity  is  about  1020.  Its  color  and  degree  of  consist- 
ence vary  much,  quite  independent  of  disease ;  but,  as  a  rule,  bile  becomes 
gradually  more  deeply  colored  and  thicker  as  it  advances  along  its  ducts, 
or  when  it  remains  long  in  the  gall-bladder,  wherein,  at  the  same  time, 
it  becomes  more  viscid  and  ropy,  darker,  and  more  bitter,  mainly  from 
its  greater  degree  of  concentration,  on  account  of  partial  absorption  of 
its  water,  but  also  from  being  mixed  with  mucus. 

Chemical  Composition  op  Human  Bile.     (Frerichs.) 

Water 859.3 

Solids— Bile  salts 91.5 

Fat 9.3 

Cholesterin        .         .         .         .         .         .3.6 

Mucus  and  coloring  matters        .         .  39.8 

Salts 7.7 

140.8 

1000.0 

(a)  Bile  salts,  sometimes  termed  Bilin,  can  be  obtained  as  colorless, 

exceedingly  deliquescent  crystals,  soluble  in  water,  alcohol,  and  alkaline 

solutions,  giving  to  the  watery  solution  the  taste  and  general  characters 

of  bile.     They  consist  of  sodium  salts  of  glycocholic  and  taurocholic 

acids.     The  formula  of  the  former  salt  being  C26H43]S[aN06,  and  of  the 

latter  C26H44NaN07S. 

The  bile  acids  are  easily  decomposed  by  the  action  of  dilute  acids  or  alkalies 

thus : 

C26H43NOB  +  H2O  =  C2H5NO2  +  C24H40O,. 
Glycocholic  Acid.  Glycin.  Cholic  Acid. 

and  C26H46NO,S  +  H^O  =  C.H^NOsS  +  C24H40O5 
Taurocholic  Acid.  Taurin.  Cholic  Acid. 

Glycin,  or  glycocin,  is  amido-acetic  acid,  i.e.,  acetic  acid  C2H4O2,  with  one 
of  the  atoms  of  H  replaced  by  the  radical  amidogen  NHo,C2H3(NH2)02, 
C2H5NO2.  Taurin  likewise  is  amido-isethionic  acid.  Isethionic  acid  is  sul- 
phurous acid  H2SO3,  in  which  an  atom  of  H  is  replaced  by  the  monotomic 
radicle  oxy-ethylene,  C2H4OH,  viz.,  H(C2H40H)S03,  and  in  amido-isethionic 
acid,  the  OH  hydroxyl  in  this  radicle  is  replaced  by  amidogen  NH2,  thus 
H(C2H4NH2)S03  =  C2H7NSO3.  The  proportion  of  these  two  salts  in  the  bile  of 
different  animals  varies,  e.g.,  in  ox  bile  the  glycocholate  is  in  great  excess, 
whereas  the  bile  of  the  dog,  cat,  bear,  and  other  carnivora  contains  taurocho- 
late  alone ;  in  human  bile  the  glycocholate  is  in  excess  (4.8  to  1.5). 

Preparation  of  Bile  Salts. — Bile  salts  may  be  prepared  in  the  following 
manner :  mix  bile  which   has  been  evaporated  to  a  quarter  of   its  bulk  with 


FOOD   AND    DIGESTION. 


301 


animal  charcoal,  and  evaporate  to  perfect  dryness  in  a  water  batli.  Next  ex- 
tract the  mass  while  still  warm  with  absolute  alcohol.  Separate  the  alcoholic 
extract  by  filtration,  and  to  it  add  perfectly  anhydrous  ether  as  long  as  a  pre- 
cipitate is  thrown  down.  The  solution  and  precipitate  should  be  set  aside  in 
a  closely  stoppered  bottle  for  some  days,  when  crystals  of  the  bile  salts  or  bilin 
will  have  separated  out.  The  glycocholate  may  be  separated  from  the  tauro- 
cholate  by  dissolving  bilin  in  water,  and  adding  to  it  a  solution  of  neutral  lead 
acetate,  and  then  a  little  basic  lead  acetate,  when  lead  glycocholate  separates 
out.  Filter  and  add  to  the  filtrate  lead  acetate  and  ammonia,  a  precipitate  of 
lead  taurocholate  will  be  formed,  which  may  be  filtered  off.  In  both  cases,  the 
lead  may  be  got  rid  of  bj^  suspending  or  dissolving  in  hot  alcohol,  adding 
hydrogen  sulphide,  filtering  and  allowing  the  acids  to  separate  out  by  the  ad- 
dition of  water. 

The  Test  for  bile  salts  is  known  as  Pettenkofer's.  If  to  an  aqueous 
solution  of  the  salts  strong  sulphuric  acid  be  added,  the  bile  acids  are 
first  of  all  precipitated,  but  on  the  further  addition  of  the  acid  are  re- 
dissolved.  If  to  the  solution  a  drop  of  solution  of  cane  sugar  be  added, 
a  fine  deep  cherry  red  to  purple  color  is  developed. 

The  reaction  will  also  occur  on  the  addition  of  grape  or  fruit  sugar  instead 
of  cane  sugar,  slowly  with  the  first,  quickly  with  the  last ;  and  a  color  similar 
to  the  above  is  produced  by  the  action  of  sulphuric  acid  and  sugar  on  albumen, 
the  crystalline  lens,  nerve  tissue,  oleic  acid,  pure  ether,  cholestei'in,  morphia, 
codeia  and  amylic  alcohol.  The  substance  which  gives  the  reaction  is  furfur- 
aldehyde,  formed  by  the  action  of  sulphuric  on  sugar.  Furfur-aldehyde  with 
cholalic  acid  gives  the  red  color. 

The  spectrum  of  Pettenkofer's  reaction,  when  the  fluid  is  moder- 
ately diluted,  shows  four  bands — the  most  marked  and  broadest  at  E, 
and  a  little  to  the  left;  another  at  F;  a  third  between  D  and  E,  nearer 
to  D;  and  the  fourth  near  D. 

{b)  The  yellow  coloring  matter  of  the  bile  of  man  and  the  Carnivora 
is  termed  Bilirubin  or  Bilifulvin  (CieHisNaOs)  crystallizable  and  in- 
soluble in  water,  soluble  in  chloroform  or  carbon  disulphide;  a  green 
coloring  matter,  BUivcrdin  (C\JI,,NjOJ  which  always  exists  in  hu-ge 
amount  in  the  bile  of  llerbivora,  being  formed  from  bilirubin  on  expo- 
sure to  the  air,  or  by  subjecting  the  bile  to  any  other  oxidizing  agency, 
as  by  adding  nitrous  acid.  Bilivcrdin  is  soluble  in  alcohol,  glacial  acetic 
acid,  and  strong  sulphuric  acid,  but  insoluble  in  water,  in  chloroform 
and  ether.  It  is  usually  amorphous  but  may  sometimes  crystallize  in 
green  rhombic  plates.  When  the  bile  has  been  long  in  the  gall-bladder, 
a  third  pigment,  Biliprasin,  may  be  also  found  in  small  amount. 

In  cases  of  biliary  obstruction,  the  coloring  matter  of  the  bile  is  re- 
absorbed and  circulates  with  the  blood,  giving  to  the  tissues  the  yellow 
tint  characteristic  of  jaundice. 

The  coloring  matters  of  human  bile  do  not  appear  to  give  character- 
istic absorption  spectra;  but  the  bile  of  the  Guinea-pig,  rabbit,  mouse. 


392  HANDBOOK    OF    PHYSIOLOGY. 

sheep,  ox,  and  crow  do  so,  the  most  constant  of  which  appears  to  be  a 
band  at  F.  The  bile  of  the  sheep  and  ox  gives  three  bands  in  a  thick 
layer,  and  four  or  five  bands  with  a  thinner  layer,  one  on  each  side  of 
D,  one  near  E,  and  a  faint  line  at  F.     (McMunn.) 

There  seems  to  be  a  close  relationship  between  the  coloring  matters 
of  the  blood  and  of  the  bile,  and  it  may  be  added,  between  these  and 
that  of  the  nrine  {uroMUfi),  and  of  the  fasces  {stercohilin)  also;  it  is 
probable  they  are,  all  of  them,  varieties  of  the  same  pigment,  or  derived 
from  the  same  sonrce.  Indeed  it  is  maintained  that  Urobilin  is  identi- 
cal with  HydrobiUruhln,  a  substance  which  in  alkaline  solution  gives  a 
green  fluorescence  with  zinc  chloride,  which  is  obtained  from  bilirubin 
by  the  action  of  sodium  amalgam,  or  by  the  action  of  sodium  amalgam 
on  alkaline  hasmatin;  both  urobilin  and  hydrobilirubin  giving  a  charac- 
teristic absorption  band  between  b  and  F.  They  are  also  identical  with 
stercobiliu,  which  is  formed  in  the  alimentary  canal  from  bile  pigments. 


Fig.  a73.— Crystalline  scales  of  cholesterin. 

The  Test  (Gmelin's)  for  the  presence  of  Ule-pigmmit  consists  of  the 
addition  of  a  small  quantity  of  nitric  acid,  yellow  with  nitrous  acid;  if 
bile  be  present,  a  play  of  colors  is  produced,  beginning  with  green  and 
passing  through  blue  and  violet  to  red,  and  lastly  to  yellow.  The  final 
yellow  substance  has  been  called  choletelin.  The  spectrum  of  Gmelin's 
test  gives  a  black  band  extending  from  near  b  to  beyond  F. 

(c)  Fatty  substances  are  found  in  variable  proportions  in  the  bile. 
Besides  these  saponifiable  fats,  there  is  a  small  quantity  of  Cholesterin, 
which  is  an  alcohol,  and,  with  the  free  fats,  is  probably  held  in  solution 
by  the  bile  salts.  It  is  a  body  belonging  to  the  class  of  monatomic  alco< 
hols  (C^JI.^OH,  Obermiiller),  and  crystallizes  in  rhombic  plates  (fig. 
273).  It  is  insoluble  in  water  and  cold  alcohol,  but  dissolves  easily  in 
boiling  alcohol  or  in  ether.  It  gives  a  red  color  with  strong  sulphuric 
acid,  and  with  nitric  acid  and  ammonia;  also  a  play  of  colors  beginning 
with  blood  red  and  ending  with  green  on  the  addition  of  sulphuric  acid 
and  chloroform.  Lecithin  (C^.H^^NPOJ  is  also  found:  it  is  a  combina- 
tion of  cholin  with  glycerophosphoric  acid  in  which  two  of  the  hydrogen 


FOOD    .VXD    1)1(1 1'.STION".  ;',03 

atoms  of  tlie  glycoriiio  arc  rfplaced  l»y  I'atlicals  of  the  fatty  acids,  usually 
oleic  and  palmitic  acids. 

{f()  The  Mucus  in  bile  is  derived  from  the  mucous  membrane  and 
ghinds  of  the  gall-bladder,  and  of  the  hepatic  ducts.  It  constitutes  tlie 
residue  after  bile  is  treated  with  alcohol.  The  epithelium  Avitli  which  it 
is  mixed  may  be  detected  in  the  bile  with  the  microscope  in  the  form  of 
cylindrical  cells,  either  scattered  or  still  held  together  in  layers.  To 
the  presence  of  the  mucus  is  probably  to  be  ascribed  the  rapid  decom- 
position of  the  bile;  for,  according  to  Berzelius,  if  the  mucus  be  sej^a- 
rated,  it  will  remain  unchanged  for  many  days. 

((?)  The  Saline  or  inorganic  constituents  of  the  bile  are  similar  to 
those  found  in  most  other  secreted  fluids.  It  is  possible  that  the  car- 
bonate and  neutral  phosphate  of  sodium  and  potassium,  found  in  the 
ashes  of  bile,  are  formed  in  the  incineration,  and  do  not  exist  as  such  in 
the  fluid.  Oxide  of  iron  is  said  to  be  a  common  constituent  of  the  ashes 
of  bile,  and  copper  is  generally  found  in  healthy  bile,  and  constantly  in 
biliary  calculi. 

(/)  Gas. — Small  amounts  of  carbonic  acid,  oxygon,  and  nitrogen 
gases,  may  be  extracted  from  bile. 

Functiojis  of  the  Bile. — Though  it  is  not  a  true  digestive  fluid,  in 
that  it  has  no  ferment  and  digests  nothing  itself,  yet  it  must  be  regarded 
as  an  important  aid  to  digestion  for  the  following  reasons:  There  is  little 
doubt  that  it  {a)  assists  in  emnUifying  the  fats  of  the  food,  and  thus 
rendering  them  capable  of  passing  into  the  lacteals  by  absorption.  For 
it  has  appeared  in  some  experiments  in  which  the  common  bile-duct 
was  tied,  that,  although  the  process  of  digestion  in  the  stomach  was  un- 
affected, chyle  was  no  longer  well  formed;  the  contents  of  the  lacteals 
consisting  of  clear,  colorless  fluid,  instead  of  being  opaque  and  white,  as 
they  ordinarily  are,  after  feeding.  It  is,  however,  the  combined  action 
of  the  bile  with  the  pancreatic  juice  to  which  the  emulsification  is  due 
rather  than  to  that  of  the  bile  alone.  The  bile  itself  has  a  very  feeble 
emulsifying  power.  If  the  theory  be  accepted  that  fats  are  absorbed  as 
fatty  acids  and  soaps,  in  solution,  the  action  of  the  bile  becomes  very 
important  because  solutions  of  bile  salts  have  the  power  of  dissolving 
the  fatty  acids. 

{b)  It  is  probable,  also,  that  the  moistening  of  the  mncous  nteuihranc 
of  the  intestines  by  bile  facilitates  absorption  of  fatty  matters  through  it, 

(c)  The  bile,  like  the  gastric  fluid,  has  a  certain  but  not  very  con- 
siderable antixeptic  power,  and  may  serve  to  prevent  the  decomposition 
of  food  during  the  time  of  its  sojourn  in  the  intestines.  Experiments 
show  that  the  contents  of  the  intestines  are  much  more  fcetid  after  the 
common  bile-duct  has  been  tied  than  at  other  times:  moreover,  it  is 
found  that  the  mixture  of  bile  with  a  fermenting  fluid  stops  or  spoils 
the  process  of  fermentation.     This  function  may,  very  probably,  be  ex- 


394  HANDBOOK    OF    PHYSIOLOGY. 

plained  by  its  so  aidiug  fat  digestion  that  tlie  fats  are  absorbed  before 
they  can  decompose, 

(d)  The  bile  has  also  been  considered  to  act  as  a  natural  purgative, 
by  promoting  an  increased  secretion  of  the  intestinal  glands,  and  by 
stimulating  the  intestines  to  the  propulsion  of  their  contents.  This  view 
receives  support  from  the  constipation  which  ordinarily  exists  in  jaun- 
dice, from  the  diarrhcBa  which  accompanies  excessive  secretion  of  bile, 
and  from  the  purgative  properties  of  ox-gall. 

(e)  The  bile  appears  to  have  the  power  of  precipitating  the  gastric 
proteoses  and  pteptones,  together  with  the  pepsin,  which  is  mixed  up  with 
them,  as  soon  as  the  contents  of  the  stomach  meet  it  in  the  duodenum. 
It  thus  stops  the  action  of  the  pepsin.  The  purpose  of  this  operation  is 
probably  both  to  delay  any  change  in  the  proteoses  until  the  pancreatic 
juice  can  act  upon  them,  and  also  to  prevent  the  pepsin  from  exercising 
its  solvent  action  on  the  ferments  of  the  pancreatic  juice.  In  some  way 
its  presence  seems  also  to  aid  the  action  of  trypsin. 

(/)  As  an  excrementitious  substance,  the  bile  may  serve  especially  as 
a  medium  for  the  separation  of  certain  highly  carbonaceous  substances 
from  the  blood;  and  its  adaptation  to  this  purpose  is  well  illustrated  by 
the  peculiarities  attending  its  secretion  and  disposal  in  the  foetus.  Dur- 
ing intra-uterine  life,  the  lungs  and  the  intestinal  canal  are  almost  in- 
active; there  is  no  respiration  of  open  air  or  digestion  of  food;  these 
are  unnecessary,  on  account  of  the  supply  of  well-elaborated  nutriment 
received  by  the  vessels  of  the  foetus  at  the  placenta.  The  liver,  during 
the  same  time,  is  proportionately  larger  than  it  is  after  birth,  and  the 
secretion  of  bile  is  active,  although  there  is  no  food  in  the  intestinal 
canal  upon  which  it  can  exercise  any  digestive  property.  At  birth, 
the  intestinal  canal  is  full  of  concentrated  bile,  mixed  with  intestinal 
secretion,  and  this  constitutes  the  meconium,  or  fseces  of  the  foetus. 
In  the  foetus,  therefore,  the  main  purpose  of  the  secretion  of  bile  must 
be  directly  excretive.  Probably  all  the  bile  secreted  in  foetal  life  is 
incorporated  in  the  meconium,  and  with  it  discharged,  and  thus  the 
liver  may  be  said  to  discharge  a  function  in  some  sense  vicarious  of 
that  of  the  lungs.  For,  in  the  foetus,  nearly  all  the  blood  coming  from 
the  placenta  passes  through  the  liver,  previous  to  its  distribution  to 
the  several  organs  of  the  body;  and  the  abstraction  of  certain  sub- 
stances will  purify  it,  as  in  extra-uterine  life  it  is  purified  by  the  separa- 
tion of  carbon  dioxide  and  water  at  the  lungs. 

Mode  of  Secretion  and  Discharge. — The  secretion  of  bile  is  contin- 
ually going  on,  but  is  retarded  during  fasting,  and  accelerated  on  taking 
food.  This  has  been  shown  by  tying  the  common  bile-duct  of  a  dog, 
and  establishing  a  fistulous  opening  between  the  skin  and  gall-bladder, 
whereby  all  the  bile  secreted  was  discharged  at  the  surface.  It  was 
noticed  that  when  the  animal  was  fasting,  sometimes  not  a  drop  of  bile 


FOOD    AND    DIGESTION.  395 

was  discharged  for  several  hours;  but  that,  in  about  ten  minutes  after 
the  introduction  of  food  into  the  stomach,  the  bile  began  to  flow  abun- 
dantly, and  continued  to  do  so  during  the  whole  period  of  digestion. 

The  bile  is  formed  in  the  hepatic  cells;  thence,  being  discharged 
into  the  minute  hepatic  ducts,  it  passes  into  the  larger  trunks,  and  from 
the  main  hepatic  duct  may  be  carried  at  once  into  the  duodenum. 
This  probably  happens  only  while  digestion  is  going  on,  i.e.,  for  5  to  7 
hours  after  the  introduction  of  food  into  the  stomach:  during  fasting, 
it  regurgitates  from  the  common  bile-duct  through  the  cystic  duct,  into 
the  gall-bladder,  where  it  accumulates  till,  in  the  next  period  of  diges- 
tion, it  is  discharged  into  the  intestine.  The  gall-bladder  thus  fulfils 
its  office,  that  of  a  reservoir;  for  its  presence  enables  bile  to  be  con- 
stantly secreted,  yet  insures  its  employment  in  the  service  of  digestion, 
although  digestion  is  periodic,  and  the  secretion  of  bile  constant. 

The  mechanism  by  which  the  bile  passes  into  the  gall-bladder  is 
simple.  The  orifice  through  which  the  common  bile-duct  communi- 
cates with  the  duodenum  is  narrower  than  the  duct,  and  appears  to  be 
closed,  except  when  there  is  sufficient  pressure  behind  to  force  the  bile 
through  it.  The  pressure  exercised  upon  the  bile  secreted  during  the 
intervals  of  digestion  appears  insufficient  to  overcome  the  force  with 
which  the  orifice  of  the  duct  is  closed;  and  the  bile  in  the  common 
duct,  finding  no  exit  in  the  intestine,  traverses  the  cystic  duct,  and  so 
passes  into  the  gall-bladder,  being  probably  aided  in  this  retrograde 
course  by  the  peristaltic  action  of  the  ducts.  The  bile  is  discharged 
from  the  gall-bladder  and  enters  the  duodenum  on  the  introduction  of 
food  into  the  small  intestine :  being  pressed  on  by  the  contraction  of 
the  coats  of  the  gall-bladder,  and  of  the  common  bile-duct  also ;  for  both 
these  organs  contain  unstriped  muscular  fibre-cells.  Their  contraction 
is  excited  by  the  stimulus  of  the  food  in  the  duodenum  acting  so  as  to 
produce  a  reflex  movement,  the  force  of  which  is  sufficient  to  open  the 
orifice  of  the  common  bile-duct,  which  is  closed  by  a  sphincter. 

Bile  is  not  pre-formed  in  the  blood.  As  just  observed,  it  is  secreted 
by  the  hepatic  cells,  although  some  of  its  constituents  may  be  brought 
to  them  almost  in  the  condition  for  immediate  secretion.  The  blood 
from  which  the  liver  cells  secrete  the  bile  is  that  supplied  to  them  by  the 
portal  vein.  This  is  shown  by  the  alterations  which  occur  in  the  pro- 
cess on  the  alteration  of  the  pressure  in  the  portal  system.  If  the  portal 
vein  be  obstructed,  the  amount  of  bile  secreted  diminishes,  and  is  ulti- 
mately suppressed,  death  resulting.  It  has,  however,  been  shown  that 
under  extraordinary  circumstances  bile  may  be  secreted  by  the  aid  of 
the  blood  from  the  hepatic  artery,  since  if  a  branch  of  the  portal  vein 
be  tied,  the  part  of  the  liver  supplied  by  it  continues  to  secrete  bile, 
though  in  diminished  quantity.  When  the  discharge  of  the  bile  into 
the  intestine  is  prevented  by  an  obstruction  of  some  kind,  as  by  a  gall- 


396  HANDBOOK    OF    PHYSIOLOGY. 

stone  blocking  the  hepatic  duct,  it  is  reabsorbed  in  great  excess  into 
the  blood,  and,  circulating  with  it,  gives  rise  to  the  well-known  phenom- 
ena of  jaundice.  This  is  explained  by  the  fact  that  the  pressure  of 
secretion  in  the  duets  although  normally  very  low,  not  exceeding  15 
mm.  in  the  dog,  is  still  higher  than  that  of  the  portal  veins,  and  if  it 
exceeds  16  mm.  the  secretion  although  formed  ceases  to  be  poured  out, 
and  if  the  opposing  force  be  increased,  the  bile  passes  into  the  blood- 
vessels through  the  lymphatics,  and  the  yellow  color  appears  in  the  skin 
and  in  the  secretions,  and  constitutes  the  condition  of  jaundice.  In 
jaundice  the  faeces  are  light  colored  and  highly  offensive,  there  is  con- 
stipation, the  heart  beats  slowly,  and  from  the  presence  of  bile  salts  as 
well  as  bile  pigment  in  the  blood,  the  red  blood  corpuscles  may  be  in 
part  dissolved.  The  latter  action  results  in  the  presence  of  haemoglobin 
and  of  an  additional  amount  of  bile  pigment  in  the  nrine. 

Disjjosal  of  the  Bile. — The  simple  excretion  of  the  foetal  bile  makes 
it  probable  that  the  bile  in  extra-uterine  life  is  also,  at  least  in  part,  des- 
tined to  be  discharged  as  excrementitious.  The  analysis  of  the  faeces 
shows,  however,  that  (except  when  rapidly  discharged  in  purgation)  they 
contain  very  little  of  the  bile  secreted,  probably  not  more  than  one-six- 
teenth part  of  its  weight,  and  that  this  portion  includes  chiefly  its  col- 
oring matter  in  the  form  of  stercobilin,  and  some  of  its  fatty  matters 
and  mucin,  but  its  salts  to  only  a  very  slight  degree,  almost  all  of  which 
have  been  reabsorbed  from  the  intestines  into  the  blood.  The  bilirubin 
is  in  part  converted  into  urobilin  and  is  reabsorbed  and  excreted  by  the 
kidneys  in  the  urine. 

The  elementary  composition  of  bile-salts  shows  such  a  preponderance 
of  carbon  and  hydrogen  that  probably,  after  absorption,  they  combine 
with  oxygen,  and  are  excreted  in  the  form  of  carbonic  acid  and  water. 
The  change  after  birth,  from  the  direct  to  the  indirect  mode  of  excre- 
tion of  the  bile  may,  with  much  probability,  be  connected  with  a  purpose 
in  relation  to  the  development  of  heat.  The  temperature  of  the  foetus 
is  largely  maintained  by  that  of  the  parent,  but,  in  extra-uterine  life, 
there  is  (as  one  may  say)  a  waste  of  material  for  heat  when  any  excre- 
tion is  discharged  unoxidized;  the  carbon  and  hydrogen  of  bilin,  there- 
fore, instead  of  being  ejected  in  the  faeces,  to  a  very  large  extent  (viz.-, 
I),  are  reabsorbed,  in  order  that  they  may  be  combined  with  oxygen,  and 
that  in  the  combination  heat  may  be  generated.  It  appears  that  tauro- 
cholic  acid  may  easily  be  split  up  in  the  intestine  into  taurin  and  chola- 
lic  acid,  and  the  same  is  probable  of  glycocholic  acid.  Taurin,  glycin, 
and  cholalic  acid  have  all  been  detected  in  small  amounts  in  the  faeces. 
So  that  the  bile  is  in  part  excreted,  but  in  part  is  reabsorbed  from  the 
intestine  (chiefly  the  large),  and  returned  to  the  liver.  What  may  be 
the  ultimate  destination  of  these  altered  or  unaltered  constituents  is  un- 
known.    Glycin  is  supposed  to  go  partly  to  form  urea,  and  taurin  is  ex- 


FOOD   AND    DIGESTION.  397 

o'ctcd  to  a  slight  e.xtcDt  in  the  urine  as  tanro-carbamic  acid,  but  it  is 
probable  that  although  part  of  this  may  unite  to  re-form  gl3'cocholic  or 
taurocholic  acid,  the  remainder  is  united  with  oxygen,  and  is  burnt  off 
in  the  form  of  carbonic  acid  and  water, 

A  substance,  contained  in  the  faeces,  and  named  stercorin,  is  closely 
allied  to  cholesterin.  Ten  grains  and  a  half  of  stercorin  are  excreted 
daily  (A.  Flint). 

From  the  peculiar  manner  in  which  the  liver  is  supplied  with  much 
of  the  blood  that  flows  through  it,  it  is  probable  that  this  organ  is  ex- 
cretory, not  only  for  such  hydro-carbonaceous  matters  as  may  need  ex- 
pulsion from  the  blood,  but  that  it  serves  for  the  direct  purification  of 
the  stream  which,  arriving  by  the  portal  vein,  has  just  gathered  up  vari- 
ous substances  in  its  course  through  the  digestive  organs — substances 
which  may  need  to  be  expelled  almost  immediately  after  their  absorjD- 
tion.  For  it  is  easily  conceivable  that  many  things  may  be  taken  up 
during  digestion,  which  not  only  are  unfit  for  jjurposes  of  nutrition,  but 
which  would  be  positively  injurious  if  allowed  to  mingle  with  the  gen- 
eral mass  of  the  blood.  The  liver,  therefore,  may  be  sujoposed  jilaced  in 
the  only  road  by  which  such  matters  can  pass  unchanged  into  the  general 
current,  jealously  to  guard  against  their  further  progress,  and  turn  them 
back  again  into  an  excretory  channel.  The  frequency  with  which  me- 
tallic poisons  are  either  excreted  by  the  liver,  or  intercepted  and  retained, 
often  for  a  considerable  time,  in  its  own  substance,  may  be  adduced  as 
evidence  for  the  probable  truth  of  this  supposition. 

The  secretion  of  the  bile  by  the  hepatic  cells  is  undoubtedly  influenced 
by  the  amount  of  blood  supplied  to  them.  This  is  well  seen  after  a  meal, 
when  the  amount  of  blood  passing  through  the  portal  circulation  incon- 
sequence of  the  congestion  of  the  secreting  organs  of  the  abdomen  is 
greatly  increased,  and  with  it  the  bile  secretion.  It  is,  however,  probable 
that  the  secretion  of  the  cells  is  in  some  more  direct  way  under  the  con- 
trol of  the  nervous  system,  but  how  this  influence  is  exercised  is  un- 
known. The  antecedents  of  the  various  substances  of  the  bile  from 
which  the  cells  manufacture  its  chief  constituents  are  not  exactly  known. 
It  is  surmised  that  the  bilirubin  is  formed  from  haemoglobin  brought 
from  the  spleen  either  actually  dissolved  in  the  jilasma  of  the  blood  or 
in  such  a  condition  in  the  corpuscles  as  to  be  easily  acted  upon  by  the 
liver  cells,  by  which  the  iron  is  separated.  The  bile  salts  are,  at  any 
rate  in  part,  formed  simply  by  the  conjunction  of  glyciuand  taurin  with 
cholalic  acid,  all  of  which  may  be  brought  to  the  liver  in  the  portal 
blood,  but  failing  this  it  is  probable  that  the  hepatic  cells  can  produce 
these  substances  anew. 


598  HANDBOOK    OF    PHYSIOLOGY. 

The  Intestinal  Secretion,  or  Succus  Entericus. 

On  account  of  the  difficulty  in  isolating  the  secretion  of  the  glands 
in  the  wall  of  the  intestine  (Brunners  and  Lieberkiihn^s)  from  other 
secretions  poured  into  the  canal  (gastric  juice,  bile,  and  pancreatic  se- 
cretion), but  little  is  known  regarding  the  composition  of  the  intestinal 
juice,  or  succus  ente?'icus. 

It  is  said  to  be  a  yellowish  alkaline  fluid  with  a  specific  gravity  of 
1011,  and  to  contain  about  2.5  per  cent  of  solid  matters  (Thiry), 

Functions. — The  secretion  is  said  to  be  able  to  convert  proteids  into 
peptones,  and  to  convert  starch  into  sugar,  but  the  evidence  in  favor  of 
these  actions  is  insufficient.  The  chief  function  of  the  juice  is  to  act 
upon  sugars.  It  possesses  the  power  of  converting  cane  into  grape 
sugar,  and  maltose  into  glucose.  It  also  contains  a  milk-curdling  fer- 
ment. 

The  reaction  which  represents  the  conversion  of  cane  sugar  into  grape 
sugar  may  be  represented  thus : 

a    OlsilaaUll       — |-       *  JdLsU        =        012x124013       -|—       012-1124011 

Saccharose.  Water.  Dextrose.  Lsevulose. 

The  conversion  is  probably  effected  by  means  of  a  hydrolytic  ferment, 
invertin  (Bernard). 

Summary  of  the  Digestive  Changes  in  the  Small 
Intestine. 

In  order  to  understand  the  changes  in  the  food  which  occur  during 
its  passage  through  the  small  intestine,  it  will  be  well  to  refer  briefly  to 
the  state  in  which  it  leaves  the  stomach  through  the  pylorus.  It  has 
been  said  before,  that  the  chief  office  of  the  stomach  is  not  only  to  mix 
into  an  uniform  mass  all  the  varieties  of  food  that  reach  it  through  the 
oesophagus,  but  especially  lo  dissolve  the  nitrogenous  portion  by  means 
of  its  secretion.  The  fatty  matters,  during  their  sojourn  in  the  stomach, 
become  more  thoroughly  mingled  with  the  other  constituents  of  the 
food  taken,  but  are  not  yet  in  a  state  fit  for  absorption.  The  conversion 
of  starch  into  sugar,  which  began  in  the  mouth,  has  been  interfered 
with,  if  not  altogether  stopped.  The  soluble  matters— both  those  which 
were  so  from  the  first,  as  sugar  and  saline  matter,  and  the  gastric  pep- 
tones— have  begun  to  disappear  by  absorption  into  the  blood-vessels,  and 
the  same  thing  has  befallen  such  fluids  as  may  have  been  swallowed. 

The  thin  pultaceous  chyme,  therefore,  which,  during  the  whole  period 
of  gastric  digestion,  is  being  constantly  squeezed  or  strained  through  the 
pyloric  orifice  into  the  duodenum,  consists  of  albuminous  matter,  broken 
down,  dissolving  and  half  dissolved;    fatty  matter  broken  down  and 


FOOD    AXD    DIGESTION.  399 

melted,  but  not  dissolved  at  all;  starch  very  slowly  in  process  of  con- 
version into  sugar,  and  as  it  becomes  sugar,  also  dissolving  in  the  fluids 
with  which  it  is  mixed;  while  with  these  are  mingled  gastric  fluid,  and 
fluid  that  has  been  swallowed,  together  with  such  portions  of  the  food 
as  are  not  digestible,  and  will  be  finally  expelled  as  part  of  the  faeces. 

On  the  entrance  of  the  chyme  into  the  duodenum,  it  is  subjected  to 
the  influence  of  the  bile  and  pancreatic  juice,  which  are  then  poured  out, 
and  also  to  that  of  the  succus  entericus.  All  these  secretions  have  a 
more  or  less  alkaline  reaction,  and  by  their  admixture  with  the  gastric 
chyme,  its  acidity  becomes  less  and  less  until  at  length,  at  about  the 
middle  of  the  small  intestine,  the  reaction  becomes  alkaline  and  contin- 
ues so  as  far  as  the  ileo-caecal  valve. 

The  special  digestive  functions  of  the  small  intestine  may  be  taken 
in  the  following  order : — 

(1.)  One  important  duty  of  the  small  intestine  is  the  alteration  of 
the  fat  in  such  a  manner  as  to  make  it  fit  for  absorption;  and  there  is 
no  doubt  that  this  change  is  chiefly  effected  in  the  upper  part  of  the 
small  intestine.  What  is  the  exact  share  of  the  process,  however,  al- 
lotted respectively  to  the  bile  and  to  the  pancreatic  secretion,  is  still  un- 
certain. The  fat  is  changed  in  two  ways.  («.)  To  a  slight  extent  it 
is  chemically  decomposed  by  the  alkaline  secretions  with  which  it  is 
mingled,  and  a  soap  is  the  result,  {h.)  It  is  emulsionized,  i.e.,  its  par- 
ticles are  minutely  subdivided  and  diffused,  so  that  the  mixture  assumes 
the  condition  of  a  milky  fluid,  or  emulsion.  As  will  be  seen  in  the  next 
Chapter,  most  of  the  fat  is  absorbed  by  the  lacteals  of  the  intestine,  but 
a  small  part,  which  is  saponified,  is  also  absorbed  by  the  blood-vessels. 

(2.)  The  albuminous  substances  which  have  been  partly  dissolved  in 
the  stomach,  and  have  not  been  absorbed,  are  subjected  chiefly  to  the 
action  of  the  pancreatic  juice.  The  pepsin  is  rendered  inert  by  being 
precipitated  together  with  the  gastric  peptones  and  proteoses,  as  soon  as 
the  chyme  meets  with  bile.  By  these  means  the  pancreatic  ferment 
trypsin  is  enabled  to  proceed  with  the  fui'ther  conversion  of  the  proteo- 
ses into  peptones,  and  part  of  the  peptones  (hemipeptone)  into  leucin 
and  tyrosin.  Albuminous  substances,  which  are  chemically  altered  in 
the  process  of  digestion  (peptones)  and  gelatinous  matters  similarly 
changed,  are  absorbed  by  the  blood-vessels  and  lymphatics  of  the  intes- 
tinal mucous  membrane.  Albuminous  matters,  in  state  of  solution, 
which  have  not  undergone  the  peptonic  change,  are  probably,  from  the 
difficulty  with  which  they  diffuse,  absorbed,  if  at  all,  almost  solely  by 
the  lymphatics. 

(3.)  The  starchy.,  or  amyloid  portions  of  the  food,  the  conversion  of 
which  into  maltose  was  more  or  less  interrupted  during  their  stay  in  the 
stomach,  are  now  acted  on  briskly  by  the  pancreatic  juice  and  the  succus 
entericus;  and  the  sugar  in  the  form  of  maltose  is  dissolved  in  the  intes- 


400  HANDBOOK    OF    PHYSIOLOGY. 

tinal  fluids,  and  is  absorbed  chiefly  by  the  blood-vessels.  During  or  just 
prior  to  its  absorption,  maltose  is  converted  into  dextrose. 

(4.)  Saline  and  saccliarine  matters^  such  as  common  salt,  and  cane 
sugar,  if  not  in  a  state  of  solution  beforehand  in  the  saliva  or  other  fluids 
which  may  have  been  swallowed  Avith  them,  are  at  once  dissolved  in  the 
stomach,  and  if  not  here  absorbed,  are  soon  taken  up  in  the  small  intes- 
tine; the  blood-vessels,  as  in  the  last  case,  being  chiefly  concerned  in  the 
absorption.  Cane  sugar  is  in  part  or  wholly  converted  into  grape  sugar 
before  its  absorption.  This  is  accomplished  partially  in  the  stomach,  but 
also  by  a  ferment  in  the  succus  entericus. 

(5.)  The  liquids,  including  in  this  term  the  ordinary  drinks,  as  water, 
wine,  ale,  tea,  etc.,  which  may  have  escaped  absorption  in  the  stomach, 
are  absorbed  probably  very  soon  after  their  entrance  into  the  intestine; 
the  fluidity  of  the  contents  of  the  latter  being  preserved  more  by  the 
constant  secretion  of  fluid  by  the  intestinal  glands,  pancreas,  and  liver, 
than  by  any  given  portion  of  fluid  whether  swallowed  or  secreted,  re- 
maining long  unabsorbed.  From  this  fact,  therefore,  it  may  be  gathered 
that  there  is  a  kind  of  circulation  constantly  proceeding  from  the  intes- 
tines into  the  blood,  and  from  the  blood  into  the  intestines  again;  for 
as  all  the  fluid — a  very  large  amount — secreted  by  the  intestinal  glands, 
must  come  from  the  blood,  the  latter  would  be  too  much  drained,  were 
it  not  that  the  same  fluid  after  secretion  is  again  reabsorbed  into  the 
current  of  blood — going  into  the  blood  charged  with  nutrient  products 
of  digestion — coming  out  again  by  secretion  through  the  glands  in  a 
comparatively  unchanged  condition. 

At  the  lower  end  of  the  small  intestine,  the  chyme,  still  thin  and 
pultaceous,  is  of  a  light  yellow  color,  and  has  a  distinctly  fascal  odor. 
This  odor  depends  upon  the  formation  of  indol  and  other  substances  to 
be  again  alluded  to.  In  this  state  it  passes  through  the  ileo-caecal  open- 
ing into  the  large  intestine. 

Summary  of  the  Digestive  Changes  in  the  Large 
Intestine. 

The  changes  which  take  place  in  the  chyme  in  the  large  intestine 
are  probably  only  the  continuation  of  the  same  changes  that  occur  in 
the  course  of  the  food's  passage  through  the  upper  part  of  the  intestinal 
canal.  From  the  absence  of  villi,  however,  we  may  conclude  that  ab- 
sorption, especially  of  fatty  matter,  is  in  great  part  comjjleted  in  the 
small  intestine;  while,  from  the  still  half-liquid,  pultaceous  consistence 
of  the  chyme  when  it  first  enters  the  csecum,  there  can  be  no  doubt  that 
the  absorption  of  liquid  is  not  by  any  means  concluded.  The  peculiar 
odor,  moreover,  which  is  acquired  after  a  short  time  by  the  contents  of 
the  large  bowel,  would  seem  to  indicate  a  further  chemical  change  in 


FOOD    AND    DIGESTION. 


401 


the  alinicutarv  matters  or  iu  the  digestive  fluids,  or  both.  The  acid 
reaction,  whicii  had  disappeared  in  the  small  bowel,  again  becomes  very 
manifest  in  the  cgecum — probably  from  acid  fermentation  processes  in 
some  of  the  materials  of  the  food. 

There  seems  no  reason  to  conclude  that  any  special  secondary  diges- 
tive process  occurs  in  the  csecum  or  in  any  other  part  of  the  large  in- 
testine. Probably  any  constituent  of  the  food  which  has  escaped 
digestion  and  absorption  in  the  small  bowel  may  be  digested  in  the  large 
intestine;  and  the  power  of  this  part  of  the  intestinal  euiial  to  absorb 
fatty,  albuminous,  or  other  matters,  may  be  gathered  from  the  good 
effects  of  nutrient  enemata,  so  frequently  given  when  from  any  cause 
there  is  difficulty  in  introducing  food  into  the  stomach.  In  ordinary 
healthy  digestion,  however,  the  changes  which  ensue  in  the  chyme  after 
its  passage  into  the  large  intestine  are  mainly  the  absorption  of  the 
more  liquid  parts;  the  chief  function  of  the  large  intestine  being  to  act 
as  a  reservoir  for  the  residues  of  digestion  before  their  expnlsion  from 
the  body. 

Action  of  Micro-organisms  in  the  Intestines. 

Certain  changes  take  place  in  the  intestinal  contents  independent  of, 
or  at  any  rate  supplemental  to,  the  action  of  the  digestive  ferments. 
These  changes  are  brought  about  by  the  action  of  micro-organisms  or 
bacteria.  We  have  indicated  elsewhere  that  the  digestive  ferments  are 
examples  of  unorganized  ferments,  so  bacteria  are  examples  of  organized 
ferments.      Organized    ferments,    of    M'hich    the    yeast    plant,    torula 


o 


"obooo" 


.^ 


/// 


^ 


^. 


>' 


<^ 


■^^^ 


7 


Fig.  274. — Types  of  micro-organisms,  a,  micrococci  arranged  singly;  in  twos,  diplococci— if  all 
the  micrococci  at  a  were  grouped  together,  they  would  be  called  staphylococci— audiu  fours,  sar- 
cinae;  6,  micrococci,  in  chains  streptococci ;  cand  d,  bacilli  of  various  kinds,  one  is  represented 
with  flagellum;  e,  various  forms  ot  spirilla;  /,  spores,  either  free  or  in  bacilli. 

{saccharomyces)  cerevisice,  may  be  taken  as  a  typical  example,  consist  of 
unicellular  vegetable  organisms,  which  when  introduced  into  a  suitable 
culture  medium  grow  with  remarkable  rapidity,  and  by  their  growth 
produce  new  substances  from  those  supplied  to  them  as  food.  Thus  for 
example,  when  the  yeast  cell  is  introduced  into  a  solution  of  grape  sugar, 

26 


402  HANDBOOK    OF    PHYSIOLOGY. 

it  grows,  aud  on  the  one  hand  alcohol,  and  on  the  other  hand  carbon 
dioxide  are  produced.  These  substances  are  not  the  direct  result  of  the 
life  of  the  cell,  but  probably  arise  from  the  formation  of  some  chemical 
substances  allied  to  the  unorganized  ferments  which  greatly  increase  in 
amount  with  the  multiplication  of  the  original  cell.  In  all  such  fer- 
mentative processes,  organisms  analogous  to  the  yeast  cell  are  present, 
and  it  is  not  strange  that  if  the  ferment  cell  is  introduced  into  a  suit- 
able medium,  it  may  by  its  rapid  reproduction  have  power  to  convert 
an  unlimited  amount  of  one  substance  into  another.  Speaking  generally 
a  special  variety  of  cell  is  concerned  with  each  ferment  action,  thus  one 
variety  has  to  do  with  alcoholic,  another  with  lactic  and  another  with 
acetous  fermentation.  A  considerable  number  of  species  of  bacteria 
exist  in  the  body  during  life,  chiefly  in  connection  with  the  mucous 
membranes,  particularly  of  the  digestive  tract.  These  bacteria  are 
unicellular  organisms,  devoid  of  chlorophyll,  sometimes  called  fission 
fungi  or  scliizomycetes.  They  multiply  chiefly  by  division,  but  many  of 
them  also  form  spores — Avhereas  the  yeast  cell  multiplies  by  gemmation. 
The  bacteria  are  very  much  smaller  than  the  yeast  cells,  being  only 
from  1  to  2!J.  in  width.  Morphologically  they  are  classified  into  i.  jnicro- 
cocci  or  globular  bacteria,  ii.  lacilli  or  rod-shaped  bacteria,  and  iii. 
sjnrilla  or  sinuous  bacteria. 

Many  forms  of  bacteria  have  been  isolated  from  the  mouth,  a  few 
varieties  from  the  stomach,  and  a  very  large  number  from  the  intestines. 
It  is  only  in  the  last  named  locality  that  their  multiplication  has  much 
eflect  from  a  physiological  point  of  view.  The  normal  (hydrochloric 
acid)  acidity  of  the  stomach  usually  destroys  all  the  micro-organisms 
taken  in  with  the  food,  but  when  the  amount  of  this  acid  is  deficient  (and 
sometimes  even  when  it  is  normal)  some  of  the  spores  may  escape.  On 
reaching  the  small  intestine  these  spores  begin  to  develop  in  its  alkaline 
medium,  and  may  increase  to  such  an  extent  as  to  stop  all  pancreatic 
and  intestinal  digestion;  the  point  where  this  occurs  varies  from  day  to 
day.  The  large  intestine  always  swarms  with  micro-organisms,  though 
the  ileo-cffical  valve,  in  some  unknown  way,  prevents  their  passage  into 
the  small  intestine;  as  a  consequence,  both  intestinal  and  pancreatic  di- 
gestion normally  cease  at  this  valve.  The  bacteria  found  in  the  intes- 
tine are  anaerobic,  i.e.,  they  do  not  exist  in  the  presence  of  free  oxygen. 

Tlie  changes  induced  in  the  intestine  by  the  activity  of  micro- 
organisms are  of  two  kinds,  fermentation  and  putrefaction;  the  former 
of  these  results  in  the  breaking  down  of  carbohydrate  matter  and  the 
latter  in  that  of  proteid  matter.  The  process  of  fermentation  is  the 
least  complex  and  probably  occurs  normally  in  the  small  intestine,  to  a 
certain  extent.  The  lactic-acid  fermentation  is  the  most  important, 
though  the  butyric-acid  fermentation  is  next;  under  their  influence  the 
carbohydrates  are  broken  down  into  lactic  and  butyric  acids,  and  perhaps 


FOOD    AND    DIGESTION.  403 

into  acetic  acid  also.  Carbouic  acid  gus  may  be  formed  at  the  same  time 
and  cause  flatulence.  Cellulose  and  other  insoluble  carbohydrate?  are 
decomposed  with  the  formation  of  marsh  gas  and  hydrogen,  which 
escape  by  the  rectum. 

In  putrefaction  the  process  is  nearly  the  same  as  in  tryptic  digestion, 
the  proteids  being  broken  down  into  peptones,  leucin,  tyiosin,  and  a 
long  row  of  other  substances  which  have  strong  odors  and  belong  to  tlie 
aromatic  grou]).  It  also  results  in  the  production  of  various  gases,  such 
as  carbon  dioxide,  suli)huretted  hydrogen,  ammonia,  hydrogen  and 
methane  (marsh  gas),  and  of  a  high  percentage  of  the  volatile  fatty  acids, 
valerianic  and  butyric.  Of  the  aromatic  substances  the  most  important 
are  indol  and  skatol,  though  their  toxicity  has  been  greatly  over- 
estimated. Some  undergo  oxidation,  indol  and  skatol  forming  indoxyl 
and  skatoxy] ;  they  are  usually  carried  off  in  the  fa?ces,  but  when  the 
bowel  is  obstructed  they  are  absorbed  and  eventually  aj^pear  in  the  urine, 
indoxyl  and  skatoxyl  forming  respectively  indoxyl-  and  skatoxyl-sulphuric 
acids  and  their  salts.  Tyrosin  is  further  broken  down  into  para-oxy- 
phenol-proprionic  acid,  paracresol  and  phenol;  para-oxy-phenol-acetic 
acid  is  also  formed. 

Movements  of  the  Intestines. 

It  remains  only  to  consider  the  manner  in  which  the  food  and  the 
several  secretions  mingled  with  it  are  moved  through  the  intestinal 
canal,  so  as  to  be  slowly  subjected  to  the  influence  of  fresh  portions  of 
intestinal  secretion,  and  as  slowly  exposed  to  the  absorbent  power  of  all 
the  villi  and  blood-vessels  of  the  mucous  membrane.  The  movement  of 
the  intestines  \% peristaltic  or  vermicular,  and  is  effected  by  the  alternate 
contractions  and  dilatations  of  successive  portions  of  the  muscular  coats. 
The  contractions,,  which  may  commence  at  any  point  of  the  intestine, 
extend  in  a  wave-like  manner  along  the  tube.  In  any  given  portion, 
the  longitudinal  muscular  fibres  contract  first,  or  more  than  the  circular; 
they  draw  a  portion  of  the  intestine  upward,  or,  as  it  were,  backward, 
over  the  substance  to  be  propelled,  and  then  the  circular  fibres  of  the 
same  portion  contracting  in  succession  from  above  downward,  or,  as  it 
were,  from  behind  forward,  press  on  the  substance  into  the  portion 
next  below,  in  which  at  once  the  same  succession  of  action  next  ensues. 
These  movements  take  place  slowly,  and,  in  health,  commonly  give  rise 
to  no  sensation;  but  they  are  perceptible  when  they  are  accelerated 
under  the  influence  of  any  irritant.  The  movements  of  the  intestines 
are  sometimes  retrograde;  and  there  is  no  hindrance  to  the  backward 
movement  of  the  contents  of  the  small  intestine.  But  almost  complete 
security  is  afforded  against  the  passage  of  the  contents  of  the  large  into 
the   small   intestine   by  the  ileo-csecal   valve.      Besides, — the  orifice  of 


404  HAIfDBOOK  OF  PHYSIOLOGY. 

cominunication  between  the  ileum  and  caecum  (at  the  borders  of  which 
orifice  are  the  folds  of  mucous  membrane  which  form  the  valve)  is  en- 
circled with  muscular  fibres,  the  contraction  of  which  prevents  the 
undue  dilatation  of  the  orifice. 

Proceeding  from  above  downward,  the  muscular  fibres  of  the  large 
intestine  become,  on  the  whole,  stronger  in  direct  proportion  to  the 
greater  strength  required  for  the  onward  moving  of  the  fa3ces,  which  are 
gradually  becoming  firmer.  The  greatest  strength  is  in  the  rectum,  at 
the  termination  of  which  the  circular  unstriped  muscular  fibres  form  a 
strong  band  called  the  internal  sphincter;  while  an  external  sphincter 
muscle  wdth  striped  fibres  is  placed  rather  lower  down,  and  more  ex- 
ternally, and  as  we  have  seen  above,  holds  the  orifice  close  by  a  con- 
stant slight  tonic  contraction. 

Experimental  irritation  of  the  brain  or  cord  produces  no  evident  or 
constant  effect  on  the  movements  of  the  intestines  during  life;  yet  in 
consequence  of  certain  mental  conditions  the  movements  are  accelerated 
or  retarded;  and  in  paraplegia  the  intestines  appear  after  a  time  much 
weakened  in  their  power,  and  costiveness,  with  a  tympanitic  condition, 
ensues.  Stimulation  of  pneumo-gastric  nerves,  if  not  too  strong,  induces 
genuine  peristaltic  movements  of  the  intestines.  Violent  irritation 
stops  the  movements. 

Influence  of  the  Nervous  System  on  Intestinal  Digestion. 

As  in  the  case  of  the  oesophagus  and  stomach,  the  peristaltic  move- 
ments of  the  intestines  may  be  directly  set  up  in  the  muscular  fibres  by 
the  presence  of  chyme  acting  as  the  stimulus.  Few  or  no  movements 
occur  when  the  intestines  are  empty.  The  intestines  are  connected 
with  the  central  nervous  system  both  by  the  vagi  and  by  the  splanchnic 
nerves,  as  well  as  by  other  branches  of  the  sympathetic  which  come  to 
them  from  the  coeliac  and  other  abdominal  plexuses. 

The  relations  of  these  nerves  respectively  to  the  movements  of  the 
intestine  and  the  secretions  are  probably  the  same  as  in  the  case  of  the 
stomach  already  treated  of. 

Duration  of  Intestinal  Digestion. — The  time  occupied  by  the  journey 
of  a  given  portion  of  food  from  the  stomach  to  the  anus  varies  consid- 
erably even  in  health,  and  on  this  account  probably  it  is  that  such  dif- 
ferent opinions  have  been  expressed  in  regard  to  the  subject.  About 
twelve  hours  are  occupied  by  the  journey  of  an  ordinary  meal  through 
the  small  intestine,  and  twenty-four  to  thirty-six  hours  by  the  passage 
through  the  large  bowel. 

The  contents  of  the  large  intestine,  as  they  proceed  toward  the  rec- 
tum, become  more  and  more  solid,  and  losing  their  more  liquid  and 
nutrient  parts,  gradually  acquire  the  odor  nnd  consistence  characteristic 


FOOD    AND    DIGESTION, 


405 


oifcBces.  After  a  sojourn  of  uncertain  duration  in  the  sigmoid  flexure 
of  the  colon,  or  in  the  rectum,  they  are  finally  expelled  by  the  act  of 
defaecation. 

The  average  quantity  of  solid  fsecal  matter  evacuated  by  the  human 
adult  in  twenty-four  hours  is  about  six  or  eight  ounces. 


Composition  of  F^ces. 

The  amount  of  water  varies  considerably,  from  6S  to  82  per  cent  and 
upward.     The  following  table  is  about  an  average  composition:  — 


Water 

Solids,  comprising : 

a.  Insoluble  residues  of  the  food,    uncooked  starch, 

cellulose,  woody  fibres,  cartilage,  seldom  mus- 
cular fibres  and  other  proteids,  fat,  cholesterin. 
korny  matter,   and  mucin      ..... 

b.  Certain  substances  resulting  from  decomposition 

of  foods,  indol,  skatol,  fatty  and  other  acids, 
calcium  and  magnesium  soaps 

c.  Special    excrementitious     constituents  : — Excretin, 

excretoleic  acid  (Marcet),  and  stercorin  (Austin 
Flint) 

d.  Salts  : — Chiefly  phosphate  of  magnesium  and  phos- 

phate of  calcium,  with  small  quantities  of  iron, 
soda,  lime,  and  silica        ..... 

e.  Insoluble  substances  accidentally  introduced  with 

the  food 

f .  Mucus,  epithelium,  altered  coloring  matter  of  bile, 
'    fatty  acids,  etc.  .         .  ... 

g.  Varying  quantities  of  other  constituents  of  bile,  and 

derivatives  from  them  ...... 


733.00 


267.00 


1000.00 


The  Gases  contained  in  the  Stomach  and  Intestines. — Under  ordi- 
nary circumstances,  the  alimentary  canal  contains  a  considerable  quan- 
tity of  gaseous  matter.  Any  one  who  has  had  occasion,  in  a  post-mortem 
examination,  either  to  lay  open  the  intestines,  or  to  let  out  the  gas 
which  they  contain,  must  have  been  struck  by  the  small  space  afterward 
occupied  by  the  bowels,  and  by  the  large  degree,  therefore,  in  which  the 
gas,  which  naturally  distends  them,  contributes  to  fill  the  cavity  of  the 
abdomen.  Indeed,  the  presence  of  air  in  the  intestines  is  so  constant, 
and,  within  certain  limits,  the  amount  in  health  so  uniform,  that  there 
can  be  no  doubt  that  its  existence  here  is  not  a  mere  accident,  but  in- 
tended to  serve  a  definite  and  important  purpose,  although,  probably,  a 
mechanical  one. 

Sources. — The  sources  of  the  gas  contained  in  the  stomach  and  bowels 
may  be  thus  enumerated: — 

1.  Air  introduced  in  the  act  of  swallowing  either  food  or  saliva;  %. 
Gases  developed  by  the  decomposition  of  alimentary  mutter,  or  of  the 
secretions  and  excretions  mingled  with  it  in  the  stomach  and  intestines; 
3.  It  is  probable  that  a  certain  mutual  interchange  occurs  between  the 


406 


HANDBOOK    OE    PHYSIOLOGY. 


gases  contained  in  the  alimentary  canal,  and  those  present  in  the  blood 
of  these  gastric  and  intestinal  blood-vessels;  but  the  conditions  of  the 
exchange  are  not  known,  and  it  is  very  doubtful  whether  anything  like 
a  true  and  definite  secretion  of  gas  from  the  blood  into  the  intestines  or 
stomach  ever  takes  place.  There  can  be  no  doubt,  however,  that  the 
intestines  may  be  the  proper  excretory  organs  for  many  odorous  and 
other  substances,  either  absorbed  from  the  air  taken  into  the  lungs  in 
inspiration,  or  absorbed  in  the  upper  part  of  the  alimentary  canal,  again 
to  be  excreted  at  a  portion  of  the  same  tract  lower  down — in  either  ease 
assuming  rapidly  a  gaseous  form  after  their  excretion,  and  in  this  way, 
perhaps,  obtaining  a  more  ready  egress  from  the  body.  It  is  probable 
that,  under  ordinary  circumstances,  the  gases  of  the  stomach  and  intes- 
tines are  derived  chiefly  from  the  second  of  the  sources  which  have  been 
enumerated. 


Composition  of  Gases  of  the  Alimentary  Canal. 

{Tabulated  from  various  authorities  ly  Brinton.) 


Composition  by  Volume. 

Oxygen. 

Nitrog. 

Carbon. 
Acid. 

Hydrog. 

Carbm-et. 
Hydrogen. 

Sulphuret. 
Hydrogen. 

Stomach    . 

Small  Intestines     . 

Caecum 

Colon 

Rectum 

Expelled  per  anum 

11 

71 
32 
67 
35 
46 
22 

14 
30 
12 
51 
43 
40 

4 

38 

8 

6 

19 

13 

8 

11 

19 

Y  trace. 

J 

The  above  table  differs  little  from  the  average  obtained  by  more 
modern  observers,  but  it  omits  an  important  point  to  which  attention 
should  be  drawn,  viz.,  that  the  amounts  of  the  gases  vary  with  the  diet. 
For  all  practical  purposes  oxygen  and  sulphuretted  hydrogen  may  be 
omitted.  An  analysis  of  the  intestinal  gases  (Ruge,  copied  by  Hallibur- 
ton) in  man  is  as  follows : — 


Gases. 

Milk    Diet. 

Meat  Diet. 

Vegetable    Diet. 

Carbon  dioxide  .... 
Hydrogen         .... 
Carburetted  hydrogen 
Nitrogen 

9  to  16 
43  to  54 

0.9 
36  to  38 

8  to  13 

0.7  to  3 

26  to  37 

45  to  64 

21  to  34 
1.5  to  4 
44  to  55 
10  to  19 

Sources  of  the  Carton  Dioxide. — From  the  carbonates  and  lactates  in 
food;  from  alcoholic  fermentation  of  sugar;  from  putrefaction  of  car- 
bohydrates and  proteids;  and  from  butyric  acid  fermentation. 

Sources  of  the  Hydrogen. — From  butyric  acid  fermentations  of  lactic 
acid — 


FOOD    AXI)    DIGESTION.  407 

2  CaHaOa      =      C,,HeO,     +     2  CO,      +     2  H, 
Lactic  Acid.         Butyric  Acid. 

Source  of  tJie  Carhuretted  Hydrogen. — From  the  decomposition  of 
acetates  and  lactates  and  from  cellulose  (Ce  Hio  O5  +  Hg  0  =  3  CO2  + 
3  CH4). 

Source  of  the  Nitrogen. — The  nitrogen  is  derived  from  the  swallowed 
air. 

Defaecation. 

The  act  of  the  expulsion  of  fseces  is  in  part  due  to  an  increased  reflex 
peristaltic  action  of  the  lower  part  of  the  large  intestine,  namely  of 
the  sigmoid  flexure  and  rectum,  and  in  part  to  the  more  or  less  volun- 
tary action  of  the  abdominal  muscles.  In  the  case  of  active  voluntary 
efforts,  there  is  usually,  first  an  inspiration,  as  in  the  case  of  coughing, 
sneezing,  and  vomiting;  the  glottis  is  then  closed,  and  the  diaphragm 
fixed.  The  abdominal  muscles  are  contracted  as  in  expiration ;  but  as 
the  glottis  is  closed,  the  whole  of  their  pressure  is  exercised  on  the  ab- 
dominal contents.  The  sphincter  of  the  rectum  being  relaxed,  the  evac- 
uation of  its  contents  takes  place  accordingly;  the  effect  being,  of  course, 
increased  by  the  peristaltic  action  of  the  intestine.  As  in  the  other 
actions  just  referred  to,  there  is  as  much  tendency  to  the  escape  of  the 
contents  of  the  lungs  or  stomach  as  of  the  rectum;  but  the  pressure  is 
relieved  only  at  the  orifice,  the  sphincter  of  which  instinctively  or  in- 
voluntarily yields. 

Nervous  Mechanism. — The  anal  sphincter  muscle  is  normally  in  a 
state  of  tonic  contraction.  The  nervous  centre  which  governs  this  con- 
traction is  probably  situated  in  the  lumbar  region  of  the  spinal  cord,  in- 
asmuch as  in  cases  of  division  of  the  cord  above  this  region  the  sphincter 
regains,  after  a  time,  to  some  extent  the  tonicity  which  is  lost  immedi- 
ately after  the  operation.  By  an  effort  of  the  will,  acting  through  the 
centre,  the  contraction  may  be  relaxed  or  increased.  In  ordinary  cases 
the  apparatus  is  set  in  action  by  the  gradual  accumulation  of  faeces  in 
the  sigmoid  flexure  and  rectum,  pressing  by  the  peristaltic  action  of 
these  parts  of  the  large  intestine  against  the  sphincter,  and  causing  by 
reflex  action  its  relaxation;  this  sensory  impulse  acting  through  the 
brain  and  reflexly  through  the  spinal  centre.  At  the  same  time  that 
the  sphincter  is  inhibited  or  relaxed,  impulses  pass  to  the  muscles  of  the 
lower  intestine  increasing  their  peristalsis,  and,  if  necessary,  to  the  ab- 
dominal muscles  as  welh     The  action  of  the  centre  is  therefore  double. 


CHAPTER  X. 

ABSORPTION. 

Absorption  is  generally  considered  to  consist  of  two  processes;  the 
first,  having  for  its  object  the  introduction  into  the  blood  of  fresh  mate- 
rial, and  which  is  called  absorption  from  without,  takes  place  chiefly 
from  the  alimentary  canal,  and  to  a  less  extent  from  the  skin  and  lungs; 
the  second,  having  for  its  object  the  gradual  removal  of  parts  of  the 
body  itself  when  they  need  removal,  is  called  absorption  from  within, 
and  takes  place  everywhere  within  the  tissues  of  the  body. 

The  conditions  of  absorption  from  the  alimentary  canal  which  may 
be  taken  as  an  example  of  the  first  of  these  processes  are  the  following: 
on  one  side  is  a  fluid  containing  matters  which  have  been  so  acted  upon 
by  the  digestive  juices  as  to  be  in  a  fit  condition  to  be  absorbed.  On 
the  other  side  are  blood-capillaries  and  capillaries  of  the  lymphatic  sys- 
tem, and  separating  the  two  are  epithelium  and  connective  tissue,  as 
well  as  the  endothelium  of  the  vessels  themselves.  The  problem  which 
has  to  be  considered  is,  how  does  the  fluid  on  the  one  side  of  the 
organic  membrane  reach  the  blood  or  lymphatic  vessel  ?  Until  within 
recent  date  it  was  assumed  that  the  passage  of  the  fluid  from  one  side 
of  this  membrane  to  the  other  came  about  solely  by  definite  physical 
laws,  and  these  were  practically  independent  of  the  vital  condition  of 
the  tissues.  In  the  first  place,  it  was  taught,  came  in  osmosis,  the  pas- 
sage of  fluids  through  an  animal  membrane,  which  occurs  independent 
of  vital  conditions,  and  in  the  next  place  came  in  filtration,  the  passage 
of  fluids  through  the  pores  of  a  membrane  under  pressure.  It  is  now 
believed,  however,  that  there  is  another  factor  concerned  in  absorption, 
viz.,  the  vital  and  selective  action  of  the  epithelium,  and  possibly  of  the 
tissue  which  separates  the  fluid  to  be  absorbed,  from  the  blood  and 
lymph  stream.  About  this  vital  action  of  the  epithelium  very  little 
definite  is  known,  but  the  mere  fact  that  fats  are  principally  absorbed 
in  one  part  of  the  intestine,  and  as  Ave  shall  see  pass  through  the  cells 
of  the  intestinal  villi,  is  some  evidence  in  its  favor.  It  will  be  as  well 
to  consider  briefly  the  two  physical  processes  of  osmosis  and  filtration. 

Methods  of  Absorption. 

Osmosis. — The  phenomenon  of  the  passage  of  fluids  through  animal 
membrane,  which  occurs  quite  independently  of  vital  conditions,  was 
first  demonstrated  by  Dutrochet.     The  instrument  which  he  employed 

4.0S 


ABSOKI'TION. 


409 


in  his  experiments  was  named  an  endosmometer.  One  form  of  this, 
represented  in  the  figure,  consists  of  a  graduated  tube  expanded  into  an 
open-mouthed  bell  at  one  end,  over  which  a  portion  of  membrane  is 
tied.  If  the  bell  be  filled  with  a  solution  of  a  salt — say  sodium  chloride, 
and  be  immersed  in  water,  the  water  will  pass  into  the  solution,  and 
part  of  the  salt  will  pass  out  into  the  water;  the  water,  however,  will 
pass  into  the  solution  much  more  rapidly  than  the  salt  will  pass  out  into 
the  water,  and  the  dilated  solution  will  rise  in  the  tube.  It  is  to  this 
passage  of  fluids  through  membrane  that  the  term  osmosis  is  applied. 
The  nature  of  the  membrane  used  as  a  septum,  and  its  affinity  for 
the  fluids  subjected  to  experiment  have  an  important  influ- 
ence, as  might  be  anticipated,  on  the  rapidity  and  dura- 
tion of  the  osmotic  current.  Thus,  if  a  piece  of  ordinary 
bladder  be  used  as  the  septum  between  water  and  alcohol, 
the  current  is  almost  solely  from  the  water  to  the  alcohol, 
on  account  of  the  much  greater  affinity  of  water  for  this 
kind  of  membrane;  while,  on  the  other  hand,  in  the  ease 
of  a  membrane  of  caoutchouc,  the  alcohol,  from  its  greater 
affinity  for  this  substance,  would  pass  freely  into  the  water. 
Absorption  by  blood-vessels  is  the  consequence  of  their 
walls  being,  like  the  membranous  septum  of  the  endosmo- 
meter, porous  and  capable  of  imbibing  fluids,  and  of  the 
blood  being  so  composed  that  most  fluids  will  mingle  with 
it.  Thus  the  relation  of  the  chyme  in  the  stomach  and 
intestines  to  the  blood  circulating  in  the  vessels  of  the 
gastric  and  intestinal  mucous  membrane  is  evidently  just 
that  which  is  required  for  osmosis.  The  chyme  contains 
substances  which  have  been  so  acted  upon  by  the  di- 
gestive juices  as  to  have  become  quite  able  to  pass  through 
an  animal  membrane,  or  to  dialyze  as  it  is  called.  The  thin  animal 
membrane  is  the  coat  of  the  blood-vessels  with  the  intervening  mucous 
membrane.  The  nature  of  the  fluid  within  the  vessels,  the  very  feeble 
power  of  dialyzation  which  the  albuminous  blood  possesses,  determines 
the  direction  of  the  osmotic  current,  viz.,  into  and  not  out  of  the  blood- 
vessels. The  current  is  of  course  aided  by  the  fact  of  the  constant 
change  in  the  blood  presented  to  the  osmotic  surface,  as  it  rapidly  circli- 
lates  within  the  vessels.  As  a  rule  the  current  is  from  the  stomach  or 
intestine  into  the  blood,  but  the  reversed  action  may  occur,  when,  for 
example,  sulphate  of  magnesia  is  taKen  into  the  stomach,  in  which  case 
there  is  a  rapid  discharge  of  water  from  the  blood-vessels  into  the  ali- 
mentary canal  resulting  in  purgation.  The  presence  of  various  sub- 
stances in  the  food  has  the  power  of  diminishing  the  rate  of  absorption; 
their  influence  is  probably  exerted  upon  the  membrane,  diminishing  its 
power  of  permitting  osmosis.     Whereas  the  presence  of  a  little  hydro- 


Fig.  275 
Endosmometer. 


4:10  HANDBOOK    O^   PHYSIOLOGY. 

chloric  acid  in  the  contents  of  the  stomach  appears  to  determine  the 
direction  of  the  osmosis,  or  at  any  rate  to  diminish  or  prevent  exosmosis. 

The  conditions  for  osmosis  exist  not  only  in  the  alimentary  mucous 
membrane,  but  also  in  the  serous  cavities  and  the  tissues  elsewhere. 

Various  substances  have  been  classified  according  to  the  degree  in 
which  they  possess  the  property  of  passing,  when  in  a  state  of  solution 
in  water,  through  membrane;  those  which  pass  freely,  inasmuch  as  they 
are  usually  capable  of  crystallization,  being  termed  crystalloids,  and  those 
which  pass  with  difficulty,  on  account  of  their  physically  glue-like  char- 
acter, colloids. 

This  distinction,  however,  between  colloids  and  crystalloids  which 
is  made  the  basis  of  their  classification,  is  by  no  means  the  only  differ- 
ence between  them.  I'he  colloids,  besides  the  absence  of  power  to  assume 
a  crystalline  form,  are  characterized  by  their  inertness  as  acids  or  bases, 
and  feebleness  in  all  ordinary  chemical  relations.  Examples  of  them 
are  found  in  albumin,  gelatin,  starch,  hydrated  alumina,  hydrated  silicic 
acid,  etc. ;  while  the  crystalloids  are  characterized  by  qualities  the  reverse 
of  those  just  mentioned  as  belonging  to  colloids.  Alcohol,  sugar,  and 
ordinary  saline  substances  are  examples  of  crystalloids. 

Filtration,  or  transudation,  means  the  passage  of  fluids  through  the 
pores  of  a  membrane  under  pressure.  The  greater  the  pressure  the 
greater  the  amount  which  passes  through  the  membrane.  Colloids  will 
filter,  although  less  easily  than  crystalloids.  The  nature  of  the  substance 
to  be  filtered  and  the  nature  of  the  membrane  which  acts  as  the  filter 
materially  affect  the  activity  of  the  process.  No  doubt  both  osmosis 
and  filtration  go  on  together  in  the  process  of  absorption.  An  excellent 
example  of  filtration  or  transudation  occurs  in  the  pathological  condition 
known  as  dropsy,  in  which  the  connective  tissues  become  infiltrated 
with  serous  fluid.  The  fluid  passes  out  of  the  vein  when  the  intra-ven- 
ous  j)ressure  passes  a  certain  point,  the  fluid  being,  as  it  were,  squeezed 
through  the  walls  of  the  vessels  by  this  excess  of  pressure. 

Rapidity  of  Absorption. — The  rapidity  with  which  matters  may  be 
absorbed  from  the  stomach,  probably  by  the  blood-vessels  chiefly,  and 
diffused  through  the  textures  of  the  body,  has  been  found  by  experiment. 
It  appears  that  lithium  chloride  may  be  diffused  into  all  the  vascular 
textures  of  the  body,  and  into  some  of  the  non-vascular,  as  the  cartilage 
of  the  hip-joint,  as  well  as  into  the  aqueous  humor  of  the  eye,  in  a  quar- 
ter of  an  hour  after  being  given  on  an  empty  stomach.  Into  the  outer 
part  of  the  crystalline  lens  it  may  pass  after  a  time,  varying  from  half 
an  hour  to  an  hour  and  a  half.  Lithium  carbonate,  when  taken  in  five 
or  ten-grain  doses  on  an  empty  stomach,  may  be  detected  in  the  urine 
in  5  or  10  minutes;  or,  if  the  stomach  be  full  at  the  time  of  taking  the 
dose,  in  20  minutes.  It  may  sometimes  be  detected  in  the  urine,  more- 
over, for  six,  seven,  or  eight  days. 


AHSOKPTiOK.  411 

Some  experiments  on  the  absorption  of  various  mineral  and  vegeta- 
ble poisons  have  brought  to  light  the  singular  fact  that,  in  some  cases, 
absorption  takes  place  more  rapidly  from  the  rectum  than  from  the 
stomach.  Strychnia,  for  example,  when  in  solution,  produces  its  jDoi- 
sonous  effects  much  more  speedily  when  introduced  into  the  rectum 
than  into  the  stomach.  When  introduced  in  the  solid  form,  however, 
it  is  absorbed  more  rapidly  from  the  stomach  than  from  the  rectum, 
doubtless  because  of  the  greater  solvent  property  of  the  secretion  of  the 
former  than  of  the  latter. 

Conditions  for  Absorption. — 1.  The  diffusibility  of  the  substance  to 
be  absorbed  is  one  of  the  chief  conditions  for  its  absorption — a  col- 
loid, as  we  have  seen,  dialyzes  very  little.  It  must  be  also  in  the  liquid  or 
gaseous  state.  Mercury  may,  however,  be  absorbed  even  in  the  metallic 
state;  and  in  that  state  may  pass  into  and  remain  in  the  blood-vessels, 
or  be  deposited  from  them;  and  such  substances  as  exceedingly  finely- 
divided  charcoal,  when  taken  into  the  alimentary  canal,  have  been  found 
in  the  mesenteric  veins.  Oil,  minutely  divided,  as  in  an  emulsion,  will 
pass  slowly  into  blood-vessels,  as  it  will  through  a  filter  moistened  with 
water;  but  it  is  donbtful  if  fatty  matters  find  tlieir  way  into  the  blood- 
vessels as  tbey  do  into  the  Ivmph-vcppcls  of  Ihe  intestinal  canal. 

2.  The  less  detise  the  fluid  to  le  absorbed,  the  more  sjjeedy,  as  a  gen- 
eral rule,  is  its  absorption  by  the  living  blood-vessels.  Hence  the  rapid 
absor2ition  of  water  from  the  stomach;  also  of  weak  saline  solutions;  but 
with  strong  solutions,  there  appears  less  absorption  into,  than  effusion 
from,  the  blood-vessels. 

3.  The  absorjDtion  is  the  less  rajnd  the  fuller  and  tenser  the  blood-ves- 
sels are;  and  the  tension  may  be  so  great  as  to  hinder  altogether  the 
entrance  of  more  fluid.  Thus,  if  water  is  injected  into  a  dog's  veins  to 
repletion,  poison  is  absorbed  very  slowly;  but  when  the  tension  of  the 
vessels  is  diminished  by  bleeding,  the  poison  acts  quickly.  So,  when 
cujiping-glasses  are  placed  over  a  poisoned  wound,  they  retard  the  ab- 
sorption of  the  poison  not  only  by  diminishing  the  velocity  of  the  cir- 
culation in  the  part,  but  by  filling  all  its  vessels  too  full  to  admit  more. 

4.  On  the  same  ground,  absorption  is  the  quicker  the  more  rapid  the 
circulation  of  the  blood;  not  because  the  fluid  to  be  absorbed  is  more 
quickly  imbibed  into  the  tissues,  or  mingled  with  the  blood,  but  because 
as  fast  as  it  enters  the  blood,  it  is  carried  away  from  the  part,  and  the 
blood  being  constantly  renewed,  is  constantly  as  fit  as  at  the  first  for 
the  reception  of  the  substance  to  be  absorbed. 

These  four  conditions  are  physical,  but  (5)  the  vital  condition  of  the 
absorptive  epithelium  must  not  be  forgotten.  It  has  been  shown,  for 
example,  that  the  absorption  by  the  frog's  skin  is  hastened  by  alcohol 
and  retarded  by  chloroform.  It  appears  also  that  absorption  is  retarded 
rather  than  hastened  by  removal  of  the  intestinal  epithelium. 


41^ 


HANDBOOK    OF    PHYSIOLOGY. 


The  Lymphatic  System. 

Having  now  discussed  the  methods  and  conditions  of  absorption  in 
general,  we  must  next  turn  to  the  system  of  vessels  in  which,  on  the 
one  hand,  materials  of  the  food  not  taken  directly  into  the  blood-vessels 
of  the  alimentary  canal  are  received  and  carried  into  the  blood-stream; 
and,  on  the  other,  fluid  which  has  exuded  from  the  blood-vessels  into  the 


Lymphatics    of    head    and 
neck,  right. 

Eight  internal  jugular  vein. 
Right  subclavian  vein. 

Lymphatics  of  right  arm. 


Receptaculutn  chyU. 


Lj;mphatics  of  lower  extrem- 
ities. 


Lymphatics  of  head  and 
neck,  left. 

Thoracic  duct. 

Left  subclavian  vein. 


Thoracic  duct. 


Lacteals. 


Lymphatics  of   lower  ex- 
tremities. 


Fig.  276.— Diagram  of  the  principal  groups  of  Lymphatic  vessels  (from  Quain). 


tissues  is  gathered  up  and  carried  back  again  into  the  blood.  This  sys- 
tem of  vessels  is  called  the  Lymphatic  System,  and  the  vessels  themselves 
are  named  Lymphatics  or  Absorbents.  They  have  often  been  incidentally 
mentioned  in  former  chapters. 

The  principal  vessels  of  the  lymphatic  system  are,  in  structure  and 
general  appearance,  like  very  small  and  thin-walled  veins.  They  are 
provided  with  valves.  They  commence  in  fine  microscopic  lympJi-cap- 
illaries,  in  the  organs  and  tissues  of  the  body,  and  they  end  directly  or 
indirectly  in  two  trunks  which  open  into  the  large  veins  near  the  heart 


ABSORPTION. 


413 


(fig.  276).  The  fluid  which  they  contain,  unlike  the  blood,  passes  only 
in  one  direction,  namely,  from  the  fine  branches  to  the  trunk  and  so  to 
the  large  veins,  on  enteriag  which  they  are  mingled  with  the  stream  of 
blood  and  form  part  of  its  constituents.  The  course  of  the  fluid  in  the 
lymphatic  vessels  is  always  toward  the  large  veins  in  the  neighborhood 
of  the  heart,  and  in  fig.  276  the  greater  part  of  the  contents  of  the  lym- 


Fig.  277. 


Fig.  278 


Fig.  277.— Superficial  lymphatics  of  right  groin  and  upper  part  of  thigh,  «.— 1.  Upper  inguinal 
glands.  2,2'.  Lower  or  inguinal  or  femoral  glands.  3,3'.  Plexus  of  lymphatics  in  the  course  of  the 
long  saphenous  vein.     (Mascagni.) 

Fig.  2(8.— Lymphatic  vessels  of  the  head  and  neck  and  the  upper  jiart  of  the  trunk  (Mascagni). 
^. — The  chest  and  pericardium  have  been  opened  on  the  left  side,  and  the  left  mamma  detached  and 
thrown  outward  over  tlie  left  arm,  so  as  to  expose  a  great  part  of  its  deep  surface.  The  principal 
lymphatic  vessels  and  glands  are  shown  on  the  side  of  the  head  and  face,  and  in  the  neck,  axilla, 
and  mediastinum.  Between  the  left  internal  jugular  vein  and  the  common  carotid  artery,  the  upper 
ascending  part  of  the  thoracic  duct  marked  i,  and  above  this,  and  descending  to 2,  the  arch  and  last 
part  of  the  duct.  The  termination  of  the  upper  lymphatics  of  the  diaphragm  in  the  mediastinal 
glands,  as  well  as  the  cardiac  and  the  deep  mammai'y  lymphatics,  is  also  shown. 


phatic  system  of  vessels  will  be  seen  to  pass  through  a  comparatively 
krge  trunk  called  the  tJioracic  duct,  which  finally  empties  its  contents 
into  the  blood-stream,  at  the  junction  of  the  internal  jugular  and  sub- 
clavian veins  of  the  left  side.  There  is  a  smaller  duct  on  the  right  side. 
The  lymphatic  vessels  of  the  intestinal  canal  are  called  ladeals,  because 
during  digestion  the  fluid  contained  in  them  resembles  milk  in  appear- 


414 


HANDBOOK    OF    PHYSIOLOGY. 


ance;  and  the  lymph 
called  cliyle.  There 
and  lymphatics.     In 


in  the  lacteals  during  the  period  of  digestion  is 
is  no  essential  distinction,  however,  between  lacteals 
some  parts  of  its  course  the  lymph-stream  must 
pass  through  lymphatic  glands. 

Lymphatic  vessels  are  distributed  in  nearly  all 
parts  of  the  body.  Their  existence,  however,  has 
not  yet  been  determined  in  the  placenta,  the  um- 
bilical cord,  the  membranes  of  the  ovum,  or  in 
any  of  the  so-called  non-vascular  parts,  as  the 
nails,  cuticle,  hair,  and  the  like. 

Origin  of  Lymph  Capillaries. — The  lymphatic 
capillaries  commence  most  commonly  either  (a) 
in  closely  meshed  networks,  or  (&)  in  irregular 
lacunar  spaces  between  the  various  structures  of 
which  the  different  organs  are  composed.  Such 
irregular   spaces,  forming   what   is   now    termed 


Fig.  279  Fig.  280. 

Fig.  279  —Superficial  lymphatics  of  the  forearm  and  palm  of  the  hand,  ^.—5.  Two  small  glands 
at  the  bend  of  the  arm.  6.  Radial  lymphatic  vessels.  7.  Uhiar  lymphatic  vessels.  8,  8.  Palniar 
arch  of  lymphatics.  9,  9'.  Outer  and  inner  sets  of  vessels,  h.  CephaUc  vem.  d.  Radial  vein, 
e  Median  vein.  /.  Ulnar  vein.  The  lymphatics  are  represented  as  lying  on  the  deep  fascia. 
(Mascagni.")  .      ,     .,,     .,  .,     ,        _, 

Fig.  280  —Lymphatics  of  central  tendon  of  rabbit's  diaphragm,  stained  with  silver  nitrat«.  The 
ground  suijstance  has  been  shaded  diagramiiiatically  to  bring  out  the  lymphatics  clearly.  I.  Lym- 
phatics lined  by  long  narrow  endotlielial  cells,  and  showing  v,  valves  at  frequent  mtervals.  Cocho- 
field.D 

the  lymph-canalicular  system,  have  been  shown  to  exist  in  many  tis- 
sues. In  serous  membranes  such  as  the  omentum  and  mesentery  they 
occur  as  a  connected  system  of  very  irregular  branched  spaces  partly 
occupied  by  connective  tissue-corpuscles,  and  both  in  these  and  in  many 
other  tissues  are  found  to  communicate  freely  with  regular  lymphatic 


ABSORPTION.  415 

vessels.  In  many  cases,  though  they  are  formed  mostly  by  the  chinks 
and  crannies  between  the  blood-vessels,  secreting  ducts,  and  other  parts 
which  may  happen  to  form  the  framework  of  the  organ  in  which  they 
exist,  they  are  lined  by  a  distinct  layer  of  endothelium. 

The  lacteals  offer  an  illustration  of  another  mode  of  origin,  namely, 
{c)  in  blind  dilated  extremities;  but  there  is  no  essential  difference  in 
structure  between  these  and  the  lymphatic  capillaries  of  other  parts. 

Structure  of  Lpnph  Capillaries. — The  structure  of  lymphatic  capil- 
laries is  very  similar  to  that  of  blood-capillaries :  their  walls  consist  of 
a  single  layer  of  elongated  endothelial  cells  with  sinuous  outline,  which 
cohere  along  their  edges  to  form  a  delicate  membrane.  They  differ 
from  blood  capillaries  mainly  in  their  larger  and  very  variable  calibre, 
and  in  their  numerous  communications  with  the  spaces  of  the  lymph- 
canalicular  system. 

Communications  of  the  Lymphatics. — The  fluid  part  of  the  blood 
constantly  exudes  from  or  is  strained  through  the  walls  of  the  blood- 
capillaries,  so  as  to  moisten  all  the  surrounding  tissues,  and  occupies 
the  interspaces  which  exist  among  their  different  elements,  which  form 
the  beginnings  of  the  lymph-capillaries;  and  the  latter,  therefore,  are  the 
means  of  collecting  the  exuded  blood  plasma,  and  returning  that  j^art 
which  is  not  directly  absorbed  by  the  tissues  into  the  blood-stream.  It 
is  not  necessary  to  assume  the  presence  of  any  special  channels  between 
the  blood  and  lymphatic  vessels,  inasmuch  as  even  blood-corpuscles  can 
pass  bodily,  without  much  difficulty,  through  the  walls  of  the  blood- 
capillaries  and  small  veins,  and  could  pass  with  still  less  trouble,  proba- 
bly, through  the  comparatively  ill-defined  walls  of  the  capillaries  which 
contain  lymph. 

It  has  been  already  mentioned  (p.  31)  that  in  certain  parts  of  the 
body,  stomata  exist,  by  which  lymjDhatic  capillaries  directly  communi- 
cate with  parts  hitherto  supposed  to  be  closed  cavities. 

Stomata  have  been  found  in  the  pleura;  and  as  they  may  be  pre- 
sumed to  exist  in  other  serous  membranes,  it  would  seem  as  if  the  serous 
cavities,  hitherto  supposed  closed,  form  but  a  large  lymph-sinus  or 
widening  out,  so  to  speak,  of  the  lymph-capillary  system  with  which 
they  directly  communicate. 

When  absorption  into  the  lymphatic  system  takes  place  in  membranes 
covered  by  epithelium  or  endothelium  through  the  interstitial  or  inter- 
cellular cement-substance,  it  is  said  to  take  place  through Jt)se^^c?o-s/oma^fl!, 
already  alluded  to  (p.  32). 

Devionstration  of  Lymphatics  of  Diaphragm. — The  stomata  on  the  peritoneal 
surface  of  the  diaphragm  are  the  openings  of  short  vertical  canals  which  lead 
up  into  the  lymphatics,  and  are  lined  by  cells  like  those  of  germinating  endo- 
thelium. By  introducing  a  solution  of  Berlin  blue  into  the  peritoneal  cavity 
of  an  animal  shortly  after  death,  and  suspending  it,  head  downward,  an  in- 


416  HANDBOOK    OF    PHYSIOLOGY. 

jection  of  the  lymphatic  vessels  of  the  diaphragm,  through  the  stomata  on  its 
peritoneal  surface,  may  readily  be  obtained  if  artificial  respiration  be  carried 
on  for  about  half  an  hour.  In  this  way  it  has  been  found  that  in  the  rabbit 
the  lymphatics  are  arranged  between  the  tendon  bundles  of  the  centrum  ten- 
dineum  ;  and  they  are  hence  termed  interfascicular.  The  centrum  tendiueum 
is  coated  by  endothelium  on  its  pleural  and  peritoneal  surfaces,  and  its  substance 
consists  of  tendon  bundles  arranged  in  concentric  rings  toward  the  pleural 
side  and  in  radiating  bundles  toward  the  peritoneal  side. 

The  lymphatics  of  the  anterior  half  of  the  diaphragm  open  into  those  of  the 
anterior  mediastinum,  while  those  of  the  posterior  half  pass  into  a  lymphatic 
vessel  in  the  posterior  mediastinum,  which  soon  enters  the  thoracic  duct. 
Both  these  sets  of  vessels,  and  the  glands  into  which  they  pass,  are  readily 
injected  by  the  method  above  described ;  and  there  can  be  little  doubt  that 
during  life  the  flow  of  lymph  along  these  channels  is  chiefly  caused  by  the 
action  of  the  diaphragm  during  respiration.  As  it  descends  in  inspiration, 
the  spaces  between  the  radiating  tendon  bundles  dilate,  and  lymph  is  sucked 
from  the  peritoneal  cavity,  through  the  widely  open  stomata,  into  the  inter- 
fascicular lymphatics.  During  expiration,  the  spaces  between  the  concentric 
tendon  bundles  dilate,  and  the  lymph  is  squeezed  into  the  lymphatics  toward 
the  pleural  surface  (Klein).  It  thus  appears  probable  that  during  health  there 
is  a  continued  sucking  in  of  lymph  from  the  peritoneum  into  the  lymphatics 
by  the  "  pumping"  action  of  the  diaphragm ;  and  there  is  doubtless  an  equally 
continuous  exudation  of  fluid  from  the  general  serous  surface  of  the  perito- 
neum. When  this  balance  of  transudation  and  absorption  is  disturbed  either 
by  increased  transudation  or  some  impediment  to  absorption,  an  accumulation 
of  fluid  necessarily  takes  place  (ascites) . 

Structure  of  Lymphatic  Vessels. — The  larger  vessels  as  before  men- 
tioned are  very  like  veins,  having  an  external  ooat  of  areolar  tissue,  with 
elastic  filaments;  within  this,  a  thin  layer  of  areolar  tissue,  with  un- 
striped  muscular  fibres,  which  have,  principally,  a  circular  direction, 
and  are  much  more  abundant  in  the  small  than  in  the  larger  vessels; 
and  again,  within  this,  an  inner  elastic  layer  of  longitudinal  fibres,  and 
a  lining  of  epithelium;  and  numerous  valves.  The  valves,  constructed 
like  those  of  veins,  and  with  the  free  edges  turned  toward  the  heart, 
are  usually  arranged  in  pairs,  and,  in  the  small  vessels,  are  so  closely 
placed,  that  when  the  vessels  are  full,  the  valves  constricting  them 
where  their  edges  are  attached,  give  them  a  peculiar  beaded  or  knotted 
appearance. 

The  Lymph  Flow. 

The  flow  of  the  lymph  toward  the  point  of  its  discharge  into  the  veins 
is  brought  about  by  several  agencies.  With  the  help  of  the  valvular 
mechanism  (1)  all  occasional  pressure  on  the  exterior  of  the  lymphatic 
and  lacteal  vessels  propels  the  lymph  onward:  thus  muscular  and  other 
external  pressure  accelerates  the  flow  of  the  lymph  as  it  does  that  of 
the  blood  in  the  veins.     The  actions  of  (2)  the  muscular  fibres  of  the 


ABSORPTION.  417 

small  intestine,  and  probably  the  layer  of  unstriped  muscle  present  in 
each  intestinal  villus,  seem  to  assist  in  propelling  the  chyle :  for,  in  the 
small  intestine  of  a  mouse,  the  chyle  has  been  seen  moving  with  inter- 
mittent propulsions  that  appeared  to  correspond  with  the  peristaltic 
movements  of  the  intestine.  But  for  the  general  propulsion  of  the 
lymph  and  chyle,  it  is  probable  that,  together  with  (3)  the  vis  a  tergo 
resulting  from  absorption  (as  in  the  ascent  of  sap  in  a  tree),  and  from 
external  pressure,  some  of  the  force  may  be  derived  (4)  from  the  con- 
tractility of  the  vessel's  own  walls.  The  respiratory  movements,  also, 
(5)  favor  the  current  of  lymph  through  the  thoracic  duct  as  they  do  the 
current  of  blood  in  the  thoracic  veins. 

Lymph-Hearts. — In  reptiles  and  some  birds,  an  important  auxiliary  to  the 
movement  of  the  lymph  and  chyle  is  supplied  in  certain  muscular  sacs,  named 
lymph-hearts,  and  it  has  been  shown  that  the  caudal  heart  of  the  eel  is  a 
Ij'mph-heart  also.  The  number  and  position  of  these  organs  vary.  In  frogs 
and  toads  tliere  are  usually  four,  two  anterior  and  two  ijosterior ;  in  the  frog, 
the  posterior  lymph-heart  on  each  side  is  situated  in  the  ischiatic  region,  just 
beneath  the  skin  ;  the  anterior  lies  deeper,  just  over  the  transverse  process  of 
the  third  vertebra.  Into  each  of  these  cavities  several  lymphatics  open,  the 
orifices  of  the  vessels  being  guarded  by  valves,  which  prevent  the  retrograde 
passage  of  the  lymph.  From  each  heart  a  single  vein  proceeds,  and  conveys 
the  h'mph  directly  into  the  venous  system.  In  the  frog,  the  inferior  lymphatic 
heart,  on  each  side,  pours  its  lymph  into  a  branch  of  the  ischiatic  vein  ;  by 
the  superior,  the  lymph  is  forced  into  a  branch  of  the  jugular  vein,  which 
issues  from  its  anterior  surface,  and  which  becomes  turgid  each  time  that  the 
sac  conti-acts.  Blood  is  prevented  from  passing  from  the  vein  into  the  lym- 
phatic heart  by  a  valve  at  its  orifice. 

The  muscular  coat  of  these  hearts  is  of  variable  thickness ;  in  some  cases  it 
can  only  be  discovered  by  means  of  the  microscope ;  but  in  every  case  it  is 
composed  of  sti'iped  fibres.  The  contractions  of  the  hearts  are  rhythmical, 
occurring  about  sixty  times  in  a  minute,  slowly,  and,  in  comparison  Avith 
those  of  the  blood-hearts,  feebly.  The  {mlsations  of  the  cervical  pair  are  not 
always  synchronous  with  those  of  the  pair  in  the  ischiatic  region,  and  even 
the  corresponding  sacs  of  opposite  sides  are  not  always  synchronous  in  their 
action. 

Unlike  the  contractions  of  the  blood-lieart,  those  of  the  lymph-heart  appear 
to  be  directly  dependent  upon  a  certain  limited  portion  of  the  spinal  cord. 
For  Volkmann  found  that  so  long  as  the  portion  of  spinal  cord  corresponding 
to  the  third  vertebra  of  the  frog  was  iminjured,  the  cervical  pair  of  lympliatic 
hearts  continued  pulsating  after  all  the  rest  of  the  spinal  cord  and  the  brain 
were  destroyed ;  while  destruction  of  this  portion,  even  though  all  other  parts 
of  the  nervous  centi-es  were  uninjured,  instantly  arrested  the  heart's  move- 
ments. The  posterior,  or  ischiatic,  pair  of  Ij-mph-hearts  were  found  to  be 
governed,  in  like  manner,  by  the  portion  of  spinal  cord  corresponding  to  the 
eighth  vertebra.  Division  of  the  posterior  spinal  roots  did  not  arrest  the  move- 
ments ;  but  division  of  the  anterior  roots  caused  them  to  cease  at  once. 

Lymphatic  Glands. — Lymphatic  glands  are  small  round  or  oval 
compact  bodies  varying  in  size  from  a  hemp-seed  to  n  beau,  interposed 

27 


418 


HANDBOOK    OF    PHYSIOLOGY. 


in  the  course  of  the  lymphatic  vessels,  and  through  which  the  chief  part 
of  the  lymph  passes  in  its  course  to  be  discharged  into  the  blood-vessels. 
They  are  found  in  great  numbers  in  the  mesentery,  and  along  the  great 
vessels  of  the  abdomen,  thorax,  and  neck;  in  the  axilla  and  groin;  a 


Fig.  281  —Section  of  a  mesenteric  gland  from  the  ox,  slightly  magnified,  a,  Hilus  ;  b  (in  the 
central  part  of  the  figure),  medullary  substance;  c,  cortical  substance  with  indistinct  alveoli;  d, 
capsule.     (KoUiker.) 

few  in  the  popliteal  spacq,  but  not  further  down  the  leg,  and  in  the 
arm  as  far  as  the  elbow.  Some  lymphatics  do  not,  however,  pass  through 
glands  before  entering  the  thoracic  duct. 

Structure. — A  lymphatic  gland  is  covered  externally  by  a  capsule  of 
connective  tissue,  generally  containing  some  unstriped  muscle.  At  the 
inner  side  of  the  gland,  which  is  somewhat  concave  {hilus),  (fig.  281,  a). 


Fig.  282— Section  of  medullary  substance  of  an  inguinal  gland  of  an  ox.  a,  a,  glandular  sub 
stance  or  pulp  forming  rounded  cords  joining  in  a  continuous  net  (dark  in  the  figure);  c,  c,  tra 
beculae;  the  space,  6,  o,  between  these  and  the  glandular  substance  is  the  lymph  sinus,  washed  clear 
of  corpuscles  and  traversed  by  filaments  of  retiform  connective-tissue.    X  90.    (Kolliker.) 


the  capsule  sends  inward  processes  called  trabeculm  in  which  the  blood- 
vessels are  contained,  and  these  join  with  other  processes  prolonged  from 
the  inner  surface  of  the  part  of  the  capsule  covering  the  convex  or  outer 
part  of  the  gland;  they  have  a  structure  similar  to  that  of  the  capsule, 
and  entering  the  gland  from  all  sides,  and  freely  communicating,  form 


ABSORPTION. 


419 


a  fibrous  supporting  stroma.  The  interior  of  the  gland  is  seen  on  sec- 
tion, even  when  examined  with  the  naked  eye,  to  be  made  up  of  two 
parts,  an  outer  or  cortical  (fig.  283,  c,  c),  which  is  light  colored,  and  an 
inner  of  redder  appearance,  the  merhiUary  portion  (fig.  281).  In  the 
outer  or  cortical  part  of  the  gland  (fig.  283)  the  intervals  between  the 
trabeculfe  are  comparatively  large,  and  form  more  or  less  triangular  in- 
tercommunicating spaces  termed  alveoli;  while  in  the  more  central  or 
medullary  part  is  a  finer  meshwork  formed  by  the  more  free  anastomosis 
of  the  trabecular  process.  Within  the  alveoli  of  the  cortex  and  in  the 
meshwork  formed   by  the  trabecular  in  the  medulla,  is  contained  the 


Fig.  283. — Diagrammatic  section  of  lymphatic  gland,  o.?.,  afferent :  e.l..  efferent  lymphatics; 
C,  cortical  substance:  l.h..  reticulating  cords  of  medullary  substance;  l.s.,  lymph-sinus;  c,  fibrous 
coat  sending  in  trabeculas  ;  i.r..  into  the  substance  of  the  gland.     (Shai-pey.) 

proper  gland  structure.  In  the  former  it  is  arranged  as  follows:  occu- 
pying the  central  and  chief  part  of  each  alveolus  is  a  more  or  less  wedge- 
shaped  mass  of  adenoid  tissue,  densely  packed  with  lymph  corpuscles; 
but  at  the  periphery  surrounding  the  central  portion  and  immediately 
next  the  capsule  and  trabecular,  is  a  more  open  mesh^vork  of  adenoid 
tissue  constituting  the  lymph  sinus  or  channel,  and  containing  fewer 
lymph-corpuscles.  The  central  mass  is  inclosed  in  endothelium,  the 
cells  of  which  join  by  their  processes,  the  processes  of  the  adenoid  frame- 
work of  the  lymph  sinus.  The  trabeculfe  are  also  covered  with  endothe- 
lium. The  lining  of  the  central  mass  does  not  prevent  the  passage  of 
fluids  and  even  of  corpuscles  into  the  lymph  sinus.  The  framework  of 
adenoid  tissue  of  the  lymph  sinus  is  nucleated,  that  of  the  central  mass 
is  non-nucleated.     At  the  inner  part  of  the  alveolus,  the  wedge-shaped 


420 


HANDBOOK   OF    PHYSIOLOGY, 


central  mass  divides  into  two  or  more  smaller  rounded  or  cord-like 
masses  which  joining  with  those  from  the  other  alveoli,  form  a  much 
closer  arrangement  of  the  gland  tissue  than  in  the  cortex;  spaces  (fig. 
284,  b),  are  left  within  those  anastomosing  cords,  in  which  are  found 
portions  of  the  trabecular  meshwork  and  the  continuation  of  the  lymph 
sinus. 

The  essential  structure  of  lymphatic-gland  substance  resembles  that 
which  was  described  as  existing,  in  a  simple  form,  in  the  interior  of  the 
solitary  and  agminated  intestinal  follicles. 

The  lymph  enters  the  gland  by  several  afferent  vessels,  which  open 


Fig.  284.— A  small  portion  of  medullary  substance  from  a  mesenteric  gland  of  the  ox.  d,  d,  tra- 
beculse;  a,  part  of  a  cord  of  glandular  substances  from  which  aU'but  a  few  of  the  lymph-corpuscles 
have  been  washed  out  to  show  its  supporting  meshwork  of  retiform  tissue  and  its  capillary  blood- 
vessels (which  have  been  injected,  and  are  dark  in  the  figure) ;  6,  b,  lymph-sinus,  of  which  the  reti- 
form tissue  is  represented  only  at  c,  c.    X  300.    (Kolliker.) 


beneath  the  capsule  into  the  lymph-channel  or  lymph-path;  at  the  same 
time  they  lay  aside  all  their  coats  except  the  endothelial  lining,  which 
is  continuous  with  the  lining  of  the  lymph-path.  The  efferent  vessels 
begin  in  the  medullary  part  of  the  gland,  and  are  continuous  with  the 
lymph-path  here  as  the  afferent  vessels  were  with  the  cortical  portion; 
the  endothelium  of  one  is  continuous  with  that  of  the  other. 

The  efferent  vessels  leave  the  gland  at  the  hilus,  the  more  or  less 
concave  inner  side  of  the  gland,  and  generally  either  at  once  or  very 
soon  after  join  together  to  form  a  single  vessel. 

Blood-vessels  which  enter  and  leave  the  gland  at  the  hilus  are  freely 
distributed  to  the  trabecular  tissue  and  to  the  gland-pulp. 


ABSORPTIOX.  421 


The  Lymph  and  Chyle. 

Lymph  is,  under  ordinary  circumstances,  a  clear,  transparent,  and 
yellowish  fluid,  of  a  sjiccific  gravity  varying  from  1012 — 1022.  It  is 
devoid  of  smell,  is  slightly  alkaline,  and  has  a  saline  taste.  As  seen  with 
the  microscoj)e  in  the  small  transparent  vessels  of  the  tail  of  the  tad- 
pole, it  usually  contains  no  corpuscles  or  particles  of  any  kind;  and  it  is 
only  in  the  larger  trunks  that  any  corpuscles  are  to  be  found.  These 
corpuscles  are  similar  to  colorless  blood-corpuscles.  The  fluid  in  which 
the  corpuscles  float  is  albuminous,  and  contains  no  fatty  particles;  but 
is  liable  to  variations  according  to  the  general  state  of  the  blood,  and  to 
that  of  the  organ  from  which  the  lymph  is  derived.  It  may  clot  on  ex- 
posure to  the  air.  As  it  advances  toward  the  thoracic  duct,  after  pass- 
ing through  the  lymphatic  glands,  it  becomes  spontaneously  coagulable 
and  the  number  of  corpuscles  is  much  increased. 

Chyle,  iound  in  the  lacteals  after  a  meal,  is  an  opaque,  whitish,  milky 
fluid,  neutral  or  slightly  alkaline  in  reaction.  Its  whiteness  and  opacity 
are  due  to  the  presence  of  innumerable  particles  of  oily  or  fatty  matter, 
of  exceedingly  minute  though  nearly  uniform  size,  measuring  on  the 
average  about  ao-^Tnr  of  an  inch  (0.8//).  These  constitute  what  is  termed 
the  molecular  base  of  chyle.  Their  number,  and  consequently  the  opac- 
ity of  the  chyle,  are  dependent  upon  the  quantity  of  fatty  matter  con- 
tained in  the  food.  The  fatty  nature  of  the  molecules  is  made  manifest 
by  their  solubility  in  ether.  Each  molecule  probably  consists  of  a  drop- 
let of  oil  coated  over  with  albumen,  in  the  manner  in  which  minute 
drops  of  oil  always  become  covered  in  an  albuminous  solution.  This  is 
proved  when  water  or  dilute  acetic  acid  is  added  to  chyle,  many  of  the 
molecules  are  lost  sight  of,  and  oil-drops  appear  in  their  place,  as  the 
investments  of  the  molecules  have  been  dissolved,  and  their  oily  con- 
tents have  run  together. 

Except  these  molecules,  the  chyle  taken  from  the  villi  or  from  lac- 
teals near  them,  contains  no  other  solid  or  organized  bodies.  The  fluid 
in  which  the  molecules  float  is  albuminous,  and  does  not  spontaneously 
coagulate.  But  as  the  chyle  passes  on  toward  the  thoracic  duct,  and 
especially  while  traversing  one  or  more  of  the  mesenteric  glands,  it  is 
elaborated.  The  quantity  of  molecules  and  oily  particles  gradually  di- 
minishes; cells,  to  which  the  name  of  chyle-corpuscles  is  given,  appear 
in  it;  and  it  acquires  the  property  of  coagulating  spontaneously.  The 
higher  in  the  thoracic  duct  the  chyle  advances,  the  greater  is  the  num- 
ber of  chyle-corpuscles,  and  the  larger  and  firmer  is  the  clot  which  forms 
in  it  when  withdrawn  and  left  at  rest.  Sucli  a  clot  is  like  one  of  blood 
without  the  red  corpuscles,  having  the  chyle-corpuscles  entangled  in  it. 
and  the  fatty  matter  forming  a  white  creamy  film  on  the  surface  of  the 


4:22  HANDBOOK    OF   PHYSIOLOGY. 

serum.  But  the  clot  of  chyle  is  softer  and  moister  than  that  of  blood. 
Like  blood,  also,  the  chyle  often  remains  for  a  long  time  in  its  vessels 
without  coagulating,  but  coagulates  rapidly  on  being  removed  from  them. 
The  existence  of  the  materials  which,  by  their  union,  form  fibrin,  is, 
therefore,  certain;  and  their  increase  appears  to  be  commensurate  with 
that  of  the  corpuscles. 

The  structure  of  the  chyle-corpuscles  was  described  when  speaking 
of  the  white  corpuscles  of  the  blood,  with  which  they  are  identical.  The 
lymph,  in  chemical  composition,  resernbles  diluted  plasma,  and  from  what 
has  been  said,  it  will  appear  that  perfect  chyle  and  lymph  are,  in  essen- 
tial characters,  nearly  similar,  and  scarcely  differ,  exceiit  in  the  prepon- 
derance of  fatty  and  proteid  matter  in  the  chyle. 

Chemical  Composition  of  Lymph  and  Chyle. 


I. 

11. 

m. 

Lymph. 

Chyle. 

Mixed  L3Tnph& 

(Donkey). 

(Donkey). 

Chyle  (Human). 

Water 

96.536 

90.237 

90.48 

Solids 

3.454 

9.763 

9.52 

Solids— 

Proteids,   including  Serum-Albu-  \ 
min,  Fibrinogen,  and  Globulin.  \ 

1.320 

3.886 

7.08 

Extractives,   including  in  (I  and  i 

II)    Sugar,  Urea,     Leucin    and  V 

1.559 

1.565 

1.08 

Cholesterin         .         .         .         .  ) 

Fatty  matter  and  Soaps 

a  trace 

3.601 

.92 

Salts 

.585 

.711 

.44 

Quantity. — The  quantity  which  would  pass  into  a  cat's  blood  in 
twenty-four  hours  has  been  estimated  to  be  equal  to  about  one-sixth  of 
the  weight  of  the  whole  body.  And,  since  the  estimated  weight  of  the 
blood  in  cats  is  to  the  weight  of  their  bodies  as  1  to  7,  the  quantity  of 
lymph  daily  traversing  the  thoracic  duct  would  appear  to  be  about  equal 
to  the  quantity  of  blood  at  any  time  contained  in  the  animals.  By  an- 
other series  of  experiments,  the  quantity  of  lymph  traversing  the  tho- 
racic duct  of  a  dog  in  twenty-four  hours  was  found  to  be  about  equal  to 
two-thirds  of  the  blood  in  the  body. 

Channels  of  Absorption. 

The  Lacteals. — During  the  passage  of  the  chyme  along  the  intestinal 
canal,  its  completely  digested  parts  are  absorbed  into  the  blood  and 
distributed  in  the  mucous  membrane.  The  absorption  into  both  sets  of 
vessels  is  carried  on  most  actively  hnt  not  exclusively,  in  the  villi  of  the 
small  intestine;  for  in  them  both  the  capillary  blood-vessels  and  the 
lacteals  are  brought  almost  into  contact  with  the  intestinal  contents. 
There  seems  to  be  no  doubt  that  absorption  of  fatty  matters  during 
digestion,  from  the  contents  of  the  intestines,  is  effected  chiefly  through 


Ais80UI'TI0N, 


423 


the  epithelial  cells  which  line  the  intestinal  tract,  and  especially  those 
which  clothe  the  surface  of  the  villi.  Thence,  the  fatty  particles  arc 
passed  on  into  the  interior  of  the  lacteal  vessels,  but  how  they  pass,  and 
what  laws  govern  their  passage,  are  not  at  present  exactly  known.  The 
lymph-corpuscles  of  the  villi  are  however,  in  some  animals,  e.g.,  the  rat 
and  frog,  important  agents  in  effecting  the  passage  of  fat-particles  into 
the  lacteals.  These  cells  take  up  the  fat  which  has  passed  through  the 
columnar  cells  and  then,  by  reason  of  their  amaeboid  movement,  carry 


Fipr,  885— Section  of  the  villus  of  a  rat  killed  during  fat  absorption,  ep.  epithelium;  str,  striated 
border;  c,  lymph-cells  ;  c',  lymph-cells  in  the  epithelium;  1,  central  lacteal  containing  disintegrating 
lymph-corpuscles.    (E.  A.  Schafer.; 


it  in  to  the  lacteal.  When  arrived  there  they  break  up  and  set  free 
both  fat  and  proteid  matter  thereby. 

The  process  of  absorption  is  assisted  by  the  pressure  exercised  on 
the  contents  of  the  intestines  by  their  contractile  walls;  and  the  absorp- 
tion of  fatty  particles  is  also  facilitated  by  the  presence  of  the  bile,  and 
the  pancreatic  and  intestinal  secretions,  which  moisten  the  absorbing 
surface. 

The  Lymphatics. — The  lympli  is  diluted  liquor  sanguinis,  which  is 
always  exuding  from  the  blood-capillaries  into  the  interstices  of  the  tis- 
sues in  which  they  lie;  and  as  these  interstices  form  in  most  parts  of 
the  body  the  beginnings  of  the  lymphatics,  the  source  of  the  lymph  is 
sufficiently  obvious.  In  connection  with  this  may  be  mentioned  the 
fact  that  changes  in  the  character  of  the  lymph  correspond  very  closely 
with  chanffes  in  the  character  of  either  the  whole  mass  of  blood,  or  of  that 


424 


HANDBOOK   OP   PHYSIOLOGY. 


in  the  vessels  of  the  part  from  which  the  lymph  is  exuded.  Thus  it  ap- 
pears that  the  coagulability  of  the  lymph,  although  always  less  than,  is 
directly  proportionate  to  that  of  the  blood ;  and  that  when  fluids  are  in- 
jected into  the  blood-vessels  in  sufficient  quantity  to  distend  them,  the 
injected  substance  may  be  almost  directly  afterward  found  in  the 
lymphatics. 

Some  other  matters  than  those  originally  contained  in  the  exuded 
liquor  sanguinis  may,  however,  find  their  way  with  it  into  the  lymphatic 
vessels.  Parts  which  having  entered  into  the  composition  of  a  tissue, 
and,  having  fulfilled  their  purpose,  require  to  be  removed,  may  not  be 
altogether  excrementitious,  but  may  admit  of  being  reorganized  and 
adapted  again  for  nutrition;  and  these  may  be  absorbed  by  the  lym- 


Fig.  286— Mucous  membrane  of  frog's  intestine  during  fat  absorption,  ep,  epithelium;  str,  striated 
border;  C,  lymph  corpuscles  ;  Z,  lacteal.    (E.  A.  Schafer.) 

phatics,  and  elaborated  with  the  other  contents  of  the  lymph  in  passing 
through  the  glands. 

The  Blood-  Vessels. — In  the  absorption  by  the  lymphatic  or  lacteal 
vessels  just  described  tbere  appears  something  like  the  exercise  of  choice 
in  the  materials  admitted  into  them.  This  is  not  the  case  with  the 
blood-vessels;  it  appears  that  every  substance,  whether  gaseous,  liquid, 
or  a  soluble,  may  be  absorbed  by  the  blood-vessels,  provided  it  is  capable 
of  permeating  their  walls,  and  of  mixing  with  the  blood. 


Where  Absorption  May    i  ake  Place. 

In  the  Alimentary  Canal. — The  greatest  activity  of  absorption  occurs 
in  the  alimentary  canal.  In  it  the  materials  of  the  duly  digested  food 
find  their  way  by  means  of  this  process  on  the  one  hand  into  the  blood- 
vessels of  the  portal  circulation,  and  on  the  other  into  the  lacteal  vessels 
which  are,  as  we  have  seen,  the  commencements  of  the  lymphatic  vessels 
of  the  intestines. 

In  the  Stomach. — Eecent  experiments  have  shown  that  though  ab- 
sorption does  take  place  in  the  stomach,  it  is  not  as  active  as  was  for- 
merly supposed,  even  in  the  case  of  water.  Von  Mering  has  found 
that  water  begins  to  pass  from  the  stomach  into  the  intestine  almost 


ABSORPTION.  425 

as  soon  as  it  is  swallowed,  and  that  very  little  of  it  is  absorbed  from 
the  stomach.  Of  500  cc.  given  b}'  month  to  a  large  dog,  only  5  cc. 
were  absorbed  in  25  minutes,  tlie  rest  having  passed  into  the  intestine. 
Peptones  and  sugars  are  absorbed  in  the  stomach,  but  only  to  a  limited 
extent,  and  the  same  is  true  of  salts.  Fats  are  not  absorbed  at  all  in  the 
stomach.  In  all  cases  absorption  from  the  stomach  is  much  increased 
by  alcohol  and  condiments,  such  as  pepper  and  mustard. 

Jn  tlie  Small  Intestine. — All  the  products  of  digestion  are  absorbed 
in  the  small  intestine,  as  is  abundantly  shown  by  experiments.  The 
absorption  of  fats  has  been  already  described.  Eecently  absorption 
from  the  small  intestine  has  been  studied  in  the  human  subject  in  the 
case  of  a  patient  who  had  a  fistulous  opening  in  the  lower  part  of  the 
ileum.  Eighty-five  per  cent  of  the  proteid  of  a  test-meal  was  absorbed 
before  the  food  reached  the  fistula.  Though  water  and  salts  are  freely 
absorbed,  the  intestinal  contents  does  not  lose  much  in  bulk  or  fluidity 
because  of  the  quantity  of  water  ailded  in  the  alimentary  secretions.  In 
absorption,  sugar  is  changed  either  just  before  or  during  its  passage 
through  the  wall  of  the  intestine  from  maltose  into  dextrose. 

In  the  Large  Intestine. — A  great  deal  of  absorption  takes  place  in 
the  large  intestine.  This  is  evident  from  the  fact  that  the  intestinal 
contents  is  very  fluid  when  it  enters  the  large  intestine,  and  almost 
solid  when  it  leaves  it.  Its  contents  passes  through  the  large  intes- 
tine very  slowly,  usually  occupying  about  12  hours.  In  addition  to 
water  and  salts,  the  sugar,  proteid,  and  fats  not  absorbed  in  the  small 
intestine  are  almost  entirely  absorbed  here. 

The  power  of  absorption  in  the  large  intestine  sometimes  forms  an 
important  feature  in  medical  practice.  "When  patients  cannot  swallow 
solid  or  liquid  food,  or  retain  what  has  been  swallowed,  they  may  be 
nourished  by  rectal  feeding.  The  large  intestine  show^s  a  remarkable 
power  in  its  ability  to  absorb  unchanged  albumins,  such  as  white  of  egg, 
as  well  as  peptones  and  proteoses. 

In  the  stomach  as  well  as  in  both  the  large  and  small  intestine,  the 
absorption  of  water,  salts,  proteids,  and  sugars  takes  place  chiefly  into 
the  blood-vessels. 

Tliroxigli  tlie  Skin. — It  has  been  shown  that  metallic  preparations 
rubbed  into  the  skin  have  the  same  action  as  when  given  internally, 
only  in  a  less  degree.  Mercury  applied  in  this  manner  exerts  its  spe- 
cific influence  upon  syphilis,  and  excites  salivation;  potassio-tartrate  of 
antimony  may  excite  vomiting,  or  an  eruption  extending  over  the  whole 
body;  and  arsenic  may  produce  poisonous  effects.  Vegetable  matters, 
also,  if  soluble,  or  already  in  solution,  give  rise  to  their  peculiar  effects, 
as  cathartics,  narcotics,  and  the  like,  when  rubbed  into  the  skin.  Tlie 
effect  of  rubbing  is  prol);il)ly  (o  convey  the  particles  of  the  matter  into 


426  HANDBOOK   OF    PHYSIOLOGY. 

the  orifices  of  the  glands,  -whence  they  are  more  readily  absorbed  than 
they  would  be  through  the  epidermis.  When  simply  left  in  contact 
with  the  skin,  substances,  unless  in  a  fluid  state,  are  seldom  absorbed. 

It  has  long  been  a  contested  question  whether  the  skin  covered  with 
the  epidermis  has  the  power  of  absorbing  water;  and  it  is  a  point  the 
more  difficult  to  determine  because  the  skin  loses  water  by  evaporation. 
But,  from  the  result  of  many  experiments,  it  may  now  be  regarded  as  a 
well-ascertained  fact  that  such  absorption  really  occurs.  The  absorption 
of  water  by  the  surface  of  the  body  may  take  placQ  in  the  lower  animals 
very  rapidly.  Not  only  frogs,  which  have  a  thin  skin,  but  lizards,  in 
which  the  cuticle  is  thicker  than  in  man,  after  having  lost  weight  by 
being  kept  for  some  time  in  a  dry  atmosphere,  are  found  to  recover  both 
their  weight  and  plumpness  very  rapidly  when  immersed  in  water. 
When  merely  the  tail,  posterior  extremities,  and  posterior  part  of  the 
body  of  the  lizard  are  immersed,  the  water  absorbed  is  distributed 
throughout  the  system.  And  a  like  absorption  through  the  skin,  though 
to  a  less  extent,  may  take  place  also  in  man. 

In  severe  cases  of  dysphagia,  when  not  even  fluids  can  be  taken  into 
the  stomach,  immersion  in  a  bath  of  warm  water  or  of  milk  and  water 
may  assuage  the  thirst;  and  it  has  been  found  in  such  cases  that  the 
weight  of  the  body  is  increased  by  the  immersion.  Sailors  also,  when 
destitute  of  fresh  water,  find  their  urgent  thirst  allayed  by  soaking  their 
clothes  in  salt  water,  and  wearing  them  in  that  state;  but  these  effects 
are  in  part  due  to  the  hindrance  to  the  evaporation  of  water  from  the 
skin. 

Through  the  Lungs. — It  is  a  remarkable  fact  that  not  only  is  the 
epithelium  of  the  pulmonary  air  vesicles  able  to  allow  the  passage 
through  it  of  gases  and  volatile  substances,  but  that  also  under  certain 
conditions  fluids  such  as  water  may  also  be  absorbed,  and  besides  this, 
the  presence  of  carbon  particles  in  the  bronchial  glands  and  elsewhere 
in  connection  with  the  lungs  must  point  to  the  pulmonary  epithelium 
as  the  only  possible  channel  of  their  absorption. 


CHAPTER   XI. 

METABOLISM,    NUTRITION.    AND  DIET. 

It  is  not  only  necessary  that  the  animal  body  should  be  supplied  with 
food  in  order  that  its  natural  functions  may  go  on  without  interrup- 
tion, but  it  is  also  equally  requisite  that  the  food  should  consist  of  proper 
materials.  It  may  be  supposed  that  each  kind  of  arimal  by  instinct 
keeps  itself  supplied  with  the  substances  which  supply  the  needs  of  its 
own  metabolism  the  best,  and  it  is  a  matter  of  every-day  experience  that 
in  the  case  of  man,  each  endeavors  to  supply  himself  with  food  accord- 
ing to  the  circumstances  of  his  surroundings.  We  may  therefore  accept 
such  data  as  we  can  obtain  from  the  observation  of  numerous  examples 
of  such  selection  in  the  Avay  of  diet  when  we  are  in  the  act  of  drawing 
up  a  diet-scale,  relying  upon  such  empiric  knowledge  alone,  or,  on  the 
other  hand,  we  may  proceed  more  scientifically,  and  endeavor  to  plan  a 
diet-scale  from  our  experimental  observation  of  the  loss  which  takes 
place  in  the  body  in  the  course  of  the  twenty-four  hours  by  the  excreta. 
If  we  do  this  we  assume  that  the  food  is  taken  in  to  supply  what  is 
generally  called  the  waste  of  the  tissues.  The  term  is  scarcely  an  accu- 
rate one,  but  if  we  take  it  to  mean  in  a  restricted  sense, — what  the 
tissues  and  organs  of  the  body  give  out  to  be  eliminated  by  the  excretory 
organs  in  the  course  of  the  day, — we  may  continue  to  use  it. 

The  food  then  may  be  supposed  as  intended  to  supply  the  place  of 
that  which  is  given  out  by  the  body.  But  in  the  choice  of  a  diet  this  is 
not  enough;  the  food  should  be  sufficient  to  supply  such  need  without 
waste  and  without  unduly  increasing  the  output  of  excreta,  while  at  the 
same  time  the  body  should  be  maintained  in  health,  without  increase 
or  loss  of  weight. 

These  requisites  of  a  diet  scale  then  allow  for  wide  alterations  in  tlie 
amount  of  different  kinds  of  foods  under  different  circumstances. 

Careful  analyses  of  the  excreta,  many  of  which  we  have  already  had 
occasion  to  call  attention  to,  show  that  they  are  made  up,  besides  water, 
chiefly  of  the  chemical  elements  carbon,  hydrogen,  oxygen,  and  nitrogen, 
but  that  they  also  contain,  to  a  less  extent,  sulphur,  phosphorus,  chlorine, 
potassium,  sodium,  and  certain  other  of  the  elements.  Since  this  is  the 
case  it  must  be  evident  that  to  balance  this  waste,  foods  must  be  supplied 
containing  all  these  elements  to  a  certain  degree,  but  some  of  them,  viz., 
those  which  take  a  principal  part  in  forming  the  excreta,  in  large  amount. 


428 


HANDBOOK    OF   PHYSIOLOGY, 


Of  tlie  excreta  the  carbon  dioxide  and  ammonia,  which  are  made  up 
of  the  elements  carbon,  oxygen,  nitrogen,  hydrogen,  are  given  ofE 
from  the  lungs.  By  the  urine  many  elements  are  eliminated  from  the 
blood,  especially  nitrogen,  hydrogen,  and  oxygen.  In  the  sweat,  the 
elements  chiefly  represented  are  carbon,  hydrogen,  and  oxygen,  and 
these  are  also  those  of  which  the  faeces  are  made.  By  all  the  excretions 
large  quantities  of  water  are  got  rid  of  daily,  but  chiefly  by  the  urine. 

The  relations  between  the  amounts  of  the  chief  elements  contained 
in  these  various  excreta  in  twenty-four  hours  may  be  thus  summarized : — 


Water. 

C. 

H. 

N. 

0 

Bv  the  lunsrs 

330 

660 

1700 

128 

248.8 
2.6 
9.8 
20. 

3.3 
3. 

? 

15.8 
3. 

651.15 

By  the  skin 

7.2 

By  the  urine 

11.1 

By  the  f  88ces     

12. 

Grammes 

2818 

281.2 

6.3 

18.8 

681.41 

Prom  this  should  be  subtracted  the  296grms.  water,  which  are  pro- 
duced by  the  union  of  hydrogen  and  oxygen  in  the  body  during  the 
process  of  oxidation  {i.  e.,  33  hydrogen  and  2G2  oxygen).  There  are  26 
grms.  of  salts  got  rid  of  by  the  urine,  and  6  by  the  faeces;  total, 
32  grms. 

The  quantity  of  carbon  daily  lost  from  the  body  amounts  to  about 
281.2  grms.  (nearly  4,500  grains),  and  of  nitrogen  18.8  grms.  (nearly 
300  grains),  and  if  a  man  could  be  fed  by  these  elements,  as  such,  the 
problem  would  be  a  very  simjDle  one ;  a  corresponding  weight  of  char- 
coal and,  allowing  for  the  oxygen  in  it,  of  atmospheric  air,  would  be  all 
that  is  necessary.  But  an  animal  can  live  only  upon  these  elements 
when  they  are  arranged  in  a  particular  manner  with  others,  in  the  form 
of  such  food-stuffs  as  we  have  already  enumerated,  p.  326  et  seq. ;  more- 
over, the  relative  proportion  of  carbon  to  nitrogen  in  either  of  these 
compounds  alone  is,  by  no  means,  the  proportion  required  in  the  diet 
of  man.  Thus,  in  proteid,  the  proportion  of  carbon  to  nitrogen 
is  only  as  3.5  to  1.  If,  therefore,  a  man  took  into  his  body,  as  food, 
sufficient  proteid  to  supply  him  with  the  needful  amount  of  carbon,  he 
would  receive  more  than  four  times  as  much  nitrogen  as  he  wanted; 
and  if  he  took  only  sufficient  to  supply  him  with  nitrogen,  he  would  be 
starved  for  want  of  carbon.  It  is  plain,  therefore,  that  he  should  take 
with  the  albuminous  part  of  his  food,  which  contains  so  large  a  relative 
amount  of  nitrogen  in  proportion  to  the  carbon  he  needs,  substances  in 
which  the  nitrogen  exists  in  much  smaller  quantities  relatively  to  the 
carbon. 


METABOLISM,    NUTKITIOX,    AND    DIET. 


429 


It  is  therefore  evident  that  the  diet  must  consist  of  several  substances, 
not  of  one  alone. 

Many  valuable  observations  have  been  made  with  a  view  of  ascertain- 
ing the  effect  upon  the  metabolism  of  a  variation  in  the  amount  and 
nature  of  food.  These  are  of  great  assistance  in  the  consideration  of 
dietetics. 

.Effect  of  a  Proteid  Diet. — Experiments  have  been  made,  to  a  consider- 
able extent  upon  dogs,  which  demonstrate  the  effect  of  proteid  food. 
After  a  period  without  food,  during  which  the  output  of  nitrogen,  as 
shown  by  the  urea,  had  diminished  to  a  certain  amount,  the  animal  is 
fed  with  a  diet  of  lean  meat  which  would  suffice  to  produce  the  amount 
of  urea,  and  so  of  flesh,  which  it  had  been  losing  during  its  starvation 
period.  The  effect  of  this,  however,  is  at  once  to  send  up  the  amount 
of  urea  excreted  to  a  point  above  that  which  it  has  been  previous  to  the 
commencement  of  its  flesh  diet,  so  that  again  the  output  of  nitrogen 
would  exceed  its  income,  and  the  weight  of  the  animal  would  continue 
slowly  to  diminish.  It  is  only  after  a  considerable  increase  of  the  flesh 
given  that  a  point  is  reached  where  the  income  and  expenditure  are 
equal,  and  at  which  the  animal  is  not  using  up  quickly  or  slowly  the 
nitrogen  of  his  own  tissue,  and  is  no  longer  losing  flesh.  This  condition 
in  which  the  nitrogen  of  the  egesta  equals  the  nitrogen  of  the  ingesta  is 
known  as  nitrorjcnous  equiUhrinm.  In  the  dog,  according  to  "Waller,  it 
does  not  occur  until  the  amount  of  flesh  of  the  food  is  over  three  times 
as  great  as  would  be  necessary  to  supply  the  nitrogen  of  the  urea  during 
a  period  of  starvation.  Thus  a  dog  excretes  during  a  starvation  period 
0.5  grms.  of  urea  per  kilo  of  body  weight;  in  order  to  satisfy  this  it 
would  be  necessary  to  administer  1.5  grms.  per  kilo  of  meat;  this  at 
once  increases  urea  excreted  to  about  0.75  grms.  per  kilo  of  body  weight, 
and  nitrogenous  equilibrium  is  not  attained  until  over  three  times — viz., 
5  grms.  per  kilo  of  body  weight  of  meat  is  given.  Foster  gives  even  a 
larger  figure.  The  effect,  therefore,  of  proteid  food  is  largely  to  increase 
the  excretion  of  urea,  which  indicates  increase  of  the  metabolism  of  the 
tissues. 

It  must  not  be  thought  however  that  during  nitrogenous  equilibrium 
there  is,  of  necessity,  equilibrium  of  carbon.  On  the  contrary,  it  is  very 
possible  that  the  carbon,  as  supplied  by  the  large  amount  of  meat,  is  not 
entirely  eliminated,  but  may  be  partially  retained  in  the  body.  If  re- 
tained in  the  body  it  is  probably  retained  in  the  form  of  fat,  although 
possibly  it  might  be  retained  partially  as  some  carbohydrate,  e.g.,  gly- 
cogen ;  but  the  amount  of  glycogen  obtained  from  the  body  is  too  small 
for  the  latter  to  be  appreciable.  The  animal  in  nitrogenous  equilib- 
rium, therefore,  may  gain  weiglit,  although  not  in  the  form  of  flesh. 
The  converse  may  also  be  the  case,  the  animal  getting  rid  of  more  carbon 


430  HANDBOOK    OF    PHYSIOLOGY. 

than  the  meat  supplies,  in  which  case  he  would  lose  weight  but  would 
not  lose  flesh. 

The  proteids  of  food  are  described  by  Voit  as  having  two  relations 
to  the  proteid  metabolism  and  to  outgoing  urea;  the  first  part  going  to 
maintain  the  ordinary  and  quiet  metabolism  of  the  tissues,  for  which 
purpose  it  is  actually  built  up  into  their  molecule,  and  the  second  part 
causing  a  more  rapid  formation  of  urea  and  rapid  proteid  metabolism, 
but  never  forming  a  part  of  the  actual  protoplasmic  molecule.  The 
former  proteids  are  called  morpliotic  or  tissue  proteids,  the  latter  circu- 
lating or  floating  proteids.  Normally  more  proteid  is  eaten  thap  is 
needed  to  supply  proteid  waste.  Pflliger  has  pointed  out,  however,  that 
the  tissues  must  have  an  excess  of  proteid  to  destroy  in  order  to  perform 
their  metabolic  processes  normally.  This  use  of  the  proteids  to  form  by 
their  oxidation  heat  and  not  to  produce  tissue  was  looked  upon  by  the 
older  physiologists  as  a  wasteful  use  of  good  material,  and  was  called  a 
luxus  consinnption. 

The  condition  of  nitrogenous  equilibrium  {i.e.,  the  income  and  out- 
put being  equal)  is  one  which  may  be  maintained  even  if  the  amount  of 
proteid  taken  as  diet  far  exceeds  the  necessities  of  the  economy,  the  urea 
being  excreted  in  excessive  amount,  and  the  wasteful  use  of  proteid  food 
which  is  so  common  may  not  be  attended  Avith  harmful  consequences, 
so  long  as  the  liver  is  able  to  do  its  work  in  the  formation  of  urea.  The 
body  may  or  may  not  increase  in  weight,  but  if  the  liver  strikes  work 
from  any  cause,  a  condition  of  lithiasis,  or  of  gout,  follows. 

It  has  not  actually  been  proved,  but  it  is  not  unlikely,  that  even  in 
the  condition  of  lithiasis,  the  nitrogen  of  the  ingesta  may  not  greatly 
exceed  that  of  the  egesta,  but  that  the  mode  of  elimination  is  different. 
It  is  only  in  cases  of  growth  or  putting  on  of  flesh,  as  in  growing  chil- 
dren, that  nitrogen  is  retained  in  the  body,  except  to  a  very  small  amount, 
in  health. 

According  to  calculations  which  have  been  made,  it  appears  that 
the  body  puts  on  thirty  grammes  of  flesh  for  every  gramme  of  nitrogen 
so  retained. 

As  regards  the  retention  of  carbon  in  the  body,  it  is  calculated  that 
one  gramme  and  a  half  of  weight  is  put  on  for  each  gramme  by  which 
the  ingesta  of  carbon  is  greater  than  the  egesta. 

The  Effect  of  an  Albuminoid  Diet. — The  albuminoid  which  is  eaten 
in  greatest  quantity  is  gelatin.  Though  gelatin  closely  resembles  the 
proteid  molecule  chemically,  it  cannot  replace  tbe  proteid  of  the  food. 
In  other  words,  nitrogenous  equilibrium  cannot  be  maintained  on  a  diet 
consisting  of  gelatin,  carbohydrates,  and  fats.  Proteid  food  is  abso- 
lutely essential  to  the  reconstruction  of  the  proteid  molecule.  Gelatin 
is  one  of  the  proteid  substances  which  does  not  have  any  food  value, 


METABOLISM,    XUTKITION,    AND    DIET.  431 

strictly  speaking,  as  tlie  following  experiments  will  prove:  In  one  case, 
when  500  grms.  of  food,  without  any  gelatin,  formed  the  diet,  the  sub- 
ject lost  22  grms,,  but  when  200  grms.  of  gelatin  were  added,  the  subject 
gained  54  grms.  In  another  experiment,  when  the  diet  consisted  of  2,000 
grms.  of  meat  without  gelatin,  the  gain  was  30  grms.,  but  when  200 
grms.  of  gelatin  were  added,  the  gain  became  376  grms.  The  lack  of 
real  food  value  is  proven  by  a  third  experiment  in  which  the  diet  con- 
sisted at  first  of  200  grms.  each  of  meat  and  of  gelatin;  here  the  gain  was 
25  grms.,  but  when  the  meat  was  omitted  and  the  gelatin  alone  given, 
there  was  a  loss  of  118  grms.  In  these  cases  gelatin  did  not  take  the 
place  of  proteid  in  any  sense,  but  rather  saved  it  from  work.  The  pro- 
teid  was  so  protected  that,  instead  of  being  used  up,  it  helped  to  form 
tissues  and  increased  the  body  weight.  Gelatin,  therefore,  saves  other 
material  for  constructive  processes. 

Formation  of  Urea. — Having  studied  the  uses  of  proteids  in  the  body, 
we  may  next  turn  our  attention  to  their  conversion  to  urea,  the  form  in 
which  the  used-up  proteids  chiefly  leave  the  body.  The  method  of  forma- 
tion of  urea,  as  well  as  the  place  where  this  occurs,  has  given  rise  to  great 
controversy,  while  most  of  the  intermediate  products  between  proteids 
and  urea  have  not  as  yet  been  determined.  We  can  state  with  certainty 
that  urea  is  not  formed  in  the  kidneys,  since  it  is  not  only  found  in  the 
blood  of  the  renal  artery,  but  it  accumulates  iu  the  blood  if  the  kidneys 
are  diseased  or  removed  and  the  separation  of  the  urine  is  interfered  with. 
Thus  it  seems  reasonable  to  assume  that  the  function  of  the  kidneys, 
so  far  as  the  more  important  solid — urea — is  concerned,  is  only  one 
of  separation.  This  will  be  discussed  under  the  heading  of  the  method 
of  the  secretion  of  the  urine.  It  remains  to  consider  here  the  cpiestion  of 
the  origin  of  the  urea  which  is  found  in  the  blood,  and  its  method  of 
formation. 

At  the  present  time  it  is  believed  that  urea  is  formed  iu  the  liver. 
This  conclusion  is  borne  out  by  a  number  of  experiments.  The  power  of 
the  liver  cells  to  form  urea  is  shown  by  the  increase  of  urea  in  the  blood 
leaving  an  isolated  (and  living)  liver,  through  which  an  artificial  circula- 
tion is  kept  up,  when  ammonium  carbonate,  or  other  ammonium  salts, 
are  added  to  the  blood.  The  same  change  occurs  even  when  liver  is 
chopped  up  and  simply  mixed  with  the  ammonium  compounds  iu  a 
beaker;  this  shows  that  the  change  is  due  to  the  metabolic  activity  of 
liver  cells.     The  reaction  is  probably  as  follows: 

(NIT).^C03-2H,0  =  COX,H,. 

If  blood  from  a  well-fed  animal  be  circulated  through  the  isolated 
liver,  there  is  a  distinct  increase  in  the  amount  of  urea  it  contains.     On 


432  HANDBOOK    OF    PHYSIOLOGY. 

tlie  other  hand,  if  the  blood  be  from  a  fasting  animal,  there  is  no  in- 
crease of  urea.  Evidently,  then,  the  blood  from  a  well-fed  animal  con- 
tains something  which  the  liver  cells  are  capable  of  transforming  to 
urea.  And,  finally,  if  the  liver  be  removed  and  the  animal  kept  alive, 
as  has  been  done  (Pawlow),  there  is  a  marked  diminution  in  the  quan- 
tity of  urea  in  the  urine.  The  power  of  the  liver  to  form  urea  is  thus 
demonstrated,  and,  moreover,  the  fact  that  the  liver  forms  from  some 
antecedent  substance  the  greater  part  of  the  urea  eliminated. 

The  question  which  now  presents  itself  is,  What  is  this  antecedent 
substance  or  substances? 

Urea  is  the  end-product  of  the  oxidation  of  proteids.  It  was  formerly 
thought  that  urea  was  formed  directly  from  some  antecedent  among  the 
closely  related  products  of  proteid  metabolism,  such  ascreatin,  creatinin, 
leucin,  tyrosin,  xanthin,  hypoxanthin,  etc.  Creatinin  at  one  time 
seemed  the  most  probable  source,  because  in  laboratory  experiments  it 
decomposes  into  urea  and  sarcosin.  Attention  was  also  directed  to 
leucin  and  tyrosin,  which  are  found  in  practically  all  the  glandular 
organs  of  the  body..  It  was  found  that  when  leucin  was  fed  to  a  dog, 
the  amount  of  urea  in  the  urine  was  considerably  increased,  but  that 
leucin  itself  did  not  appear;  the  same  phenomena  were  noticed  with 
glycin,  sarcosin,  and  the  amido  acids.  It  was  also  known  that  in 
acute  yellow  atrophy  of  the  liver,  a  disease  characterized  by  degeneration 
of  the  liver  cells  with  consequent  loss  of  functional  power,  the  urea  of 
the  urine  was  replaced  by  leucin  and  tyrosin.  Experimental  investiga- 
tion, however,  did  not  justify  any  of  these  theories. 

Finally  it  was  found  that  when  ammonia  was  fed  to  animals,  the 
nitrogen  appeared  in  the  urine  in  the  form  of  urea.  Due  investigation 
of  this  fact  led  to  the  belief  that  proteids  were  first  broken  down  to  an 
ammonia  stage  and  then  again  built  up  into  urea  by  the  liver.  For  a 
long  time  it  was  thought  that  this  stage  was  represented  by  ammonium 
carbonate,  but  in  view  of  recent  experiments  this  idea  has  been  given 
up,  and  it  is  now  believed  that  ammonium  mrhamate  is  the  true  ante- 
cedent. 

In  these  experiments  the  liver  was  first  shut  out  of  the  general  cir- 
culation by  (Eck's  fistula)  connectiiig  the  portal  vein  with  the  hepatic 
artery;  the  results  of  this  operation  are,  for  all  practical  purposes, 
equivalent  to  actual  removal  of  the  liver.  When  animals  survived  this 
operation  it  was  found  that  they  could  live  if  fed  very  carefully  on  a 
mixed  diet  from  which  proteids  were  almost  entirely  eliminated,  but 
that  if  the  food  contained  an  excess  of  proteids,  convulsions  ensued  and 
proved  fatal.  Further  investigation  of  the  composition  of  the  urine 
and  blood  showed  that  proteid  metabolism  was  represented  in  them  by 
ammonium  carbamate  and  not  by  urea.     Ammonium  carbamate  was  then 


METABOLISM,    NL'TRITION,    AND    DIET.  4:33 

injected  into  the  blood  of  other  animals  ;  when  a  larger  quantity  was 
used  than  the  liver  could  dispose  of,  death  ensued,  following  couvulsions 
of  the  same  nature  as  those  produced  by  an  excess  of  proteid  food  in  the 
animals  which  had  been  ojierated  on. 

Animouiuni  carbamate  is  thus  shown  to  be,  in  part  at  least,  the  direct 
antecedent  of  urea;  it  is  also  shown  to  be  a  toxic  substance  which  may 
cause  death  by  accumulating  in  excess.  The  reaction  by  which  the  liver 
changes  it  to  the  inert  form  of  urea  is  as  follows: 

(Ammonium  carbamate. )  (Urea.) 

The  manner  in  which  absorbed  proteids  are  changed  to  ammonium 
carbamate,  etc.,  is  as  yet  undecided.  According  to  one  theory,  while 
still  in  the  circulating  medium,  they  are  metabolized  by  direct  contact 
with  the  living  bioplasm  of  the  tissues;  according  to  another,  they  must 
first  be'incorporated  in  the  body  tissues  and  then  changed.  The  inter- 
mediate steps  occur  chiefly  in  muscle  tissue,  and  there  is  great  reason  to 
suppose  that  some  of  the  steps  are  represented  by  various  muscle  extrac- 
tives such  as  creatinin,  hyposanthin,  etc.  These  substances  probably 
break  down  into  carbon  dioxide,  ammonia,  and  amido-acids,  and  are 
then  built  up  by  synthetic  processes  into  ammonium  carbonate,  and 
then  by  dehydration  changed  to  ammonium  carbamate.  Another  possible 
antecedent  is  ammonium  lactate;  this  is  derived  from  the  lactic  acid 
which  is  produced  in  large  quantities  in  the  muscles.  Muscular  activity 
increases  the  elimination  of  urea,  but  the  increase  is  very  slight,  and 
there  is  no  direct  relationship  between  the  amount  of  work  done  and  the 
amount  of  nitrogen  excreted. 

There  is  experimental  evidence  to  show  that  while  the  liver  pro- 
duces the  major  part  of  the  urea  eliminated,  other  organs  or  tissues 
are  capable  of  forming  it  to  a  limited  degree. 

Formation  of  Uric  Acid. — Uric  acid  probably  arises  much  in  the 
same  way  as  urea.  The  relation  which  uric  acid  and  urea  bear  to  each 
other,  as  we  have  seen,  is  still  obscure.  The  fact  that  they  often  exist 
together  in  the  same  urine,  makes  it  seem  probable  that  they  have  differ- 
ent origins;  but  the  entire  replacement  of  one  by  the  other,  as  of  urea 
by  uric  acid  in  the  urine  of  birds,  serpents,  and  many  insects,  and  of 
uric  acid  by  urea,  in  the  urine  of  the  feline  tribe  of  Mammalia,  shows 
their  close  relationship.  But  although  it  is  true  that  one  molecule  of 
uric  acid  is  capable  of  splitting  up  into  two  molecules  of  urea  and  one 
of  mes-oxalic  acid,  this  is  no  evidence  that  uric  acid  is  an  antecedent  of 
urea  in  the  nitrogenous  metabolism  of  the  body. 

The  intimate  relations  which  exist  between  several  other  of  the  ni- 
28 


i34  HANDBOOK    OF    PHYSIOLOGY. 

trogenous  extractives  and  uric  acid  will  be  seen  by  a  reference  to  their 

turmulffi: — 

Hypoxanthin  or  Camin C«H4N40. 

Xanthin C6H4N4O,. 

Uric  Acid C6H4N4O3. 

Formation  of  Hippuric  Acid. — The  source  of  hippuric  acid  is  not  sat- 
isfactorily determined;  in  part  it  is  probably  derived  from  some  constit- 
uents of  vegetable  diet,  though  man  has  no  hippuric  acid  in  his  food, 
nor,  commonly,  any  benzoic  acid  that  might  be  converted  into  it;  in 
part  from  the  natural  disintegration  of  tissues,  independent  of  vegetable 
food,  for  Weismann  constantly  found  an  appreciable  quantity,  even  when 
living  on  an  exclusively  animal  diet.  Hippuric  acid  arises  from  the 
union  of  benzoic  acid  with  glycin  (C,H,NO,  +  C,H,0,  =  C,H,N03  + 
HjjO),  which  union  probably  takes  place  in  the  kidneys  themselves.  It  is 
possible  that  the  aromatic  radicle  in  this  reaction  is  obtained  from  the 
splitting  up  of  tyrosin,  which  appears  so  frequently  as  a  result  of  the 
decomposition  of  proteid,  the  ammonia  radicle  with  which  it  is  associ- 
ated going  to  form  urea. 

The  source  of  the  extractives  of  the  urine  is  probably  in  chief  part 
metabolism  of  the  nitrogenous  tissues,  but  we  are  unable  to  say  whether 
these  nitrogenous  bodies  are  merely  accidental,  having  resisted  further 
decomposition  into  urea,  or  whether  they  are  the  representatives  of  the 
decomposition  of  special  tissues,  or  of  special  forms  of  metabolism  of 
the  tissues.  There  is,  however,  one  exception,  and  that  is  in  the  ease 
of  kreatinin  ;  this  represents  not  only  the  kreatinin  which  enters  the 
body  in  ordinary  flesh  food,  but  nitrogenous  waste  as  well. 

Effects  of  Fats  and  Carbohydrates  as  Food. — Experiments  illustrating 
the  ill-effects  j)roduced  by  feeding  animals  upon  one  or  two  alimentary 
substances  only  have  been  often  performed. 

Dogs  were  fed  exclusively  on  sugar  and  distilled  loater.  During  the 
first  seven  or  eight  days  they  were  brisk  and  active,  and  took  their  food 
and  drink  as  lisual;  but  in  the  course  of  the  second  week  they  began  to 
get  thin,  although  their  appetite  continued  good,  and  they  took  daily 
between  six  and  eight  ounces  of  sugar.  The  emaciation  increased  during 
the  third  week,  and  they  became  feeble,  and  lost  their  activity  and  ap- 
petite. At  the  same  time  an  ulcer  formed  on  each  cornea,  followed  by 
an  escape  of  the  humors  of  the  eye:  this  took  place  in  repeated  experi- 
ments. The  animals  still  continued  to  eat  three  or  four  ounces  of  sugar 
daily ;  but  became  at  length  so  feeble  as  to  be  incapable  of  motion,  and 
died  on  a  day  varying  from  the  thirty-first  to  the  thirty-fourth.  On  dis- 
section their  bodies  presented  all  the  appearances  produced  by  death  from 
starvation;  indeed,  dogs  will  live  almost  the  same  length  of  time  without 
any  food  at  all. 

When  dogs  were  fed  exclusively  on  gum.,  results  almost  similar  to  the 


METABOLISM,    XUTRITIOX,    AND    DIET.  435 

above  ensued.  When  they  were  kept  on  olive-oil  and  vmter,  all  the 
phenomena  produced  were  the  same,  except  that  no  ulceration  of  the 
cornea  took  place;  the  effects  were  also  the  same  with  butter.  The  ex- 
periments of  Chossafc  and  Letellier  prove  the  same;  and  in  men,  the 
same  is  shown  by  the  various  diseases  to  which  those  who  consume  but 
little  nitrogenous  food  are  liable,  and  especially  by  the  affection  of  the 
cornea  which  is  observed  in  Hindus  feeding  almost  exclusively  on  rice. 

The  nutritive  function  of  fats  and  carbohydrates  in  the  body  is  to 
serve  as  a  source  of  energy.  They  are  oxidized,  with  the  ultimate  pro- 
duction of  carbon  dioxide  and  water,  and  must  liberate  the  same  amount 
of  energy  as  when  burned  outside  the  body.  A  given  amount  of  fat, 
however,  furnishes  more  energy  than  a  corresponding  amount  of  either 
proteid  or  carbohydrate.  The  stock  of  fat  in  the  animal  body  will  de- 
lay the  fatal  consequences  of  the  deprivation  of  food.  The  percentage 
loss  of  fat  in  a  starving  animal  is  given  on  page  440. 

The  Formation  of  Glycogen  {Glycogenesis). — The  important  fact  that 
the  liver  normally  forms  sugar,  or  a  substance  readily  convertible  into 
it,  was  discovered  by  Claude  Bernard  in  the  following  way:  he  fed  a 
dog  for  seven  days  with  food  containing  a  large  quantity  of  sugar  and 
starch;  and,  as  might  be  expected,  found  sugar  in  both  the  portal  and 
hepatic  blood.  But  when  this  dog  was  fed  with  meat  only,  to  his  sur- 
prise, sugar  was  still  found  in  the  blood  of  the  hepatic  veins.  Repeated 
experiments  gave  invariably  the  same  result;  no  sugar  being  found, 
under  a  meat  diet,  in  the  portal  vein,  if  care  were  taken,  by  applying  a 
ligature  on  it  at  the  transverse  fissure,  to  prevent  reflux  of  blood  from 
the  hepatic  venous  system.  Bernard  found  sugar  also  in  the  substance 
of  the  liver.  It  thus  seemed  cei'tain  that  the  liver  formed  sugar,  even 
when,  from  the  absence  of  saccharine  and  amyloid  matters  in  the  food, 
none  could  be  brought  directly  to  it  from  the  stomach  or  intestines. 

Bernard  found,  subsequently  to  tiie  before-mentioned  experiments, 
that  a  liver,  removed  from  the  body,  and  from  which  all  sugar  had  been 
completely  washed  away  by  injecting  a  stream  of  water  through  its 
blood-vessels,  after  the  lapse  of  a  few  hours  contained  sugar  in  abun- 
dance. This  post-mortem  production  of  sugar  was  a  fact  which  could 
only  be  explained  on  the  supposition  that  the  liver  contained  a  substance 
readily  convertible  into  sugar;  and  this  theory  was  proved  correct  by  the 
discovery  of  a  substance  in  the  liver  allied  to  starch,  and  now  generally 
termed  glycogen. 

We  may  believe  that  glycogen  is  first  formed  and  stored  in  the  liver 
cells,  and  that  the  sugar,  when  present,  is  the  result  of  its  transformation. 

Source  of  Glycogen. — Although,  as  before  mentioned,  the  greatest 
amount  of  glycogen  is  produced  by  the  liver  upon  a  diet  of  starch  or 
sugar,  a  certain  quantity  is  produced  upon  a  proteid  diet.  The  glyco- 
gen when  stored  in  the  liver  cells  may  readily  be  demonstrated  in  sec- 


436  HANDBOOK    OF    PHYSIOLOGY. 

tioDS  of  liver  containing  it  by  its  reaction  (red  or  port-wine  color)  with 
iodine,  and  moreover,  when  the  hardened  sections  are  so  treated  that 
the  glycogen  is  dissolved  out,  the  protoplasm  of  the  cell  is  so  vacuolated 
as  to  appear  little  more  than  a  framework.  There  is  no  doubt  that  in 
the  liver  of  a  hibernating  frog  the  amount  of  glycogen  stored  up  in  the 
outer  parts  of  the  liver  cells  is  very  considerable. 

Average  amount  of  Glycogen  in  the  Liver  of  Dogs  under   Various  Diets 

(Pavy). 

Diet.  Amount  of  Glycogen  in  Liver. 

Animal  food      .         .         .         .         .         .         .         ,         7.19  per  cent. 

Animal  food  with  sugar  (about  ^  lb.  of  sugar  daily)  14.5         " 

Vegetable  diet  (potatoes,  with  bread  or  barley  meal)  17.23       " 

The  dependence  of  the  formation  of  glycogen  on  the  kind  of  food 
taken  is  also  well  shown  by  the  following  results,  obtained  by  the  same 
experimenter : 

Average  quantity  of  Glycogen  found  in  the  Liver  of  Rabbits  after  Fast- 
ing, and  after  a  diet  of  Starch,  and  Sugar  respectively. 

Average  Amount  of  Glycogen  in  Liver. 

After  fasting  for  three  days  .  .  .     Practically  absent, 

diet  of  starch  and  grape-sugar         .          .     15.4  per  cent, 
cane-sugar  .  .          .          .16.9 

Glycogen  is  also  formed  on  a  gelatin  diet,  but  fats  taken  in  as  food  do 
not  increase  its  amount  in  the  cells.  The  diet  most  favorable  to  the 
production  of  a  large  amount  of  glycogen  is  a  mixed  diet  containing  a 
large  amount  of  carbo-hydrate,  but  with  some  proteid.  Glycerin  injected 
into  the  alimentary  canal  may  also  increase  the  glycogen  of  the  liver. 

Destination  of  Glycogen. — There  are  two  chief  theories  as  to  the  desti- 
nation of  hepatic  glycogen.  (1.)  That  the  glycogen  is  converted  into 
sugar  during  life  by  the  agency  of  a  ferment  {liver  diastase)  also  formed 
in  the  liver;  and  that  the  sugar  is  conveyed  away  by  the  blood  of  the 
hepatic  veins,  to  undergo  combustion  in  the  tissues.  (2.)  That-  the 
conversion  into  sugar  only  occurs  after  .death,  and  that  during  life  no 
sugar  exists  in  healthy  livers;  glycogen  not  undergoing  this  transforma- 
tion. The  chief  arguments  advanced  in  support  of  this  view  are,  (a) 
that  scarcely  a  trace  of  sugar  is  found  in  blood  drawn  during  life  from 
the  right  ventricle,  or  in  blood  collected  from  the  right  side  of  the  heart 
iwme(^m^e/y/ after  an  animal  has  been  killed;  while  if  the  examination 
be  delayed  for  a  very  short  time  after  death,  sugar  in  abundance  may 
be  found  in  such  blood;  {b)^  that  the  liver,  like  the  venous  blood  in  the 
heart,  is,  at  the  moment  of  death,  completely  free  from  sugar,  although 
afterward  its  tissue  speedily  becomes  saccharine,  unless  the  formation  of 


METABOLISM,    XUTKITIUX,    AND    DIET.  437 

sugar  be  prevented  by  boiling,  or  other  means  calculated  to  interfere 
with  the  action  of  a  ferment. 

Instead  of  adopting  the  view  that  normally,  during  life,  glycogen 
acts  as  a  store  of  earbo-liydrate  material  to  be  converted,  little  by  little, 
into  sugar  as  occasion  requires,  and  that  it  passes  as  sugar  into  the  lie- 
patic  venous  blood,  to  be  conveyed  to  the  tissues  to  be  further  disposed 
of,  Pavy  inclines  to  the  belief  that  it  may  represent  an  intermediate 
stage  in  the  formation  of  fat  from  materials  absorbed  from  the  alimen- 
tary canal.  There  is  little  evidence  in  favor  of  this  view,  and  although 
it  is  possible  that  the  liver  cells  may,  in  some  way  or  other  (not  at  pres- 
ent understood),  be  able  to  convert  part  of  its  store  of  glycogen  into  fat, 
the  consensus  of  opinion  inclines  to  the  belief  that  most  of  the  glycogen 
leaves  tlie  liver  as  sugar. 

Indeed,  wherever  glycogen  is  found,  in  the  muscles,  in  the  placenta, 
or  elsewhere,  it  must  be  looked  upon  as  a  store  of  carbo-hydrate  material 
which  may  be  oxidized  to  furnish  energy  to  the  body.  Whether  the 
glycogen  which  probably  reaches  the  muscles  as  sugar  is  reconverted  into 
glycogen  before  it  is  built  up  as  it  were  into  the  protoplasmic  molecule 
is  not  known. 

The  relation  of  glycogen  to  the  cell  metabolism. — It  is  not  exactly  known 
whether  the  glycogen  is  formed  simply  by  a  j)rocess  of  dehydration  of 
the  sugar  which  reaches  the  cells  in  the  portal  blood,  or  whether 
the  cells  by  their  metabolism  are  usually  in  the  habit  of  form- 
ing glycogen  or  sugar  which,  during  fasting  and  other  simihir  conditions, 
is  at  once  discharged  into  the  hepatic  blood  to  be  used  up  by  the  tissues, 
but  which  is  stored  uj?  in  the  cells  as  glycogen  as  long  as  there  is  suffic- 
ient sugar  in  the  blood  without  it,  or  as  long  as  the  tissues  are  so  quiescent 
as  not  to  require  more  than  a  small  quantity  of  the  total  amount  of 
carbo-hydrate  secreted  by  the  hepatic  cells. 

Glycosuria. — Sugar  may  be  present  not  only  in  the  hepatic  veins, 
but  in  the  systemic  blood  to  excess,  and  when  such  is  the  case,  the  sugar 
is  excreted  by  the  kidneys,  and  appears  in  variable  quantities  in  the 
urine.      This  condition  is  known  as  glycosuria. 

Influence  of  the  Nervous  ^System. — Glycosuria  may  be  experimentally 
produced  by  puncture  of  the  medulla  oblongata  in  the  region  of  the 
vaso-motor  centre.  The  better  fed  the  animal  the  larger  is  the  amount 
of  sugar  found  in  the  urine;  in  the  case  of  a  starving  animal  no  sugar 
appears.  It  is,  therefore,  highly  probable  that  the  sugar  comes  from 
the  hepatic  glycogen,  since  in  the  one  case  glycogen  is  in  excess,  and  in 
the  other  it  is  almost  absent.  The  nature  of  the  influence  is  uncertain. 
It  may  be  exercised  in  dilating  the  hepatic  vessels,  or  possibly  may  be 
exerted  on  the  liver  cells  themselves.     The  whole  course  of  the  nervous 


-i3h'  HAXDBUOlv    OF    PHYSIOLOGY. 

stimulus  cannot  be  traced  to  the  liver,  but,  at  any  rate,  it  is  not  con- 
ducted by  the  vagi  or  by  the  splanchnics,  but  at  first  it  passes  from  the 
lower  part  of  the  iioor  of  the  fourth  ventricle  and  medulla  down  the 
spinal  cord  as  far  as — in  rabbits — the  fourth  dorsal  vertebra,  and  hence 
to  the  first  thoracic  ganglion.  The  formation  of  sugar  by  the  liver  is 
also  not  a  vaso-dilator  effect,  since  it  will  occur  when  the  vessels  are 
constricted. 

Many  other  circumstances  will  cause  glycosuria.  It  has  been  observed 
after  the  administration  of  various  drugs — e.g.,  strychnine  (in  frogs), 
phloridzin,  a  glucoside,  and  phloretin,  a  derivative  of  phloridzin,  not  a 
glucoside,  morphine,  nitrite  of  amyl,  etc. — after  the  injection  of  urari, 
poisoning  with  carbonic  oxide  gas,  the  inhalation  of  ether,  chloroform, 
etc.,  the  injection  of  oxygenated  blood  into  the  portal  venous  system. 
It  has  been  observed  in  man  after  injuries  to  the  head,  and  in  the  course 
of  various  diseases. 

In  all  such  cases,  at  any  rate,  the  glycosuria  appears  to  be  due  to  some 
abnormal  activity  of  the  liver  cells  themselves  set  up  by  the  direct  action 
of  the  secretory  nerves  upon  them. 

The  well-known  disease,  diabetus  mellitus,  in  which  a  large  quantity  of 
sugar  is  persistently  secreted  daily  with  the  urine,  has,  doubtless,  some 
close  relation  to  the  normal  functions  of  the  pancreas.  The  nature  of 
the  relationship  has  not  yet  been  determined,  though  some  recent  experi- 
ments seem  to  be  pertinent  (see  p.  318). 

Effect  of  too  much  Food. — All  the  three  classes  of  food-stuffs  men- 
tioned— fats,  carbohydrates,  and  gelatin — have  their  distinct  uses  when 
combined  with  proteids.  A  small  amount  of  fat  or  a  larger  amount  of 
carbohydrate  (starch  or  sugar)  added  to  some  proteid  diminishes  the 
amount  of  proteid  required  before  nitrogenous  equilibrium  is  attained 
(in  a  dog  to  the  extent  of  50  per  cent  or  more),  but  if  the  carbohydrate 
exceed  a  certain  minimum  it  is  retained  in  the  body  as  fat.*  If  the  pro- 
teid be  increased,  the  metabolism  is  increased  likewise,  and  so  fat  may 
not  be  deposited,  even  if  the  carbohydrate  of  the  diet  be  excessive.  It 
is  even  possible  that  some  of  the  already  stored-up  fat  may  be  used  up, 
and  so  loss  of  weight  (fat)  might  result. 

Persistent  excess  of  carbohydrate  food  produces  an  accumulation  of 
fat,  which  may  not  only  be  an  inconvenience  causing  obesity,  but  may 
interfere  with  the  proper  nutrition  of  muscles,  and  a  feebleness  of  the 
action  of  the  heart,  with  other  troubles.     Starches  when  taken  in  great 


*The  result  of  various  feeding  experiments,  e.g..  of  the  milch  cow  fed  upon 
grass,  have  proved  beyond  all  doubt  that  fat  is  formed  by  the  tissues  chiefly  from 
carbohydrate  food,  but  to  a  less  extent  from  proteids.  Fatty  foods,  even  if  they 
indirectly  lead  to  the  deposition  of  fats,  are  not  as  such  deposited  in  the  tissues. 
Fat  is  everywhere  in  the  body  an  effect  of  artual  protoplasmic  metabolism. 


METABOLISM,    KUTRITION,    AND    DIET.  .}3H 

excess  are  almost  certain  to  give  rise  to  dyspepsia,  with  acidity  and  flat- 
ulence. Excess  of  starch  or  of  sugar  in  the  food  may,  however,  be  got 
rid  of  by  the  urine  in  the  form  of  sugar.  There  is  evidently  a  limit  to 
the  absorption  of  fat  as  well  as  of  starch,  since  if  in  excessive  amount 
they  may  appear  in  the  faeces. 

That  salts  are  necessary  as  food  is  proved  by  tlie  presence  of  scurvy 
when  they  are  not  present,  and  we  know  that  there  is  a  consant  excre- 
tion of  chlorides,  phosphates  and  sulphates  in  tlic  urine,  so  that  in  order 
to  balance  the  income  and  output,  these  salts  in  combination  with 
sodium,  potassium,  calcium,  etc.,  must  be  taken  in. 

The  necessity  for  the  taking  in  of  watei\  in  order  to  balance  the  ex 
cretion,  is  sufficiently  obvious. 

To  summarize  what  has  been  said: — 

Proteid. — i.  If  the  nitrogen  of  the  income  is  less  than  that  of  the 
output,  the  animal  loses  flesh  and  starves,  gradually  or  quickly,  accord- 
ing to  the  extent  of  the  deficiency. 

ii.  If  the  nitrogen  of  the  income  be  evenly  balanced,  the  proteid 
being  only  just  sufficient,  the  animal  does  not  lose  flesh,  but  may  increase 
or  diminish  in  weight  (fat). 

iii.  If  the  nitrogen  of  the  ingesta  exceed  that  of  the  egesta,  the  ex- 
cess is  mainly  retained  in  the  form  of  flesh. 

iv.  If  the  proteid  be  in  great  excess,  although  there  be  a  condition 
of  nitrogenous  equilibrium,  there  may  be  increase  in  weight,  but  also  a 
likelihood  of  gout  and  similar  affections. 

Fatty  and  Carbohydrate  Foods  are  of  no  use  either  together  or  sepa- 
rately without  the  addition  of  the  other  food-stuffs.  In  moderation, 
either  may  diminish  the  amount  of  proteid  necessary  to  produce  nitro- 
genous equilibrium.  If  the  quantity  of  either  be  increased  beyond  a 
certain  amount,  it  is  retained  in  the  body  in  form  of  fat  (and,  in  the 
case  of  the  carbohydrate,  as  glycogen).  If  in  great  excess,  disorders  of 
digestion  occur.  Fats  have  more  potential  energy  than  carbohydrates, 
but  are  less  digestible.  Fatty  foods  need  more  oxygen  than  carbohy- 
drates when  they  are  used  up  in  the  body. 

Gelatin  will  not  entirely,  but  will  partly  replace  the  proteid  in  a  diet. 

Salts  of  sodium,  potassium,  calcium,  etc.,  are  necessary  in  food,  the 
chlorides,  phosphates  and  sulphates,  and  possibly  the  citrates,  being  the 
most  important  of  those  required. 

Water  is  absolutely  essential  to  life — an  animal  will  not  survive 
deprivation  for  longer  than  a  few  days. 

Effects  of  Deprivation  of  Food. — The  animal  body  deprived  of  all  food 
in  the  course  of  a  variable  time  dies  from  starvation.  The  length  of 
time  that  any  given  animal  will  live  in  such  a  condition  depends  upon 
many  circumstances;  the  chief  may  be  supposed  to  be  the  nature  and 
activity  of  the  metabolism  of  its  tissues. 


440 


HANDBOOK    OF    PHYSIOLOGY. 


The  effect  of  starvation  on  the  lower  animals,  as  recorded  by  varioii.'^ 
experimenters  is: — (1.)  One  of  the  most  notable  eflEects  of  starvation,  us 
might  be  expected,  is  Joss  of  iveiglit ;  the  loss  being  greatest  at  first,  as  a 
rule,  but  afterward  not  varying  very  much,  day  by  day,  until  death 
ensues.  Chossat  found  that  the  ultimate  proportional  loss  was,  in  dif- 
ferent animals  experimented  on,  almost  exactly  the  same;  death  occur- 
ring when  the  body  had  lost  two-fifths  (forty  per  cent)  of  its  original 
weight.  Different  parts  of  the  body  lose  weight  in  very  different  pro- 
portions. The  following  most  noteworthy  losses  are  taken,  in  round 
numbers,  from  the  table  given  by  Chossat: — 


Fat      . 

loses  93  per  cent. 

Liver 

.  loses  52  per  cent 

Blood      . 

.     75 

Muscles 

43        " 

Spleen 

71 

Nervous  tissues 

.       2 

Pancreas 

.     64 

These  figures  are  in  practical  agreement  with  those  of  later  experi- 
menters. They  show  that  the  chief  losses  are  sustained  by  the  adipose 
tissue,  the  muscles  and  glands. 

(2.)  The  effect  of  starvation  on  the  temperature  of  the  various  ani- 
mals experimented  on  by  Chossat  was  very  distinct.  For  some  time  the 
variation  in  the  daily  temperature  was  more  marked  than  its  absolute 
and  continuous  diminution,  the  daily  fluctuation  amounting  to  3°  0.  (5°  or 
%"  F.),  instead  of  5°  to  1°  C.  (1°  or  2''  F.),  as  in  health.  But  a  short  time 
before  death, the  temperature  fell  very  rapidly,  and  death  ensued  when  the 
loss  had  amounted  to  about  16.2°  C.  (30°  F.).  It  has  been  often  said, 
and  with  truth,  although  the  statement  requires  some  qualification,  that 
death  by  starvation  is  really  death  from  want  of  heat;  for  not  only  has  it 
been  found  that  differences  of  time  with  regard  to  the  period  of  the  fatal  re- 
sult are  attended  by  the  same  ultimate  loss  of  heat,  but  the  effect  of  the 
application  of  external  warmth  to  animals  cold  and  dying  from  starvation, 
is  more  effectual  in  reviving  them  than  the  administration  of  food. 

The  symptoms  produced  by  starvation  in  the  human  subject  are  hun- 
ger, accompanied,  or  it  may  be  replaced,  by  pain,  referred  to  the  region 
of  the  stomach;  insatiable  thirst;  sleeplessness;  general  weakness  and 
emaciation.  The  exhalations  both  from  the  lungs  and  skin  are  foetid, 
indicating  the  tendency  to  decomposition  which  belongs  to  badly  nor. r- 
ished  tissues;  and  death  occurs,  sometimes  after  the  additional  exhaustion 
caused  by  diarrhoea,  often  with  symptoms  of  nervous  disorder,  delirium 
or  convulsions. 

In  the  human  subject  death  commonly  occurs  within  six  to  ten  days 
after  total  deprivation  of  food.  But  this  period  may  be  considerably 
prolonged  by  taking  a  very  small  quantity  of  food,  or  even  water  only. 
The  cases  so  frequently  related  of  survival  after  many  days,  or  even  some 
weeks,  of  abstinence,  have  been  due  either  to  the  last-mentioned  circum- 


METABOLISM,    NTTRITTOX,    AXD    DIET.  4-11 

stances,  or  to  others  no  less  effectual,  which  prevented  the  loss  of  heat 
and  moisture.  Cases  in  which  life  has  continued  after  total  abstinence 
from  food  and  drink  for  uiaiiv  weeks,  or  months,  exist  only  in  the  imag- 
ination of  the  vulgar. 

(3.)  During  the  starvation  period  the  excreta  tliniinish.  The  urea, 
as  representing  the  nitrogen,  falls  quickly  in  amount,  reaches  a  mini- 
mum and  remains  constant  at  this  point  for  several  days,  and  then  rises 
again  and  finally  falls  rapidly  immediately  before  death;  the  sulphates 
and  phosphates  undergo  much  the  same  form  of  reduction.  The  carbon 
dioxide  given  out  and  the  oxygen  taken  in  diminish.  The  fgeces  dimin- 
ish, as  well  as  the  bile.  It  has  been  concluded  as  highly  probable  that 
the  greater  part  of  the  urea  represents  the  loss  of  w'eight  of  the  muscles. 

The  appearances  presented  after  death  from  starvation  are  those  of 
general  wasting  and  bloodlessness,  the  latter  condition  being  least  notice- 
able in  the  brain.  The  stomach  and  intestines  are  empty  and  contracted, 
and  the  walls  of  the  latter  appear  remarkably  thinned  and  almost  trans- 
parent. The  various  secretions  are  scanty  or  absent,  with  the  exception 
of  the  bile,  w'liich,  not  being  discharged,  usually  fills  the  gall-bladder. 
All  parts  of  the  body  readily  decompose. 

In  starvation,  then,  we  see  that  the  only  income  consists  of  the  in- 
spired ox)'gen.  The  whole  of  the  energy  of  the  body  given  out  in  the 
direction  of  heat  and  mechanical  labor  is  obtained  at  the  expense  of  the 
using  up  of  its  own  tissues,  there  being  as  a  result  a  constant  drain  of 
the  nitrogen  and  carbon,  not  to  mention  the  other  elements  of  which 
they  are  made  up.  It  is  obvious  that  such  a  condition  cannot  be  en- 
dured for  any  length  of  time. 

Requisites  of  a  Normal  Diet. 

It  will  have  been  understood  that  it  is  necessary  that  a  normal  diet 
should  be  be  made  up  of  various  articles,  that  they  should  be  well  cooked, 
and  that  they  should  contain  about  the  same  amount  of  carbon  and  ni- 
trogen as  are  got  rid  of  by  the  excreta.  No  doubt  these  desiderata  may 
be  satisfied  in  many  ways,  and  it  would  be  unreasonable  to  expect  the 
diet  of  every  adult  to  be  unvarying.  The  age,  sex,  strength,  dnd  cir- 
cumstances of  each  individual  must  ultimately  determine  what  he  takes 
as  food.  A  dinner  of  bread  and  cheese  with  an  onion  contains  all  the 
requisites  for  a  meal,  but  such  diet  would  be  suitable  only  for  those  pos- 
sessing strong  digestive  powers.  It  is  a  well-known  fact  that  the  diet 
of  the  continental  tuitions  differs  from  that  of  our  own  country,  and 
that  of  cold  from  that  of  hot  climates,  but  the  same  principle  underlies 
them  all,  viz.,  the  replacement  of  the  loss  of  the  excreta  in  the  most 
convenient  and  economical  way  possible.      Without  going  into  detail  in 


4-1:2  HANDBOOK    OF    PHYSIOLOGY. 

the  matter  here,  it  may  be  said  that  any  one  in  active  work  requires  more 
food  than  one  at  rest,  and  that  children  and  women  require  less  food 
than  do  adult  men. 

Of  the  various  diet-scales  which  have  been  drawn  out  with  the  object 
of  supplying  the  proximate  principles  in  the  required  proportions,  the 
foregoing  is  slightly  modified  from  Moleschott : — 

Dry  Food—  N.  c. 

Proteid        .     120  grms.  (4.232  oz.)  supplying  18.88  grms.  64.18  grms. 

Fat      .         .       90     "  (3.174  oz.)         "  70.20      " 

Carbohydrate  820     "  (11.64  oz.)         "  146.82      " 

N.  18.88       C.  281.3 
Salts      .         .     30     "  (nearly  1  oz.) 

Water   .    .     2800    " 

Two  other  diet-scales  may  be  mentioned,  which  are  often  quoted, 
viz: — 

Ranke's  Diet-Scale. 

Proteid 100  grms,. 

Fats 100     " 

Carbohydrates 250      " 

Salts 25      " 

Water 2600      " 

Pettenkofer  &  VoiT'8  DiET-ScALE  is  as  foUows : — 

Proteids 118  to  137  grms. 

Fats 56  to  117     " 

Carbohydrates 352  to  500     " 

Salts 

Water 2016  grms. 

The  amount  of  the  excreted  carbon  and  nitrogen  is  not,  of  course, 
always  the  same,  it  having  been  unfortunately  proved  possible,  for  example, 
to  subsist  on  9  or  10  grms.  of  nitrogen  and  200  grms.  of  carbon  per 
diem  (the  ordinary  diet  for  needle- women  in  London,  and  the  average  of 
the  cotton  operatives  in  Lancashire  during  the  famine,  1862),  the 
amount  of  these  elements  excreted  falling  to  figures  corresponding  to 
such  an  income.  Of  course,  upon  such  a  diet  the  metabolism  is  low, 
and  persistent  weakness  must  be  the  result. 

The  9  or  10  grms.  of  N  in  such  a  semi-starvation  diet  would  be 
equivalent  to  58.5  to  65  grms.  of  proteids,  whereas  the  amount  of  pro- 
teids in  some  diets  may  be  as  high  as  150-159  grms.  per  diem  (English 
navvies),  or  165  gras.  (Munich  brewers'  men).  The  English  and 
Bavarian  soldier  in  time  of  peace  consumes  126  grms.  of  proteid  per 
diem  (4.4  oz.). 

Not  only  the  proteids  but  also  the  fats  may  vary ;  the  amount  may  be 
as  low  as  56  grms,  and  as  high  as  117  grms.  The  carbohydrates  may 
vary  from  200  grms.  to  500  grms.  and  upward.  Sometimes,  with  a 
small  proportion  of  fat,  the  carbohydrate  may  be  correspondingly 
increased  to  make  up  the  necessary  carbon.     A  useful  table  after  Payen 


METABOLISM,    NUTRITIOX,    AND    DIET. 


443 


will   help  to  show  in  what  ways  it  is  possible  to  obtain  tlie  requisite 
amount  of  nitrogen  and  carbon  from  the  most  common  food-stuffs. 

In  100  parts  of  the  following  substances  the  proportion  of  N  and  C 
is  indicated: 


N. 

c. 

N. 

C. 

Beef  (without  bone 

3 

11 

Oatmeal 

.     1.95 

44 

Roast  Beef  . 

3.528 

17.76 

Bread 

1 

28 

Eggs 

1.9 

13.5 

Potatoes 

.       .33 

11 

Cow's  Milk 

.66 

8 

Eels  . 

2 

30 

Cheese     . 

2  to  7 

35  to  71 

Mackerel 

.     3.74 

19.26 

Beans  . 

4.5 

42 

Sardines  in  oil 

6 

29 

Lentils    . 

4.1 

48 

Butter    . 

.64 

83 

In  order  to  obtain  the  amount    of    proteid  present  from  the  proportion  of 
nitrogen,  multiply  bj-  6.5. 

From  these  data  it  is  possible  to  form  various  diet-scales  which  shall 
supply  the  needs  of  different  conditions.  Assuming  that  the  average 
amount  of  carbon  and  nitrogen  required  is  about  300  grms.  and  20  grms. 
respectively,  this  may  be  obtained  as  follows:— 


340  grms.    j  'l\^^-  avoirdupois  /  ^^^^  uncooked  meat  *  10  gmis. 
906      "         (33  oz.  or  2  lbs.  avoirduiwis)  bread     .         .     9     " 


O. 
37  grms. 

252      " 


19  grms.       289  grms. 

But  this  diet  is  not  a  usual  one;  a  certain  proportion  of  the  carbon 
is  usually  supplied  as  butter,  or  bacon,  and  so  if  90  grms.  (3.1  oz.)  of 
butter  or  bacon  be  used  they  would  supply  about  72  grms.  of  carbon,  and 
the  carbohydrate  would  be  diminished  nearly  one-third;  but  the  nitro- 
gen would  also  be  diminished  from  9  grms.  to  6  grms.  It  would  be 
necessary  to  supply  some  extra  nitrogenous  principle,  and  this  might 
be  done  by  the  addition  of  eggs,  milk,  cheese,  beans,  or  of  any  of  the 
food-stuffs  already  enumerated  at  p.  326  et  seq.,  as  supplying  nitrogenous 
food  chiefly.  For  example,  56  grms.  (2  oz.)  cheese,  would  supply,  on 
an  average,  3  grms.  nitrogen  and  20  grms.  carbon;  or  28  grms.  cheese, 
supplying  1.5  grms.  nitrogen  and  about  10  grms.  carbon,  and  225 
grms.  (-^  lb.)  potatoes,  and  225  grms.  (^  lb.)  carrots,  supplying  together 
about  1  grm.  of  nitrogen  and  35  grms.  of  carbon.  The  diet  would  then 
read  as  follows : — 


340  grms.  lean  uncooked  meat 
600       "       Bread 

90       "       Butter      . 

28       "       Cheese 
325       "       Potatoes    i 
225       "      CaiTots     ) 


N. 

10  grms. 

6      " 

.5  " 

1.5  " 


C. 

37  grms. 

168      " 

73      " 

10      " 

35       " 


N   19 


C.  332 


*As  meat  loses  23  to  34    per  cent  on  cooking,  the  weight  of    cooked  meat 
would  be  proportionately  be  less. 


444  HANDBOOK    OF    PHYSIOLOGY. 

The  salts,  over  ^0  grms.,  Avonkl  be  supplied  by  the  meat  16  grms., 
the  bread  12  grms.,  and  vegetables  about  4  grms.  The  fluids  should 
consist  of  about  2,500-2,800  grms.,  and  might  be  given  as  water,  with 
or  without  tea,  coSee,  or  cocoa  (which  are  chiefly  stimulants),  together 
with  a  small  proportion  of  alcohol. 


Variations  in  Diet  Tables. 

For  infancy. — Milk  afllords  a  natural  and  perfect  diet  for  infants. 
The  amount  which  an  infant  during  the  first  month  should  take  is  not 
less  than  1  kilogramme  (2^  lbs.)  per  diem.  In  1,000  grms.  there  would 
be  about  6.6  grms.  nitrogen  and  80  to  90  of  carbon.  This  allows  for  a 
gain  of  weight  of  2  to  5  oz.  in  the  time. 

For  climate. — Very  slight  alteration  is  necessary.  For  warm  climates, 
slightly  increase  the  carbohydrates. 

For  hard  laior. — All  the  articles  of  diet  should  be  increased  to  make 
up  for  the  increased  metabolism. 

Fattening  diet. — In  such  a  diet  an  excess  of  carbohydrates  should  be 
present. 

To  reduce  obesity. — The  fats  and  carbohydrates  should  be  diminished, 
but  the  proteids  should  be  relatively  increased. 

To  increase  muscle. — It  has  been  found  that  a  diet  consisting  largely 
of  proteids  in  considerable  amount  combined  with  such  passive  exercise 
as  that  obtained  by  massage,  will  cause  the  body  to  put  on  flesh. 

For  training. — The  whole  diet  should  be  increased,  possibly  preceded 
by  a  diet  in  which  the  proteid  is  in  excess. 

For  brain  tcork. — The  chief  essential  is  that  the  diet  should  consist  of 
easilv  digestible  materials. 


Income  and  Output  of  Energy. 

The  food  must  be  considered  from  another  point  of  view  in  addition 
to  that  from  which  we  have  been  considering  it.  It  not  only  makes 
up  for  the  substances  eliminated  from  the  body,  but  it  also  supplies 
potential  energy  to  balance  the  energy  set  free  in  the  living  body  as 
heat  and  movement.  The  amount  of  heat  is  measured  in  terms  of 
calories,  as  has  been  already  pointed  out.  The  work  done  may  be  ex- 
pressed in  terms  of  foot-pounds  (Euglish  system),  or  metre-grammes, 
or  metre-kilogrammes  (metric  system).  The  calories  may  also  be  ex- 
pressed in  terms  of  work,  as  heat  is  also,  as  has  been  said,  a  mode  of  mo- 
tion. The  heat-unit  Ca,  may  be  transformed  into  metric  work-unit  by 
multiplying  by  42  and  dividing  by  1000,  and  the  converse. 


METABOLISM,    XITRITIOX,    AXD    DIET.  445 

Manifestations  of  Force  in  the  form  either  of  Heat  or  Motion. — In  the 
former  case  (Heat),  the  combustion  must  be  sufficient  to  maintain  a  tem- 
perature of  about  37.8"  C.  (100"  F.)  throughout  the  whole  substance  of 
the  body,  in  all  varieties  of  external  temperature,  notwithstanding  the 
large  amount  continually  lost  in  the  ways  previously  enumerated.  In 
the  case  of  Motion,  there  is  the  expenditure  involved  in  the  (a)  Ordi- 
nary muscular  movements,  as  in  Prehension,  Mastication,  Locomotion, 
and  numberless  other  ways:  as  well  as  in  {b)  Various  involuntary  move- 
ments, as  in  Respiration,  Circulation,  Digestion,  etc. 

Manifestation  of  Kerveforce;  as  in  the  general  regulation  of  all 
physiological  processes,  e.g.,  Eespiration,  Circulation,  Digestion;  and 
in  Volition  and  all  other  manifestations  of  cerebral  activity. 

Tlie  energy  expended  in  all  physiological  pi-ocesses,  e.g., 'Nntrition^ 
Secretion,  Growth,  and  the  like. 

The  total  expenditure  or  total  manifestation  of  energy  by  an  animal 
body  can  be  measured,  with  fair  accuracy.  All  statements,  however, 
must  be  considered  for  the  present  approximate  only,  and  especially  is 
this  the  case  with  respect  to  the  comparative  share  of  expenditure  to 
be  assigned  to  the  various  objects  just  enumerated. 

The  amount  of  energy  daily  manifested  by  the  adult  human  body 
in  (a)  the  maintenance  of  its  temperature;  (b)  in  internal  mechani- 
cal work,  as  in  the  movements  of  the  respiratory  muscles,  the  heart, 
etc. ;  and  (c)  in  external  mechanical  work,  as  in  locomotion,  and  all 
other  voluntary  movements,  is  made  up,  according  to  McKendrick,  as 
follows : — 

Metre-  Gramme- 

kilogrammes,  calories. 

Work  of  heart  per  diem      .         .         .         88,000 
Work  of  respiratory  muscle  .         .  14,000 

Eight  hours'  active  work  .         .       213,344 


315,334  or  743,000 

Amount  of  heat  produced  iu  24  hours    1,582,700  or       3,724,000 


1,898.034  or        4,467,000 


So  that  4,  467  kilogramme  calories  represent  the  total  energy  manifested  in 
24  hours,  8  of  which  were  employed  in  mechanical  work,  one-sixth  of  t lie 
total  energy  being  work.  This  estimation  considerably  exceeds  those  of  others, 
and  the  most  general  view  is  that  the  total  energy  exhibited  in  24  houi-s  by 
the  average  adult  is  rather  under  than  over  1, 000, 000  ki  log.  metres. 

Taking  the  diet-scale  as  given  above  (modified  from  Moleschott),  we  may 
see  how  this  supplies  the  energy  which  is  given  out,  remembering  tliat  1  grni. 
proteid  —  5,000  to  5,500  calories;  minus  the  value  of  i  grni.  urea  =  700  or  800 
calories.  =  say  4.500;  1  grm.  fat  =  9,000  calories ;  and  t  gnu.  carbohydrate  = 
4,000  calories. 


•146  HAlfDBOOK    OF    PHYSIOLOGY. 


Gramme- 
calories. 


120  grniB.  Proteid  at  4, 500  per  grm.  =      544, 500 

90     "        Fat  at  9, 000  per  grm.  =      810, 000 

330     "        Carbohydrate  at  4000  per  grm.    =1,320,000 

2. 694, 500 

Or  roughly,  2, 694  kilog.  calories,  equivalent  to  1, 144, 950  metre-kilogrammes 
of  energy.  This  shows,  although  the  calculation  is  only  rough,  that  the  diet 
wliich  from  other  reasons  was  considered  to  be  correct  contains  the  potential 
energy  to  set  free  one  million  metre-kilogrammes  of  kinetic  energy,  and  to 
leave  a  fair  margin  for  errors  of  calculation. 

To  the  foregoing  amounts  of  expenditure  must  be  added  the  quite 
unknown  quantity  expended  in  the  various  manifestations  of  nerve-force, 
and  in  the  work  of  nutrition  and  growth  (using  these  terms  in  their 
widest  sense).  By  comparing  the  amount  of  energy  which  should  be 
produced  in  the  body  from  so  much  food  of  a  given  kind,  with  that 
which  is  actually  manifested  (as  shown  by  the  various  products  of  com- 
bustion, in  the  excretions),  attempts  have  been  made,  indeed,  to  estimate, 
by  a  process  of  exclusion,  these  unknown  quantities ;  but  all  such  calcu- 
lations must  be  at  present  considered  only  very  doubtfully  approximate. 

Sources  of  Error. — Among  the  sources  of  error  in  any  such  calcula- 
tions as  the  one  above  given  must  be  reckoned,  as  a  chief  one,  the, 
at  present,  entirely  unknown  extent  to  which  forces  external  to  the  body 
(mainly  heat)  can  be  utilized  by  the  tissues.  We  are  too  apt  to  think 
that  the  heat  and  light  of  the  sun  are  directly  correlated,  as  far  as  living 
beings  are  concerned,  with  the  chemico-vital  transformations  involved 
in  the  nutrition  and  growth  of  the  members  of  the  vegetable  world  only. 
But  animals,  although  comparatively  independent  of  external  heat  and 
other  forces,  probably  utilize  them,  to  the  degree  occasion  offers.  And 
although  the  correlative  manifestation  of  energy  in  the  body,  due  to  ex- 
ternal heat  and  light,  may  still  be  measured  in  so  far  as  it  may  take 
the  form  of  mechanical  work;  yet,  in  so  far  as  it  takes  the  form  of  ex- 
penditure in  nutrition  or  nerve-force,  it  is  evidently  impossible  to  include 
it  by  any  method  of  estimation  yet  discovered;  and  all  accounts  of  it 
must  be  matters  of  the  purest  theory.  These  considerations  may  help 
to  explain  the  apparent  discrepancy  between  the  amount  of  energy  which 
is  capable  of  being  produced  by  the  usual  daily  amount  of  food,  with 
that  which  is  actually  manifested  daily  by  the  body ;  the  former  leaving 
but  a  small  margin  for  anything  beyond  the  maintenance  of  heat,  and 
mechanical  work. 

It  is  of  much  interest  to  consider  the  way  in  which  protoplasm  acts 
in  converting  food  into  energy  plus  decomposition  products.  It  is  certain 
that  the  substance  itself  does  not  undergo  much  change  in  the  process 
except  a  slight  amount  of  wear  and  tear.     We  may  assume  that  it  is  the 


METABOLISM,    NUTRITION,    AND    DIET,  447 

property  of  protoplasm  to  separate  from  the  blood  the  materials  which 
it  may  require  to  produce  secretions,  in  the  case  of  the  protoplasm  of 
secreting  glands,  or  to  enable  it  to  evoke  heat  and  energy  as  in  the 
case  of  the  protoplasm  of  muscle.  The  properties  of  the  protoplasm  are 
very  possibly  differently  developed  in  each  case,  and  the  decomposition 
products,  too,  may  be  different  in  quality  or  quantity.  Proteid  materials 
appear  to  be  specially  needed,  as  is  shown  by  the  invariable  presence  of 
urea  in  the  urine  even  during  starvation ;  and  as  in  the  latter  case  there 
has  been  no  food  from  which  these  materials  could  have  been  derived, 
the  urea  is  considered  to  be  derived  from  the  disintegration  of  the  nitro- 
genous tissues  themselves.  Which,  if  not  all,  of  the  three  varieties  of 
proteid  of  the  blood,  viz.,  serum-albumin,  serum-globulin,  and  fibrino- 
gen, is  necessary  for  muscular  metabolism  is  not  certainly  known, 
opinion  appears  to  incline  toward  the  first  as  the  most  important.  The 
removal  of  all  fat  from  the  body  in  a  starvation  period,  as  the  first  appar- 
ent change,  would  lead  to  the  supposition  that  fat  is  also  a  specially 
necessary  pabulum  for  the  production  of  protoplasmic  energy;  and  the 
fact  that,  as  mentioned  above,  with  a  diet  of  lean  meat  an  enormous 
amount  appears  to  be  required,  suggests  that  in  that  case  protoplasm 
obtains  the  fat  it  needs  from  the  proteid  food,  which  process  must  be 
evidently  a  source  of  much  waste  of  nitrogen.  The  fat  which  is 
deposited  in  the  tissues  has  for  its  origin,  as  we  have  before  remarked, 
in  great  part  carbohydrate  food,  and  is  looked  uj^on  as  a  store  of  carbo- 
naceous material;  it  has  been  suggested  that  as  it  leaves  the  tissue  to  be 
used  up,  it  is  reconverted  into  a  carbohydrate,  viz.,  dextrose.  Salts 
appear  to  be  absolutely  essential  for  protoplasmic  life.  The  idea  that 
proteid  food  has  two  destinations  in  the  economy,  viz.,  to  form  organ  or 
tissue  proteid  which  builds  up  organs  and  tissues,  and  circulating  jjro- 
teid,  from  which  the  organs  and  tissues  derive  the  nuxterials  of  their 
secretions  or  for  producing  their  energy,  is  a  convenient  one,  but  cannot 
be  said  to  rest  upon  any  very  certain  facts.  Except  in  the  possible  case 
of  the  appearance  of  leucin  and  tyrosin  in  pancreatic  digestion,  already 
fully  discussed,  it  must  not  be  looked  upon  as  more  than  a  convenient 
hypothesis. 

One  question  which  has  been  little  considered  by  physiologists,  is 
what  relationship,  if  any,  there  is  between  each  tissue  and  the  waste  pro- 
ducts of  other  tissues,  or  perhaps  it  should  be  said,  the  products  of  the 
metabolism  of  other  tissues.  It  is  not  known  whether,  as  the  result  of 
the  katabolism  of  one  tissue,  products,  proteid  or  otherwise,  are  not 
taken  up  by  the  blood  and  carried  to  other  tissues,  supplying  exactly 
what  is  necessary  for  their  complete  auabolism ;  whether,  for  example, 
a  proteid  residue  docs  not  arise  from  the  metabolism  of  muscle  which 


418  HANDBOOK    OF    PHYSIOLOGY. 

may  be  used  further  by  glands.  One  step,  at  all  events,  in  this  direction 
has  been  taken;  it  has  been  suggested  that  the  sarco-lactic  acid  contin- 
ually produced  by  muscle  is  carried  to  the  liver,  either  to  be  converted 
itself  into  glycogen,  or  by  its  influence  on  the  hepatic  cells  to  cause  them 
to  store  up  that  substance. 


CHAPTER  XII. 

ANIMAL    HEAT. 

One  of  the  most  importaut  results  of  the  metabolism  of  the  tissues  is 
the  production  of  the  heat  of  the  body.  It  is  by  this  means  that  the 
bodily  temperature  is  raised  to  such  a  point  as  to  make  life  possible. 
In  man  and  in  such  animals  as  are  called  warm-blooded,  inchiding  only 
mammals  and  birds,  it  is  found  on  the  one  hand,  that  there  is  an  aver- 
age temperature  which  is  maintained  with  only  slight  variations  in  spite 
of  changes  in  their  environment,  and  on  the  other  hand,  tliat  the  pos- 
sible variations  above  and  below  this  average  are  comparatively  slight. 
It  must  not  be  thought,  however,  that  the  average  temperature  in  all 
mammals  and  birds  is  the  same;  for  example,  as  we  shall  see.  the  average 
temperature  of  man  is  just  37°  C.  (98.6°  F.),  in  some  birds  it  is  as  high 
as  44°  C.  (111°  F.),  whereas  in  the  wolf  it  is  said  to  be  under  36°  0 
(96°  F.). 

The  average  temperature  of  the  human  body  in  those  internal  parts 
which  are  most  easily  accessible,  as  the  mouth  and  rectum,  is  from  36.9° 
-37.4°  C.  (98.5°  to  99.5°  F.).  In  different  parts  of  the  external  surface 
of  the  human  body  the  temperatui-e  varies  only  to  the  extent  of  one  or 
two  degrees  (C),  when  all  are  alike  protected  from  cooling  influences; 
and  the  difference  which  under  these  circumstances  exists,  depends  chiefly 
upon  the  different  degrees  of  blood-supply.  In  the  axilla — the  most 
convenient  situation,  under  ordinary  circumstances,  for  examination  by 
the  thermometer — the  average  temperature  is  36.9°  C.  (98.6°  F.).  In 
different  internal  parts,  the  variation  is  one  or  two  degrees;  those  parts 
and  organs  being  warmest  which  contain  most  blood,  ami  in  which  there 
occurs  the  greatest  amount  of  chemical  change,  e.g.,  the  muscles  and 
the  glands;  and  the  temperature  is  highest,  when  they  are  in  a  condi- 
tion of  activity:  wliile  those  tissues  which,  subserving  only  a  mechanical 
function,  are  the  seat  of  least  active  circulation  and  chemical  change, 
are  the  coolest.  These  differences  of  temperature,  however,  are  actually 
but  slight,  on  account  of  the  provisions  which  exist  for  maintaining 
uniformity  of  temperature  in  different  parts. 

Cireuinstancci  causing  Va7'iotio77s  in  Temperature. — The  cliief  circumstances 
by  which  tlie  temperature  of  a  healthy  body  is  influenced  are  the  following: — 

Age. — The  average  temperature  of  the  new-born  child  is  only  about  half  a 
degree  C.    {V  F.)  above  that  of  the  adult;  and  the   uiilerence  becomecs  still 


450  HANDBOOK    OF    PHYSIOLOGY. 

more  trifling  during  infancy  and  early  childhood.  The  temperature  falls  to 
the  extent  of  about  .2°  C.  (.5°  F. )  from  early  infancy  to  puberty,  and  by 
about  the  same  amount  from  puberty  to  fifty  or  sixty  years  of  age.  In  old  age 
the  temperature  again  rises,  and  approaches  that  of  infancy. 

Sex. — The  average  temperature  of  the  female  is  slightly  higher  than  that  of 
the  male. 

Period  of  tlie  Day. — The  temperature  undergoes  a  gradual  alteration,  to  the 
extent  of  about  .54°-. 8°  C.  (1°  to  1.5°  F.)  in  the  course  of  the  day  and  night; 
the  minivium  being  at  night  or  in  the  early  morning,  the  maxwuim  late  in  the 
afternoon. 

Exercise. — Active  exercise  raises  the  temperature  of  the  body  from  .54°-!. 08° 
C.   (1°  to  3°  F.). 

Climate  and  Season. — The  temperature  of  the  human  body  is  practically  the 
same  in  temperate  as  in  tropical  climates.  In  summer  the  temperature  of  the 
body  is  a  little  higher  than  in  ^vinter ;  the  difference  amounting  to  about  a 
fifth  of  a  degree  0. 

Food  and  Drink.  — The  effect  of  a  meal  upon  the  temperature  of  a  body  is  but 
small.  A  very  slight  rise  usually  occurs.  Cold  alcoholic  drinks  slightly 
depress  the  temperature  about  half  a  degree  C.  Warm  alcoholic  drinks,  as 
well  as  warm  tea  and  coffee,  raise  the  temperature  about  a  third  of  a  degree  C. 

Disease. — In  disease  the  temperature  of  the  bodj'  deviates  from  the  normal 
standard  to  a  greater  extent  than  would  be  anticipated  from  the  slight  effect 
of  external  conditions  during  health.  Thus,  in  some  disease,  as  pneumonia 
and  typhus,  it  occasionally  rises  as  high  as  41°-41.6°  C.  (106°  or  107°  F. ),  and 
considerably  higher  temperatures  have  been  noted.  In  Asiatic  cholera,  on  the 
other  hand,  a  thermometer  placed  in  the  mouth  may  sometimes  rise  only  to 
25°-26.3°  C.   (77°  or  79°  F.). 

The  temperature  maintained  by  Mammalia  in  an  active  state  of  life,  accord- 
ing to  the  tables  of  Tiedemann  and  Rudolphi,  averages  38.3°  C.  (101°  F.). 
The  extremes  recorded  by  them  were  34.6°  C.  (96°  F.)  and  41°  C.  (106°  F.),  the 
former  in  the  narwhal,  the  latter  in  a  bat  (Vespertilio  pipisti-ella) .  In  Birds, 
the  average  is  as  high  as  41.2°  C.  (107°  F. )  ;  the  highest  temperature,  46.2°  C. 
(111.25°  F. )  being  in  the  small  species,  the  linnets,  etc.  Among  Reptiles,  while 
the  medium  they  were  in  was  23. 9°  C  (75°  F. )  their  average  temperature  was 
31.2°  C.  (82.5°  F. ).  As  a  general  rule,  their  temperature,  though  it  falls  with 
that  of  the  surrounding  medium,  is,  in  temperate  media,  two  or  more  degrees 
higher ;  and  though  it  rises  also  with  that  of  the  medivim,  yet  at  very  high 
degrees  it  ceases  to  do  so,  and  remains  even  lower  than  that  of  the  medium, 
fish  and  invertebrata  present,  as  a  general  rule,  the  same  temperature  as  the 
medium  in  which  they  live,  whether  that  be  high  or  low ;  only  among  fish,  the 
tunny  tribe,  with  strong  hearts  and  red  meat-like  muscles,  and  more  blood 
than  the  average  of  fish  have,  are  generally  3. 8°  C.  (7°  F. )  warmer  than  the 
water  around  them. 

The  difference,  therefore,  between  what  are  commonly  called  the  warm  and 
the  cold-blooded  animals,  or  homoiothermal  {o(ioloq,  like,  Ospfiv,  heat)  and  poikilo- 
thermal  {■woLK.iTMg,  changeful,  Gepi^iri,  heat),  is  not  one  of  absolutely  higher  or  lower 
temperature ;  for  the  animals  which  to  us  in  a  temperate  climate  feel  cold  (be- 
ing like  the  air  or  water,  colder  than  the  surface  of  our  bodies) ,  would  in  an 
external  temperature  of  37.8°  C.  (100°  F.)  have  nearly  the  same  temperature 
and  feel  hot  to  us.  The  real  difference  is  that  warm-blooded  animals  have  a 
ceitain  permanent  heat  in  all  atmospheres,  while  the  temperature  of  cold- 
blooded animals  is  variable  with  every  atmosphere. 


animal  heat.  451 

The   Production   o^  the   Body   Heat, 

The  heat  which  is  produced  in  the  body  arises  from  the  metabolic 
changes  of  the  tissues,  the  chief  part  of  which  are  of  the  nature  of  oxida- 
tion, since  it  may  be  supposed  that  the  oxygen  of  the  atmosphere  taken 
into  the  system  is  uUimatelij  combined  with  carbon  and  hydrogen,  and 
discharged  from  the  body  as  carbonic  acid  and  water.  Any  changes, 
indeed,  which  occur  in  the  protoplasm  of  the  tissues,  resulting  in  an 
exhibition  of  their  function,  are  attended  by  the  evolution  of  heat  and 
the  formation  of  carbonic  acid  and  Avater.  The  more  active  the 
changes  the  greater  is  the  heat  produced  and  the  greater  is  the  amount 
of  the  carbonic  acid  and  water  formed.  But  in  order  that  the  proto- 
plasm may  perform  its  function,  the  waste  of  its  own  tissue  (destructive 
metabolism),  must  be  repaired  by  the  due  supply  of  food  m'aterial  to  be 
built  u])  in  some  way  into  the  protoplasmic  molecule.  For  the 
production  of  heat,  therefore,  food  is  necessar3^  In  the  tissues, 
as  we  have  several  times  remarked,  two  processes  are  continually 
going  on:  the  building  up  of  the  protoplasm  from  the  food  (constructive 
metabolism)  which  is  not  accompanied  by  the  evolution  of  heat,  possibly 
even  by  its  storing,  and  the  oxidation  of  the  protoplastic  materials 
resulting  in  the  production  of  energy,  by  which  heat  is  set  free  and 
carbonic  acid  and  water  are  evolved. 

It  is  not  necessary  to  assume  that  the  combustion  processes,  indeed, 
are  as  simple  as  the  bare  statement  of  the  fact  might  seem  to  indicate; 
and,  we  have  indicated,  in  treating  of  muscular  metabolism,  the  process 
appears  to  consist  first  of  all  of  building  up  of  the  oxygen  into  the 
molecule.  But  complicated  as  the  various  stages  may  be,  the  ultimate 
res'ilt  is  as  simple  as  in  ordinary  combustion  outside  the  body,  and  the 
products  are  the  same. 

This  theory  that  the  maintenance  of  the  temperature  of  the  living 
body  depends  on  continual  chemical  change,  chiefly  by  oxidation  of 
combustible  materials  in  the  tissues,  has  long  been  established  by  the 
demonstration  that  the  quantity  of  carbon  and  hydrogen  as  supplied  as 
food,  which,  in  a  given  time,  unites  in  the  body  with  oxygen,  is  sufficient 
to  account  for  the  amount  of  heat  generated  in  the  animal  within  the 
same  period:  an  amount  cajiable  of  maintaining  the  temperature  of  the 
body  at  from  3C.8°-3.87°  C.  (98°-100°  F.),  notwithstanding  a  large 
loss  by  radiation  and  evaporation.  This  estimation  depends  upon  the 
chemical  uxiom  that  when  a  body  undergoes  a  chemical  change  the 
amount  of  energy  set  free  is  the  same,  supposing  the  resulting  products 
are  the  same,  whether  the  change  takes  place  suddenly  or  gradually.  If 
a  certain  nunibcr  of  grammes  of  different  substances  are  introduced  as 
food,  and  if  they  undergo  complete  oxidation,  the  amount  of   kinetic 


452  HANDBOOK    OF    PHYSIOLOGY. 

energy  as  shown  in  the  amount  of  heat,  and  mechanical  work,  is  the 
same  if  the  same  bodies  are  completely  oxidized  outside  the  body;  so 
that  if  1  gramme  of  fat  be  taken  into  the  body  and  the  oxidation 
completely  oxidized,  resulting  in  the  production  of  a  definite  amount 
of  carbon  dioxide  and  water,  it  may  be  supposed  to  have  produced  the 
same  amount  of  heat  as  it  would  have  produced  outside  the  body.  In 
the  caseof  proteidfood  it  is  a  little  different,  since  it  is  never  completely 
oxidized  within  the  body,  but  may  be  supposed  to  give  rise  to  a  definite 
amount  of  urea,  not  a  completely  oxidized  body.  In  this  case  the 
gramme  of  proteid  may  be  considered  to  perform  the  same  amount  of 
heat  as  the  proteid  would  outside  the  body  minus  the  amount  which 
"would  be  obtained  from  the  complete  oxidation  of  the  resulting  urea. 

The  actual  amount  of  heat  produced  per  diem  has  been  experimentally 
ascertained  in  the  case  of  small  animals  by  the  aid  of  an  apparatus 
called  a  Calorimeter.  The  animal  is  inclosed  in  a  metal  box  com- 
pletely contained  in  a  second  box  containing  water,  and  air  is  led  into 
and  out  of  the  inner  box  by  means  of  metal  tubes ;  the  one  through  which 
the  air  is  led  out  of  the  chamber  has  several  coils  in  it.  The  heat  given 
out  by  the  animal  warms  the  water  in  the  outside  box,  and  may  be 
estimated  by  the  rise  of  its  temperature,  the  amount  of  which  is  known. 

The  amount  of  heat  produced  and  of  energy  in  the  form  of  mechanical 
work  set  free  in  a  given  time  arise  from  the  oxidation  of  the  substances 
taken  in  as  food  in  so  far  as  they  are  oxidized.  In  order  that  there  may 
be  correct  data  to  assist  in  the  consideration  of  the  subject,  the  amount 
of  heat  evolved  by  the  oxidation  of  various  food-stuffs  has  been  carefully 
measured.  The  results  may  be  set  down  in  terms  of  gramme-calories 
(Ca),  a  calorie  being  the  heat  unit,  and  meaning  the  amount  of  heat 
required  to  raise  1  gramme  of  water  1  degree  C,  or,  more  strictly,  from 
15°  C.  to  16°  C*  The  number  of  gramme-calories  which  1  gramme 
of  the  following  substances  equals  will  be  seen  in  the  annexed  table. 

Hydrogen     .     3450        Fat        .         .     9000        Urea  .  3200 

Carbon    .     .     8100        Carbohydrate    4000 

Proteid  .     5000—5500 

1  gramme  of  proteid  giving  rise  to  i  gramme  of  urea. 

The  relation  between  the  income  and  expenditure  of  the  body  has 
been  already  considered  in  detail  in  the  preceding  chapter.  We  may 
now  turn  to  the  question  of  the  chief  heat-producing  tissues. 

Heat-producing  Tissues. — (1.)  The  Muscles. — As  the  muscles 
form  so  large  a  part  of  the  body,  and  as  in  them  metabolism  is  particularly 
active,  it  is  only  reasonable  to  consider  the  muscular  as  the  chief  heat- 

*  Sometimes  the  term  kilogramme- calorie   is  used  ;  one  kilogramme- calorie 
being  equal  to  1000  gramme-calories. 


ANIMAL   HEAT.  453 

producing  tissue.  It  will  shortly  be  pointed  out  that  the  manifesta- 
tion of  muscular  energy  is  always  accompanied  by  the  evolution  of  heat 
and  the  production  of  carbon  dioxide.  This  production  of  carbon 
dioxide  goes  on  while  the  muscles  arc  at  rest,  only  in  a  less  degree  to 
that  which  is  noticed  during  muscular  activity,  and  so  it  is  certain  that 
an  active  metabolism  is  going  on  in  resting  as  well  as  in  contracting 
muscles.  This  metabolism  is  a  source  of  much  heat,  and  so  the  total 
amount  of  heat  produced  in  the  muscular  tissues  per  diem  must  be  very 
great.  It  has  been  calculated  that,  even  neglecting  the  heat  produced 
by  the  quiet  metabolism  of  muscular  tissue,  the  amount  of  heat  gener- 
ated by  muscular  activity  would  supj^ly  the  princijjal  j^art  of  the  total 
heat  produced  within  the  body.  (2.)  The  Secreting  glands,  and  prin- 
cipally the  liver,  as  being  the  largest  and  most  active,  come  next  to  the 
muscles  as  heat-producing  tissue.  It  has  been  found  by  experiment  that 
the  blood  leaving  the  glands  is  considerably  warmer  than  that  entering 
them.  The  metabolism  in  the  glands  is  ver}^  active,  and,  as  we  have 
seen,  the  more  active  the  metabolism  the  greater  the  heat  produced. 
(3.)  The  Brain;  the  venous  blood  has  a  higher  temjDcrature  than  the 
arterial.  It  must  be  remembered,  however,  that  although  the  organs 
above  mentioned  are  the  chief  heat-producing  parts  of  the  body,  all 
living  tissues  contribute  their  quota,  and  this  in  direct  proportion  to 
their  activity.  The  blood  itself  is  also  the  seat  of  metabolism,  and, 
therefore,  of  the  production  of  heat;  but  the  share  which  it  takes  in 
this  respect,  apart  from  the  tissues  in  which  it  circulates,  is  very  incon- 
siderable. There  are  two  other  means  by  which  the  heat  produced  by 
metabolism  of  the  tissues  is  added  to  in  slight  degree,  viz.,  by  friction, 
i.e.,  in  the  movements  of  muscles,  in  the  circulation  of  blood,  and  else- 
where. This  contributes  a  slight  but  undetermined  amount  of  heat, 
and  by  the  taking  in  of  warm  foods,  solid  or  liquid,  a  further  small 
amount  of  heat  is  at  the  same  time  acquired. 

Eegulation   of  the  Temperature   of  the  Human   Body. 

The  average  temperature  of  the  body  is  maintained  under  different 
conditions  of  external  circumstances  by  mechanisms  which  permit  of 
(1)  variation  in  the  loss  of  heat,  and  (2)  variations  in  the  production  of 
heat.  In  healthy  warm-blooded  animals  the  loss  and  gain  of  heat  are  so 
nearly  balanced  one  by  the  other  that,  under  all  ordinary  circumstances, 
an  uniform  temperature,  within  a  degree  or  two,  is  preserved. 

Variation  in  the  Loss  of  Heat. — The  loss  of  heat  from  the  human 
body  is  principally  regulated  by  the  amount  given  oif  (1)  by  radiation 
and  conduction  from  its  surface,  and  by  means  of  the  (2)  constant  evapo- 
ration of  water  from  the  same  part,  heat  being  thus  rendered  latent,  and 


454  HANDBOOK   OF   PHYSIOLOGY. 

to  a  mucli  less  degree  (3)  from  the  air-passages;  in  each  act  of  respira- 
tion, heat  is  lost  to  a  greater  or  less  extent  according  to  the  temperature 
of  the  atmosphere;  unless  indeed  the  temperature  of  the  surrounding 
air  exceed  that  of  the  blood.  We  must  remember  too  that  (4)  all  food 
and  drink  which  enter  the  body  at  a  lower  temperature  than  itself  ab- 
stract a  small  measure  of  heat ;  (5)  while  the  urine  and  fseces  which 
leave  the  body  at  about  its  own  temperature  are  also  means  by  which  a 
small  amount  is  lost. 

{a. )  From  the  Surface  of  the  Body.  — By  far  the  most  important  loss 
of  heat  from  the  body, — probably  90  per  cent  and  upward  of  the  whole 
amount,  is  that  which  takes  place  by  radiation,  conduction,  and  evapora- 
tion from  the  skin.  The  actual  figures  are  as  follows: — of  100  calories 
of  heat  produced,  2.6  are  lost  in  heating  food  and  drink;  2.6  in  heating 
air  inspired;  14.7  in  evaporation ;  andbO.l  by  radiation  and  conduction. 
The  means  by  which  the  skin  is  able  to  act  as  one  of  the  most  impor- 
tant organs  for  regulating  the  temperature  of  the  blood,  are — (1),  that 
it  offers  a  large  surface  for  radiation,  conduction,  and  evaporation;  (2), 
that  it  contains  a  large  amount  of  blood;  (3),  that  the  quantity  of 
blood  contained  in  it  is  the  greater  under  those  circumstances  which 
demand  a  loss  of  heat  from  the  body,  and  vice  versa.  For  the  circum- 
stance which  directly  determines  the  quantity  of  blood  in  the  skin,  is 
that  which  governs  the  supply  of  blood  to  all  the  tissues  and  organs  of 
the  body,  namely,  the  power  of  the  vaso-motor  nerves  to  cause  a  greater 
or  less  tension  of  the  muscular  element  in  the  walls  of  the  arteries,  and, 
in  correspondence  with  this,  a  lessening  or  increase  of  the  calibre  of 
the  vessel,  accompanied  by  a  less  or  greater  current  of  blood.  A  warm 
or  hot  atmosphere  so  acts  on  the  nerve  fibres  of  the  skin,  as  to  lead 
them  to  cause  in  turn  a  relaxation  of  the  muscular  fibre  of  the  blood- 
vessels; and,  as  a  result,  the  skin  becomes  full-blooded,  hot,  and  sweat- 
ing; and  much  heat  is  lost.  "With  a  low  temperature,  on  the  other 
hand,  the  blood-vessels  shrink,  and  in  accordance  with  the  consequently 
diminished  blood-supply,  the  skin  becomes  pale,  and  cold,  and  dry;  and 
no  doubt  a  similar  effect  may  be  produced  through  the  vaso-motor  cen- 
tre in  the  medulla  and  spinal  cord.  Thus,  by  means  of  a  self-regulating 
apparatus,  the  skin  becomes  the  most  important  of  the  means  by  which 
the  temperature  of  the  body  is  regulated. 

In  connection  with  loss  of  heat  by  the  skin,  reference  has  been  made 
to  that  which  occurs  both  by  radiation  and  conduction,  and  by  evapora- 
tion; and  the  subject  of  animal  heat  has  been  considered  almost  solely 
with  regard  to  the  ordinary  case  of  man  living  in  a  medium  colder  than 
his  body,  and  therefore  losing  heat  in  all  the  ways  mentioned.  The 
importance  of  the  means  however,  adopted,  so  to  speak,  by  the  skin  for 
regulating  the  temperature  of  the  body,  will  depend  on  the  conditions 


ANIMAL   HEAT.  455 

by  which  it  is  surrounded ;  un  inverse  projiortion  existing  in  most  cases 
between  a  loss  by  radiation  and  conduction  on  the  one  liaud,  and.  by 
evaporation  on  the  other.  Indeed,  the  small  loss  of  heat  by  evaporation 
in  cold  climates  may  go  far  to  compensate  for  the  greater  loss  hy  radia- 
tion ;  as,  on  the  other  hand,  the  great  amount  of  fluid  evaporated  in 
hot  air  may  remove  nearly  as  much  heat  as  is  commonly  lost  by  both 
radiation  and  evaporation  together  in  ordinary  temperatures;  and  thus, 
it  is  possible  tliat  the  quantities  of  heat  required  for  the  maintenance  of 
a  uniform  proper  temperature  in  various  climates  and  seasons  are  not 
so  diiferent  as  they,  at  first  sight,  seem. 

Many  examples  may  be  given  of  thejJOiver  tohicli  the  body  possesses  of  resist- 
ing the  effects  of  a  high  teinperature,  in  virtue  of  evaporation  from  the  skin. 
Blagden  and  others  supported  a  temperature  varying  between  92°-100''  C. 
(198''-212°  F. )  in  dry  air  for  several  minutes  ;  and  in  a  subsequent  experiment 
he  remained  eight  minutes  in  a  tempei-ature  of  126.5"  C.  (260°  F. ).  "The 
workmen  of  Sir  F.  Chantrey  were  accustomed  to  enter  a  furnace,  in  which 
his  moulds  were  dried,  while  the  floor  was  red-hot,  and  a  thermometer  in  the 
air  stood  at  177.8°  C.  (350°  F. ),  and  Chabert,  the  fire-king,  was  in  the  habit  of 
entering  an  oven,  the  temperature  of  which  was  from  205°-315''  C.  (400°-600'' 
F.)."     (Carpenter.) 

But  such  heats  are  not  tolerable  when  the  air  is  moist  as  well  as  hot,  so 
as  to  prevent  evaporation  from  the  body.  C.  James  states,  that  in  the  vapor 
baths  of  Nero  he  was  almost  suflfocated  in  a  temperature  of  44.5°  C.  (112°  F. ), 
while  in  the  caves  of  Testaccio,  in  which  the  air  is  dry,  he  was  but  little 
incommoded  by  a  temperature  of  80°  C.  (176°  F.).  In  the  former,  evaporation 
from  the  skin  was  impossible ;  in  the  latter  it  was  abundant,  and  the  layer 
of  vapor  which  would  rise  from  all  the  surface  of  the  body  would,  by  its  veiy 
slowly  conducting  power,  defend  it  for  a  time  from  the  full  action  of  the  ex- 
ternal heat. 

We  are  able  by  suitable  clothing  to  increase  or  to  diminish  the  amount 
of  heat  lost  by  the  skin. 

The  Avays  by  which  the  skin  may  be  rendered  more  efficient  as  a  cool- 
ing-apparatus too,  by  exposure,  by  baths,  and  by  other  means  which 
man  instinctively  adopts  for  lowering  his  temperature  when  necessary, 
are  too  well  known  to  need  more  than  passing  mention. 

Although  under  any  ordinary  circumstances  the  external  application  of 
cold  only  temporarily  depresses  the  temperature  to  a  sliglit  extent,  it  is  other- 
wise in  cases  of  high  temperature  in  fever.  In  these  cases  a  tepid  bath  may 
reduce  the  temperature  several  degrees,  and  the  effect  so  produced  last  la 
some  cases  for  many  hours. 

{h)  From  the  Lungs. — As  a  means  for  lowering  the  temperature,  the 
lungs  and  air-passages  are  very  inferior  to  the  skin;  although,  by  giving 
heat  to  the  air  we  breathe,  they  stand  next  to  the  skin  in  importance. 
As  a  regulating  power,  the  inferiority  is  still  more  marked.  The  air 
which  is  expelled  from  the  lungs  leaves  the  body  at  about  the  tempera,- 


456  HANDBOOK    OF    PHYSIOLOGY. 

ture  of  the  blood,  and  is  always  saturated  with  moisture.  No  inverse 
proportion,  therefore,  exists,  as  in  the  case  of  the  skin,  between  the  loss 
of  heat  by  radiation  and  conduction  on  the  one  hand,  and  by  evaporation 
on  the  other.  The  colder  the  air,  for  example,  the  greater  will  be  the 
loss  in  all  ways.  Neither  is  the  quantity  of  blood  which  is  exposed  to 
the  cooling  influence  of  the  air  diminished  or  increased,  so  far  as  is 
known,  in  accordance  with  any  need  in  relation  to  temperature.  It  is 
true  that  by  varying  the  number  and  depth  of  the  respirations,  the 
quantity  of  heat  given  off  by  the  lungs  may  be  made,  to  some  extent, 
to  vary  also.  But  the  respiratory  passages,  while  they  must  be  considered 
important  means  by  which  heat  is  lost,  are  altogether  subordinate,  in 
the  power  of  regulating  the  temperature,  to  the  skin. 

(c)  By  Warming  Cold  Foods. — ^This  is  an  obvious  method  of  expendi- 
ture of  heat  which  may  be  resorted  to,  but  the  loss  of  heat  by  the  excreta 
discharged  from  the  body  at  a  high  temperature,  must  be  of  little  use  as 
a  means  of  regulating  the  temperature,  since  the  amount  so  lost  must  be 
capable  of  little  variation. 

Variation  in  the  Production  of  Heat. — It  may  seem  to  have  been 
assumed,  in  the  foregoing  pages,  that  the  only  regulating  apparatus  for 
temperature  required  by  the  human  body  is  one  that  shall,  more  or  less, 
produce  a  cooling  effect;  and  as  if  the  amount  of  heat  produced  were 
always,  therefore,  in  excess  of  that  which  is  required.  Such  an  assump- 
tion would  be  incorrect.  We  have  the  power  of  regulating  the  produc- 
tion of  heat,  as  well  as  its  loss. 

The  regulation  of  the  production  of  heat  in  the  body  is  apparently 
different  for  each  animal,  as  the  absolute  amount  of  heat  set  free  by 
different  animals  in  a  given  period  varies;  in  one  the  production  of  heat 
exceeds  that  in  another.  It  is  even  said  that  each  individual  has  his 
own  coefficient  of  heat  production.  From  all  that  has  been  said  on  the 
subject  it  will  be  seen  that  the  amount  of  heat  for  all  practical  purposes 
depends  upon  the  metabolism  of  the  tissues  of  the  body,  everything 
therefore  which  increases  that  metabolism  will  increase  the  heat  produc- 
tion, so  therefore  the  absolute  amount  of  heat  produced  by  a  large 
animal,  having  a  larger  amount  of  tissues  in  which  metabolism  may  go 
on,  will  be,  cceteris  paribus,  greater  than  that  of  a  small  animal.  But  of 
course  the  activity  of  the  tissue  change  in  a  small  animal  may  be  greater 
than  in  a  large  one,  and  naturally  no  strict  line  can  be  drawn  between 
the  two. 

The  ingestion  of  food  has  been  proved  to  increase  the  metabolism  of 
the  tissues,  and  so,  as  one  would  expect,  the  rate  of  heat  production  is 
found  by  experiment  upon  the  dog  to  be  increased  after  a  meal,  and 
in  this  animal  the  heat  production  reaches  its  height  about  6  to  9  houra 
after  a  meal. 


ANIMAL   HEAT.  457 

It  has  also  been  experimentally  ascertained  that  the  rate  of  heat 
production  varies  somewhat  with  the  kind  of  food  taken,  for  example, 
if  sugar  be  added  to  the  meal  of  meat  given  to  the  dog,  tlic  height  of 
maximum  production  is  reached.  It  was  always  said  that  various  nations 
had  found  by  experience  what  food  was  most  suitable  for  the  climate  in 
Avhich  they  lived,  and  that  snch  experience  could  be  trusted  to  regulate 
the  quantity  consumed.  Although  there  have  been  no  very  conclusive 
experiments  to  prove  this  view,  yet  it  is  a  matter  of  general  observation 
that  in  northern  climates  and  in  colder  seasons  the  quantity  of  food 
taken  is  greater  than  in  warmer  climates  or  in  warmer  seasons.  More- 
over, the  kind  of  food  is  dillerent.  For  example,  persons  living  in  the 
<3o]der  climates  require  much  fat  in  order  to  produce  the  requisite 
amount  of  heat. 

In  exercise,  we  have  an  important  means  of  raising  the  temperature  of 
our  bodies,  by  it  the  muscular  metabolism  is  increased,  as  is  shown  by 
the  increased  output  of  carbon  dioxide. 

Influence  cf  the  Nervous  System. — The  influence  of  the  nervous 
system  in  modifying  the  production  of  heat  must  be  very  important,  as 
upon  nervous  influence  dejiends  the  amount  of  the  metabolism  of  the 
tissues.  The  experiments  and  observations  which  best  illustrate  it  are 
those  showing,  first,  that  when  the  supply  of  nervous  influence  to  a  part 
is  cut  off,  the  temperature  of  that  part  after  a  time  falls  below  its  ordi- 
nary degree;  and,  secondly,  that  when  death  is  caused  by  severe  injury 
to,  or  removal  of,  the  nervous  centres,  the  temperature  of  the  body 
rapidly  falls,  even  though  artificial  respiration  be  performed,  the  circu- 
lation maintained,  and  to  all  appearance  the  ordinary  chemical  changes 
of  the  body  be  completely  effected.  It  has  been  repeatedly  noticed,  that 
after  division  of  the  nerves  of  a  limb  its  temperature  ultimately  falls; 
and  this  diminution  of  heat  has  been  remarked  still  more  jilainly  in 
limbs  deprived  of  nervous  influence  by  paralysis. 

With  equal  certainty,  though  less  definitely,  the  influence  of  the 
nervous  system  on  the  production  of  heat  is  shown  in  the  rapid  and 
momentary  increase  of  temperature,  sometimes  general,  at  other  times 
quite  local,  which  is  observed  in  states  of  nervous  excitement;  in  the 
general  increase  of  warmth  of  the  body,  excited  by  passions  of  the  mind; 
in  the  sudden  rush  of  heat  to  the  face,  which  is  not  a  mere  sensation; 
and  in  the  equally  rapid  diminution  of  temperature  in  the  depressing 
passions.  All  of  these  examples,  however,  are  explicable,  on  tlie  suppo- 
sition that  the  nervous  system  alters,  by  its  power  of  controlling  the 
calibre  of  the  blood-vessels,  the  quantity  of  blood  supplied  to  a  part. 

Apart,  however,  from  this  vaso-motor  power  of  increasing  the  blood- 
supply  to  internal  organs,  and  to  the  tissues  in  general,  by  means  of 
which  it  is  possible  to  increase  their  metabolism  and  so  their  production 
of  heat,  there  is  evidence  to  suppose  that  there  is  another  nervous  appa- 


458  HANDBOOK    OF    PHYSIOLOGY. 

ratus  close]y  comparable  to  that  "which  regulates  the  secretion  of  saliva 
or  of  sweat,  by  means  of  which  the  production  of  heat  in  the  warm- 
blooded animals  is  increased  or  diminished  as  occasion  requires.  This 
apparatus  probably  consists  of  a  centre  or  centres  which  may  be  reflexly 
stimulated,  as  for  example  by  impulses  from  the  skin,  and  which  act 
through  special  nerves  supplied  to  the  various  tissues.  The  evidence 
upon  which  the  existence  of  this  regulating  apparatus  depends  is  the 
marked  effect  in  the  increase  of  the  oxygen  taken  in  by  a  warm-blooded 
animal  when  exposed  to  cold  and  the  corresponding  increase  in  the  output 
of  carbon  dioxide,  indicating  that  there  is  an  increase  of  the  metabolism 
and  so  an'  increased  production  of  heat,  under  such  circumstances  -and 
not  a  mere  diminution  of  the  amount  of  heat  lost  by  the  skin,  etc.  A  cold- 
blooded animal  reacts  very  differently  to  exposure  to  cold ;  instead  of  as  in 
the  case  of  the  warm-blooded  animal,  increasing  the  metabolism,  cold 
diminishes  the  metabolism  of  its  tissues.  It  appears  clear,  therefore, 
that  in  warm-blooded  animals  there  is  some  extra  apparatus  which 
counteracts  the  effects  of  cold  which  in  cold-blooded  animals  causes 
diminished  metabolism.  In  warm-blooded  animals  poisoned  by  urari, 
or  in  which  section  of  the  bulb  has  been  done,  it  has  been  found  that 
this  regulating  apparatus  is  no  longer  in  action,  and  under  such  circum- 
stances no  difference  appears  to  exist  between  such  animals  and  those 
which  are  naturally  cold-blooded.  Warmth  increases  their  temperature 
and  cold  lowers  it,  and  with  this  there  is  of  course  evidence  of  dimin- 
ished metabolism.  The  explanation  of  these  experiments  as  given  by 
modern  physiologists  is  that  in  such  animals  the  connection  which  natu- 
rally exists  between  the  skin  and  the  muscles  through  the  nervous  chain, 
such  as  a  thermotaxic  nervous  apparatus  might  be  supposed  to  afford,  is 
broken  either  at  the  termination  of  the  nerves  in  the  muscles  or  at  the 
section  point  of  the  bulb.  The  position  of  this  hypothetical  centre  is  a 
matter  of  some  difference  of  opinion.  It  has  been  demonstrated  that 
stimulation  of  different  parts  of  the  brain  may,  among  other  symptoms, 
produce  increased  metabolism  of  the  tissues  with  increased  output  of 
carbon  dioxide  and  a  raised  temperature:  the  parts  of  which  this  may  be 
asserted  are  parts  of  the  corpus  striatum  and  of  the  optic  thalamus. 
The  exact  situation  of  the  heat  centres,  however,  is  at  present  not  known 
with  certainty. 

Experimental  observations  such  as  have  been  made  upon  animals 
receive  confirmation  from  the  observations  of  patients  who  suffer  from 
fever  or  pyrexia;  in  them  the  temperature  of  the  body  may  be  raised 
several  degrees,  as  we  have  already  pointed  out  (p.  450.)  This  increase 
of  temperature  might  of  course  be  due  to  diminished  loss  of  heat  from 
the  skin,  but  this  although  in  all  probability  entering  into  its  causation, 
is  not  the  only  cause.     The  amount  of  oxygen  taken  in  and  the  amount 


ANIMAL   HEAT.  45!) 

of  carbon  dioxide  given  out  are  both  increased,  and  with  this  there  must 
be  increased  metabolism  of  the  tissues,  and  particuhirly  of  the  muscular 
tissues,  since  at  the  same  time  the  amount  of  urea  in  the  urine  is 
increased.  Every  one  is  familiar  with  the  rapid  wasting  which  is  such 
a  characteristic  of  high  fever;  it  must  indicate  not  only  too  rapid 
metabolism  of  the  body,  but  also  insufficient  time  for  the  tissues  to  build, 
themselves  up.  In  fever  then  there  may  be  supposed  to  be  some  inter- 
ference in  the  ordinary  channel  by  which  the  skin  is  able  to  communi- 
cate to  the  nervous  system  the  necessity  of  an  increased  or  diminislied 
production  of  heat  in  the  muscles  and  other  tissues.  In  consequence  of 
this,  and  in  spite  of  the  condition  of  heat  of  the  surface  of  the  body, 
the  production  of  heat  goes  on  at  an  abnormal  rate.  It  is  not  certain 
in  what  way  the  centre  acts,  whether  it  is  one  which  keeps  the  meta- 
bolism in  check,  and  when  out  of  gear  it  is  no  longer  able  to  do  this,  oi 
whether,  on  the  other  hand,  it  is  a  centre  by  means  of  which  the  meta- 
bolism of  the  tissues  may  be  increased  by  stimuli  jjroceeding  from  it. 
Impulses  from  the  skin  would,  according  to  these  two  possible  modes 
of  action,  act  either  in  the  direction  of  increasing  its  inhibitory  action, 
or  in  the  direction  of  increasing  or  of  diminishing  the  different  stimuli 
causing  increased  production. 

Influence  of  Extreme  Heat  and  Cold. — In  connection  with  the 
regulation  of  animal  temperature,  and  its  maintenance  in  health  at  the 
normal  height,  may  be  noted  the  result  of  circumstances  too  powerful, 
either  in  raising  or  lowering  the  heat  of  the  body,  to  be  controlled  by  the 
proper  regulating  apparatus.  AValther  found  that  rabbits  and  dogs  kept 
exposed  to  a  hot  sun,  reached  a  temperature  of  46°  C.  (114.8°  F.),  and 
then  died.  Cases  of  sunstroke  furnish  us  with  several  examples  in 
the  case  of  man;  for  it  would  seem  that  here  death  ensues  chiefly  or 
solely  from  elevation  of  the  temperature. 

The  effect  of  mere  loss  of  bodily  temperature  in  man  is  less  well  known 
than  the  effect  of  heat.  From  experiments  by  "Walther,  it  appears  that 
rabbits  can  be  cooled  down  to  8.9°  C.  (48°  F.),  before  they  die,  if  arti- 
ficial respiration  be  kept  up.  Cooled  down  to  17.8°  C.  (G4°  F.),  they 
cannot  recover  unless  external  Avarmth  be  applied  together  with  the 
employment  of  artifical  respiration.  Rabbits  not  cooled  below  25°  C- 
(77°  F.)  recover  by  external  warmth  alone. 


OHAPTEE  XIII. 

EXCRETION. 

We  have  now  considered  the  methods  by  which  the  food  is  digested 
and  prepared  for  absorption,  as  well  as  the  methods  by  which  the  changed 
materials  reach  the  general  blood-stream,  either  by  means  of  the  lymph- 
atics of  the  intestinal  wall  or  by  the  capillaries  of  the  portal  circulation. 
We  have  also  discussed  the  most  difficult  problems  of  physiology,  viz., 
those  concerned  with  the  exact  changes  which  take  place  in  the  tissues 
and  organs  of  the  body,  when  they  are  supplied  with  the  food  necessary 
for  life.  We  have  mentioned  the  chief  forms  in  which  the  waste  mate- 
rials resulting  from  the  metabolism  of  the  tissues  leave  the  body.  We 
have  seen  how  carbon  dioxide  and  other  matters  are  eliminated  by  the 
lungs,  and,  further,  we  have  devoted  some  time  to  the  consideration  of 
the  amount  and  composition  of  the  faeces.  The  highly  important  func- 
tion of  the  kidneys,  in  excreting  the  urine,  and  thus  removing  certain 
waste  materials,  and  the  functions  of  the  skin  remain,  and  it  is  to  these 
that  we  must  now  direct  our  attention. 

The  Structure  and  Functions  of  the  Kidneys. 

The  kidneys  are  two  in  number,  and  are  situated  deeply  in  the  lum- 
bar region  of  the  abdomen  on  either  side  of  the  spinal  column  behind 
the  peritoneum.  They  correspond  in  position  to  the  last  two  dorsal  and 
two  upper  lumbar  vertebrse;  the  right  being  slightly  below  the  left  in 
consequence  of  the  position  of  the  liver  on  the  right  side  of  the  abdo- 
men. They  are  about  4  inches  long,  2^  inches  broad,  and  1^  inches 
thick.     The  weight  of  each  kidney  is  about  4|-  oz. 

Structure. — The  kidney  is  covered  by  a  tough  fibrous  capsule,  which 
is  slightly  attached  by  its  inner  surface  to  the  proper  substance  of  the 
organ  by  means  of  very  fine  fibres  of  areolar  tissue  and  minute  blood- 
vessels. From  the  healthy  kidney,  therefore,  it  may  be  easily  torn  off 
without  injury  to  the  subjacent  cortical  portion  of  the  organ.  At  the 
hilus  or  notch  of  the  kidney,  it  becomes  continuous  with  the  external 
coat  of  the  upper  and  dilated  part  of  the  ureter  (fig.  287). 

On  dividing  the  kidney  into  two  equal  parts  by  a  section  carried 

4G0 


EXCREIION. 


4G1 


through  its  long  convex  border  (fig.  287),  the  main  part  of  its  substance 
is  seen  to  be  composed  of  two  cliief  portions  called  respectively  cortical 
and  medullar ij,  the  latter  being  also  sometimes  called  pyramidal,  from 
the  fact  of  its  being  composed  of  about  a  dozen  conical  bundles  of  urine 
tubes,  each  bundle  forming  what  is  called  a  pyramid.  The  upper  jiart 
of  the  ureter  or  duct  of  the  organ,  is  dilated  into  the  pelvis  ;  and  this, 
again,  after  separating  into  two  or  three  principal  divisions,  is  finally 
subdivided  into  still  smaller  portions,  varying  in  number  from  about  8 
to  12,  or  even  more,  and  called  cahjces.  Each  of  these  little  calyces  or 
cups,  which  are  often  arranged  in  a  double  row,  receives  the  pointed 


.y" '/ 


\ 


Fig.  ~'ttr 


Fig.  28s 


Fig.  287.— Plan  of  a  longitudinal  section  through  the  pehns  and  substance  of  the  right  kidney, 
^  ;  a,  the  cortical  substance  :  6,  b,  broad  partof  the  pyramids  of  Malpighi;  c,  c,  the  divisions  of  the 
pelvis  named  calyces,  laid  open  ;  c',  one  of  those  unopened  ;  d,  summit  of  the  pyramids  of  papilltc 
projecting  into  calyces  ;  e,  c,  section  of  the  narrow  part  of  two  pyramids  near  the  calyces;  p,  pel- 
vis or  enlarged  divisions  of  the  ureter  within  the  kidney;  it,  the  ureter;  s,  the  sinus;  /i,  the  hilus. 

Fig.  288.— A.  Portion  of  a  secreting  tubule  from  the  cortical  substance  of  the  kiduej*.  b.  The  epi- 
thelial or  gland-cells.     X  ("OO  times. 

extremity  ox  papilla  of  a  pyramid.  Sometimes,  however,  more  than  one 
papilla  is  received  by  a  calyx. 

The  kidney  is  a  compound  tubular  gland,  and  both  its  cortical  and 
medullary  portions  are  composed  essentially  of  tubes,  the  tuhuli  urini- 
feri,  which,  by  one  extremity,  in  the  vortical  portion,  end  commonly  in 
little  saccules  containing  blood-vessels,  called  Malpiyhian  bodies,  and, 
by  the  other,  opened  through  the  papillre  into  the  pelvis  of  the  kidney, 
and  thus  discharge  the  urine  which  flows  through  them. 

In  the  pyramids  the  tubes  are  chiefly  straight — dividing  and  diverg- 
ing as  they  ascend  through  these  into  the  cortical  portion;  while  in  the 
latter  region  they  spread  out  more  irregularly,  and  become  much 
branched  and  convoluted. 

Tubuli  Uriniferi. — The  tubuli  uriniferi  (fig.  288)  are  composed  of 


402 


HANDBOOK    OF    PHYSIOLOGY. 


a  nearly  homogeneous  membrane,  and  are  lined  internally  by  epithelium. 
They  vary  considerably  in  size  in  different  parts  of  their  course,  but  are, 
on  an  average,  about  g-fg-  of  an  inch  {^^  mm.)  in  diameter,  and  are  found 


Fig.  a89.— A  diagram  of  the  sections  of  uriniferous  tubes.  A,  Cortex  limv'-ed  externally  by  the 
capsule;  a,  subcapsular  layer  not  containing;  Malpighian  corpuscles;  a',  inner  stratunn  of  cort-ex, 
also  without  Malpighian  capsules  ;  B,  boundary  layer;  C,  papillary  part  next  ^.be  boundary  layer  ; 
1,  Bowman's  capsules  of  Malpighian  corpuscle;  2,  neck  of  capsule;  3,  proximal  covwoluted  tubule;  4, 
spiral  tubule;  5.  descending  limb  of  Henle's  loop;  G,  the  loop  proper;  7,  thicl<  part  of  the  ascending 
limb  ;  8,  spiral  part  of  ascending  limb;  9,  narrow  ascending  limb  in  the  medullary  rny;  10,  the  ir- 
regular tubule;  11,  the  intercalated  section,  or  the  distal  convoluted  tubule;  12,  thi  curved  collect- 
ing tubule;  13,  the  straightcollecting  tubule  of  the  medullary  ray  ;  14,  the  collecting  tube  of  the 
boundary  layer;  1.5,  the  laige  collecting  tube  of  the  papillary  part  which,  3oinirig  with  similar 
tubes,  forms  the  duct.    (Klein.) 

to  be  made  up  of  several  distinct  sections  which  differ  from  one  another 
very  markedly,  both  in  situation  and  structure.  According  to  Klein, 
the  following  segments  may  be  made  out:  (1)  The  Malpighian  corpus- 


EXCRETION. 


4G3 


de  (figs.  289,  294),  composed  of  a  hyaline  membrana  propria,  thickened 
by  a  varying  amount  of  fibrous  tissue,  and  lined  by  flattened  nucleated 
epithelial  plates.  This  capsule  is  the  dilated  extremity  of  the  urinif- 
erous  tubule,  and  contains  within  it  a  glomerulus  of  convoluted  capil- 
lary blood-vessels  supported  by  connective  tissues,  and  covered  by  flat- 
tened epithelial  plates.  The  glomerulus  is  connected  with  an  efferent 
and  an  afferent  vessel.  (2)  The  constricted  neck  of  the  capsule  (fig. 
289,  2),  lined  in  a  similar  manner,  connects  it  with  (3)  The  Proximal 
convoluted  tubule,  which  forms  several  distinct  curves  and  is  lined  with 


^«®a32J2SaKissE=!=«3E!EIS!5t^^ 


Fifr.  290.— From  a  vertical  section  through  the  kidney  of  a  dog— the  capsule  of  which  is  supposed 
to  be  on  the  riglit.  a,  the  capillaries  of  the  Malpighian  corpuscle — viz.,  the  glomerulus,  are  ar- 
ranged in  lobules;  ?i,  neck  of  capsule  ;  c,  convoluted  tubes  cut  in  various  directions  ;  6,  irregular 
tubule  ;  d,  e,  and/,  are  straight  tubes  running  toward  capsules  forming  a  so-called  medullary  ray; 
d,  collecting  tube  ;  e,  spiral  tube;  /,  narrow  section  of  ascending  limb.  X  3H0.  (Klein  and  Noble 
Smith.) 

short  columnar  cells,  which  vary  somewhat  in  size.  The  tube  next 
passes  almost  vertically  downward,  forming  (4)  The  Spiral  Tubule, 
which  is  of  much  the  same  diameter,  and  is  lined  in  the  same  way  as 
the  convoluted  portion.  So  far  the  tube  has  been  contained  in  the  cortex 
of  the  kidney;  it  now  passes  vertically  downward  through  the  most 
external  part  (boundary  layer)  of  the  Malpighian  pyramid  into  the  more 
internal  part  (papillary  layer),  where  it  curves  up  sharply,  forming 
altogether  the  (5  and  6)  Loop  of  Henle,  which  is  a  very  narrow  tube 
lined  with  flattened  nucleated  cells.  Passing  vertically  upward  just  as 
the  tube  reaches  the  boundary  layer  (7),  it  suddenly  enlarges  and  be- 
comes lined  with  polyhedral  cells.     (8)  About  midway  in  the  boundary 


464 


HANDBOOK    OF    PHYSIOLOGY. 


layer  the  tube  again  narrows,  forming  the  ascending  spiral  of  Henle's 
loop,  but  is  still  lined  with  polyhedral  cells.  At  the  point  where  the  tube 
enters  the  cortex  (9)  the  ascending  limb  narrows,  but  the  diameter 
varies  considerably;  here  and  there  the  cells  are  more  flattened,  but 
both  in  this  as  in  (8),  the  cells  are  in  many  places  very  angular,  branched, 
and  imbricated.  It  then  Joins  (10)  the  "irregular  tubule,"  which  has  a 
very  irregular  and  angular  outline,  and  is  lined  with  angular  and  imbri- 
cated cells.  The  tube  next  becomes  convoluted  (11),  forming  the  distal 
convoluted  tube  or  intercalated  section  of  ScJiweigger-Seidel,  which  is 
identical  in  all  respects  with  the  proximal  convoluted  tube  (13  and  13). 
The  curved  and  straight  collecting  tubes,  the  former  entering  the  latter 


Fig.  291 — Transverse  section  of  arena!  papilla;  a,  large  tubes  or  papillary  ducts;  6,  c,  andrf,  smaller 
tubes  of  Henle;  e,  /,  blood  capillaries,  distinguished  by  their  flatter  epithelium.    (Cadiat.) 


at  right  angles,  and  the  latter  passing  vertically  downward,  are  lined 
with  polyhedral,  or  spindle-shaped,  or  flattened,  or  angular  cells.  The 
straight  collecting  tube  now  enters  the  boundary  layer  (14)  and  passes 
on  to  the  papillary  layer,  and,  joining  with  other  collecting  tubes,  forms 
larger  tubes,  which  finally  open  at  the  apex  of  the  papilla.  These  col- 
lecting tubes  are  lined  with  transparent  nucleated  columnar  or  cubical 
cells  (14,  15). 

The  cells  of  the  tubules  with  the  exception  of  Henle's  loop  and  all 
parts  of  the  collecting  tubules,  are,  as  a  rule,  possessed  of  the  intra- 
nuclear as  well  as  of  the  intra- cellular  network  of  fibres,  of  which  the 
vertical  rods  are  most  conspicuous. 

In  some  places,  it  is  stated  that  a  distinct  membrane  of  flattened 
cells  can  be  made  out  lining  the  lumen  of  the  tubes  {centrotubular  mem- 
brane). 


EXCRETION. 


465 


Blood-Vessels. 

Blood-supply. — In  connection  with  the  general  distribution  of  blood- 
vessels to  the  kidney,  the  MalpigMan  Corpuscles  must  be  further  con- 
sidered.    They  (fig.  293)  are  found  only  in  the  cortical  part  of  the  kid- 
./  ney,  and  are  confined  to  the  central 

part,  which,  however,  makes  up  about 
seven-eighths  of  the  whole  cortex. 
On  a  section  of  the  organ,  some  of 
them  are  just  visible  to  the  naked 
eye  as  minute  red  points;  others  are 
too  small  to  be  thus  seen.  Their 
average  diameter  is  about  ystt  of  an 
inch  {\  mm.).  Each  of  them  is  com- 
posed, as  we  have  seen  above,  of  the 
dilated  extremity  of  an  uriniferous 
tube,  or  Malpighian  capsule,  which 
encloses  a  tuft  of  blood-vessels. 

The  renal  artery  divides  into  sev- 
eral branches,  which,  passing  in  at 
the  hiluB  of  the  kidney,  and  covered 
by  a  fine  sheath  of  areolar  tissue  de- 
rived from  the  capsule,  enter  the  sub- 
stance of  the  organ  chiefly  in  the  in- 
tervals between  the  papillag,  and  at  the 
junction  between  the  cortex  and  the 
boundary  layer.  The  main  branches 
then  pass  almost  horizontally,  form- 
ing more  or  less  com^:»lete  arches  and 
giving  off  branches  upward  to  the 
cortex  and  downward  to  the  medulla. 
The  former  are  for  the  most  part 
straight;  they  pass  almost  vertically 
par/of  af4TaTrcS'UZ'^i^bl.^L're?y:c;  to  the  surfacc  of  the  kidney,  giving 
;^l2SasV4^ar;:da,;!^:;'r^S^;i^so!  off  laterally  in  all  directions    longer 

and  shorter  branches,  which  ulti- 
mately supply  the  Malpighian  bodies. 
The  small  afferent  artery  (figs.  293  and  294)  which  enters  the  Malpig- 
hian corpuscle,  breaks  up  in  the  interior  as  before  mentioned  into  a 
dense  convoluted  and  looped  capillary  plexus,  which  is  ultimately  gath- 
ered up  again  into  several  small  efferent  vessels,  comparable  to  minute 
veins,  which  leave  the  capsule  at  one  or  more  places  near  the  point  at 


capill 

cortex;/,  capillaries  of  medulla;  g,  venous 
arch  ;  h,  straight  veins  of  medulla;  j,  vena  stel 
lula;  I,  interlobular  veiu.    (Cadiat.) 


466 


HANDBOOK    OF    PHYSIOLOGY. 


which  the  afferent  artery  enters  it.  On  leaving,  they  do  not  immediately 
join  other  small  veins  as  might  have  been  expected,  but  again  breaking 
up  into  a  network  of  capillary  vessels,  are  distributed  on  the  exterior  of 


Fig.  a93.— Diagram  showing  the  relation  of  the  Blalpighian  body  to  the  uriniferous  ducts  and 
blood-vessels,  a,  one  of  the  interlobular  arteries;  a',  afferent  artery  passing  into  the  glomerulus  ; 
c,  capsule  of  the  Malpighian  body,  forming  the  termination  of  and  continuous  with  t,  the  uriniferous 
tube  ;  e',  e',  efferent  vessels  which  subdivide  in  the  plexus,  p,  surrounding  the  tube,  and  finally 
term.inate  in  the  branch  of  the  renal  vein  e  (after  BowmanJ). 

the  tubule.     After  this  second  breaking  up  the  capillary  plexus  termi- 
nates in  a  small  vein,  which,  by  union  with  others  like  it,  helps  to  form 


Fig.  294.— Malpighian  capsule  and  tuft  of  capillaries,  injected  through  the  renal  artery  with 
colored  gelatin,  a,  glomerular  vessels  ;  b,  capsule  ;  c,  anterior  capsule;  d,  glomerular  artery  ;  e, 
efferent  veins;  /,  epithelium  of  tubes.    (Cadiat.) 


the  radicles  of  the  renal  vein.  These  small  veins  pass  into  others  which 
form  venous  arches  corresponding  to  the  arterial  arches,  but  which  are 
more  distinct,  situated  between  the  medulla  and  cortex. 


EXCKETION. 


467 


Thus,  iu  the  kidney,  tlic  lilood  eiitcTing  hy  tlu'  renal  artery,  traverses 
two  sets  of  capilliiries  before  enit'r<,'inj,^  by  the  renal  vein,  an  arrangement 
which  may  be  compared  to  tha portal  system  in  miniuture. 

The  tuft  of  vessels  within  the  Malpighian  capsule  in  the  course  of  de- 
velopment has  been  thrust  into  the  dilated  extremity  of  the  urinary 
tubule,  which  finally  completely  invests  it.  Thus  within  the  Malpighian 
capsule  there  are  two  layers  of  squamous  epithelium,  a  parietal  layer 
lining  the  capsule  proper,  and  a  visceral  or  reflected  layer  immediately 
covering  the  vascular  tuft  (hg.  295),  and  sometimes  dipping  down  into 
its  interstices.  Tliis  reflected  hiyer  of 
epithelium  is  readily  seen  in  young 
subjects,  but  cannot  always  be  demon- 
strated iu  the  adult.  (See  figs.  295 
and  296.) 


Fig.  295. 


Fig.  296. 


Fig.  295.— Transverse  sectiou  of  a  developing  Malpighian  capsule  and  tuft  (human),  x  300. 
From  a  fcEtus  at  about  the  fourth  month;  o,  flattened  cells  growing  to  form  the  capsule;  b,  more 
rounded  cells,  coutimious  witli  the  above,  reflected  round  c,  and  finally  enveloping  it;  c,  mass  of 
embryonic  cells  which  will  later  become  developed  into  blood-vessels.     (W.  Pye.) 

Fig.  29G.— Kpithelial  elements  of  a  Malpighian  capsule  and  tuft,  with  the  commencement  of  a 
urinary  tubule  showing  the  afferent  and  efferent  vessel ;  a,  layer  of  flat  epithelium  forming  the 
capsule;  b,  similar,  but  rather  larger  epithelial  cells,  placed  in  the  walls  of  the  tube;  c.  cells,  covering 
the  vessels  of  the  capillary  tuft;  d.  conimeucenient  of  the  tubule,  somewhat  narrower  that  the  rest 
of  it.    (W.  Pye.) 

The  vessels  which  enter  the  medullary  layer  break  up  into  smaller 
arterioles,  which  pass  through  the  boundary  layer,  and  proceed  in  a 
straight  course  between  the  tubules  of  the  papillary  layer,  giving  off  on 
their  way  branches,  which  form  a  fine  arterial  meshwork  around  the 
tubes,  and  ending  in  a  similar  plexus  from  which  the  venous  radicles 
arise. 

Besides  the  small  afferent  arteries  of  the  M:il})ighian  bodies,  there 
are,  of  course,  others  which  are  distributed  in  the  ordinary  manner,  for 
the  nutrition  of  the  different  parts  of  the  organ;  and  in  the  pyramids, 
between  the  tubes,  there  are  numerous  straight  vessels,  the  vasa  recta, 
some  of  which  arc  branches  of  rasa  efferent i((  from  Malpighian  bodies, 
and  therefore  coni])ar;iblc  to  the  \enous  ])loxus  around  the  tubules  in 


468  HANDBOOK    OF    PHYSIOLOGY. 

the  cortical  portion,  while  others  arise  directly  as  small  branches  of  the 
renal  arteries. 

Between  the  tubes,  vessels,  etc.,  which  make  up  the  substance  of 
the  kidney,  there  exists,  in  small  quantity,  a  fine  matrix  of  areolar 
tissue. 

Nerves. — The  nerves  of  the  kidney  are  derived  from  the  renal  plexus 
of  each  side.  This  consists  of  both  medullated  and  non-medullated 
nerve-fibres,  the  former  of  varying  size,  and  of  nerve-cells.  The  renal 
plexus  is  derived  from  the  solar  plexus,  particularly  from  the  semilunar 
ganglion.  The  renal  plexus  is  thus  indirectly  connected  with  the  vagi  and 
with  the  splanchnic  nerves.  It  is  also  directly  connected  with  them  by 
fibres  which  pass  to  them  without  first  joining  the  solar  plexus.  Fibres 
from  the  anterior  roots  of  the  eleventh,  twelfth,  and  thirteenth  dorsal 
nerves  in  the  dog  also  pass  to  the  same  plexus,  either  directly  through 
the  sympathetic  chain  or  by  first  passing  into  the  solar  plexus. 


Fig.  297.— Epithelium  of  the  bladder;  o,  one  of  the  cells  of  the  first  row;  6,  a  cell  of  the  second  row; 
c,  cells  in  situ,  of  first,  second,  and  deepest  layers.    (Obersteiner.) 

The  Ureters. — The  duct  of  each  kidney,  or  ureter,  is  a  tube  about 
the  size  of  a  goose-quill,  and  from  twelve  to  sixteen  inches  in  length, 
which,  continuous  above  with  the  pelvis  of  the  kidney,  ends  below  by 
perforating  obliquely  the  walls  of  the  bladder,  and  opening  on  its  inter- 
nal surface. 

Structure. — It  is  constructed  of  three  principal  coats  {a)  an  outer, 
tough,  fibrous  and  elastic  coat;  {h)  a  middle  muscular  cout,oi  which  the 
fibres  are  unstriped,  and  arranged  in  three  layers — the  fibres  of  the  cen- 
tral layer  being  circular,  and  those  of  the  other  two  longitudinal  in 
direction;  and  (c)  an  internal  mucous  lining  continuous  with  that  of 
the  pelvis  of  the  kidney  above,  and  of  the  urinary  bladder  below.  The 
epithelium  of  all  these  parts  (fig.  297)  is  alike  stratified  and  of  a  some- 
what peculiar  form ;  the  cells  on  the  free  surface  of  the  mucous  mem- 
brane being  usually  spheroidal  or  polyhedral  with  one  or  more  spherical 
or  oval  nuclei;  while  beneath  these  are  pear-shaped  cells,  of  which  the 
broad  ends  are  directed  toward  the  free  surface,  fitting  in  beneath  the 
cells  of  the  first  row,  and  the  apices  are  prolonged  into  processes  of  va- 


EXCRETIOK.  iOU 

rious  lengths,  among  which,  again,  the  deepest  cells  of  the  epithelium 
are  found  spheroidal,  irregularly  oval,  spindle-shaped  or  conical. 

The  Urinary  Bladder. — The  urinary  bladder,  which  forms  a  re- 
ceptacle for  the  temporary  lodgment  of  the  urine  in  the  intervals  of  its 
expulsion  from  the  bod3\  is  more  or  less  pyriform,  its  widest  part,  which 
is  situate  above  and  behind,  being  termed  the  fundus;  and  the  narrow 
constricted  portion  in  front  and  below,  by  which  it  becomes  continuous 
with  the  urethra,  being  called  its  cervix  or  neck. 

Structure. — It  is  constructed  of  four  principal  coats —  serous,  mus- 
cular, areolar  or  submucous,  and  mucous,  {a.)  The  serous  coat,  which 
covers  only  the  posterior  and  upper  part  of  the  bladder,  has  the  same 
structure  as  that  of  the  peritoneum,  with  which  it  is  continuous,  (b) 
The  fibres  of  the  muscular  coat,  which  are  unstriped,  are  arranged  in 
three  principal  layers,  of  which  the  external  and  internal  have  a  general 
longitudinal,  and  the  middle  layer  a  circular  direction.  The  latter  are 
especially  develoi^ed  around  the  cervix  of  the  organ,  and  are  described 
as  forming  a  sphincter  vesicce.  The  muscular  fibres  of  the  bladder,  like 
those  of  the  stomach,  are  arranged  not  in  simple  circles,  but  in  figure- 
of-8  loops,  (c)  The  areolar  or  submucous  coat  is  constructed  of  connec- 
tive tissue  with  a  large  proportion  of  elastic  fibres,  {d)  The  mucous 
membrane,  which  is  rugose  in  the  contracted  state  of  the  organ,  does 
not  differ  in  essential  structure  from  mucous  membranes  in  general. 
Its  epithelium  is  stratified  and  closely  resembles  that  of  the  pelvis  of  the 
kidney  and  the  ureter  (fig.  297). 

The  mucous  membrane  is  provided  with  mucous  glands,  which  are 
more  numerous  near  the  neck  of  the  bladder. 

The  bladder  is  well  provided  with  blood-  and  lymph-vessels,  and  with 
nerves.  The  latter  are  both  medullated  and  non-medullated  fibres, 
both  branches  from  the  sacral  plexus  (spinal)  and  hypogastric  plexus 
(sympathetic).  Ganglion-cells  are  found,  here  and  there,  in  the  course 
of  the  nerve-fibres. 

The  Urine. 

Physical  Properties. — Healthy  urine  is  a  perfectly  transparent,  am- 
ber-colored liquid,  with  a  peculiar,  but  not  disagreeable  odor,  a  bitterish 
taste,  and  slight  acid  reaction.  Its  specific  gravity  varies  from  1015  to 
1025.  On  standing  for  a  short  time,  a  little  mucus  appears  in  it  as  a 
flocculent  cloud,  consisting  chemically,  it  is  said,  of  nncleo-albumiu  and 
not  mucin. 

Chemical  Composition. — The  urine  consists  of  water,  holding  in  solu- 
tion certain  organic  and  saline  matters  as  its  ordinary  constituents,  and 
occasionally  various  other  matters;  some  of  the  latter  are  indications  of 
diseased  states  of  the  system,  and  others  are  derived  from  unusual  articles 
of  food  or  drugs  taken  into  the  stomach. 


4ro 


HANDBOOK    OF    PHYSIOLOGY. 


Chemical  Composition  of  the  Ukine. 

Water 

Solids- 
Urea       

Other  nitrogenous  crystalline  bodies — 

Uric  acid,    principally  in  the  form  of  alka- 
line Urates,  a  trace  only  free. 
Kreatinin,  Xanthin,  Hypoxathin. 
Hippuric  acid. 

Mucus,  Pigments,  and  Ferments. 
Salts : — 

Inorganic — 

Principally  Sulphates,  Phosphates,  and 
Chlorides  of  Sodium  and  Potassium,  with 
Phosphates  of  Magnesium  and  Calcium, 
traces  of  Silicates  and  Chlorides. 


967 


14.230 


10.635 


Organic — 

Lactates,  Hippurates,  Oxalates,  Acetates  and 
Formates,  which  only  appear  occasion- 
ally. 

Sugar    

Gases  (nitrogen  and  carbonic  acid  principally) . 


8.135 


33 

a  trace  sometimes. 


1000 


Reaction. — The  normal  reaction  of  the  urine  is  slightly  acid.  This 
acidity  is  due  to  acid  phosphate  of  sodium,  and  is  less  marked  soon  after 
meals.  The  urine  contains  no  appreciable  amount  of  free  acid,  as  it 
gives  no  precipitate  of  sulphur  with  sodium  hyposulphite.  After  stand- 
ing for  some  time  the  acidity  increases  from  a  kind  of  acid  fermentation, 
due  in  all  probability  to  the  presence  of  mucus  and  fungi,  and  acid 
urates  or  free  uric  acid  is  deposited.  After  a  time,  varying  in  length 
according  to  the  temperature,  the  reaction  becomes  strongly  alkaline 
from  the  change  of  urea  into  ammonium  carbonate,  due  to  the  presence 
of  one  or  more  specific  micro-organisms  {micrococcus  urem).  The  urea 
takes  up  two  molecules  of  water — a  strong  ammoniacal  and  foetid  odor 
appears,  and  deposits  of  triple  phosphates  and  alkaline  urates  take  place. 
This  does  not  occur  unless  the  urine  is  freely  exposed  to  the  air,  or, 
at  least,  until  air  has  had  access  to  it. 


Reaction  of  Urine  in  Different  Classes  of  Animals. — In  most  herbivorous  ani- 
mals the  urine  is  alkaline  and  turbid.  The  difference  depends  not  on  any 
peculiarity  in  the  mode  of  secretion,  but  on  the  difference  in  the  food  on  which 
the  two  classes  subsist ;  for  when  carnivorous  animals,  such  as  dogs,  are  re- 
stricted to  a  vegetable  diet,  their  urine  becomes  pale,  turbid,  and  alkaline  like 
that  of  an  herbivorous  animal,  but  resumes  its  former  acidity  on  the  return  to 
an  animal  diet;  while  the  urine  voided  by  herbivorous  animals,  e.g.,  rabbits, 
fed  for  some  time  exclusively  upon  animal  substances,  presents  the  acid  reac- 
tion and  other  qualities  of  the  urine  of  Carnivora,  its  ordinary  alkalinity 
being  restored  only  on  the  substitution  of  a  vegetable  for  the  animal  diet. 
^  Human  urine  is  not  usually  rendered  alkaline  by  vegetable  diet,  but  it  becomes 
so  after  the  free  use  of  alkaline  medicines,  or  of  the  alkaline  salts  with  car- 


EXCRETION.  471 

bonic  or  vegetable  acids ;  for  these  latter  are  changed  into  alkaline  carbonates 
previous  to  elimination  by  the  kidneys. 

Average  daily  quantity  of  the  chief  urinary  constituents  (modified  from  Parkes). 


Per  Kilo  of 

body  weight. 

Water        .... 

\rm 

cc. 

or 

52^  oz. 

23.         grms. 

Solids — 

Urea 

33.180  grms 

" 

512.4  grains. 

.  5           " 

Kreatiniu    . 

.910 

" 

" 

14.0 

" 

.0140     " 

Uric  Acid 

.555 

" 

" 

8.569 

" 

.0084     " 

Hippuric  Acid    . 

.400 

" 

" 

6.16 

" 

.0060     " 

Pigment  and  Extrac- 

tives    . 

10. 

•' 

" 

154. 

" 

.1510     " 

Sulphuric  Acid  . 

3.012 

u 

" 

30.98 

" 

.0480     " 

Phosphoric  Acid     . 

3.164 

" 

a 

48.80 

" 

.0305     " 

Chlorine 

7.000 

u 

" 

107.8 

. 1260     " 

Ammonia 

.770 

" 

" 

11.8 

•' 

Potassium  . 

2.500 

u 

" 

38.5 

•' 

Sodium 

11.090 

u 

" 

170.78 

" 

Calcium 

.260 

" 

" 

4. 

a 

Magnesium     . 

.207 

*' 

t( 

3. 

u 

72. 

Variations  in  the  Quantity  of  the  Constituents. — From  the  propor- 
tions given  in  the  above  table,  most  of  the  constituents  are,  even  in 
health,  liable  to  variations.  The  variations  of  the  ivater  in  different 
seasons,  and  according  to  the  quantity  of  drink  and  exercise,  have  al- 
ready been  mentioned.  The  water  of  the  urine  is  also  liable  to  be  influ- 
enced by  the  condition  of  the  nervous  system,  being  sometimes  greatly 
increased,  e.g.,  in  hysteria  and  in  some  other  nervous  affections;  and  at 
other  times  diminished.  In  some  diseases  it  is  enormously  increased ; 
and  its  increase  may  be  either  attended  with  an  augmented  quantity  of 
solid  matter,  as  in  ordinary  diabetes,  or  may  be  nearly  the  sole  change, 
as  in  the  affection  termed  diabetes  insipidus.  In  other  diseases,  e.g., 
the  various  forms  of  albuminuria,  the  quantity  ijiay  be  considerably 
diminished.  A  febrile  condition  almost  always  diminishes  the  quantity 
of  water;  and  a  like  diminution  is  caused  by  any  affection  which  draws 
off  a  large  quantity  of  fluid  from  the  body  through  any  other  channel 
than  that  of  the  kidneys,  e.g.,  the  bowels  or  the  skin. 

Method  of  Estimating  the  Solids. — A  useful  rule  for  approximately  estimating 
the  total  solids  in  any  given  specimen  of  healthy  urine  is  to  multiply  the  last 
two  figures  representing  the  specific  gravity  by  2.33.  Thus,  in  urine  of  sp. 
gr.  1025,  2.33  X  25  =  58.25  grains  of  solids,  are  contained  in  1000  grains  of  the 
urine.  In  using  this  method  it  must  be  remembered  that  the  limits  of  erroi-s 
are  much  wider  in  diseased  than  in  healtliy  urine. 

Variations  in  the  Specific  Gravity.— The  average  specific  gravity  of 
the  human  urine  is  about  1020.  The  relative  quantity  of  water  and  of 
solid  constituents  of  which  it  is  composed  is  materially  influenced  by 
the  condition  and  occupation  of  the  body  during  tlie  time  at  which  it  is 


472  HANDBOOK    OF    PHYSIOLOGY. 

secreted ;  by  the  length  of  time  which  has  elapsed  since  the  last  meal ; 
and  by  several  other  accidental  circumstances.  The  existence  of  these 
causes  of  difference  in  the  composition  of  the  urine  has  led  to  the  secre- 
tion being  described  under  the  three  heads  of  Urina  sanguinis^  Urina 
potus,  and  Urina  cidi.  The  first  of  these  names  signifies  the  urine,  or 
that  part  of  it  which  is  secreted  from  the  blood  at  times  in  which 
neither  food  nor  drink  has  been  recently  taken,  and  is  applied  especially 
to  the  urine  which  is  evacuated  in  the  morning  before  breakfast.  The 
term  urina  iMus  indicates  the  urine  secreted  shortly  after  the  intro- 
duction of  any  considerable  quantity  of  fluid  into  the  body:  and  the 
urina  cihi,  the  portions  secreted  during  the  period  immediately  succeed- 
ing a  meal  of  solid  food.  The  last  kind  contains  a  larger  quantity  of 
solid  matter  than  either  of  the  others ;  the  first  or  second,  being  largely 
diluted  with  water,  possesses  a  comparatively  low  specific  gravity.  Of 
these  three  kinds,  the  morning  urine  is  the  best  calculated  for  analysis 
in  health,  since  it  represents  the  simple  secretion  unmixed  with  the 
elements  of  food  or  drink;  if  it  be  not  used,  the  whole  of  the  urine 
passed  during  a  period  of  twenty-four  hours  should  be  taken.  The 
specific  gravity  of  the  urine  may  thus,  consistently  with  health,  range 
widely  on  both  sides  of  the  usual  average.  It  may  vary  from  1015  in 
the  winter  to  1025  in  the  summer ;  but  variations  of  diet  and  exercise,  and 
many  other  circumstances,  may  make  even  greater  differences  than  these. 
In  disease,  the  variation  may  be  greater;  sometimes  descending,  in  albu- 
minuria, to  1004,  and  frequently  ascending  in  diabetes,  when  the  urine 
is  loaded  with  sugar,  to  1050,  or  even  to  1060. 

Quantity. — The  total  quantity  of  urine  passed  in  twenty-four  hours 
is  affected  by  numerous  circumstances.  On  taking  the  mean  of  many 
observations  by  several  experiments,  the  average  quantity  voided  in 
twenty-four  hours  by  healthy  male  adults  from  20  to  40  years  of  age 
has  been  found  to  amount  to  about  52^  fluid  ounces  (1|  to  2  litres). 

Abnormal  Constituents. — In  disease,  or  after  the  ingestion  of  special 
foods,  various  abnormal  substances  occur  in  urine,  of  which  the  follow- 
ing may  be  mentioned — Serum- albumin,  Olobulin,  Ferments  (appar- 
ently present  in  health  also),  Proteoses,  Blood,  Sugar,  Bile  acids  and 
pigments,  Casts,  Fats,  various  Salts  taken  as  a  medicine,  Micro-organ- 
isms of  various  kinds,  and  other  matters. 

The  Solids  of  the  Urine. 

Urea  (CH4"N'20). — Urea  is  the  principal  solid  constituent  of  the 
urine,  forming  nearly  one-half  of  the  total  quantity.  It  is  also  the 
most  important  ingredient,  since  it  is  the  chief  substance  by  which  the 
nitrogen  which  is  derived  from  the  metabolic  changes  in  the  tissues  as 
well  as  that  which  is  derived  from  any  superfluous  food  is  excreted 


EXCRETION. 


473 


from  the  body.     For  its  removal,  the  secretion  of  urine  seems  especially 
provided,  though  urea  itself  is  not  toxic. 

Propei'ties.—JJrea,  like  the  other  solid   constituents  of  the  urine, 
exists  in  a  state  of  solution.     When  in  the  solid  state,  it  appears  in  the 


Fig.  298.— Crystals  of  Urea. 

form  of  delicate  silvery  acicular  crystals,  which,  under  the  microscope, 
appear  as  four-sided  prisms  (fig.  298).  It  may  be  obtained  in  this  state 
by  evaporating  urine  carefully  to  the  consistence  of  honey,  acting  on 
the  inspissated  mass  with  four  parts  of  alcohol,  then  evaporating  the 
alcoholic  solution  to  dryness,  and  purifying  the  residue  by  repeated 
solution  in  water  or  in  alcohol,  and  finally  allowing  it  to  crystallize.  It 
readily  combines  with  some  acids,  like  a  weak  base:  and  may  thus  be 
conveniently  procured  in  the  form  of  crystals  of  nitrate  or  oxalate  of* 
urea  (figs.  299  and  300). 

Urea  is  colorless  when  pure;   when  impure  it  may  be  yellow  or 


Fig.  209.— Crystals  of  Urea  nitrate. 


Fip.  300.— Crystals  of  Urea  oxalate. 


brown:  it  is  without  smell,  and  of  a  cooling  nitre-like  taste;  it  has 
neither  an  acid  nor  an  alkaline  reaction,  and  deliquesces  in  a  moist  and 
warm  atmosphere.  At  15°  C.  (59°  F.)  it  requires  for  its  solution  less 
than  its  own  weight  of  water;  it  is  dissolved  in  all  proportions  by  boil- 
ing water;  but  it  requires  five  times  its  weight  of  cold  alcohol  for  its 
solution.     It  is  insoluble  in  ether.     At  120°  C.  (248°  F.)  it  melts  with- 


474  HANDBOOK    OF    PHYSIOLOGY. 

out  undergcing  decomposition;  at  a  still  higher  temperature  ebullition 
takes  place,  and  carbonate  of  ammonium  sublimes.  When  heated  with 
water  in  a  sealed  tube  to  100°  C,  urea  splits  up  into  carbonic  acid  and 
ammonia;  when  heated  to  a  high  temperature  urea  loses  ammonia  and 
first  yields  hiuret,  C2H5N3O2J  which  gives  a  rose  color  with  caustic  potash 
and  a  trace  of  copper  sulphate,  and  afterward  cycmuric  acid,  C3H3O3N3, 
which  gives  a  violet  color  with  caustic  potash  and  a  trace  of  copper  sul- 
phate. It  is  decomposed  b}'  sodium  hypochlorite  or  hypobromite  or  by 
nitrous  acid,  with  evolution  of  X.  It  forms  compounds  with  acids,  of 
which  the  chief  are  urea  hydrochloride,  CH4N20.IICL;  urea  nitrate, 
CH4iSi20HiSr03;  and  urea  phosphate,  CH4N2O.H3PO4.  It  forms  com- 
pounds with  metals  such  as  HgO.CH4]SI"20;  with  silver  CH2N20Ag2; 
and  with  salts  such  as  HgCl2  and  HgNOs. 

Chemical  Nature. — Urea  is  isomeric  with  ammonium  cyanate 
NH4,CN0c     It  was  first  of  all  artificially  prepared  from  that  substance. 

It  may  also  he  produced   artificially  by  treating   carbonyl  chloride  (CO  CI2) 

OP  FT 
■withammonia;  or  by  heating  ethyl  carbonate  icith  ammonia  CO  Qfi^rr^  +  2  NH3  = 

NHo 
CON0H4  2C2H6O ;     by    heating    ammonium    carbonate    CO  qj^-tt   =C0N2H4-|- 

HoO ;  by  adding  water  to  cyanamide  CN. NH2,  or  by  evaporating  ammonium 
cyanate  in  aqueous  solution. 

It  is  usually  considered  to  be  a  diamide  of  carbonic  acid,  in  other 
words,  carbonic  acid,  CO  (OH) '2,  with  two  of  hydroxyl,  (OH) '2,  replaced 
by  two  of  amidogen  (NH2)'2-  It  may  also  be  written  as  if  it  were  a 
monamide  of  carbamic  acid  (COOHNH2),  thus  CONH2.NH2;  one  of 
amidogen,  N'H2,  in  the  latter  replacing  one  of  hydroxyl  in  the  former. 
Decomposition  of  the  urea  with  development  of  ammonium  carbonate 
takes  place  from  the  action  of  the  bacteria  (micrococcus  ureae),  when 
urine  is  kept  for  some  days  after  being  voided,  and  explains  the  ammo- 
niacal  odor  then  evolved.  The  urea  is  sometimes  decomposed  before  it 
leaves  the  bladder,  when  the  mucous  membrane  is  diseased,  and  the 
mucus  secreted  by  it  is  abundant;  but  decomposition  does  not  often  occur 
unless  atmospheric  germs  have  had  access  to  the  urine. 

Variations  in  the  Quantitij  excreted. — The  quantity  of  urea  excreted 
is,  like  that  of  the  urine  itself,  subject  to  considerable  variation.  For 
a  healthy  adult  about  512.4  grains  (about  33.18  grms.)  per  diem  may  be 
taken  as  rather  a  high  average.  Its  percentage  in  healthy  urine  is  from 
1.5  to  2.5.  Its  amount  is  materially  influenced  by  diet,  being  greater 
when  animal  food  is  exclusively  used,  less  when  the  diet  is  mixed,  and 
least  of  all  with  a  vegetable  diet.  As  a  rule,  men  excrete  a  larger  quan- 
tity than  women,  and  persons  in  the  middle  periods  of  life  a  larger 
quantity  than  infants  or  old  people.     The  quantity  of  urea  excreted  by 


EXCRETIOK  475 

children,  relatively  to  their  body-weight,  is  much  greater  than  by  adults; 
Thus  the  quantity  of  urea  excreted  per  kilogram  of  weight  was  found  to 
be,  in  a  child,  0.8  grm.;  in  an  adult  only  0.4  grm.  Regarded  in  this 
way,  too,  the  excretion  of  carbonic  acid  gives  similar  results,  the  pro- 
l^ortions  in  the  child  and  adult  being  as  82 :  34. 

The  quantity  of  urea  does  not  necessarily  increase  and  decrease  with 
that  of  the  urine,  though  on  the  whole  it  would  seem  that  whenever  the 
amount  of  urine  is  much  augmented,  the  quantity  of  urea  also  is  usually 
increased;  and  it  appears  that  the  quantity  of  urea,  as  of  urine,  may  be 
especially  increased  by  drinking  large  quantities  of  water.  In  various 
diseases  the  quantity  is  reduced  considerably  below  the  healthy  stan- 
dard, while  in  other  affections  it  is  above  it. 

Quantitaiive  Estimation. — There  are  two  cliief  methods  of  estimating  the 
amount  of  urea  in  the  urine.  (1.)  By  decomposing  it  hy  means  of  an  alkaline 
solution  of  sodium  hypobromite,  or  hj'pochlorite,  and  calculating  the  amount 
in  a  measured  quantity,  by  collecting  and  measuring  the  amount  of  nitrogen 
evolved  under  such  circumstances.  Urea  contains  nearly  half  its  weight  of 
niti'ogen,  hence  the  amount  of  the  gas  collected  may  be  taken  as  a  measui-e  of 
the  urea  decomposed,  remembering  that  1  litre  of  nitrogen  at  the  standard 
temperature  and  pressure  weighs  14  X  08936,  or  1.251  grms.  The  percentage 
of  urea  can  thus  be  readily  calculated  from  the  volume  of  nitrogen  evolved 
from  a  measured  quantity  of  the  urine,  but  this  calculation  is  avoided  by 
graduating  the  tube  in  which  the  nitrogen  is  collected  with  numbers  which 
indicate  the  corresponding  percentage  of  urea.  The  reaction  is  CONo  H4  -j- 
3NaBrO  +  '2NaH0  =  SNaBr  +  3H.0  +  Na.COg  +  N-,.  (2. )  By  precipitating  the 
urea  by  adding  to  a  given  amount  of  urine,  freed  from  sulphates  and  phos- 
phates, a  standard  solution  of  mercuric  niti'ate  from  a  burette,  until  the  whole 
of  it  has  been  thrown  down  in  an  insoluble  form  ;  then  reading  off  the  exact 
amount  of  the  mercuric  niti'ate  solution,  which  it  was  necessary  to  use.  As 
the  amount  of  urea  which  each  cubic  centimetre  of  the  standard  solution  will 
precipitate  is  previously  known,  it  is  easy  to  calculate  the  amount  in  the  sam- 
ple of  urine  taken.  The  precipitate  which  is  formed  was  generally  said  to  be 
composed  of  mercuric  oxide  and  urea.  Some,  however,  now  consider  that  it 
is  a  mixture  of  mercuric  nitrate  itself  and  vn-ea. 


Uric  Acid  (CsIIiN^Os). — Uric  or  lithic  acid  is  rarely  absent  from 
the  urine  of  man  or  animals,  though  in  the  feline  tribe  it  seems  to  be 
sometimes  entirely  replaced  by  urea. 

Propertie!<. — Uric  acid  when  pure  is  colorless,  but  when  deposited 
from  the  urine  is  yellowish-brown.  It  cr3'stallizes  in  various  forms,  of 
which  the  most  common  are  smooth  transparent,  rhomboid  plates, 
diamond-shaped  plates,  hexagonal  tables,  etc.  (fig.  301).  It  is  odorless 
and  tasteless.  It  is  very  slightly  soluble  in  cold  water,  and  a  little  more 
so  in  hot  water,  quite  insoluble  in  alcohol  and  ether.  It  dissolves  freely 
in  solution  of  the  alkaline  carbonates  and  other  salts. 


4'76  HANDBOOK   OF  PHYSIOLOGY. 

The  proportionate  quantity  of  uric  acid  varies  considerably  in  different 
animals.  In  man,  and  Mammalia  generally,  especially  the  Herbivora,  it  is 
comparatively  small.  In  the  w^hole  tribe  of  birds,  and  of  serpents,  on  the  other 
hand,  the  quantity  is  very  large,  greatly  exceeding  that  of  the  urea.  In  the 
urine  of  granivorous  birds,  indeed,  urea  is  rarely  if  ever  found,  its  place  being 
entirely  supplied  by  uric  acid. 

Variations  in  Quantity. — The  quantity  of  uric  acid,  like  that  of 
urea,  in  human  urine,  is  increased  by  the  use  of  animal  food,  and  de- 
creased by  the  use  of  food  free  from  nitrogen,  or  by  an  exclusively  vege- 
table diet.  In  most  febrile  diseases,  and  in  plethora,  it  is  formed  in 
unnaturally  large  quantities;  and  in  gout  it  is  deposited  in  and  around 
joints,  in  the  form  of  urate  of  soda,  of  which  the  so-called  chalk-stones 
of  this  disease  are  principally  composed.  The  average  amount  secreted 
in  twenty-four  hours  is  about  one-third  of  a  gramme. 

Condition  in  the  Urine. — The  condition  in  which  uric  acid  exists  in 
solution  in  the  urine  has  formed  the  subject  of  some  discussion.  The 
uric  acid  exists  as  urate  of  soda,  produced  by  the  uric  acid  as  soon  as  it 
is  formed  combining  with  part  of  the  base  of  the  alkaline  sodium  phos- 
phate of  the  blood.  Hippuric  acid,  which  exists  in  human  urine  also, 
acts  upon  the  alkaline  phosphate  in  the  same  way,  and  increases  still 
more  the  quantity  of  acid  phosphate,  on  the  presence  of  which  it  is 
probable  that  a  part  of  the  natural  acidity  of  the  urine  depends.  It  is 
scarcely  possible  to  say  whether  the  union  of  uric  acid  with  the  bases 
sodium  and  ammonium  takes  place  in  the  blood,  or  in  the  act  of  secre- 
tion in  the  kidney:  the  latter  is  more  likely;  but  the  quantity  of  either 
uric  acid  or  urates  in  the  blood  is  probably  too  small  to  allow  of  this 
question  being  solved. 

Owing  to  its  existence  in  combination  in  healthy  urine,  uric  acid  for 
examination  must  generally  be  precipitated  from  its  bases  by  a  stronger 
acid,  e.g.,  hydrochloric  or  nitric.  When  excreted  in  excess,  however,  it 
is  deposited  in  a  crystalline  form  (fig.  301),  mixed  with  large  quanti- 
ties of  ammonium  or  sodium  urate.  In  such  cases  it  may  be  procured 
for  microscopic  examination  by  gently  warming  the  portion  of  urine 
containing  the  sediment ;  this  dissolves  urate  of  ammonium  and  sodium, 
while  the  comparatively  insoluble  crystals  of  uric  acid  subside  to  the 
bottom. 

The  most  common  form  in  which  uric  acid  is  deposited  in  urine,  is 
that  of  a  brownish  or  yellowish  powdery  substance,  consisting  of  gran- 
ules of  ammonium  or  sodium  urate.  When  deposited  in  crystals,  it  is 
most  frequently  in  rhombic  or  diamond-shaped  lamiu^,  but  other  forms 
are  not  uncommon  (fig,  301).  When  dejDOsited  from  urine,  the  crystals 
are  generally  more  or  less  deeply  colored,  from  being  combined  with 
the  coloring  principles  of  the  urine. 

Tests. — There  are  two  chief  tests  for  uric  acid  besides  the  micro- 


BXCEETION". 


477 


fecopic  evidence  of  its  crystalline  structure:  (1)  The  Mrirexide  test, 
^hich  consists  of  evaporating  to  dryness  a  mixture  of  strong  nitric  acid 
Acd  uric  acid  in  a  water  bath.  This  leaves  a  yellowish-red  residue  of 
Alloxan  (C4H2N2O.1)  and  urea,  and  on  addition  of  ammonium  hydrate,  a 
oeautiful  purple  color  (ammonium  purpurate,  C8H4(NH4)iSr50fi),  deep- 
ened on  addition  of  caustic  potash,  takes  place.  (2)  Schiff's  test  con- 
sists of  dissolving  the  uric  acid  in  sodium  carbonate  solution,  and  of 
dropping  some  of  it  on  a  filter  paper  moistened  with  silver  nitrate.  A 
black  spot  appears,  which  corresponds  to  the  reduction  of  silver  by  the 
uric  acid. 

Hippuric  Acid    (C9H9NO3)   has  long  been  known  to  exist  in  the 
urine  of  herbivorous  animals  in  combination  with  soda.     It  also  exists 


Fig.  301.— Various  forms  of  uric  acid  crystals. 


Fig.  302.— Crystals  of  hippuric  acid. 


naturally  in  the  urine  of  man,  in  a  quantity  equal  or  rather  exceeding 
that  of  the  uric  acid. 

The  quantity  of  hippuric  acid  excreted  is  increased  by  a  vegetable 
diet.  It  appears  to  be  formed  in  the  body  from  benzoic  acid  or  from 
some  allied  substance.  The  benzoic  acid  unites  Avith  glycin,  probably 
in  the  kidneys,  and  hippuric  acid  and  water  are  formed  thus,  CtHeOo 
(Benzoic  acid)  -|-  C2H5NO2  (Glycin)  =  CgHgNO.^  (Hippuric  acid)  +  H2O 
(water).     It  may  be  decomposed  by  acids  into  benzoic  acid  and  glycin. 

Properties. — It  is  a  colorless  and  odorless  substance  of  bitter  taste, 
crystallizes  in  semi-transparent  rhombic  prisms  (fig.  302).  It  is  more 
soluble  in  cold  water  than  uric  acid,  and  much  more  soluble  in  hot 
water.     It  is  soluble  in  alcohol. 

Pigments, — The  pigments  of  the  urine  are  the  following: — 1.  Uro- 
chrome,  a  yellow  coloring  matter,  giving  no  absorption  band;  of  which 
but  little  is  known.  Urine  owes  its  yellow  color  mainly  to  the  pres- 
ence of  this  body.  2.  Urohilin,  an  orange  pigment,  of  which  traces  .may 
be  found  in  nearly  all  urines,  and  which  is  especially  abundant  in  the 
urines  passed  by  febrile  patients.  It  is  characterized  by  a  well-marked 
spectroscopic  absorption  bnnd   at   the  jnnctiou  of  green  and  blue,  best 


478  HA:^rDB00K  of  physiology. 

seen  in  acid  solutions;  and  by  giving  a  green  fluorescence  when  excess 
of  ammonia  with  a  little  chloride  of  zinc  is  added  to  it.  The  very 
v«xed  question  of  the  relation  of  the  pigments  of  urine  to  bile  j^igments 
turns  largely  upon  the  spectroscopic  a^^pearances  of  urobilin;  for  orange- 
colored  solutions  having  the  same  absorption  band  as  urobilin  may  be 
prepared  from  bile  pigments  in  two  diiferent  ways — i,  by  reduction  with 
sodium  amalgam — HydrohiUriihin  (Maly);  ii,  by  oxidation  with  nitric 
acid — Choletelin  (Jaflfe),  and  both  these  bile  derivatives  give  a  fluores- 
cence with  ammonia  and  a  drop  of  chloride  of  zinc.  It  is  not  satisfac- 
torily settled  which  of  these^  if  either,  is  the  same  as  urobilin  of  urine. 
It  is  worth  noting  that  choletelin  maybe  oxidized  a  stage  further;  it 
then  loses  its  absorption  band,  remaining  however  of  a  yellow  color.  It 
is  very  possible  thtit  the  urochrome  of  normal  urine  may  be  this  oxi- 
dized choletelin,  and  that  the  presence  of  the  absorption  band  of  urobilin 
in  urines  may  mean  that  some  of  the  pigment  is  in  the  stage  of  cholete- 
lin ;  i.e.,  that  its  oxidation  is  not  quite  completed. 

Those  who  believe  urobilin  to  be  identical  with  hydrobilirubm  sup- 
pose that  the  bilirubin  is  reduced  by  the  putrefactive  processes  in  the 
intestines,  and  is  conveyed  in  its  reduced  form  by  the  blood  stream  to 
the  kidneys. 

3.  XJro-erytlirin  is  the  pigment  which  is  found  in  the  pink  deposits 
of  urates  which  are  sometimes  seen  in  urines;  it  communicates  a  rich 
red-orange  color  to  urine  when  in  solution,  and  its  solutions  have  two 
broad  faint  absorption  bands  in  the  gTeen. 

4.  Uromelanin.  When  urine  is  boiled  with  strong  acids  it  darkens 
to  a  reddish- brown  color.  This  change,  once  ascribed  to  the  forma- 
tion of  a  new  pigment  uromelanin,  is  now  believed  to  be  due  to  the 
presence  in  urine  of  pyrocatechin  and  allied  bodies  which  are  capable 
of  taking  up  oxygen  when  boiled  with  acids,  yielding  CO2  and  brown 
or  black  residual  products. 

5.  Indigo  is  rarely  found  in  urines,  to  which  it  may  communicate  a 
blue  or  green  color.  Urine  frequently  contains  a  compound  which  is 
either  a  ghicoside,  Indican;  or  more  probably  a  salt  of  indoxyl-sulphuric 
acid.  It  yields  indigo  blue  when  treated  with  strong  hydrochloric  acid 
and  left  to  stand  for  some  hours  exposed  to  the  air;  the  indigo  may  be 
separated  by  treatment  with  boiling  chloroform,  which  takes  it  up, 
forming  a  blue  solution. 

There  is  a  similar  compound  of  skatol  and  sulphuric  acid  which  is 
sometimes  recognized  in  the  urine,  by  the  production  of  a  red  color 
when  nitric  acid  is  added  to  it. 

Many  medicinal  substances  color  the  urine,  for  instance  Ehubarb, 
Santonin,  Senna,  Fuchsine,  Carbolic  Acid. 

Bromides  and  Iodides  yield  Bromine  or  Iodine,  when  nitric  acid  is 
added  to  the  urine  of  patients  taking  these  drugs.     In  the  case  of  iodides 


EXCRETION.  479 

the  liberated  iodine  communicates  a  strong  mahogany  color  to  the  urine 
thus  treated. 

Mucus. — MiicuK  in  the  urine  coiisists  principally  of  the  epithelial 
debris  from  the  mucous  surface  of  the  urinary  passages.  Particles  of 
epithelium,  in  greater  or  less  abundance,  may  be  detected  in  most  sam- 
ples of  urine,  especially  if  it  has  remained  at  rest  for  some  time,  and  the 
lower  strata  are  then  examined  (fig.  303).  As  urine  cools,  the  mucus  is 
sometimes  seen  suspended  in  it  as  a  delicate  opaque  cloud,  but  generally 
it  falls.  In  inflammatory  affections  of  the  urinary  passages,  especially 
of  the  bladder,  mucus  in  large  quantities  is  poured  forth,  and  sjoeedily 
undergoes  decomposition.  The  presence  of  the  decomiaosing  mucus 
excites  chemical  changes  in  the  urea,  whereby  carbonate  of  ammonium 
is  formed,  which,  combining  with  the  excess  of  acid  in  the  superphos- 
phates in  the  urine,  produces  insoluble  neutral  or  alkaline  phosphates 
of  calcium  and  magnesium,  and  phosphate  of  ammonium  and  magne- 
sium. These,  mixing  with  the  mucus,  constitute  the  peculiar  white, 
viscid,  mortar-like  substance  which  collects  ujaon  the  mucous  surface  of 
the  bladder,  and  is  often  passed  with  the  urine,  forming  a  thick  tena- 
cious sediment. 

Extractives. — In  addition  to  those  already  considered,  urine  con- 
tains a  considerable  number  of  nitrogenous  compounds.  These  are 
usually  described  under  the  generic  name  of  Extractives.  Of  these,  the 
chief  are:  (1)  Kreatinin  (C.H^NjO),  a  substance  derived  almost  en- 
tirely from  muscle  taken  as  food,  crystallizing  in  colorless  oblique 
rhombic  prisms;  a  fairly  definite  amount  of  this  substance,  about  15 
grains  (1  grm.),  appears  in  the  urine  daily,  so  that  it  must  be  looked 
upon  as  a  normal  constituent;  it  is  increased  by  increasing  the  ni- 
trogenous constituents  of  the  food;  (2)  Xantliin  (C^N.H^OJ,  when 
isolated,  is  an  amorphous  powder  soluble  in  hot  water;  (3)  Sarkin,  or 
hypo-xa)ithin  (C,N,H^O);  (4)  Oxaluric  acid  (CjH^N.OJ,  in  combi- 
nation with  ammonium  in  the  urine  of  the  new-born  child;  (5)  Allantoin 
(CiHeKiOa).  All  these  extractives  are  chiefly  interesting  as  being  closely 
connected  with  urea,  and  mostly  yielding  that  substance  on  oxidation. 
Leucin  and  tyrosin  can  scarcely  be  looked  upon  as  normal  constituents 
of  urine. 

Saline  Matter. — {a)  The  Sidphtiric  acid  in  the  urine  is  combined 
chiefly  or  entirely  with  sodium  or  potassium;  forming  salts  which  are 
taken  in  very  small  quantity  with  the  food,  and  are  scarcely  found  in 
other  fluids  or  tissues  of  the  body;  for  the  sulphates  commonly  enumer- 
ated among  the  constituents  of  the  ashes  of  the  tissues  and  fluids  are 
for  the  most  part,  or  entirely,  produced  by  the  changes  that  take  jalace 
in  the  burning.  Only  about  one-third  of  the  sulphuric  acid  found  in 
the  urine  is  derived  directly  from  the  food  (Parkes).  Hence  the  greater 
part  of  the  sulphuric  acid  which  the  sulphates  in  the  urine  contain, 


480 


HANDBOOK    OF    PHYSIOLOGY. 


must  be  formed  during  the  metabolism  of  nitrogenotis  foods;  the 
sulphur  of  which  the  acid  is  formed  being  probably  derived  from  the 
decomposing  nitrogenous  tissues,  the  other  elements  of  which  are  re- 
solved into  urea  and  uric  acid.  It  may  be  in  part  derived  also  from  the 
sulphur-holding  taurin  and  cystin,  which  can  be  found  in  the  liver, 
lungs,  and  other  parts  of  the  body,  but  not  generally  in  the  excretions; 
and  which,  therefore,  must  be  broken  up.  The  oxygen  is  supplied 
through  the  lungs,  and  the  heat  generated  during  combination  with  the 
sulphur  is  one  of  the  subordinate  means  by  which  the  animal  tempera- 
ture is  maintained. 

Besides  the  sulphur  in  these  salts,  some  also  appears  to  be  in  the 
urine  uncombined  with  oxygen;  for  after  all  the  sulphates  have  been 
removed  from  urine,  sulphuric  acid  may  be  formed  by  drying  and  burn- 


Fig.  303. 


Fig.  304. 


Fig.  303.— Mucus  deposited  from  ui-ine. 

Fig.  304. — Urinary  sediment  of  triple  phosphates  (large  [prismatic  crystals)  and  urate  of  ammo- 
nium,  from  urine  which  had  undergone  alkaline  fermentation. 


ing  it  with  nitre.  From  three  to  five  grains  of  sulphur  are  thus  daily 
excreted.  The  combination  in  which  it  exists  is  uncertain :  possibly  it 
is  in  some  compound  analogous  to  cystin  or  cystic  oxide.  Sulphuric 
acid  also  exists  normally  in  the  urine  in  combination  with  phenol 
(C'eHeO)  as  phenol-sulphuric  acid  or  its  corresponding  salts,  with 
sodium,  etc. 

(h)  The  pliosplioric  acid  in  the  urine  is  combined  partly  with  the 
alkalies,  partly  with  the  alkaline  earths — about  four  or  five  times  r.s 
much  with  the  former  as  with  the  latter.  In  blood,  saliva,  and  other 
alkaline  fluids  of  the  body,  phosphates  exist  in  the  form  of  alkaline, 
neutral,  or  acid  salts.  In  the  urine  they  are  acid  salts,  viz.,  the  sodium, 
ammonium,  calcium,  and  magnesium  phosphates,  the  excess  of  acid 
being  (Liebig)  due  to  the  appropriation  of  the  alkali  with  which  the 
phosphoric  acid  in  the  blood  is  combined,  by  the  several  new  acids 
which  are  formed  or  discharged  at  the  kidneys,  namely,  the  uric,  hip- 
puric,  and  sulphuric  acids,  all  of  which  are  neutralized  with  soda. 


EXCRETION". 


481 


The  phosphates  are  taken  largely  in  both  vegetable  and  animal  food; 
some  thus  taken  are  excreted  at  once;  others,  after  being  transformed 
and  incorporated  with  the  tissues.  Calcium  phosphate  forms  the  prin- 
cipal earthy  constituent  of  bone,  and  from  the  decomposition  of  the 
osseous  tissue  the  urine  derives  a  large  quantity  of  this  salt.  The  de- 
composition of  other  tissues  also,  but  especially  of  the  brain  and  nerve- 
substance,  furnishes  large  supplies  of  phosphorus  to  the  urine,  which 
phosphorus  is  supposed,  like  the  sulphur,  to  be  united  with  oxygen,  and 
then  combined  with  bases.  The  quantity  is,  however,  liable  to  consid- 
erable variation.  Any  undue  exercise  of  the  brain  and  all  circumstances 
producing  nervous  exhaustion  increase  it.  The  earthy  phosphates  are 
more  abundant  after  meals,  whether  of  animal  or  vegetable  food,  and 
are  diminished  after  long  fasting.     The  alkaline  phosphates   are    in- 


Fig.  3U5.— Crystals  of  Cystin. 


Fig.  306.— Crystals  of  Calcium  Oxalate. 


creased  after  animal  food,  diminished  after  vegetable  food.  Exercise 
increases  the  alkaline,  but  not  the  earthy  phosphates.  Phosphorus 
uncombined  with  oxygen  appears,  like  sulphur,  to  be  excreted  in  the 
urine.  When  the  urine  undergoes  alkaline  fermentation  phosphates  are 
deposited  in  the  form  of  a  urinary  sediment,  consisting  chiefly  of 
ammonio-magnesium  phosphates  (triple  phosphate)  (fig.  304).  '  The 
compound  does  not,  as  such,  exist  in  healthy  urine.  The  ammonia  is 
chiefly  or  wholly  derived  from  the  decomposition  of  urea. 

(c.)  The  Chlorine  of  the  urine  occurs  chiefly  in  combination  with 
sodium  (next  to  urea,  sodium  chloride  is  the  most  abundant  solid  con- 
stituent of  the  urine),  but  slightly  also  with  ammonium,  and,  perhaps, 
potassium.  As  the  chlorides  exist  largely  in  food,  and  in  most  of  the 
animal  fluids,  their  occurrence  in  the  urine  is  easily  understood. 

Occasional  Constituents.— (7//6^^iw  (C3H7N  SO2)  (fig.  305)  is  an 
occasional  constituent  of  urine.  It  resembles  taurin  in  containing  a 
large  quantity  of  sulphur — more  than  25  per  cent.  It  does  not  exist  in 
healthy  urine. 

Another  common  morbid  constituent  of  the  urine  is  Oxalic  acid, 
31 


482  HANDBOOK    OF    PHYSIOLOGY. 

which  is  frequently  deposited  in  combination  with  calcium  (fig.  30G)  as 
a  urinary  sediment.  Like  cystin,  but  much  more  commonly,  it  is  the 
chief  constituent  of  certain  calculi. 

Of  the  other  abnormal  constituents  of  the  urine  which  were  men- 
tioned on  p.  4:72,  it  will  be  unnecessary  to  speak  at  length  in  this  work. 

Gases. — A  small  quantity  of  gas  is  naturally  present  in  the  urine  in 
a  state  of  solution.  It  consists  of  carbonic  acid  (chiefly)  and  nitrogen 
and  a  small  quantity  of  oxygen. 

The  Method  of  the  Excretion  of  Urine. 

The  excretion  of  the  urine  by  the  kidney  is  believed  to  consist  of 
two  more  or  less  distinct  processes— viz.,  (1)  of  Filtration,  by  which 
the  water  and  the  ready-formed  salts  are  eliminated;  and  (2)  of  True 
Secretion,  by  which  certain  substances  forming  the  chief  and  more  im- 
portant part  of  the  urinary  solids  are  removed  from  the  blood.  This 
division  of  function  corresjaonds  more  or  less  to  the  division  in  the 
functions  of  other  glands  of  which  we  have  already  treated.  It  will  be 
as  well  to  consider  them  separately. 

Filtration. — This  part  of  the  renal  function  is  performed  withiii 
the  Malpighian  corpuscles  by  the  renal  glomeruli.  By  it  not  only  the  water 
is  strained  off,  but  also  certain  other  constituents  of  the  urine,  e.g., 
sodium  chloride,  are  separated.  The  amount  of  the  fluid  filtered  off  de- 
pends almost  entirely  upon  the  blood-pressure  in  the  glomeruli. 

The  greater  the  blood-pressure  in  the  arterial  system  generally,  and 
consequently  in  the  renal  arteries,  the  greater,  cceteris  paribus,  will  be 
the  blood-pressure  in  the  glomeruli,  and  the  greater  the  quantity  of 
urine  separated;  but  even  without  increase  of  the  general  blood-pres- 
sure, if  the  renal  arteries  be  locally  dilated,  the  pressure  in  the  glomeruli 
will  be  increased  and  with  it  the  secretion  of  urine.  All  the  causes, 
therefore,  which  increase  the  general  blood-pressure  will  secondarily 
increase  the  secretion  of  urine.     Of  these — ■ 

(1)  The  heart's  action  is  among  the  most  important.  When  the 
cardiac  contractions  are  increased  in  force  or  frequency,  increased 
diuresis  is  the  result. 

(2)  Since  the  connection  between  the  general  blood-pressure  and  the 
nervous  system  is  so  close  it  will  be  evident  that  the  amount  of  urine 
secreted  depends  greatly  upon  the  influence  of  the  latter.  This  may  be 
demonstrated  experimentally.  Thus,  division  of  the  spinal  cord,  by 
producing  general  vascular  dilatation,  causes  a  great  diminution  of  blood- 
pressure,  and  so  diminishes  the  amount  of  water  passed;  since  the  local 
dilatation  in  the  renal  arteries  is  not  sufficient  to  counteract  the  general 
diminution  of  pressure.  Stimulation  of  the  cut  cord  produces,  strangely 
enough,  the  same  results — i.e.,  a  diminution  in  the  amount  of  the  urine 


EXCRETION. 


483 


passed,  bat  in  a  different  way,  viz.,  by  constricting  the  arteries  generally, 
and,  among  others,  the  renal  arteries;  the  diminution  of  blood-pressure 
resulting  from  the  local  resistance  in  the  renal  arteries  being  more 
potent  to  diminish  blood-pressure  in  the  glomeruli  than  the  general 
increase  of  blood-pressure  is  to  increase  it.  Section  of  the  renal  nerves 
which  produces  local  dilatation  without  greatly  diminishing  the  general 
blood-pressure  will  cause  an  increase  in  the  quantity  of  fluid  passed. 

(3)  The  fact  that  in  summer  or  in  hot  weather  the  urine  is  dimin- 
ished may  be  attributed  partly  to  the  copious- elimination  of  water  by 
the  skin  in  the  form  of  sweat  which  occurs  in  summer,  as  contrasted 
with  the  greatly  diminished  functional  activity  of  the  skin  in  winter, 


Fi's.  307.— Diagraui  of  Roy's  Oncometer,  a.  represents  the  kidney  inclosed  iu  a  metal  box, 
which  opens  h.v  hinge/;  b.  the  renal  vessels  and  duct.  Surrounding  tlie  kidney  are  two  chambers 
formed  by  membranes,  the  edges  of  which  are  tirnily  fixed  by  being  clamped  between  the  outsidi- 
metal  capsule,  and  one  mot  represented  in  the  figure)  inside,  the  two  being  firmly  screwed  together 
by  screws  at  /i.  and  below.  The  membranous  chandier  below  is  filled  with  a  varying  amount  of 
warm  oil.  according  to  the  size  of  the  kidne.v  experimented  with,  through  the  opening  then  clo.sed 
with  the  plug  /.  After  the  kidney  has  been  inclosed  in  the  cajisule,  the  mend)rano> is  chamber  above 
is  filled  with  warm  oil  through  the  tube  e,  wluch  is  then  closed  b.v  a  tap  (not  re]>resente(i  in  the 
diagram);  the  tube  d  coumiunicates  with  a  recording  ajiparatus,  and  any  alteration  iu  the  volume 
of  tne  kidney  is  communicated  by  the  oil  in  the  tube  to  the  chamber  d  of  the  Oncograph,  fig.  295. 

but  also  to  the  dilated  condition  of  the  vessels  of  the  skin  causing  a 
decrease  in  the  general  blood-pressure.  Thus  we  see  that  in  regard  to 
the  elimination  of  water  from  the  system,  the  skin  and  kidneys  perform 
similar  functions,  and  are  capable  to  some  extent  of  acting  vicariously, 
one  for  the  other.  Their  relative  activities  are  inversely  proportional 
to  each  other. 

The  intimate  conuectiou  which  exists  between  the  volume  of  the  kiduey 
and  the  variations  of  blood -pressure  is  exceedingly  well  shown  with  the 
Oncometer,  introduced  by  Roy,  which  is  a  modification  of  the  plethysmo- 
f^raph,  fig-.  307.  By  means  of  thi.s  ajijiaratus  any  alteration  in  the  volume  of 
the  kidney  is  c-oiuinunicated  to  an  apparatus  [oncograph],  capable  of  recording 
grapliically,  with  a  writing  lever,  such  variations. 


484 


HANDBOOK    OF   PHT8I0L0GT. 


It  has  been  found  that  the  kidney  is  extremely  sensitive  to  any 
alteration  in  the  general  blood-pressure,  every  fall  in  the  general  blood- 
pressure  being  accompanied  by  a  decrease  in  the  volume  of  the  kidney, 
and  every  rise,  unless  produced  by  considerable  constriction  of  the 
peripheral  vessels,  including  those  of  the  kidney,  being  accompanied  by 
a  corresponding  increase  of  volume.  Increase  of  volume  is  followed 
by  an  increase  in  the  amount  of  urine  secreted,  and  decrease  of  volume 
by  a  decrease  in  the  secretion.  In  addition,  however,  to  the  response  of 
the  kidney  to  alterations  in  the  general  blood-pressure,  it  has  been 
further  observed  that  certain  substances,  when  injected  into  the  blood, 
will  also  produce  an  increase  in  volume  of  the  kidney,  and  consequent 
increased  flow  of  urine,  without  affecting  the  general  blood-pressure — 


Fig.  308.— Roy's  Oncograph,  or  apparatus  for  recording  alterations  in  the  volume  of  the  kidney, 
etc.,  as  shown  by  the  oncometer — a,  upright,  supporting  recording  lever  i!,  which  is  raised  or  lowered 
by  needle  b,  which  works  through  /,  and  which  is  attached  to  the  piston  e,  working  in  the  chamber 
d,  with  which  the  tube  f  i-om  the  oncometer  communicates.  The  oil  is  prevented  from  being  squeezed 
out  as  the  piston  descends  by  a  membrane,  which  is  clamped  between  the  ring-shaped  surfaces  of 
cylinder  by  the  screw  i  working  upward;  the  tube  h  is  for  filling  the  instrument. 


such  bodies  as  sodium  acetate  and  other  diuretics.  These  observations 
appear  to  prove  that  local  dilatation  of  the  renal  vessels  may  be  produced 
by  alterations  in  the  blood  acting  upon  a  local  nervous  mechanism,  as  this 
happens  when  all  of  the  renal  nerves  have  been  divided.  The  altera- 
tions are  not  only  produced  by  the  addition  of  drugs,  but  also  by  the  in- 
troduction of  comparatively  small  quantities  of  water  or  saline  solution. 
To  this  alteration  of  the  blood  acting  upon  the  renal  vessels  (either 
directly  or)  through  a  local  vaso-motor  mechanism,  and  not  to  any  great 
alteration  in  the  general  blood-pressure,  must  we  attribute  the  effects  of 
meals,  etc.,  observed  by  Roberts.  The  renal  excretion  is  increased  after 
meals  and  diminished  during  fasting  and  sleep.  The  increase  begins 
within  the  first  hour  after  breakfast,  and  continues  during  the  succeed- 
ing two  or  three  hours;  then  a  diminution  sets  in,  and  continues  until 
a,n  hour  or  two  after  dinner.     The  effect  of  dinner  does  not  appear  until 


EXCRETION".  4g5 

two  or  three  hours  after  the  meal;  and  it  reaches  its  maximum  til  ion  t 
the  fourth  hour.  From  this  period  the  excretion  steadily  decreases 
until  bed-time.  During  sleep  it  sinks  still  lower,  and  reaches  its  mini- 
mum— being  not  more  than  one-third  of  the  quantity  excreted  during 
the  hours  of  digestion.  The  increased  amount  of  urine  passed  after 
drinking  large  quantities  of  Huid  depends  upon  the  temporary  increase 
of  blood-pressure  thus  caused. 

The  following  table*  will  help  to  explain  the  dependence  of  the 
nitration  function  upon  the  blood-pressure  and  the  nervous  syptem : — 

Table  of  the  relation  of  the  secretion  of  Urine  to  Arterial  Pressure. 

A.  Secretion  of  urine  may  be  increased — 

a.  By  increasing  tlia  general  blood -jn-essure;  by 

1.  Increase  of  the  force  or  frequency  of  heart-beat. 

2.  Constriction  of  the  small  arteries  of  areas  other  thau  that  of  the 

kidneJ^ 
h.  By   increasing   the    local   blood-pressure,    by    relaxation   of   the    renal 
artery,  without  compensating  relaxation  elsewhere  ;  by 

1.  Division  of  the  renal  nerves  (causing  polyuria). 

2.  Division  of  the  renal  nerves  and  stimulation  of  the  cord,  below 

the  medulla  (causing  greater  polyuria) . 

3.  Division  of  the  splanchnic  nerves ;    but  the  polyuria  produced  is 

less  than  in  1  or  2,  as  these  nerves  are  distributed  to  a  wider 
area,  and  the  dilatation  of  the  renal  artery  is  accompanied  by 
dilatation  of  other  vessels,  and  therefore  with  a  somewhat  di- 
minished general  blood  supply. 

4.  Puncture  of  the  floor  of  fourth  ventricle  or  mechanical  irritation 

of  the  superior  cervical  ganglion  of  the  sympathetic,  possibly 
from  the  production  of  dilatation  of  the  renal  arteries. 

B.  Secretion  of  urine  may  be  diminished — 

a.  By  diminishing  tlie  general  blood-pressure;  by 

1.  Diminution  of  the  force  or  frequency  of  the  heart-beats. 

2.  Dilatation  of  capillary  areas  other  than  that  of  the  kidney. 

3.  Division  of  spinal  cord  below  the  medulla,  which  causes  dilata- 

tion of  general  abdominal  area,    and  urine  generally   ceases 
being  secreted. 
h.   By  increasing  the  blood- pressure,  by  stimulation  of  the  spinal  cord 
below  the  medulla,  the  constriction  of  the  renal  artery,  which  follows, 
not  being  compensated  for  by  the  increase  of  general  blood-pressure, 
c.  By   constriction   of   the    renal    artery,    by    stimulating    the    renal    or 
splanchnic  nerves,  or  the  spinal  cord. 

Though  the  quantity  of  urine  secreted  corresponds  closely  "with  the 
local  blood-pressure,  it  must  be  stated  that  it  is  more  directly  dependent 
on  the  quantity  of  blood  flowing  through  the  kidney  in  a  given  unit  of 
time.  Under  normal  conditions  increased  blood-pressure  and  increased 
blood-flow  go  hand  in  hand.     But  the  local  pressure  may  be  enormously 

*  Modified  from  Foster. 


486 


HA2srDB00K    OF    PHYSIOLOGY. 


increased  by  clamping  the  renal  vein,  in  which  circumstance  the  secre- 
tion of  urine  is  suspended. 

Although  it  is  convenient  to  call  the  processes  which  go  on  in  the 
renal  glomeruli,  filtration,  there  is  reason  to  believe  that  they  are  not 
absolutely  mechanical,  as  the  term  might  seem  to  imply,  since,  when  the 
epithelium  of  the  Malpighian  capsule  has  been,  as  it  were,  put  out  of 
order  by  ligature  of  the  renal  artery,  on  removal  of  the  ligature,  the 
urine  has  been  found  temporarily  to  contain  albumen,  indicating  that  a 
selective  power  resides  in  the  healthy  epithelium,  which  allows  certain 
constituent  parts  of  the  blood  to  be  filtered  off,  and  not  others. 

Secretion. — That  there  is  a  second  part  iu  the  j)rocess  of  the  excre- 
tion of  urine,  which  is  true  secretion,  is  suggested  by  the  structure  of 
the  tubuli  uriniferi,  and  the  idea  is  supported  by  various  experiments. 
It  will  be  remembered  that  the  convoluted  portions  of  the  tubules  are 
lined  with  an  epithelium,  which  bears  a  close  resemblance  to  the  secre- 
tory epithelium  of  other  glands,  whereas  the  Malpighian  capsules  and 
portions  of  the  loops  of  Henle  are  lined  simjaly  by  flattened  epithelium. 
The  two  functions  of  the  different  parts  of  an  uriniferous  tube  are,  then, 
suggested  by  the  differences  of  epithelium,  and  also  by  the  fact  that  the 
blood  supply  to  the  different  parts  is  different,  since,  as  we  have  seen. 


Fig.  309.— Curve  taken  by  renal  oncometer  compressed— with  that  of  ordinary  blood-pressure. 
ri,  Kidney  curve;  b,  blood-pressure  curve.     (Roy.) 


the  convoluted  tubes  are  surrounded  by  capillary  vessels  derived  from 
the  breaking  up  of  the  efferent  vessels  of  the  Malpighian  tufts.  As  to 
the  functions  of  the  different  parts  of  the  uriniferous  tubes  in  the 
secretion  of  urine,  two  chief  theories  have  been  brought  forward.  The 
first,  suggested  by  Bowman  (1842),  and  still  generally  accepted,  is  that 
the  cells  of  the  convoluted  tubes,  by  a  process  of  true  secretion,  separate 
from  the  blood  substances  such  as  urea,  whereas  from  the  glomeruli 
are  separated  the  water  and  the  inorganic  salts.  The  second,  suggested 
by  Ludwig  (1844),  is  that  in  the  glomeruli  are  filtered  off  from  the 
blood  all  the  constituents  of  the  urine  in  a  very  diluted  condition. 
When  this  passes  along  the  tortuous  uriniferous  tube,  part  of  the  water 
is  re-absorbed  into  the  vessels  surrounding  them,  leaving  the  urine  in 
a  more  concentrated  condition — retaining  all  its  proper  constituents. 
This  osmosis  is  promoted  by  the  high  specific  gravity  of  the  blood  in 


EXCRETION".  487 

the  capillaries  surroundiug  the  convoluted  tubes,  but  the  return  of  the 
urea  and  similar  substances  is  prevented  by  the  secretory  epithelium  of 
the  tubules.  The  first  theory  is,  however,  more  strongly  supported  by 
direct  experiment. 

By  using  the  kidney  of  the  newt,  -which  has  two  distinct  vascular 
supplies,  one  from  the  renal  artery  to  the  glomeruli,  and  the  other  from 
the  renal-portal  vein  to  the  convoluted  tubes,  Nussbaum  has  shown  that 
certain  substances,  e.g.,  peptones  and  sugar,  when  injected  into  the 
blood,  are  eliminated  by  the  glomeruli,  and  so  are  not  got  rid  of  when 
the  renal  arteries  are  tied;  whereas  certain  other  substances,  e.g.,  urea, 
when  injected  into  the  blood,  are  eliminated  by  the  convoluted  tubes, 
even  when  the  renal  arteries  have  been  tied.  This  evidence  is  very 
direct  that  urea  is  excreted  by  the  convoluted  tubes,  that  is  to  say,  if  it 
is  certain  that  ligature  of  the  renal  artery  assists  the  circulation  through 
the  glomeruli,  which,  however,  is  denied  by  Adami. 

Heidenhain  also  has  shown  by  experiment  that  if  a  substance  (sodium 
sulph-indigotate),  which  ordinarily  produces  blue  urine,  be  injected 
into  the  blood  after  section  of  the  medulla  which  causes  lowering  of  the 
blood-pressure  in  the  renal  glomeruli,  that  when  the  kidney  is  examined, 
the  cells  of  the  convoluted  tubules  (and  of  these  alone)  are  stained  with 
the  substance,  which  is  also  found  in  the  lumen  of  the  tubules.  This 
appears  to  show  that  under  ordinary  circumstances  the  pigment  at  any 
rate  is  eliminated  by  the  cells  of  the  convoluted  tubules,  and  that  when 
by  diminishing  the  blood-pressure,  the  filtration  of  urine  ceases,  the 
pigment  remains  in  the  convoluted  tubes,  and  is  not,  as  it  is  under 
ordinary  circumstances,  swept  away  from  them  by  the  flushing  of  them 
which  ordinarily  takes  place  with  the  watery  part  of  urine  derived  from 
the  glomeruli.  It  therefore  is  probable  that  the  cells,  if  they  excrete 
the  pigment,  excrete  urea  and  other  substances  also.  But  urea  acts 
somewhat  difl'ercntly  to  the  pigment,  as  when  it  is  injected  into  the 
blood  of  an  animal  in  which  the  medulla  has  been  divided,  and  the 
secretion  of  urine  stopped,  a  copious  secretion  of  urine  results,  Avhieh 
is  not  the  case  when  the  pigment  is  used  instead  under  similar  condi- 
tions. The  flow  of  urine,  independent  of  the  general  blood-jn-essure, 
might  be  supposed  to  be  due  to  the  action  of  the  altered  blood  upon 
some  local  vaso-motor  mechanism;  and,  indeed,  the  local  blood-jiressure 
is  directly  ali'ected  in  this  way,  but  there  is  reason  for  believing  that 
part  of  the  increase  of  the  secretion  is  due  to  the  direct  stimulation  of 
the  cells  by  the  urea  contained  in  the  blood. 

To  sum  up,  then,  the  relation  of  the  two  functions:  (1.)  The  process 
of  filtration,  by  which  the  chief  part,  if  not  the  whole,  of  the  fluid  is 
eliminated,  together  with  certain  inorganic  salts  and  possibly  other 
solids,  is  indirectly  dependent  upon  blood-pressure,  is  accomplished  by 
the  renal  glomeruli,  and  is  accompanied  by  a  free  discharge  of  solids 
from  the  tubules.      ('2.)   The  process  of  secretion  proper,  by  which  urea 


488  HANDBOOK    OP    PHYSIOLOGY. 

and  the  principal  urinary  solids  are  eliminated,  is  accomplished  by  the 
cells  of  the  convoluted  tubes,  and  is  sometimes  (as  in  the  case  of  the 
elimination  of  urea  and  similar  substances)  accompanied  by  the  elimina- 
tion of  copious  fluid,  produced  by  the  chemical  stimulation  of  the  epi- 
thelium of  '^'.16  same  tubules. 

The  Passage  of  Urine  into  the  Bladder. 

As  each  portion  of  urine  is  secreted  it  propels  that  which  is  already 
in  the  uriniferous  tubes  onward  into  the  pelvis  of  the  kidney.  Thence 
through  the  ureter  the  urine  passes  into  the  bladder,  into  which  its  rate 
and  mode  of  entrance  has  been  watched  in  cases  of  ectopia  vesicce,  i.e., 
of  such  fissures  in  the  anterior  or  lower  part  of  the  walls  of  the  abdo- 
men, and  of  the  front  wall  of  the  bladder,  as  expose  to  view  its  hinder 
wall  together  with  the  orifices  of  the  ureters.  The  urine  does  not  enter 
the  bladder  at  any  regular  rate,  nor  is  there  a  synchronism  in  its  move- 
ment through  the  two  ureters.  During  fasting,  two  or  three  drops 
enter  the  bladder  every  minute,  each  drop  as  it  enters  first  raising  up 
the  little  papilla  on  which,  in  these  cases,  the  ureter  opens,  and  then 
passing  slowly  through  its  orifice,  which  at  once  again  closes  like  a 
sphincter.  In  the  recumbent  posture,  the  urine  collects  for  a  little  time 
in  the  ureters,  then  flows  gently,  and,  if  the  body  be  raised,  runs  from 
them  in  a  stream  till  they  are  empty.  Its  flow  is  aided  by  the  peristaltic 
contractions  of  the  ureters,  and  is  increased  in  deep  inspiration,  or  by 
straining,  and  in  active  exercise,  and  in  fifteen  or  twenty  minutes  after 
a  meal.  The  urine  collecting  is  prevented  from  regurgitation  into  the 
ureters  by  the  mode  in  which  these  pass  through  the  walls  of  the  blad- 
der, namely,  by  their  lying  for  between  half  and  three-quarters  of  an  inch 
between  the  muscular  and  mucous  coats  before  they  turn  rather  abruptly 
forward,  and  open  through  the  latter  into  the  interior  of  the  bladder. 

Micturition. — The  contraction  of  the  muscular  walls  of  the  bladder 
may  by  itself  expel  the  urine  with  little  or  no  help  from  other  muscles. 
In  so  far,  however,  as  it  is  a  voluntary  act,  it  is  performed  by  means  of 
the  abdominal  and  other  expiratory  muscles,  which  in  their  contraction, 
as  before  explained,  press  on  the  abdominal  viscera,  the  diaphragm  being 
fixed,  and  cause  the  expulsion  of  the  contents  of  those  whose  sphincter 
muscles  are  at  the  same  time  relaxed.  The  muscular  coat  of  the  blad- 
der co-operates,  in  micturition,  by  reflex  involuntary  action,  with  the 
abdominal  muscles;  and  the  act  is  completed  hy  the  accelerator  urince, 
which,  as  its  name  implies,  quickens  the  stream,  and  expels  the  last 
drop  of  urine  from  the  urethra.  The  act,  so  far  as  it  is  not  directed  by 
volition,  is  under  the  control  of  a  nervous  centre  in  the  lumbnr  spinal 
cord,  through  which,  as  in  the  case  of  the  similar  centre  for  defascation, 
the  various  muscles  concerned  are  harmonized  in  their  action.  It  is 
well  known  that  the  act  may  be  reflexly  induced,  e.g.,  in  children  who 


EXOKETION",  -IS!) 

suffer  from  intestinal  worms,  or  other  such  irritation.  Generally  tlie 
afferent  impulse  which  calls  into  action  the  desire  to  micturate  is  excited 
by  over-distention  of  the  bladder,  or  even  by  a  few  drops  of  urine 
passing  into  the  urethra.  This  passes  up  to  the  lumbar  centre  (or  cen- 
tres) and  produces  on  the  one  hand  inhibition  of  the  sphincter  and  on 
the  other  hand  contraction  of  the  necessary  muscles  for  the  exj)ulsion  of 
the  contents  of  the  bladder. 

The  Structure  and  Functions  of  the  Skin. 

The  skin  serves — (I),  us  an  external  integument  for  the  protection 
of  the  deeper  tissues,  and  (3),  as  a  sensitive  organ  in  the  exercise  of 
touch,  a  subject  to  be  considered  in  the  Chapter  on  the  Special  Senses; 
it  is  also  (3),  an  important  secretory  and  excretory,  and  (4),  an  absorb- 
ing organ,  already  noticed,  p.  425;  while  it  plays  an  important  part  in 
(5)  the  regulation  of  the  temperature  of  the  body.  (See  the  Chapter  on 
Animal  Heat.) 

Structure. — The  skin  consists  principally  of  a  vascular  tissue  named 
the  coriuni,  derma,  or  cutis  vera,  and  of  an  external  covering  of  epithe- 
lium termed  the  epidermis  or  cuticle.  Within  and  beneath  the  corium 
are  imbedded  several  organs  with  special  functions,  namely,  sudoriferous 
glands,  selaceous  glands,  and  hair  follicles;  and  on  its  surface  are  sensi- 
tive papillcB.  The  so-called  appendages  of  the  skin — the  hair  and  nails 
— are  modifications  of  the  epidermis. 

Epidermis. — The  epidermis  is  composed  of  several  strata  of  cells  of 
various  shapes  and  sizes;  it  closely  resembles  in  its  structure  the  epithe- 
lium of  the  mucous  membrane  that  lines  the  mouth.  The  following 
four  layers  may  be  distinguished  in  a  more  or  less  developed  form:  1. 
Stratum  corneum  (fig.  310,  a),  consisting  of  sujDerposed  layers  of  horny 
scales.  The  different  thickness  of  the  epidermis  in  different  regions  of 
the  body  is  chiefly  due  to  variations  in  the  thickness  of  this  layer;  e.g., 
on  the  horny  parts  of  the  palms  of  the  hands  and  soles  of  the  feet  it  is 
of  great  thickness.  The  stratum  corneum  of  the  buccal  epithelium 
chiefly  differs  from  that  of  the  epidermis  in  the  fact  that  nuclei  are  to 
be  distinguished  in  some  of  the  cells  even  of  its  most  superficial  layers. 

2.  Stratum  lucidnm,  a  bright  homogeneous  membrane  consisting  of 
squamous  cells  closely  arranged,  in  some  of  which  a  nucleus  can  be  seen. 

3.  Stratum  gramilosum,  consisting  of  one  layer  of  flattened  cells 
which  appear  fusiform  in  vertical  section:  they  are  distinctly  nucleated, 
and  a  number  of  granules  extend  from  the  nucleus  to  the  margins  of 
the  cell. 

4.  Stratum  Malpighii  or  Eete  mticosiim  consists  of  many  strata. 
The  deepest  cells,  placed  immediately  above  the  cutis  vera,  are  columnar 
with  oval  nuclei:  this  layer  of  columnar  cells  is  succeeded  by  a  number 
of  layers  of  more  or  less  polyhedi-al  cells  with  spherical  nuclei;  the  cells 


490 


HANDBOOK    OF    PHYSIOLOGY. 


of  the  more  superficial  layers  are  considerably  flattened.  The  deeper 
surface  of  the  rete  mucosum  is  accurately  adapted  to  the  papillifi  of  the 
true  skin,  being,  as  it  were,  moulded  on  them.  It  is  very  constant  in 
thickness  in  all  parts  of  the  skin.  The  cells  of  the  middle  layers  of 
the  stratum  Malpighii  are  almost  all  connected  by  processes,  and  thus 
form  prickle  cells  (fig,  35).  The  pigment  of  the  skin,  the  varying  quan- 
tity of  which  causes  the  various  tints  observed  in  different  individuals 
and  different  races,  is  contained  in  the  deeper  cells  of  rete  mucosum; 
the  pigmented  cells  as  they  approach  the  free  surface  gradually  losing 
their  color.     Epidermis  maintains  its  thickness  in  spite  of  the  constant 


'^^^^=^^:: 


Fig.  310.— Vertical  section  of  the  epidermis  of  the  prepuce,  a,  stratum  corneum,  of  very  few 
layers,  the  stratum  lucidum  and  stratum  granulosum  not  being  distinctly  represented;  6,  c,  d,  and  e, 
the  layers  of  the  stratum  Malpighii,  a  certain  number  of  the  cells  in  layers  d  and  e  showing  signs  of 
segmentation;  layer  c  consists  chiefly  of  prickle  or  ridge  and  furrow  cells;  /,  basement  membrane; 
g.  cells  in  cutis  vera.     (Cadiat.) 


wear  and  tear  to  which  it  is  subjected.  The  columnar  cells  of  the  deep- 
est layer  of  the  rete  mucosum  elongate,  and  their  nuclei  divide  into  two 
(fig.  310,  e).  Lastly  the  upper  part  of  the  cell  divides  from  the  lower; 
thus  from  a  long  columnar  cell  are  produced  a  polyhedral  cell  and  a 
short  columnar  cell:  the  latter  elongates  and  the  process  is  repeated. 
The  polyhedral  cells  thus  formed  are  pushed  up  toward  the  free  surface 
by  the  production  of  fresh  ones  beneath  them,  and  become  flattened 
from  pressure:  they  also  become  gradually  horny  by  evaporation  and 
transformation  of  their  protoplasm  into  keratin,  till  at  last  by  rubbing 
in  ordinary  wear  and  tear  they  are  detached  as  dry  horny  scales  at  the 
free  surface.     There  is  thus  a  constant  production  of  fresh  cells  in  the 


EXCEETtON.  491 

deeper  layers,  uud  a  constant  throwing  off  of  old  ones  from  tlie  free  sur- 
face. When  these  two  processes  are  accurately  balanced,  the  epidermis 
maintains  its  thickness.  When,  by  intermittent  pressure  a  more  active 
cell-growth  is  stimulated,  the  production  of  cells  exceeds  their  waste  and 
the  epidermis  increases  in  thickness,  as  we  see  in  the  horny  hands  of  the 
laborer. 

The  thickness  of  the  epidermis  on  the  different  portions  of  the  skin 
is  directly  proportioned  to  the  friction,  pressure,  and  other  sources  of 
injury  to  which  it  is  exposed;  for  it  serves  as  well  to  protect  the  sensi- 
tive and  vascular  cutis  from  injury  from  without,  as  to  limit  the  evap- 
oration of  fluid  from  the  blood-vessels.  The  adaptation  of  the  epider- 
mis to  the  latter  purposes  may  be  well  shown  by  exj^osing  to  the  air  two 
dead  hands  or  feet,  of  which  one  has  its  epidermis  perfect,  and  the 
other  is  deprived  of  it;  in  a  day,  the  skin  of  the  latter  will  become 
brown,  dry  and  horn-like,  while  that  of  the  former  will  almost  retain  its 
natural  moisture. 

Cutis  vera. — The  corinm  or  cutis  vera,  which  rests  upon  a  layer  of 
adipose  and  cellular  tissue  of  varying  thickness,  is  a  dense  and  tough, 
but  yielding  and  highly  elastic  structure,  composed  of  fasciculi  of  areolar 
tissue,  interwoven  in  all  directions,  and  forming,  by  their  interlace- 
ments, numerous  spaces  or  areolas.  These  areolfe  are  large  in  the  deeper 
layers  of  the  cutis,  and  are  there  usually  filled  with  little  masses  of  fat 
(fig.  298) :  but,  in  the  superficial  parts,  they  are  small  or  entirely  oblit- 
erated.    Unstriped  muscular  fibres  are  also  abundantly  present. 

Papillae. — The  cutis  vera  presents  numerous  conical  papills,  with  a 
single  or  divided  free  extremity,  which  are  more  prominent  and  more 
densely  set  at  some  parts  than  at  others.  This  is  especially  the  case  on 
the  palmar  surface  on  the  hands  and  fingers,  and  on  the  soles  of  the  feet 
— parts,  therefore,  \n  which  the  sense  of  touch  is  most  acute.  On  these 
parts  they  are  disposed  in  double  rows,  in  parallel  curved  lines,  separated 
from  each  other  by  depressions.  Thus  they  may  be  easily  seen  on  the 
palm,  whereon  each  raised  line  is  comjaosed  of  a  double  row  of  papillae, 
and  is  intersected  by  short  transverse  lines  or  furrows  corresponding 
with  the  interspaces  between  the  successive  jiairs  of  papilla?.  Over 
other  parts  of  the  skin  they  are  more  or  less  thinly  scattered,  and  are 
scarcely  elevated  above  the  surface.  Their  average  length  is  about  y^ 
of  an  inch  {^  mm.),  and  at  their  base  they  measure  about  tjI-^  of  an 
inch  in  diameter.  Each  papilla  is  abundantly  supplied  with  blood,  re- 
ceiving from  the  vascular  plexus  in  the  cutis  one  or  more  minute  arte- 
rial twigs,  which  divide  into  capillary  loops  in  its  substance,  and  then 
reunite  into  a  minute  vein,  which  passes  out  at  its  base.  This  abun- 
dant supply  of  blood  explains  the  turgescence  or  kind  of  erection  which 
they  undergo  when  the  circulation  through  the  skin  is  active.  The 
majority,  but  not  all,  of  the  papillfe  contain  also  one  or  more  terminal 


492 


HANDBOOK    OP    PHYSIOLOGY. 


uerve-fibres,  from  the  ultimate  ramifications  of  the  cutaneous  plexus, 
on  which  their  exquisite  sensibility  depends. 

The  nerve-terminations  in  the  skin  haye  been  described  under  the 
Sensory  Nerve  Terminations  (p.  102  et  seq.). 

Glands  of  the  Skin. — The  skin  possesses  glands  of  two  kinds:  {a) 
Sudoriferous,  or  Sweat  Glands;  {b)  Sebaceous  glands. 

(a)  Sudoriferous,  or  Stueat  Glands. — Each  of  these  glands  consists 
of  a  small  lobular  mass,  formed  of  a  coil  of  tubular  gland-duct,  sur- 


F  IK.  311.— Vertical  section  of  skin.  A.  Sebaceous  gland  opening  into  hair  follicle.  B.  Muscular 
fibres.  U.  Sudoriferous  or  sweat-gland.  D.  Subcutaneous  fat.  E.  Fundus  of  hair-follicle,  with 
hair-papillae.    (Klein.) 

rounded  by  blood-vessels  and  embedded  in  the  subcutaneous  adipose 
tissue  (fig.  311,  C).  From  this  mass,  the  duct  ascends,  for  a  short  dis- 
tance in  a  spiral  manner  through  the  deeper  part  of  the  cutis,  then 
passing  straight,  and  then  sometimes  again  becoming  spiral,  it  passes 
through  the  epidermis  and  opens  by  an  oblique  valve-like  aperture. 
In  the  parts  where  the  epidermis  is  thin,  the  ducts  themselves  are 
thinner  and  more  nearly  straight  in  their  course  (fig.  311).  The  duct, 
which  maintains  nearly  the  same  diameter  throughout,  is  lined  with  a 


EXCRETION.  493 

layer  of  columnar  epithelium  (fig.  311)  continuous  with  the  epidermis; 
while  the  part  which  passes  through  the  epidermis  is  a  mere  passage 
through  the  epidermal  cells  not  being  bounded  by  any  special  lining; 
but  the  cells  which  immediately  form  the  boundary  of  the  canal  in  this 
part  are  somewhat  differently  arranged  from  those  of  the  adjacent  cuti- 
cle. The  coils  or  terminal  portions  of  the  gland  are  lined  with  at  least 
two  layers  of  short  columnar  cells  with  very  distinct  nuclei  (fig.  312), 
and  possess  a  large  lumen  distinctly  bounded  by  a  special  lining  of 
cuticle. 

The  sudoriferous  glands  are  abundantly  distributed  over  the  whole 
surface  of  the  body;  but  are  especially  numerous,  as  well  as  very  large, 
in  the  skin  of  the  palm  of  the  hand  and  of  the  sole  of  the  foot.  The 
glands  by  which  the  peculiar  odorous  matter  of  the  axillae  is  secreted 


Fifr.  312.— Terminal  tubules  of  sudoriferous  glands,  cut  in  various  directions  from  the  skin  of  the 

pig's  ear.    (Y.  D.  Harris.) 

form  a  nearly  complete  layer  under  the  cutis,  and  are  like  the  ordinary 
sudoriferous  glands,  except  in  being  larger  and  having  very  short  ducts. 

The  peculiar  bitter  yellow  substance  secreted  by  the  skin  of  the  ex- 
ternal auditory  passage  is  named  cerumen,  and  the  glands  themselves 
ceruminous  glands;  but  they  do  not  much  differ  in  structure  from  the 
ordinary  sudoriferous  glands. 

{h)  Sebaceous  Glands. — The  sebaceous  glands  (figs.  311,  310),  like 
sudoriferous  glands,  are  abundant  in  most  parts  of  the  surface  of  the 
body,  particularly  in  parts  largely  supplied  with  hair,  as  the  scalp  and 
face.  They  are  thickly  distributed  about  the  entrances  of  the  various 
passages  into  the  body,  as  the  anus,  nose,  lips,  and  external  ear.  They 
are  entirely  absent  from  the  palmar  surface  of  the  hand  and  the 
plantar  surfaces  of  the  feet.  They  are  racemose  glands  composed  of  an 
aggregate  of  small  tubes  or  sacculi  lined  with  columnar  epithelium  and 
filled  with  an  opaque  white  substance,  like  soft  ointment,  which  consists 
of  broken-up  epithelial  cells  which  have  undergone  fatty  degeneration. 
Minute   capillary  vessels  overspread  them :   and  their   ducts   open   on 


494 


HANDBOOK    OF    PHTSIOLOGY. 


either  the  surface  of  the  s"kin,  close  to  a  hair,  or,  which  is  more  usual, 
directly  into  the  follicle  of  the  hair.  In  the  latter  case,  there  are  gener- 
ally two  or  more  glands  to  each  hair  (fig.  31'2). 

Hair. — A  hair  is  produced  hy  a  peculiar  growth  and  modification  of 
the  epidermis.  Externally  it  is  covered  by  a  layer  of  fine  scales  closely 
imbricated,  or  overlapping  like  the  tiles  of  a  house,  hut  with  the  free 
edges  turned  upward  (fig.  314,  a).  It  is  called  the  cuticle  of  the  hair. 
Beneath  this  is  a  much  thicker  layer  of  elongated  horny  cells,  closely 
packed  together  so  as  to  resemble  a  fibrous  structure.  This,  very  com- 
monly, in  the  human  subject,  occupies  the  whole  inside  of  the  hair;  but 


Fig.  313. — Trausvei-se  section  of  a  hair  and  hair-follicle  made  below  the  opening  of  the  sebaceous 
^laiia.  «,  medulla  or  pith  of  the  hair;  t>,  fibrous  layer  or  cortex;  c,  cuticle;  d,  Huxley's  layer:  e, 
Heiile's  layer  of  iTiternal  root-sheatli ;  /  and  a,  layers  of  external  root-sheath,  outside  of  f/  is  a  light 
layer,  or  "  glassy  membrane,"  whicli  is  equivalent  to  the  basement  membrane;  /;,  fibrous  coat  of 
hair  sac;  /,  vessels.    (Cadiat.) 


in  some  cases  there  is  left  a  small  central  space  filled  by  a  substance 
called  the  mefZwZfe  or  J9^YA,  comjDosed  of  small  collections  of  irregularly 
shaped  cells,  containing  sometimes  pigment  granules  or  fat,  but  mostly 
air. 

The  follicle,  in  which  the  root  of  each  hair  is  contained  (fio-.  315), 
forms  a  tubular  dejDression  from  the  surface  of  the  skin, — descending 
into  the  subcutaneous  fat,  generally  to  a  greater  depth  than  the  sudor- 
iferous glands,  and  at  its  deepest  part  enlarging  in  a  bulbous  form,  and 
often  curving  from  its  previous  rectilinear  course.  It  is  lined  through- 
out by  cells  of  epithelium,  continuous  with  those  of  the  epidermis,  and 
its  vralls  are  formed  of  pellucid  membrane,  which  commonly  in  the 
follicles  of  the  largest  hairs  has  the  structure  of  vascular  fibrous  tissue. 


EXCRETIOSr. 


■i'J5 


At  the  bottom  of  the  follicle  is  a  small  papilla,  or  projection  of  true 
skin,  and  it  is  by  the  production  and  outgrowth  of  epidermal  cells  from 
the  surface  of  this  papilla  that  the  hair  is  formed.  The  inner  wall  of 
the  follicle  is  lined  by  epidermal  cells  continuous  Avith  those  covering 


■^.   ^ 


Fig.  314.— Surface  of  a  white  hair,  magnified  100  diameters.    The  wave  lines  mark  the  upper  or  free 
edges  of  the  cortical  scales.    B,  separated  scales,  magnified  .350  diameters.     (KoUiker.) 

the  general  surface  of  the  skin;  as  if  indeed  the  follicle  had  been  formed 
by  a  simple  thrusting  in  of  the  surface  of  the  integument  (fig.  315). 
This  epidermal  lining  of  the  hair-follicle,  or  root-sheath  of  the  hair,  is 
composed  of  two  layers,  the  inner  one  of  which  is  so  moulded  on  the 
imbricated  scaly  cuticle  of  the  hair,  that  its  inner  surface  becomes  im- 
bricated also,  but  of  course   in  the  opposite  direction.     When  a  hair  is 

tcic  cl'   & 


Fig.  815.— Longitudinal  section  of  a  liaii-  follicle,  a.  Stratum  of  Malpighi,  deep  layer  forming 
the  external  root-sht-ath.  and  continued  to  the  surface  of  the  papilla  to  form  the  medullary  sheath 
of  the  hair;  ii,  second  external  sheath;  c,  internal  root-sheath;  d,  fibroid  sheath  of  the  hair:  e. 
medullary  sheath  or  medulla; /,  hair  papilla:  g,  blood-vessels  of  the  hair-papilla;  /i,  fibro-vascular 
sheath.     (Cadiat.) 

pulled  out,  the  inner  layer  of  the  root-sheath  and   part  of  the  outer 
layer  also  are  commonly  pulled  out  with  it. 

Nails. — A  nail,  like  a  hair,  is  a  peculiar  arrangement  of  epidermal 
cells,  the  undermost  of  Avhich,  like  those  of  the  general  surface  of  the 
integument,  are  rounded  or  elongated,  while  the  superficial  are  flat- 
tened, and  of  more  horny  consistence.     That  specially  modified  portion 


HANDBOOK   OF   PHYSIOLOGY. 

of  the  corium^  or  true  skin,  by  which  the  nail  is  secreted  is  called  the 
matrix. 

The  back  edge  of  the  nail,  or  the  root  as  it  is  termed,  is  received  into 
a  shallow  crescentic  groove  in  the  matrix,  while  the  front  part  is  free 
and  projects  beyond  the  extremity  of  the  digit.  The  intermediate  por- 
tion of  the  nail  rests  by  its  broad  under  surface  on  the  front  part  of  the 
matrix,  which  is  here  called  the  led  of  the  nail.  This  part  of  the  matrix 
is  not  uniformly  smooth  on  the  surface,  but  is  raised  in  the  form  of 
longitudinal  and  nearly  parallel  ridges  or  laminfe,  on  which  are  moulded 
the  epidermal  cells  of  which  the  nail  is  made  up. 

The  growth  of  the  nail,  like  that  of  the  hair,  or  of  the  epidermis  gen- 
erally, is  effected  by  a  constant  production  of  cells  from  beneath  and 
behind,  to  take  the  place  of  those  which  are  worn  or  cut  away.  Inas- 
much, however,  as  the  posterior  edge  of  the  nail,  from  its  being  lodged  in 
a  groove  of  the  skin,  cannot  grow  backward,  on  additions  being  made 
to  it,  so  easily  as  it  can  pass  in  the  opposite  direction,  any  growth  at  its 
hinder  part  pushes  the  whole  forward.  At  the  same  time  fresl;  cells 
are  added  to  its  under  surface,  and  thus  each  portion  of  the  nail  becomes 
gradually  thicker  as  it  moves  to  the  front,  until,  projecting  beyond  the 
surface  of  the  matrix,  it  can  receive  no  fresh  addition  from  beneath,  and 
is  simply  moved  forward  by  the  growth  at  its  root,  to  be  at  last  worn 
away  or  cut  off. 

Functions  of  the  Skin. 

The  function  of  the  skin  to  be  considered  in  this  chapter  is  that  of 
the  excretion  of  the  sweat.  The  fluid  secreted  by  the  sweat-glands  is 
usually  formed  so  gradually  that  the  watery  portion  of  it  escapes  by 
evaporation  as  fast  as  it  reaches  the  surface.  But  during  strong  exer- 
cise, exposure  to  great  external  warmth,  in  some  diseases,  and  when 
evaporation  is  prevented,  the  secretion  becomes  more  sensible,  and  col- 
lects on  the  skin  in  the  form  of  drops  of  fluid. 

The  perspiration,  as  the  term  is  sometimes  employed  in  physiology, 
includes  all  that  portion  of  the  secretions  and  exudations  from  the  skin 
which  passes  off  by  evaporation ;  the  siveat  includes  that  which  may  be 
collected  only  in  drops  of  fluid  on  the  surface  of  the  skin.  The  two 
terms  are,  hov/ever,  most  often  used  synonymously;  and  for  distinction, 
the  former  is  called  insensihle  perspiration;  the  latter,  sensible  perspira- 
tion. The  fluids  are  the  same,  except  that  the  sweat  is  commonly  mingled 
with  various  substances  lying  on  the  surface  of  the  skin.  The  contents 
of  the  sweat  are,  in  part,  matters  capable  of  assuming  the  form  of  vapor, 
such  as  carbonic  acid  and  water,  and  in  part,  other  matters  which  are 
deposited  on  the  skin,  and  mixed  vi^ith  the  sebaceous  secretions. 

The  secretion  of  the  sebaceous  glands  and  hair-follicles  consists  of 
cast-off  epithelium  cells,  with  nuclei  and  granules,  together  with  an  oily 


EXCRETION.  497 

matter,  extractive  matter,  and  stearin;  in  certain  parts,  also,  ft  is  mixed 
with  a  peculiar  odorous  principle,  which  contains  caproic,  butyric,  and 
rutic  acids.  It  is,  perhaps,  nearly  similar  in  composition  to  the  unctu- 
ous coating,  or  vernix  caseosa,  which  is  formed  on  the  body  of  the 
foetus  while  in  the  uterus,  and  which  contains  large  quantities  of 
ordinary  fat.  Its  purpose  seems  to  be  that  of  keeping  the  skin  moist 
and  supple,  and,  by  its  oily  nature,  of  both  hindering  the  evaporation 
from  the  surface,  and  guarding  the  skin  from  the  effects  of  the  long- 


Fig.  316.— Sebaceous  gland  from  human  skin.    (Klein  and  Noble  Smith.) 

continued  action  of  moisture.  But  while  it  thus  serves  local  purposes, 
its  removal  from  the  body  entitles  it  to  be  reckoned  among  the  excre- 
tions of  the  skin. 

Chemical  Composition  of  Sweat. 

Water .995 

Solids  :— 

Organic  Acids  (formic,  acetic,  butjTic,  pro-  [  g 

pionic,  caproic,  caprylic)             .         .            \  ' 
Salts,  chiefly  sodium  chloride  .         .         .         .1.8 

Neutral  fats  and  cholesterin            .         .         .  .7 

Extractives  (including  urea),  with  epithelium  1.6           5 

1(XK) 
The  sweat  is  a  colorless,  slightly  turbid  fluid,  alkaline,  neutral  or 
acid  in  reaction,  of  a  saltish  taste,  and  peculiar  characteristic  odor. 

Of  the  several  substances  it  contains,  however,  only  the  carbonic  acid 
and  ivate?'  need  particular  consideration. 

Wafer)/  Vapor. — The  quantity  of  watery  vapor  excreted  from  the 
32 


498  HANDBOOK   OF   PHYSIOLOGY. 

skin  is  on  an  average  between  1|-  and  2  lb.  daily  (about  1  kilo).  This 
subject  has  been  very  carefully  investigated  by  Lavoisier  and  Sequin. 
The  latter  chemist  enclosed  his  body  in  an  air-tight  bag,  with  a  mouth- 
piece. The  bag  being  closed  by  a  strong  band  above,  and  the  mouth- 
piece adjusted  and  gummed  to  the  skin  around  the  mouth,  he  was 
weighed,  and  then  remained  quiet  for  several  hours,  after  which  time 
he  was  again  weighed.  The  difference  in  the  two  weights  indicated  the 
amount  of  loss  by  pulmonary  exhalation.  Having  taken  off  the  air- 
tight dress,  he  was  immediately  weighed  again,  and  a  fourth  time  after 
a  certain  interval.  The  difference  between  the  two  weights  last  ascer- 
tained gave  the  amount  of  the  cutaneous  and  pulmonary  exhalation  to- 
gether; by  subtracting  from  this  the  loss  by  pulmonary  exhalation 
alone,  while  he  was  in  the  air-tight  dress,  he  ascertained  the  amount  of 
cutaneous  transpiration.  During  a  state  of  rest,  the  average  loss  by 
cutaneous  and  pulmonary  exhalation  in  a  minute,  is  eighteen  grains, — 
the  minimum  eleven  grains,  the  maximum  thirty-two  grains;  and  of  the 
eighteen  grains,  eleven  pass  off  by  the  skin,  and  seven  by  the  lungs. 

The  quantity  of  watery  vapor  lost  by  transpiration  is  of  course  influ- 
enced by  all  external  circumstances  which  affect  the  exhalation  from 
other  evaporating  surfaces,  such  as  the  temperature,  the  hygrometric 
state,  and  the  stillness  of  the  atmosphere.  But,  of  the  variations  to 
which  it  is  subject  under  the  influence  of  these  conditions,  no  calcula- 
tion has  been  exactly  made. 

Carionic  Acid. — The  quantity  of  carlonic  acid  exhaled  by  the  skin 
on  an  average  is  about  y^  to  2W  o^  ^^^^  furnished  by  the  pulmonary 
respiration. 

The  cutaneous  exhalation  is  most  abundant  in  the  lower  classes  of  animals, 
more  particularly  the  naked  Amphibia,  as  frogs  and  toads,  whose  skin  is  thin  and 
moist,  and  readily  permits  an  interchange  of  gases  between  the  blood  circulating 
in  it,  and  the  surrounding  atmosphere.  Bischoff  found  that,  after  the  hmgs  of 
frogs  had  been  tied  and  cut  out,  about  a  quarter  of  a  cubic  inch  of  carbonic 
acid  gas  was  exhaled  by  the  skin  in  eight  hours.  And  this  quantity  is  very 
large,  when  it  is  remembered  that  a  full-sized  frog  will  generate  only  about 
half  a  cubic  inch  of  carbonic  acid  by  his  lungs  and  skin  together  in  six  hours. 

The  importance  of  the  respiratoiy  function  of  the  skin,  which  was  once 
thought  to  be  proved  by  the  speedy  death  of  animals  whose  skins,  after  removal 
of  the  hair,  were  covered  with  an  impermeable  varnish,  has  been  shown  by 
further  observations  to  have  no  foundation  in  fact ;  the  immediate  cause  of 
death  in  such  cases  being  the  loss  of  temperature.  A  varnished  animal  is  said 
to  have  suffered  no  harm  when  surroimded  by  cotton  wadding,  and  to  have  died 
when  the  wadding  was  removed. 

Influence  of  the  Nervous  System. 

The  secretion  of  sweat  is  closely  connected  with  the  quantity  of  blood 
flowing  through  the  cutaneous  vessels.  The  quantity  of  sweat  in- 
creases with  vaso-dilatation  and  diminishes  with  vaso-constriction.     It 


EXCRETION.  499 

is  practically  certain  that  the  sweat-glands  are  also  under  the  control 
of  efferent  impulses  passing  to  them  from  the  special  sweat  centres 
in  the  brain  and  spinal  cord  through  special  sweat  nerves.  Thus,  if 
the  sciatic  nerve  be  divided  in  a  cat  and  the  peripheral  end  be  stim- 
ulated, beads  of  sweat  are  seen  to  appear  upon  the  pad  of  the  correspond- 
ing foot,  although  at  the  same  time  the  blood-vessels  are  constricted  or 
while  the  aorta  is  pressed  upon,  whereas  if  atropin  have  been  injected 
previously  to  the  stimulation,  no  sweat  appears,  although  dilatation  of 
the  vessels  be  present.  Secretion  of  sweat,  too,  may  be  reflexly  br-ought 
about. 

The  circulation  of  venous  blood  in  the  spinal  bulb  causes  the  sweating 
of  phthisis  and  of  dyspnoea  generally,  by  stimulating  the  sweat  centre. 
If  the  cat  whose  sciatic  nerve  is  divided  be  rendered  dyspnoeic,  abundant 
sweat  occurs  upon  the  foot  of  the  uninjured,  and  none  on  the  injured 
side.  The  effect  of  heat  in  producing  sweating  may  be  both  local  and 
general,  and  again,  the  various  drugs  which  produce  an  increased  secre- 
tion of  sweat  do  not  all  act  in  the  same  way;  thus,  there  is  reason  for 
thinking  that  pilocarjym  acts  upon  the  local  apparatus,  that  strychnia 
and  picrotoxin  act  upon  the  sweat  centres,  and  that  nicotin  acts  both 
upon  the  central  and  upon  the  local  apparatus. 

The  sjDecial  sweat-nerves  appear  to  issue  from  the  spinal  cord,  in  the 
case  of  the  hind  limb  of  the  cat  by  the  last  two  or  three  dorsal  and  first 
two  or  four  lumbar  nerves,  pass  to  the  abdominal  sympathetic  and  from 
thence  to  the  sciatic  nerve.  In  the  case  of  the  fore  limb,  the  nerves 
leave  the  cord  by  the  5th  and  6th  cervical  nerves  into  the  thoracic  sym- 
pathetic, and  then  join  the  brachial  plexus,  reaching  the  arm  through 
the  median  and  ulnar  nerves. 

It  will  be  as  well  to  repeat  here  the  other  functions  which  the  skin 
subserves.  In  addition  to  its  excretory  oflSce,  we  have  seen  that  it  acts 
as  a  channel  for  alsorption.  It  is  also  concerned  with  a  special  sense, 
viz.,  that  of  touch,  to  the  consideration  of  which  as  well  as  to  its  func- 
tion of  regulating  the  temperature  of  the  body  we  shall  presently  return. 
It  should  be  recollected,  however,  that  apart  from  these  special  func- 
tions, by  means  of  its  toughness,  flexibility  and  elasticity,  the  skin  is 
eminently  qualified  to  serve  as  the  general  integument  of  the  body,  for 
defending  the  internal  parts  from  external  violence,  while  readily  yield- 
ing and  adapting  itself  to  their  various  movements  and  changes  of 
position. 


CHAPTER  XIT. 

MUSCLE- NERVE  PHYSIOLOGY. 

Chemical  Composition  of  Muscle. 

The  muscles  make  up  about  one-half  of  the  total  body  weight.     The 

principal  substance  which  can  be  extracted  from  muscle,  when  examined 
after  death,  is  the  proteid  body,  Myosin,  some  of  the  reactions  of  which 
have  been  already  discussed,  p.  116.  This  body  appears  to  bear  some- 
what the  same  relation  to  the  living  muscle  as  fibrin  does  to  the  living 
blood,-  since  the  coagulation  of  muscle  after  death  is  due  to  the  formation 
of  myosin.  Thus,  if  coagulation  be  delayed  in  muscles  removed  imme- 
diately from  recently  killed  animals,  by  subjecting  them  to  a  temperature 
below  0°  Co,  it  is  possible  to  obtain  from  them  by  expression  a  viscid 
fluid  of  slightly  alkaline  reaction,  called  7nuscle-plasma  (Kiihne,  Halli- 
burton). And  muscle  plasma,  if  exposed  to  the  ordinary  temperature  of 
the  air  (and  more  quickly  at  37°-40°  C),  undergoes  coagulation  much 
in  the  same  way  as,  under  similar  circumstances,  does  blood  plasma, 
separated  from  the  blood  corpuscles  by  the  action  of  a  low  temperature. 
The  appearances  presented  by  the  fluid  during  the  process  are  also  very 
similar  to  the  phenomena  of  blood-clotting,  viz.,  that  first  of  all  an  in- 
creased viscidity  appears  on  the  surface  cf  the  fluid,  and  at  the  sides  of 
the  containing  vessel,  which  gradually  extends  throughout  the  entire 
mass,  until  a  fine  transparent  clot  is  obtained.  In  the  course  of  some 
hours  the  clot  begins  to  contract,  and  to  squeeze  out  of  its  meshes  a  fluid 
corresponding  to  blood-serum.  In  the  course  of  coagulation,  therefore, 
muscle  plasma  separates  into  muscle-clot  and  muscle-serum.  The  muscle 
clot  is  the  substance  myosin.  It  differs  from  fibrin  in  being  easily  soluble 
in  a  2  per  cent  solution  of  hydrochloric  acid,  and  in  a  10  per  cent  solu- 
tion of  sodium  chloride.  It  is  insoluble  in  distilled  water,  and  its  solu- 
tions coagulate  on  application  of  heat.  It  isinshort  a^Mt^/m.  During 
the  process  the  reaction  of  the  fluid  becomes  distinctly  acid. 

The  coagulation  of  muscle  plasma  cannot  only  be  prevented  by  cold, 
but  also,  as  Halliburton  has  shown,  by  the  presence  of  neutral  salts  in 
certain  proportions;  for  example,  of  sodium  chloride,  of  magnesium 
sulphate,  or  of  sodium  sulphate.  It  will  be  remembered  that  this  is 
also  the  case  with  blood  plasma.  Dilution  of  the  salted  muscle  plasma 
will  produce  its  slow  coagulation,  which  is  prevented  by  the  presence  of 
the  neutral  salts  in  strong  solution. 

It  is  highly  probable  that  the  formation  of  muscle-clot  is  due  to  the 

500 


MUSCLE-NERVE   PHYSIOLOGY.  501 

presence  of  a  ferment  (myosin-ferment) .  The  antecedent  myosin  in  liv- 
ing muscle  has  received  the  name  of  myosinogen^  in  the  same  way  as  tire 
fibrin-forming  element  in  the  blood  is  called  fibrinogen.  Myosinogen 
is,  however,  made  up  of  two  globulins,  which  coagulate  at  the  tempera- 
tures 47°  C.  and  50°  0.  respectively.  Myosin  may  also,  as  we  have  before 
mentioned,  p.  482,  be  obtained  from  dead  muscle  by  subjecting  it,  after 
all  the  blood,  fat,  and  fibrous  tissue,  and  substances  soluble  in  water  have 
been  removed,  to  a  10  ])er  cent  solution  of  sodium  chloride,  or  5  per 
cent  solution  of  magnesium  sulphate,  or  10  to  15  per  cent  solution  of 
ammonium  chloride,  filtering  and  allowing  the  filtrate  to  drop  into  a 
large  quantity  of  water;  the  myosin  separates  out  as  a  white  flocculent 
precipitate. 

A  very  remarkable  fact  with  regard  to  the  properties  of  myosin  has 
been  demonstrated  hy  Halliburton,  namely,  that  a  solution  of  dead 
muscle  in  strong  neutral  saline  solution,  possesses  very  much  the  same 
properties  as  muscle  plasma,  and  that  if  diluted  with  twice  or  three 
times  its  bulk  of  water,  myosin  will  separate  out  as  a  clot,  which  clot  can 
be  again  dissolved  in  a  strong  neutral  saline  solution,  and  the  solution 
can  be  again  made  to  clot  on  dilution.  This  process  can  often  be  re- 
peated ;  but  in  the  fluid  which  exudes  from  the  clot  there  is  no  proteid 
present.  Myosin  when  dissolved  in  neutral  saline  fluids  is  converted  in- 
to myosinogen,  but  reappears  on  dilution  of  the  fluid.  Muscle  clot  is 
almost  pure  myosin;  but  it  appears  to  be  combined  with  a  certain 
amount  of  salts,  for  if  it  be  freed  of  salts,  especially  of  those  of  calcium, 
by  prolonged  dialysis,  it  loses  its  solubility.  If  a  small  amount  of  cal- 
cium salts  be  added,  however,  it  regains  that  property. 

Muscle  serum  is  acid  in  reaction,  and  almost  colorless.  It  contains 
three  proteid  bodies,  viz. — [a)  K globulin  {myoglohulin),  which  can  be  pre- 
cipitated by  saturation  with  sodium  chloride,  or  magnesium  sulphate,  and 
which  can  be  coagulated  at  63°  C.  (145°  F.).  [b)  Serum-alhiiniiu  [myo- 
albumin),  which  coagulates  at  73°  C.  (163°  F.),  but  is  not  precipitated 
by  saturation  with  either  of  those  salts.  And  (c)  31  go-alb umose,  which 
is  neither  jirecipitated  by  heat,  nor  by  saturation  Avith  sodium  chloride 
or  magnesium  sulphate,  but  may  be  precipitated  by  saturation  with  am- 
monium suli)hate.  It  is  closely  connected  with,  even  if  it  is  not  itself, 
myosin  ferment.  Neither  casein  nor  jjeptone  has  been  found  by  Halli- 
burton in  muscle  extracts.  In  extracts  of  muscles,  especially  of  red 
muscles,  there  is  a  certain  amount  of  Ilo'moglobiu,  and  also  of  a  jjigment 
special  to  muscle,  called  by  ]\[e]\Iunn  Mgo-lupmatin,  Avliich  has  a  spectrum 
quite  distinct  from  hfemoglobin,  viz.,  a  narrow  band  just  before  D,  two 
very  narrow  betAveen  D  and  E,  and  two  other  faint  bands,  nearly  violet, 
E  b,  and  between  E  and  F  close  to  F. 

In  addition  to  muscle  fcruieNfs,  already  mentioned,  muscle  extracts 


502  HANDBOOK  OF   PHYSIOLOGY. 

contain  certain  small  amounts  oi  pepsin  and  fibrin  ferment^  and  also  an 
amylolytic  ferment. 

Certain  acids  are  also  present,  particularly  sarco-lactic,  as  well  as 
acetic  and  formic. 

Of  carbohydrates,  glycogen  and  glucose  (or  maltose),  also  inosite. 

Nitrogenous  crystalline  bodies,  sncli  as  kreatm.,kreatinin,xanthin, 
hypo-xantliin^  or  carnin,  taurin,  vrea,  in  very  small  amount,  tiric  acid 
and  inosi7iic  acid. 

Salts,  the  chief  of  which  is  potassiiim  phosphate. 

Muscle  at  Rest. 

Physical  Condition. — During  rest  or  inactivity  a  muscle  has  a  slight 
but  very  perfect  Elasticity;  it  admits  of  being  considerably  stretched, 
but  returns  readily  and  completely  to  its  normal  condition.  In  the  liv- 
ing body  the  muscles  are  always  stretched  somewhat  beyond  their  natural 
length,  they  are  always  in  a  condition  of  slight  tension ;  an  arrangement 
which  enables  the  whole  force  of  the  contraction  to  be  utilized  in  ap- 
proximating the  points  of  attachment.  It  is  obvious  that  if  the  muscles 
were  lax,  the  first  part  of  the  contraction  until  the  muscle  became  tight 
would  be  wasted. 

There  is  no  doubt  that  even  in  a  condition  of  rest  Oxygen  is  abstracted 
from  the  Mood,  and  carbonic  acid  is  given  out  by  a  muscle;  for  the  blood 
becomes  venous  in  the  transit,  and  since  the  muscles  form  by  far  the 
largest  element  in  the  composition  of  the  body,  chemical  changes  must 
be  constantly  going  on  in  them  as  in  other  tissues  and  organs,  although 
not  necessarily  accompanied  by  contraction.  When  cut  out  of  the  body 
such  muscles  retain  their  contractility  longer  in  an  atmosphere  of  oxygen 
than  in  an  atmosphere  of  hydrogen  or  carbonic  acid,  and  during  life,  an 
amount  of  oxygen  is  no  doubt  necessary  to  the  manifestation  of  energy 
as  well  as  for  the  metabolism  going  on  in  the  resting  condition. 

The  reaction  of  living  muscle  in  a  resting  or  inactive  condition  is 
neutral  or  faintly  alkaline. 

In  muscles  which  have  been  removed  from  the  body,  it  has  been  found 
that  for  some  little  time  electrical  currents  can  be  demonstrated  passing 
from  point  to  ^wint  on  their  surface;  but  as  soon  as  the  muscles  die  or 
enter  into  rigor  mortis,  these  currents  disappear. 

The  demonstration  of  muscle  currents  is  usually  done  as  follows  : — The  frog's 
muscles  are  the  most  convenient  for  experiment ;  and  a  muscle  of  regular 
shape,  in  which  the  fibres  are  parallel,  is  selected.  The  ends  are  cut  off  by- 
clean  vertical  cuts,  and  the  resulting  piece  of  muscle  is  called  a  regular  muscle 
prism.  The  muscle  prism  is  insulated,  and  a  pair  of  non-polarizable  electrodes 
connected  with  a  very  delicate  galvanometer  (fig.  317)  is  applied  to  various 
points  of  the  prism,  and  by  a  deflection  of  the  needle  to  a  greater  or  less  extent 


MUSCLE-ITERVE   PHYSIOLOGY. 


503 


in  one  direction  or  another,  the  strength  and  direction  of  the  currents  in  the 
piece  of  muscle  can  be  estimated.  It  is  necessary  to  use  non -polar izable  and 
not  metallic  electrodes  in  this  experiment,  as  otherwise  there  is  no  certainty 
that  the  whole  of  the  current  observed  is  communicated  from  the  muscle  itself, 
and  is  not  derived  from  the  metallic  electrodes  arising  in  consequence  of  the 
action  of  the  saline  juices  of  the  tissues  upon  them.  The  form  of  the  non- 
polarizable  electrodes  is  a  modification  of  Du  Bois  Reymond's  apparatus  (fig. 
318) ,  which  consists  of  a  somewhat  flattened  glass  cylinder,  a,  drawn  abruptly 


•m 


Fix.  317.— Reflecting  galvanometer.  (Thomson.)  A.  The  galvanometer,  -which  consists  of 
two  systems  of  small  astatic  needles  suspended  by  a  fine  hair  from  a  support,  so  that  each  set  of 
needles  is  within  a  coil  of  tine  insulated  copper  wire,  that  forming  the  lower  coil  is  wound  in  an 
opposite  direction  to  the  upper.  Attached  to  the  upper  set  of  needles  is  a  small  mirror  about 
14  incli  in  diameter;  the  liglit  from  the  lamp  at  B  is  thrown  upon  this  little  mirror,  and  is  re- 
flected upon  the  scale  on  tiie  other  side  of  B,  not  shown  in  figure.  The  coils  /  /  are  arranged 
uDon  brass  upriglits,  and  thi^'ir  ends  are  carried  to  the  binding  screws.     The  whole  apparatus  is 

E laced  upon  a  vulcanite  jilatt'  capable  of  being  levelled  by  the  screw  supports,  and  is  covered 
y  a  brass-bound  glass  sliude,  L,  the  cover  of  which  is  also  of  brass,  and  supports  a  brass  rod, 
6,  on  which  moves  a  weak  curved  magnet,  m.  C  is  the  shunt  by  means  of  which  the  amount  of 
the  current  sent  into  the  galvanometer  may  be  regulated.  When  in  use  the  scale  is  placed 
about  three  feet  from  the  galvanometer,  which  is  arranged  east  and  west,  the  lamp  is  lighted, 
the  mirror  is  made  to  swing,  and  tlie  light  from  the  lamp  is  adjusted  to  fall  upon  it,  and  it  is 
then  regulated  until  the  reflected  spot  of  light  from  it  falls  upon  the  zero  of  the  scale.  The 
wires  from  the  non-polarizable  electrotles  touching  the  muscle  are  attached  to  the  outer  binding 
screws  of  the  galvanometer,  a  key  intervening  for  short -(.•ircuiting.  or  if  a  portion  only  of  the 
current  is  to  pass  into  the  galvanometer,  the  shunt  should  intervene  as  well  with  the  appropriate 
plug  in.  When  a  current  passes  into  the  galvanometer  tlie  needles  and,  with  them,  tiie  mirror, 
are  turned  to  the  right  or  left  according  to  the  direction  of  the  current.  The  amount  of  the  de- 
flection of  the  needle  is  marked  on  the  scale  by  the  spot  of  light  travelling  along  it. 

to  a  point,  and  fitted  to  a  socket  capable  of  movement,  and  attached  to  a  stand, 
A,  so  that  it  can  be  raised  or  lowered  as  required.  The  lower  portion  of  the 
cylinder  is  filled  witli  china  clay  moistened  with  saline  solution,  part  of  which 
projects  through   its  drawn-out  point ;  the  rest  of  the  cj-linder  is  fitted  with  a 


504 


HANDBOOK    OF    PHYSIOLOGY. 


saturated  solution  of  zinc  sulphate  into  which  dips  a  well  amalgamated  piece 
of  zinc  connected  by  means  of  a  wire  with  the  galvanometer.  In  this  way 
the  zinc  sulphate  forms  a  homogeneous  and  non-polarizable  conductor  between 
the  zinc  and  the  china  clay.  A  second  electrode  of  the  same  kind  is,  of  course, 
necessary. 


Fig.  318.— Diagram  of  Du  Bois  Reymond's  non-polarizable  electrodes,  a,  Glass  tube  filled 
with  a  saturated  solution  of  zinc  sulphate,  in  the  end,  c,  of  which  is  china  clay  drawn  out  to  a 
point ;  in  the  solution  a  well  amalgamated  zinc  rod  is  immersed  and  connected,  by  means  of  the 
wire  which  passes  through  a,  with  the  galvanometer.  The  remainder  of  the  apparatus  is  simply 
for  convenience  of  application.  The  muscle  and  the  end  of  the  second  electrode  are  to  the 
right  of  the  figure. 

In  a  regular  muscle  prism  tlie  currents  are  found  to  be  as  follows: — 

If  from  a  point  in  the  surface  aline — the  equator — be  drawn  across  the 

muscle  prism  equally  dividing  it,  currents  pass  from  this  point  to  points 

«way  from  it,  which  are  weak  if  the  points  are  near,  and  increased  in 


Fig.  319. — Diagram  of  the  currents  in  a  muscle  prism.    (Du  Bois  Reymond.) 


streDgth  as  the  points  are  further  and  further  away  from  the  equator; 
the  strongest  passing  from  the  equator  to  a  point  representing  the  middle 
of  the  cut  ends  (fig.  319,  2);  currents  also  pass  from  points  nearer  the 
equator  to  those  more  remote  (fig.  319,  1,  3,  4),  but  not  from  points 


MUSCLE-NEEVE    PHYSIOLOGY.  fiO.«) 

equally  distant  or  iso-electrio  points  (fig.  319,  6,  7,  8).  The  cut  ends 
are  always  negative  to  the  equator.  These  currents  are  constant  for  some 
time  after  removal  of  the  muscle  from  the  body,  and  in  fact  remain  as 
long  as  the  muscle  retains  its  life.  They  are  in  all  probability  due  to 
chemical  changes  going  on  in  the  muscles. 

The  currents  are  diminished  by  fatigue  and  are  increased  by  an  increase 
of  temperature  within  natural  limits,  if  the  uninjured  tendon  be  used  as 
the  end  of  the  muscle,  and  the  muscle  be  examined  -without  re- 
moval from  the  body,  the  currents  are  very  feeble,  but  they  are  at  once 
much  increased  by  injuring  the  muscle,  as  by  cutting  off  its  tendon. 
The  last  observation  appears  to  show  that  they  are  riglit  Avho  believe 
that  the  currents  do  not  exist  in  uninjured  muscles  insitn,  but  that  in- 
jury, either  mechanical,  chemical  or  thermal,  will  render  the  injured 
part  electrically  negative  to  other  points  on  the  muscle.  In  a  frog's 
heart  it  has  been  shown,  too,  that  no  currents  exist  during  its  inactivity, 
but  that  as  soon  as  it  is  injured  in  any  way  they  are  developed;  the  in- 
jured part  being  negative  to  the  rest  of  the  muscle.  The  currents  which 
have  been  above  described  are  called  either  natural  muscle  currents  or 
currents  of  rest,  according  as  they  are  looked  upon  as  always  existing  in 
muscle  or  as  developed  when  a  part  of  the  muscle  is  subjected  to  injury; 
in  either  case,  up  to  a  certain  point,  it  is  agreed  that  the  strength  of  the 
currents  is  in  direct  proportion  to  the  injury. 

Muscle  in  Activity. 

The  property  of  muscular  tissue,  by  Avhich  its  peculiar  functions  are 
exercised,  is  its  Contractilitu,  which  is  excited  by  all  kinds  of  stimuli  ap- 
plied either  directly  to  the  muscles,  or  indirectly  to  them  through  the 
medium  of  their  motor  nerves.  This  property,  although  commonly 
brought  into  action  through  the  nervous  system,  is  inherent  in  the 
muscular  tissue.  For — (1.)  it  may  be  manifested  in  a  muscle  which  is 
isolated  from  the  influence  of  the  nervous  system  by  division  of  the  nerves 
s-upplying  it,  so  long  as  the  natural  tissue  of  the  muscle  is  dulv  nourished ; 
and  (2.)  it  is  manifest  in  a  portion  of  muscular  fibre,  in  Avhich,  under 
the  microscope,  no  nerve-fibre  can  bo  traced.  (.3.)  Substances  such  as 
urari,  which  paralyze  the  nerve-endings  in  muscles,  do  not  at  all  dimin- 
ish the  irritability  of  the  muscle  itself. 

(4.)  When  a  muscle  is  fatigued,  a  Iccal  stimulation  is  followed  by  a 
contraction  of  a  small  part  of  the  fibre  in  the  immediate  vicinity  without 
any  regard  to  the  distribution  of  nerve-fibres. 

The  Conditions  which  Affect  the  Irritability  of  Muscle— that 
is,  its  readiness  of  resjionsc  t(i  stinnili — are  numerous.  The  chief  causes 
of  variation  in  irritability  are  the  following: 

Mood-Supply. — The  irritability  of  muscles  is  also  soon  lost,  unless  a 


506  HANDBOOK   OF   PHYSIOLOGY. 

supply  of  arterial  blood  to  them  is  kept  up.  Thus,  after  ligature  of  the 
main  arterial  trunk  of  a  limb,  the  power  of  moving  the  muscles  is  par- 
tially or  wholly  lost,  until  the  collateral  circulation  is  established;  and 
when,  in  animals,  the  abdominal  aorta  is  tied,  the  hind  legs  are  ren- 
dered almost  powerless. 

The  same  fact  may  be  readily  shown  by  compressing  the  abdominal 
aorta  in  a  rabbit  for  about  10  minutes;  if  the  pressure  be  released  and 
the  animal  be  placed  on  the  ground,  it  will  work  itself  along  with  its 
front  legs,  while  the  hind  legs  sprawl  helplessly  behind.  Gradually  the 
muscles  recover  their  power  and  become  quite  as  efficient  as  before. 

So,  also,  it  is  to  the  imperfect  supply  of  arterial  blood  to  the  muscular 
tissue  of  the  heart  that  the  cessation  of  the  action  of  this  organ  in  as- 
phyxia is  in  some  measure  due. 

Fatigue. — The  irritability  of  muscle  is  decreased  by  undue  functional 
activity.  The  cause  of  the  diminished  irritability  is  twofold — when  a 
muscle  contracts,  part  of  its  substance  is  expended,  part  of  its  store  of 
nutriment  is  exhausted,  and  it  cannot  readily  contract  again  until  the 
loss  is  made  up.  To  this  extent  fatigue  is  much  the  same  in  its  effect 
as  cutting  off  or  diminishing  the  blood-supply.  The  other  cause  for  the 
diminution  of  irritability  is  the  accumulation  of  poisonous  products  in 
the  lymphatics  of  the  muscle — substances  generated  during  contraction. 

Separation  from  Central  Nervous  System. — Generally  a  muscle  begins 
to  lose  its  irritability  to  all  forms  of  stimuli  about  two  weeks  after  its 
nerve  is  severed.  "Within  a  short  time,  however,  its  readiness  of  re- 
sponse to  mechanical  stimuli  and  to  direct  battery  currents  is  height- 
ened, while  to  induction  shocks  it  is  lessened.  The  increase  of  irrita- 
bility reaches  its  maximum  in  about  seven  weeks,  after  which  the 
irritability  to  all  forms  of  stimuli  diminishes,  until  it  is  completely  lost 
toward  the  end  of  the  seventh  or  eighth  month. 

The  loss  of  irritability  in  muscle  is  due  to  degenerative  changes  in 
its  protoplasm.  But  the  cause  of  the  degeneration  is  a  matter  of  con- 
troversy, being  considered  due  to  loss  of  trophic  influences  from  the 
central  nervous  system  on  the  one  hand,  and  to  circulatory  disturbances 
on  the  other. 

Use. — Not  only  irritability  but  strength  and  power  of  endurance  in 
muscle  are  increased  by  use.  The  effect  of  properly  regulated  exercises 
on  muscles  is  too  well  known  to  need  more  than  bare  mention.  And, 
on  the  contrary, 

Disuse  leads  to  diminution  or  loss  of  irritability.  This  fact  is  famil- 
iarly shown  Avhen  a  limb  is  disabled  for  a  time,  as  through  breaking  a 
bone,  in  the  stiffness  of  the  muscles  and  the  slowness  with  which  they 
respond  to  the  will. 


MUSCLE-NERVE    PHYSIOLOGY.  507 

Temperature. — The  irritability  of  muscle  is  increased  by  raising  its 
temperature  slightly  above  that  of  the  animal  from  which  it  has  been 
taken,  while  it  is  decreased  by  cooling.  If,  however,  the  temperature 
be  raised  too  high  (45°  C.  for  frog,  50°  C.  for  mammal),  the  muscle  en- 
ters into  a  condition  of  heat  rigor  and  its  irritability  is  forever  lost. 
After  cooling,  unless  the  cold  be  too  severe  and  prolonged,  the  irritabil- 
ity returns  as  the  temperature  is  raised.  The  effect  of  cold  on  irritabil- 
ity is  shown  in  the  superficial  muscles  of  the  face  in  winter. 

Chemicals  and  Drugs. — Most  chemical  substances  cause  a  marked 
alteration  of  irritability  in  muscle.  In  general  terms,  it  may  be  said 
that  those  which  produce  any  effect  at  all  at  first  increase  and  then 
diminish  irritability. 

Mechanical  stimuli  at  first  increase  and  then  diminish  the  irritability 
of  muscle.     If  they  are  powerful  enough,  the  muscle  is  destroyed. 

The  Phenomena  of  Muscular  Contraction. 

The  power  Avhich  muscles  possess  of  contraction  may  then  be  called 
forth  by  stimuli  of  various  kinds,  and  these  stimuli  may  also  be  applied 
directly  to  the  muscle  or  indirectly  to  the  nerve  supplying  it.  There  are 
distinct  advantages,  however,  in  applying  the  stimulus  to  the  nerve,  as 
it  is  more  convenient,  as  well  as  more  potent.  The  stimuli  are  of  four 
kinds,  viz. : — 

(1.)  Mechanical  stimuli,  as  by  a  blow,  pinch,  prick  of  the  muscle  or 
its  nerve,  will  produce  a  contraction,  repeated  on.  the  repetition  of  the 
stimulus;  but  if  applied  to  the  same  point  for  a  limited  number  of  times 
only,  as  such  stimuli  will  soon  destroy  the  irritability  of  the  preparation. 

(2.)  Thermal  Stimuli. — If  a  needle  be  heated  and  applied  to  a  muscle 
or  its  nerve,  the  muscle  will  contract.  A  temperature  of  over  45°  C. 
(113°  F.)  will  cause  the  muscles  of  a  frog  to  pass  into  a  condition  known 
as  heat  rigor. 

(3.)  Chemical  Stimuli. — A  great  variety  of  chemical  substances  will 
excite  the  contraction  of  muscles,  some  substances  being  more  potent  in 
irritating  the  muscle  itself,  and  other  substances  having  more  effect  upon 
the  nerve.  Of  the  former  may  be.  mentioned,  dilute  acids,  salts  of  cer- 
tain metals,  e.g.,  zinc,  copper  and  iron;  to  the  latter  belong  strong 
glycerin,  strong  acids,  ammonia  and  bile  salts  in  strong  solution. 

(4.)  Electrical  Stimuli. — For  the  purpose  of  experiment  electrical 
stimuli  arc  most  frequently  used,  as  the  strength  of  the  stimulus  may  be 
more  conveniently  regulated.  Any  form  of  electrical  current  may  bo 
employed  for  this  purpose,  but  galvanism  or  the  induced  current  is  usu- 
ally chosen. 


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HANDBOOK   OF   rHYSIOLOGY. 


Galvanic  currents  are  usually  obtained  by  the  employment  of  a  continuouti 
current  batterj'^  such  as  that  of  Daniell,  by  which  an  electrical  current  which 
varies  but  little  in  intensitj^  is  obtained.  The  battery  (fig.  320)  consists  of  a 
positive  plate  of  well-amalgamated  zinc  immersed  in  a  porous  cell,  containing 
dilute  sulphuric  acid ;  and  this  cell  is  again  contained  within  a  large  copper 
vessel  (forming  the  negative  plate),  containing  besides  a  saturated  solution  of 
copper  sulphate.  The  electrical  current  is  made  continuous  by  the  use  of  the 
two  fluids  in  the  following  manner.  The  action  of  the  dilute  sulphuric  acid 
upon  the  zinc  plate  partly  dissolves  it,  and  liberates  hydrogen,  and  this  gas 
passes  through  the  porous  vessel,  and  decomposes  the  copper  sulphate  into  copper 


CnSO- 


Fig.  320.— Diagram  of  a  Daniell's  battery. 

and  sulphuric  acid.  The  former  is  deposited  upon  the  copper  plate,  and  the 
latter  passes  through  the  porous  vessel  to  renew  the  sulphuric  acid  which  is 
being  used  up.  The  copper  sulphate  solution  is  renewed  by  spare  crystals  of 
the  salt,  which  are  kept  on  a  little  shelf  attached  to  the  copper  plate,  and 
slightly  below  the  level  of  the  solution  in  the  vessel.  The  current  of  electricity 
supplied  by  this  battery  will  continue  without  variation  for  a  considerable  time. 
Other  continuous  current  batteries,  such  as  Grove's,  may  be  used  in  place  of 
Daniell's.  The  way  in  which  the  apparatus  is  an-anged  is  to  attach  wires  to 
the  copper  and  zinc  plates,  and  to  bring  them  to  a  key,  which  is  a  little  appa- 
ratus for  connecting  the  wires  of  a  battery.  One  often  employed  is  Du  Bois 
Reymond's  (fig.  321)  ;  it  consists  of  two  pieces  of  brass  about  an  inch  long,  in 
each  of  which  are  two  holes  for  wires  and  binding  screw,  to  hold  them  tightly  ; 
these  pieces  of  brass  are  fixed  upon  a  vulcanite  plate,  to  the  under  surface  of 
which  is  a  screw  clamp  by  which  it  can  be  secured  to  the  table.  The  interval 
between  the  pieces  of  brass  can  be  bridged  over  by  means  of  a  third  thinner 
piece  of  similar  metal  fixed  by  a  screw  to  one  of  the  brass  pieces,  and  capable 
of  movement  by  a  handle  at  right  angles,  so  as  to  touch  the  other  piece  of 
brass.  If  the  wires  from  the  battery  are  brought  to  the  inner  binding  screws, 
and  the  bridge  connects  them,  the  current  jDasses  across  it  and  back  to  the 
battery.  Wires  are  connected  with  the  outer  binding  screws,  and  the  other 
ends  are  joined  together  for  about  two  inches,  but,  being  covered  except  at 
their  points,  are  insulated ;  the  uncovered  points  are  about  an  eighth  of  an 
inch  apart.  These  wires  are  the  electrodes,  and  the  electrical  stimulus  is  applied 
to  the  muscle  through  them,  if  they  are  placed  behind  its  nerve.  When  the 
connection  between  the  two  brass  plates  of  the  key  is  broken  by  depressing  the 
iiandle  of  the  bridge,  the  key  is  then  said  to  be  opened. 

An  induced  current  is  developed  hy  means  of  an  apparatus,  called  an  indue- 


MUSCL£-:s'£KVE    PlllblOLUGY. 


509 


Hon  coil,  and  the  one  employed  for  physiological  pui-poses  is  mostly  Du  Bois 
Reymond's,  the  one  seen  in  fig.   323. 

"Wires  from  a  battery  are  brought  to  the  two  binding  screws  d'  and  d.  a  key 
intervening.     These  binding  screws  are  the  ends  of  a  coil  of  coarse  covered  wire 


Fig.  321.— Du  Bois  Reymond's  Key. 


Fig  322.— Mercury  Key. 


c,  called  the  primary  coil.  The  ends  of  a  coil  of  finer  covered  wire  g,  are  attached 
to  two  binding  screws  to  the  left  of  the  figure,  one  only  of  which  is  visible. 
This  is  the  secondary  coil,  and  is  capable  of  being  moved  nearer  to  c  along  a 
groove  and  graduated  scale.  To  the  binding  screws  to  the  left  of  g,  the  wires 
of  electrodes  used  to  stimulate  the  inuscle  are  attached.     If  the  key  in  the  cir- 


K^g*- 


Fig.  823.— Du  Bois  Reymond's  induction  coil. 

cuit  of  wires  from  the  battery  to  the  primaiy  coil  (primary  circuit)  be  closed, 
the  current  from  the  battery  passes  through  the  primary  coil,  and  across  the 
key  to  the  battery,  and  continues  to  pass  as  long  as  (he  key  continues  closed. 
At  the  moment  of  closure  of  tlie  key,  at  thn  exact  instant  of  the  completion  of 


510 


HANDBOOK   OF   PHYSIOLOGY. 


the  primary  circuit,  an  instantaneous  current  of  electricity  is  induced  in  the 
secondary  coil,  g,  if  it  be  sufficiently  near  and  in  line  with  the  primaiy  coil ; 
and  the  nearer  it  is  to  c,  the  stronger  is  the  current  induced.  The  current 
is  only  momentary  in  duration  and  does  not  continue  during  the  whole  of  the 
period  while  the  primary  circuit  is  complete.  When,  however,  the  primary 
current  is  broken  by  opening  the  key,  a  second,  also  momentary,  current  is 
induced  in  g.  The  former  induced  current  is  called  the  making  and  the  latter 
the  breaking  shock ;  the  former  is  in  the  opposite  direction  to,  and  the  latter  in 
the  same  as,  the  primary  current. 

The  induction  coil  may  be  used  to  produce  a  rapid  series  of  shocks  by  means 
of  another  and  accessory  part  of  the  apparatus  at  the  right  of  the  fig. ,  called 
the  magnetic  intei^nipter.  If  the  wires  from  a  battery  are  connected  with  the 
two  pillars  by  the  binding  screws,  one  below  c,  and  the  other,  a,  the  course  of 


Fig.  334.— Diagram  of  the  course  of  the  current  in  the  magnetic  interrupter  of  Du  Bois  Rey- 
mond's  induction  coil.     (Helmholz's  modification.) 

the  current  is  indicated  in  fig.  324,  the  direction  being  indicated  by  the  arrows. 
The  current  passes  up  the  pillar  from  e,  and  along  the  springs  if  the  end  of  d 
is  close  to  the  spring,  the  current  passes  to  the  primary  coil  c,  and  to  wires 
covering  two  upright  pillars  of  soft  iron,  from  them  to  the  pillar  a,  and  out 
by  the  wires  to  the  battery ;  in  passing  along  the  wire,  h,  the  soft  iron  is  con- 
verted into  a  magnet,  and  so  attracts  the  hammer,  /,  of  the  spring,  breaks  the 
connection  of  the  spring  with  d' ,  and  so  cuts  off  the  current  from  the  primary 
coil,  and  also  from  the  electro-magnet.  As  the  pillars,  h,  are  no  longer  mag- 
netized the  spring  is  released,  and  the  current  passes  in  the  first  direction, 
and  is  in  like  manner  interrupted.  At  each  make  and  break  of  the  primary 
current,  currents  corresponding  are  induced  in  the  secondary  coil.  These  cur- 
rents are  opposite  in  direction,  but  are  not  equal  in  intensity,  .the  break  shock 
being  greater.  In  order  that  the  shocks  should  be  nearly  equal  at  the  make 
and  break,  a  wire  (fig.  324,  e')  connects  e  andd',  and  the  screw  d'  is  raised  out 
of  reach  of  the  spring,  and  d  is  raised  (as  in  fig.  324) ,  so  that  part  of  the  cur- 
rent always  passes  through  the  primary  coil  and  electro- magnet.  When  the 
spring  touches  d,  the  current  in  h  is  diminished,  but  never  entirely  withdrawn, 
and  the  primary  current  is  altered  in  intensity  at  each  contact  of  the  spring 
with  d,  but  never  entirely  broken. 

Record  of  Muscular  Contraction  under  Stimuli. — The  muscles  of  the  frog  are 
most  convenient  for  the  purpose  of  recording  contractions.  The  frog  is  pithed, 
that  is  to  say,  its  central  nervous  system  is  entirely  destroyed  by  the  insertion 
of  a  stout  needle  into  the  spinal  cord,  and  the  parts  above  it.  One  of  its  lower 
extremities  is  used  in  the  following  manner.  The  large  trunk  of  the  sciatic 
nexve  is  dissected  out  at  the  back  of  the  thigh,  and  a  pair  of  electrodes  is 


MU80LB-KERVE    PHT8I0L0OY. 


511 


Fig.  325.— Ai-rauK'einent  of  the  apparatus  necessary  for  recording  muscle  contractions 
with  a  revolving  cylinder  carrying  smoked  paper.  A,  Revolving  cylinder;  B,  the  frog  arranged 
upon  a  cork-covei-ed  board  which  is  capable  of  being  raised  or  lowered  on  the  upright,  which 
also  can  be  moved  along  a  solid  triangular  bar  of  metal  attached  to  the  base  of  the  recording 
apparatus— the  tendon  of  the  gastrocnemius  is  attached  to  Uie  writing  lever,  properly  weighted, 
by  a  ligature.  The  electrodes  from  the  secondary  coil  pass  to  the  apparatus— being,  for  the 
sake  of  convenience,  first  of  all  brought  to  a  key,  D  CDu  Bois  Reymond's) ;  C,  the  induction 
coil;  F,  the  battery  (in  this  fig.  a  bichromate  one);  E,  the  key  (Morse's)  in  the  primary  circuit. 

inserted  behind  it.  The  tendo-achillis  is  divided  from  its  attachment  to  the 
OS  calcis,  and  a  ligature  is  tightly  tied  round  it.  This  tendon  is  part  of  the 
broad  muscle  of  the  thigh  (gastrocnemius),  which  arises  from  above  the  con- 


Fig,  sac.— Moist  Chamber. 


513 


HANDBOOK   OF    PHYSIOLOGY. 


dyles  of  the  femur.  The  femur  is  now  fixed  to  a  board  covered  with  cork, 
and  the  ligature  attached  to  the  tendon  is  tied  to  the  upright  of  a  piece  of 
metal  bent  at  right  angles  (fig.  325,  b)  ,  which  is  capable  of  movement  about  a 
pivot  at  its  knee,  the  horizontal  portion  carrying  a  writing  lever  (myograph) . 
When  the  muscle  conti'acts,  the  lever  is  raised.  It  is  necessary  to  attach  a 
small  weight  to  the  lever.  In  this  arrangement  the  muscle  is  in  situ,  and  the 
nerve  disturbed  from  its  relations  as  little  as  possible. 

The  muscle  may,  however,  be  detached  from  the  body  with  the  lower  end  of 
the  femur  from  which  it  arises,  and  the  nerve  going  to  it  may  be  taken  away 
with  it.  The  femur  is  divided  at  about  the  lower  third.  The  bone  is  held  in  a 
firm  clamp,  the  nerve  is  placed  upon  two  electrodes  connected  with  an  induc- 
tion apparatus,  and  the  lower  end  of  the  muscle  is  connected  by  means  of  a 
ligature  attached  to  its  tendon  with  a  lever  which  can  write  on  a  recording 
apparatus. 

To  prevent  evaporation  this  so-called  nerve-muscle  preparation  is  placed  under 


Fi=r.  327.— Simple  form  of  pendulum  myograph  and  accessory  parts.  A,  Pivot  upon  which 
peniiiiium  swing:s:  B,  catch  on  lower  end  of  myograph  opening  the  key,  C,  in  its  swing;  A  a 
spring-catch  which  retains  myograph,  as  indicated  by  dotted  lines,  and  on  pressing  down  the 
liandle  of  which  the  pendulum  swings  along  the  arc  to  D  on  the  left  of  figure,  and  is  caught  by 
its  spring. 

a  glass  shade  (moist  chamber,  fig.  326),  the  air  in  wliicli  is  kept  moist  by  mean.s 
of  blotting  paper  saturated  with  saline  solution. 

Effects  of  a  Single  Induction  Shock,— With  a  nerve-muscle  preparation 
arranged  in  either  of  the  above  ways,  on  closing  or  opening  the  key  in  the  pri- 
mary circuit,  we  obtain  and  can  record  a  contraction,  and  if  we  use  the  clock 
work  apparatus  revolving  rapidly,  a  curve  is  traced  such  as  is  shown  in  fig.  £>2» 

Another  way  of  recording  the  contraction  is  by  the  use  of  the  pendulum 
myograph  (fig.  327).  Here  the  movement  of  the  pendulum  along  a  certain  arc 
issubstituted  for  the  clockwork  DioveiiK'nt  of  the,  other  apparatus.     The  pen- 


MUaCLE-JsrJiltVE   PHYaiOLOGY. 


513 


dulum  carries  a  smoked  glass  plate  upon  which  the  writing  lever  of  a  myo- 
graph is  made  to  mark.  The  opening  or  breaking  shock  is  sent  into  the 
nerve-muscle  preparation  by  the  pendulum  in  its  swing  opening  a  key  (fig. 
337,   C.)  in  the  primary  circuit. 

Single  Muscle  Contractions. — The  tracing  {muscle  curve)  ob- 
tained of  a  single  muscle  contraction  or  twitch  is  seen  in  fig.  328,  and 
may  be  thus  explained. 

The  upper  line  {m)  represents  the  curve  traced  by  the  end  of  the  lever 
in  connection  with  a  muscle  after  stimulation  of  the  muscle  by  a  single 


Fig.  328.— Muscle-curve  obtained  by  means  of  the  pendulum  myograph,  s,  indicates  the 
exact  instant  of  the  induction  shock ;  c,  commencement ;  and  m  x,  the  maximum  elevation  of 
lever;  ^  the  line  of  a  vibrating  tuning-fork.     (M.  Foster.) 

induction-shock:  the  middle-line  (?)  is  that  described  by  the  marking- 
lever,  and  indicates  by  a  sudden  drop  the  exact  instant  at  which  the 
induction-shock  was  given.  The  lower  wavy  line  (/)  is  traced  by  a 
vibrating  tuning-fork,  and  serves  to  measure  precisely  the  time  occupied 
in  each  part  of  the  contraction. 

It  will  be  observed  that  after  the  stimulus  has  been  applied,  as  indi- 
cated by  the  vertical  line  s,  there  is  an  interval  before  the  contraction 
commences,  as  indicated  by  the  line  c.  This  interval,  termed  (a)  the 
latent  period,  when  measured  by  the  number  of  vibrations  of  the  tun- 
ing-fork between  the  lines  s  and  c,  is  found  to  be  about  y^  sec.  The 
latent  period  is  longer  in  some  muscles  than  in  others,  and  differs  also 
according  to  the  condition  of  the  muscle,  being  longer  in  fatigued  mus- 
cles, and  the  kind  of  stimulus  employed.  During  the  latent  period  there 
is  no  apparent  change  in  the  muscle. 

The  second  part  is  the  (h)  stage  of  contraction  proper.  The  leve; 
is  raised  by  the  sudden  contraction  of  the  muscle.  The  contraction  is  at 
first  very  rapid,  but  then  progresses  more  slowly  to  its  maximum,  indi- 
cated by  the  line  m  .r,  drawn  through  its  highest  point.  It  occupies  in 
the  figure  y|^  sec.  (c)  The  next  stage,  stage  of  elongation.  After 
33 


514  HANDBOOK   OF    PHYSIOLOGY. 

reaching  its  highest  point,  the  lever  begins  to  descend,  in  consequence 
of  the  elongation  of  the  muscle.  At  first  the  fall  is  rapid,  but  then  be- 
comes more  gradual  until  the  lever  reaches  the  abscissa  or  base  line,  and 
the  muscle  attains  its  pre-contraction  length,  indicated  in  the  figure  by 
the  line  c'.  The  stage  occupies  yf-^  second.  Very  often  after  the  main 
contraction  the  lever  rises  once  or  twice  to  a  slight  degree,  producing 
curves,  one  of  which  is  seen  in  fig.  330.  These  contractions,  due  to  the 
elasticity  of  the  muscle,  are  called  most  properly  (d)  stage  of  elastic 
after-vibration,  or  contraction  remainder. 

The  latent  period  has  been  found  by  exact  methods  of  determination 
to  be  only  j^-g-  second  in  length.  The  remainder  of  the  time  indicated 
above  is  occupied  in  the  propagation  of  the  impulse  along  the  nerve  and 
in  overcoming  the  resistance  of  the  apparatus  used  for  recording  the 
curve. 

Accompaniments  of  Muscular  Contraction. 

(1.)  Heat  is  developed  in  the  contraction  of  muscles.  Becquerel  and 
Breschet  found,  with  the  thermo-multiplier,  about  .5°  0.  of  heat  pro- 
duced by  each  forcible  contraction  of  a  man's  biceps;  and  when  the 
actions  were  long  continued,  the  temperature  of  the  muscle  increased  1°. 
This  estimate  is  probably  high,  as  in  the  frog's  muscle  a  considerable 
contraction  has  been  found  to  produce  an  elevation  of  temperature  equal 
on  an  average  to  less  than  ^°  C.  The  cause  of  the  rise  of  temperature 
is  the  increased  chemical  activity  at  the  time  of  contraction.  As  we 
have  already  seen  (Animal  Heat),  muscles  produce  heat  even  when 
uncontracted. 

(2.)  Somid  is  produced,  as  mentioned  above,  when  voluntary  muscles 
contract.  "Wollaston  showed  that  this  sound  might  be  easily  heard  by 
placing  the  tip  of  the  little  finger  in  the  ear,  and  then  making  some 
muscles  contract,  as  those  of  the  ball  of  the  thumb,  whose  sound  may  be 
conducted  to  the  ear  through  the  substance  of  the  hand  and  finger.  A 
low  shaking  or  rumbling  sound  is  heard.  The  sound  is  due  to  the  vi- 
bration of  the  individual  muscle  fibres.  Experimentally  it  has  been 
found  that  the  number  of  vibrations  corresponds  to  the  number  of  ex- 
citations, and  that  muscle  exhibits  no  normal  rate  of  vibration,  except 
in  so  far  as  a  rate  is  expressed  in  the  discharge  of  nerve  impulses  from 
the  cells  controlling  the  muscle.  Nerve  cells  do  not  send  out  a  single, 
but  a  series  of  impulses.  Moreover,  the  muscle  sound  corresponds  to 
the  rate  at  which  the  muscle  is  stimulated. 

Helmholtz  found  that,  in  the  voluntary  contraction  of  muscle,  only 
reeds  having  a  vibration  of  18-20  per  second  were  thrown  into  motion; 
and  since  this  rate  is  too  slow  to  produce  a  tone,  he  concluded  that  th^ 


MUSCLE-NERVE    PHYSIOLOGY.  515 

sound  heard  was  the  first  overtone.  But  tliis  rate  has  been  called  into 
question  by  later  experiments,  in  which  a  tambour,  connected  with  a 
recording  apparatus,  is  placed  on  a  contracting  muscle.  The  rate  of 
vibration  thus  obtained  is  stated  to  be  from  8-13  per  second,  according 
to  the  muscle  investigated  and  its  condition.  Tremors  are  shown  by  a 
muscle  in  fatigue  and  in  many  conditions  of  disease.  Since  the  reso- 
nance tone  of  tlie  membrana  tympani  corresponds  to  36-40  vibrations  a 
second,  the  muscle  sound  does  not  indicate  the  number  of  vibrations  in 
a  contracting  muscle. 

(3.)  Changes  in  Shape. — There  is  a  considerable  difference  of  opinion 
as  to  the  mode  in  which  the  transversely  striated  muscuhir  fibres  con- 
tract The  most  probable  account  is,  that  the  contraction  is  effected 
by  an  approximation  of  the  constituent  parts  of  the  fibrils,  which,  at 
the  instant  of  contraction,  without  any  alteration  in  their  general  direc- 
tion, become  closer,  flatter,  and  wider;  a  condition  which  is  rendered 
evident  by  the  approximation  of  the  transverse  stride  seen  on  the  surface 
of  the  fasciculus,  and  by  its  increased  breadth  and  thickness.  The 
appearance  of  the  zigzag  lines  into  which  it  was  supposed  the  fibres  are 
thrown  in  contraction,  is  due  to  the  relaxation  of  a  fibre  which  has  been 
recently  contracted,  and  is  not  at  once  stretched  again  by  some  antago- 
nist fibre,  or  whoso  extremities  are  kept  close  together  by  the  contractions 
of  other  fibres.  The  contraction  is  therefore  a  simple  and,  according  to 
Ed.  Weber,  a  uniform,  simultaneous,  and  steady  shortening  of  each  fibre 
and  its  contents.  What  each  fibril  or  fibre  loses  in  length,  it  gains  in 
thickness:  the  contraction  is  a  change  of  form  not  of  size;  it  is,  there- 
fore, not  attended  with  any  diminution  in  bulk,  from  condensation  of 
the  tissue.  This  has  been  proved  for  entire  muscles,  by  making  a  mass 
of  muscles,  or  many  fibres  together,  contract  in  a  vessel  full  of  water, 
with  which  a  fine,  perpendicular,  graduated  tube  communicates.  Any 
diminution  of  the  bulk  of  the  contracting  muscle  would  be  attended  by 
a  fall  of  fluid  in  the  tube;  but  when  the  experiment  is  carefully  per- 
formed, the  level  of  the  water  in  the  tube  remains  the  same,  whether 
the  muscle  be  contracted  or  not. 

In  thus  shortening,  muscles  appear  to  swell  up,  becoming  rotrnder,  mure 
prominent,  harder,  and  apparently  tougher.  But  this  hardness  of  muscle 
in  the  state  of  contraction  is  not  due  to  increased  firmness  or  condensa- 
tion of  the  muscular  tissue,  but  to  the  increased  tension  to  which  the 
fibres,  as  well  as  their  tendons  and  other  tissues,  are  subjected  from  tlio 
resistance  ordinarily  opposed  to  their  contraction.  AVhen  no  resistance 
is  offered,  as  when  a  muscle  is  cut  off  from  its  tendon,  not  only  is  no 
hardness  perceived  during  contraction,  but  the  muscular  tissue  is  even 
softer,  more  extensile,  and  less  elastic  than  in  its  ordinary  uncontracteil 
state.     During  contraction  in  each  fil)re  it  is  said  that  the  anisotropous 


516 


HANDBOOK   OF   PHYSIOLOGY. 


or  doubly  refractive  elements  become  less  refractive  and  the  singly  re- 
fractive more  so  {lag.  329). 

(4.)  Chemical  Changes. — (a)  The  reaction  of  the  muscle  which  is 
normally  alkaline  or  neutral  becomes  decidedly  acid,  from  the  develop- 
ment of  sarcolactic  acid,  (i)  The  muscle  gives  out  carbonic  acid  gas 
and  takes  up  oxygen,  the  amount  of  the  CO^  given  out  not  appearing  to 
be  entirely  dependent  upon  the  0  taken  in,  and  so  doubtless  in  part 
arising  from  some  other  source.  (c)  Certain  imperfectly  understood 
chemical  changes  occur,  in  all  probability  connected  with  (a)  and  (b). 
Glycogen  is  diminished,  and  glucose,  or  muscle  sugar  (inosite)  appears; 
the  extractives  are  increased. 

(o.)  Electrical  Changes. — When  a  muscle  contracts  the  natural  muscle 
current  or  currents  of  rest  undergo  a  distinct  diminution,  which  is  due 
to  the  appearance  in  the  actively  contracting  muscle  of  currents  in  an 
opposite  direction  to  those  existing  in  the  muscle  at  rest.  This  causes 
a  temporary  deflection  of  the  needle  of  a  galvanometer  in  a  direction 
opposite  to  the  original  current,  and  is  called  by  some  the  negative  vari- 
ation of  the  muscle  current,  and  by  others  a  current  of  action. 


Fig.  329. — The  microscopie  appearances  during  a  muscular  contraction  in  the  individual 
fibrillae,  after  Engelmann.  1.  A  passive  muscle-fibre;  c  to  d  =  doubly  refractive  discs,  with 
median  disc  a  b  in  it;  h  and  g  are  lateral  discs;  f  and  e  are  secondary  discs,  only  slightly  doubly 
refractive;  fig.  on  right  same  fibre  in  polarized  light;  bright  partis  doubly  refracted,  black  ends 
not  so.  2.  Transition  stage;  and  3.  Stage  of  entire  contraction;  in  each  case  the  right-hand 
figure  represents  the  effect  of  polarized  light.  (Landois  after  Engelmann.) 

Conditions  which  Affect  the  Characters  of  the  Contraction. 

— In  addition  to  the  factors  already  cousidered  which  influence  the  irri- 
tability of  muscle  as  such,  these  and  others  may  affect  the  characters  of 
its  contraction  and  hence  the  curve  produced. 

Effect  of  Load. — "Within  certain  limits  a  muscle  contracts  more  pow- 
erfully when  acting  against  resistance — that  is,  when  it  is  loaded.  Be- 
yond this  point  of  maximum  contraction,  however,  increase  of  load  di- 
minishes the  height  and  duration  of  contraction  and  increases  the  length 
of  the  latent  period. 

Effect  of  Fatigue. — As  already  stated,  exercise  increases  the  strength 
of  muscles,  so  that  the  first  effect  of  contraction  is  to  increase  the  height 
of  the  curve;  but  if  the  stimulation  be  kept  up  and  the  muscle  be  made 
to  contract  frequently,  both  the  height  and  form  of  the  curve  are  altered. 
The  latent  period  is  lengthened,  the  height  of  the  curve  is  lessened,  and 


MUSCLE-NEKVE    PHYSIOLOGY.  517 

the  duration  of  the  contraction  is  much  prolonged.  Later  a  condition 
is  reached  in  ^vhich  the  nmsclo  remains  more  or  less  contracted  for  a 
considerable  time,     Tliis  condition  is  called  contracture. 

Effect  of  Temperature. — Heat  up  to  a  certain  point  increases  the  irri- 
tability of  muscle  and  favors  rapidity  in  chemical  activity,  with  the  re- 
sult that  when  it  contracts  the  latent  period  is  shortened,  the  height  of 
the  wave  is  increased,  and  the  duration  of  the  contraction  is  lessened. 
Cold  produces  contrary  effects. 

Eff'ect  of  Drugs. — Veratrine  does  not  alter  the  rapidity  with  which 
contraction  occurs,  hut  enormously  prolongs  the  stage  of  relaxation. 
The  salts  of  barium  act  similarly,  and  to  a  less  extent  those  of  calcium 
and  strontium.  In  this  connection  it  is  interesting  to  recall  that  supra- 
renal extract  acts  likewise  on  voluntary  muscles. 

Effect  of  Strength  of  Stimulus. — A  strength  of  current  that  is  just 
sufficient  to  give  a  contraction  is  called  a  minimal  stimulus.  As  the 
strength  of  the  current  is  increased,  the  height  of  the  contraction  curve 
increases  until  the  maximal  stimulus  is  reached,  beyond  which  no  in- 
crease occurs.  The  latent  period  shortens  with  increased  strength  of 
stimulus. 

Effect  of  Rate  of  Stimulation. — If  we  stimulate  the  nerve-muscle 
preparation  with  two  induction  shocks,  one  immediately  after  the  other, 
when  the  point  of  stimulation  of  the  second  one  corresponds  to  the 
maximum  of  the  first,  a  second  curve  (fig.  330)  will  occur,  which  will 


Fitr  330  — Traciner  of  a  double  muscle-curve.  To  be  read  from  left  to  right.  While  the 
tnuscle  was  engaged  in  the  first  contraction  (whose  complete  course,  had  nothing  intervened  is 
indicated  by  the  dotted  line^),  a  second  induction-shock  was  thrown  in  at  such  a  time  that  the 
secoml  contraction  began  just  as  the  first  was  beginning  to  decline  The  second  curve  is  seen 
to  start  from  the  first,  as  does  the  first  from  the  base  line.     (M.  Foster.; 

commence  at  the  highest  point  of  the  first  and  will  rise  nearly  as  high, 
so  that  the  sum  of  the  height  of  the  two  curves  almost  exactly  equals 
twice  the  height  of  the  first.  If  a  third  and  fourth  shock  be  passed,  a 
similar  effect  will  ensue,  and  curves  one  above  the  other  will  be  traced, 
the  third  being  slightly  lower  than  the  second,  and  the  fourth  than  the 
third.     If  a  more  numerous  series  of  shocks  occur,  however,  the  lever 


518  HANDBOOK   OF   PHYSIOLOGY. 

after  a  time  ceases  to  rise  any  further,  and  the  contraction,  which  has 
reached  its  maximum,  is  maintained.  The  condition  which  ensues  is 
called  Tetanus.  A  tetanus  is  really  a  summation  of  contractions,  but 
unless  the  stimuli  become  very  rapid  indeed,  the  muscle  will  still  be  in  a 
condition  of  vibratory  contraction  and  not  of  unvarying  contraction. 


Fig.  331.— Curve  of  tetanus,  oDtained  from  the  gastrocnemius  of  a  frog,  where  the  shocks 
were  sent  in  from  an  induction  coil,  about  sixteen  times  a  second,  by  the  interruption  of  the 
primary  current  by  means  of  a  vibrating  spring,  which  dipped  into  a  cup  of  mercury,  and  broke 
the  primary  current  at  each  vibration. 

If  the  shocks,  however,  be  repeated  at  very  short  intervals,  being  15 
per  second  for  the  frog's  muscle,  but  varying  in  each  animal,  the  muscle 
contracts  to  its  utmost  suddenly  and  continues  at  its  maximum  contrac- 
tion for  some  time  and  the  lever  rises  almost  perpendicularly,  and  then 
describes  a  straight  line  (fig.  332).  If  the  stimuli  are  not  quite  so  rapid 
the  line  of  maximum  contraction  becomes  somewhat  wavy,  indicating  a 
slight  tendency  of  the  muscle  to  relax  during  the  intervals  between,  the 
stimuli  (fig.  331). 

Muscular  Work. — We  have  seen  that  ivorh  is  estimated  by  multi- 
plying the  weight  raised,  by  the  height  through  which  it  has  been  lifted. 
It  has  been  found  that  in  order  to  obtain  the  maximum  of  work  a  mus- 
cle must  be  moderately  loaded:  if  the  weight  is  increased  beyond  a  cer- 
tain point,  however,  the  muscle  becomes  strained  and  raises  it  through 


Fig.  333,— Curve  of  tetanus,  from  a  series  of  very  rapid  shocks  from  a  magnetic  interrupter. 

SO  small  a  distance  that  less  work  is  accomplished.  If  the  load  is  still 
further  increased,  the  muscle  is  completely  overtaxed  and  cannot  raise 
the  weight.  No  work  is  then  done  at  all.  Practical  illustrations  of 
these  facts  must  be  familiar  to  every  one. 


MUSCLE -NERVE    PHYSIOLOGY.  519 

The  power  of  a  muscle  is  usually  measured  by  the  maximum  weight  which 
it  will  support  without  stretching.  In  man  this  is  readily  determined  by  weight- 
ing the  body  to  such  an  extent  that  it  can  no  longer  be  raised  on  tiptoe :  thus 
the  power  of  the  calf -muscles  is  determined.  The  power  of  a  muscle  thus  esti- 
mated depends  of  course  upon  its  cross-section.  The  power  of  a  human  muscle 
is  from  two  to  tlxree  times  as  great  as  a  frog's  muscle  of  the  same  sectional  area. 

Fatigue  of  Muscle. — A  muscle  becomes  rapidly  exhausted  from  re- 
peated stimulation,  and  the  more  rapidly,  the  more  quickly  the  induc- 
tion-shocks succeed  each  other.  This  is  indicated  by  the  diminished 
height  of  the  muscular  contractions. 

A  fatigued  muscle  has  a  much  longer  latent  period  than  a  fresh  one. 
The  slowness  with  which  muscles  respond  to  the  will  when  fatigued,  must 
be  familiar  to  every  one. 

In  a  muscle  which  is  exhausted,  stimulation  only  causes  a  contraction 
producing  a  local  bulging  near  the  point  irritated.  A  similar  effect 
may  be  produced  in  a  fresh  muscle  by  a  sharp  blow,  as  in  striking  the 
biceps  smartly  with  the  edge  of  the  hand,  when  a  hard  muscular  swelling 
is  instantly  formed. 

As  we  have  seen  in  discussing  the  irritability  of  muscle,  the  cause  of 
fatigue  is  twofold,  being  in  part  due  to  its  nutritive  condition,  and  in 
part  to  the  accumulation  of  poisonous  products  formed  during  contrac- 
tion— probably  sarcolactic  acid,  chiefly.  In  a  living  animal  these  poi- 
sonous products  exert  their  influence  not  only  upon  the  muscle  or  mus- 
cles immediately  concerned  in  contraction,  but  upon  the  musculature  of 
the  body  generally,  and  the  effect  remains  until  they  are  eliminated 
from  the  body.  Massage  of  the  muscles  increases  the  passage  of  them 
into  the  general  blood-stream  and  the  rapidity  of  their  elimination. 

Under  normal  circumstances  muscles  do  not  become  completely  fa- 
tigued, for  the  reason  that  the  nerve  cells  which  send  out  the  impulses 
for  contraction  become  fatigued  sooner  than  the  muscles  themselves  do. 
Nerve  cells,  however,  recover  from  fatigue  more  quickly  than  muscles. 
These  facts  are  sometimes  shown  when  one  feels  utterly  exhausted  and 
scarcely  able  to  drag  one  foot  after  another,  yet  under  a  strong  effort  of 
will,  as  from  fright,  is  able  to  make  unwonted  effort. 

Response  to  Stimuli  in  Voluntary  and  Involuntary  Muscles. 
— The  two  kinds  of  fibres,  the  striped  and  the  unstriped,  havT  charac- 
teristic differences  in  the  mode  in  which  they  act  on  the  application  of 
the  same  stimulus;  differences  which  maybe  ascribed  in  great  part  to 
their  respective  differences  of  structure^  but  in  some  degree,  possibly,  to 
their  respective  viodes  of  connection  loith  tlie  nervous  system.  When  ir- 
ritation is  applied  directly  to  a  muscle  with  striated  fibres,  or  to  the 
motor  nerve  supplying  it,  contraction  of  the  part  irritated,  and  of  that 
only,  ensues;  and  this  contraction  is  instantaneous,  and  ceases  on  the  in- 
stant of  withdrawing  the  irritation.  But  when  any  part  with  unstriped 
muscular  fibres,  e.g.^  the  intestines  or  bladder,  is  irritated,  the  subse- 


g-20  fiAKDBOOK   OF   PHTSIOLOGY. 

quent  contraction  ensues  more  slowly,  extends  beyond  the  part  irritated, 
and,  with  alternating  relaxation,  continues  for  some  time  after  the 
withdrawal  of  the  irritation.  The  difference  in  the  modes  of  contrac- 
tion of  the  two  kinds  of  muscular  fibres  may  be  particularly  illustrated 
by  the  effects  of  the  repeated  stimuli  with  the  magnetic  interrupter. 


Fig.  838.— Muscle-curves  from  the  gastrocnemius  of  a  frog,  iUustrating  effects  of  alterations  in 

temperature. 

-The  rapidly  succeeding  shocks  given  by  this  means  to  the  nerves  of  mus- 
cles excite  in  all  the  transversely  striated  muscles,  except  in  the  case  of 
the  heart,  a  fixed  state  of  tetanic  contraction  as  previously  described, 
which  lasts  as  long  as  the  stimulus  is  continued,  and  on  its  withdrawal 
instantly  ceases;  but  in  the  muscles  with  unstriped  fibres  they  excite  a 
slow  vermicular  movement,  which  is  comparatively  slight  and  alternates 
with  rest.     It  continues  for  a  time  after  the  stimulus  is  withdrawn. 

In  their  mode  of  responding  to  these  stimuli,  all  the  skeletal  muscles,  or 
those  with  transverse  strise,  are  alike  ;  but  among  those  with  unstriped  fibres 
there  are  many  diffei'ences — a  fact  which  tends  to  confirm  the  opinion  that 
their  peculiarity  depends  as  well  on  their  connection  with  nerves  and  ganglia 
as  on  their  own  properties.  The  uretei'S  and  gall-bladder  are  the  parts  least 
excited  by  stimuli ;  they  do  not  act  at  all  till  the  stimulus  has  been  long  applied, 
and  then  contract  feebly,  and  to  a  small  extent.  The  contractions  of  the  csecum 
and  stomach  are  quicker  and  wider  spread  :  still  quicker  those  of  the  iris,  and  of 
the  urinary  bladder  if  it  be  not  too  full.  The  actions  of  the  small  and  large 
intestines,  of  the  vas  deferens,  aud  pregnant  uterus,  are  yet  more  vivid,  more 
regular,  and  more  sustained  ;  and  they  require  no  more  stimulus  than  that  of  the 
air  to  excite  them.  The  heart,  on  account,  doubtless,  of  its  striated  muscle,  is 
the  quickest  and  most  vigorous  of  all  the  muscles  of  organic  life  in  contracting 
upon  irritation,  and  appears  in  this,  as  in  nearly  all  other  respects,  to  be  the  con- 
necting member  of  the  two  classes  of  muscles. 

All  the  muscles  retain  their  property  of  contracting  under  the  influence  of 
stimuli  applied  to  them  or  to  their  nerves  for  some  time  after  death,  the  period 
being  longer  in  cold-blooded  than  in  warm-blooded  Vertebrata,  and  shorter  in 
Birds  than  in  Mammalia.  It  would  seem  as  if  the  more  active  the  respiratory 
process  in  the  living  animal,  the  shorter  is  the  time  of  duration  of  the  irrita- 
bility in  the  muscles  after  death ;  and  this  is  confirmed  by  the  comparison  of 
different  species  in  the  same  order  of  Vertebrata.  But  the  period  during  which 
this  irritability  lasts  is  not  the  same  in  all  persons,  nor  in  all  the  muscles  of 
the  same  person.  In  a  man  it  ceases,  according  to  Nysten,  in  the  following 
order: — first  in  the  left  ventricle,  then  in  the  intestines  and  stomach,  the 
urinary  bladder,  right  ventricle,  oesophagus,  iris ;  then  in  tlie  voluntary  mus- 
cles of  the  trunk,  lower  and  upper  extremities ;  lastly,  in  il>«»  right  and  left 
auricle  of  the  heart. 


MUSCLE-XERVE    PHYSIOLOGY.  52l 

Muscle  in  Rigor  Mortis. 

After  the  muscles  of  tlio  dead  body  have  lost  their  irritability  or  capa 
bility  of  being  excited  to  contraction  Ijy  the  application  of  a  stimulus, 
they  spontaneously  pass  into  a  state  of  contraction,  aj^parentl}'  identical 
with  that  which  ensues  during  life.  It  affects  all  the  muscles  of  the 
body;  and,  when  external  circumstances  do  not  prevent  it,  commonly 
fixes  the  limbs  in  that  which  is  their  natural  joosture  of  equilibrium  or 
rest.  Hence,  and  from  the  simultaneous  contraction  of  all  the  muscles 
of  the  trunk,  is  produced  a  general  stiffening  of  the  body,  constituting 
the  rigor  mortis  ox  post-mortem  rigidity. 

When  this  condition  has  set  in,  the  muscle  {a)  hecomes  acid  in  reaction 
(due  to  development  of  sarcolactic  acid),  {h)  gives  off  carlionic  acid  in 
great  excess,  (c)  diminishes  in  volume  sliglithj,  {d)  lecomes  shortened  and 
opaque,  its  substance  setting  firm.  Eigor  comes  on  much  more  rapidly 
after  muscular  activity,  and  is  hastened  by  warmth.  It  may  be  brought 
on,  in  muscles  exposed  for  exjjeriment,  by  the  action  of  distilled  water 
and  many  acids,  also  by  freezing  and  thawing. 

Cause. — The  immediate  cause  of  rigor  seems  to  be  a  chemical  one, 
'  namely,  the  coagulation  of  the  muscle  plasma.  We  may  distinguish 
three  main  stages — (1.)  Gradual  coagulation.  ("3.)  Contraction  of  cong- 
ulated  muscle-clot  (myosin),  and  squeezing  out  of  muscle-serum.  (.3.) 
Putrefaction.  After  the  first  stage,  restoration  is  possible  through  the 
circulation  of  arterial  blood  through  the  muscles,  and  even  when  the 
second  stage  has  set  in,  vitality  may  be  restored  by  dissolving  the  coag- 
ulum  of  the  muscle  in  salt  solution,  and  passing  arterial  blood  through 
the  vessels.     In  the  third  stage  recovery  is  impossible. 

It  has  been  noticed  that  the  relaxation  in  muscles  after  rigor  some- 
times occurs  too  quickly  to  be  caused  by  jmtrefaction,  and  the  suggestion 
that  iu  such  cases  at  any  rate  such  relaxation  is  due  to  a  ferment-action 
is  very  plausible.  It  is  known  that  pepsin  is  jircscnt  in  muscles,  and 
that  this  ferment  "will  act  in  an  acid  medium.  The  conditions  for  the 
solution  of  the  coagulated  myosin  are  therefore  present  as  the  reaction 
of  rigored  muscle  is  acid. 

Order  of  Occurrence. — The  muscles  are  not  affected  simultaneously  oy 
rigor  mortis.  It  affects  the  neck  and  lower  jaw  first;  next,  the  upper 
extremities,  extending  from  above  downward;  and  lastly,  reaches  the 
lower  limbs;  in  some  rare  instances  only,  it  affects  the  lower  extremities 
before,  or  simultaneously  with,  the  upper  extremities.  It  usually  ceases 
in  the  order  in  which  it  begins:  first  at  the  head,  then  iu  the  upper 
extremities,  and  lastly  in  the  lower  extremities.  It  never  commences 
earlier  than  ten  minutes,  aiul  never  later  than  seven  hours  after  death; 
and  its  duration  is  greater  in  proportion  to  the  lateness  of  its  accession. 


522  HANDBOOK   OF   PHYSIOLOGY. 

Heat  is  developed  during  the  passage  of  a  muscular  fibre  into  the  condi- 
tion of  rigor  mortis. 

Since  rigidity  does  not  ensue  until  muscles  have  lost  the  capacity  of 
being  excited  by  external  stimuli,  it  follows  that  all  circumstances  which 
cause  a  speedy  exhaustion  of  muscular  irritability,  induce  an  early  oc- 
currence of  the  rigidity,  while  conditions  by  which  the  disappearance  of 
the  irritability  is  delayed,  are  succeeded  by  a  tardy  onset  of  this  rigidity. 
Hence  its  speedy  occurrence,  and  equally  speedy  departure  in  the  bodies 
of  persons  exhausted  by  chronic  diseases;  and  its  tardy  onset  and  long 
continuance  after  sudden  death  from  acute  diseases.  In  some  cases  of 
sudden  death  from  lightning,  violent  injuries,  or  paroxysms  of  passion, 
rigor  mortis  has  been  said  not  to  occur  at  all;  but  this  is  not  always  the 
case.  It  may,  indeed,  be  doubted  whether  there  is  really  a  complete 
absence  of  the  post-mortem  rigidity  in  any  such  cases;  for  the  experi- 
ments of  Brown-Sequard  make  it  probable  that  the  rigidity  may  supervene 
immediately  after  death,  and  then  pass  away  -with,  such  rapidity  as  to  be 
scarcely  observable. 

The  occurrence  of  rigor  mortis  is  not  prevented  by  the  previous  exist- 
ence of  paralysis  in  a  part,  provided  the  paralysis  has  not  been  attended 
with  very  imperfect  nutrition  of  the  muscular  tissue. 

The  rigidity  affects  the  involuntary  as  well  as  the  voluntary  muscles, 
whether  they  be  constructed  of  striped  or  unstriped  fibres.  The  rigidity 
of  involuntary  muscles  with  striped  fibres  is  shown  in  the  contraction  of 
the  heart  after  death.  The  contraction  of  the  muscles  with  unstriped 
fibres  is  shown  by  an  experiment  of  Valentin,  who  found  that  if  a  grad- 
uated tube  connected  with  a  portion  of  intestine  taken  from  a  recently- 
killed  animal,  be  filled  with  water,  and  tied  at  the  opposite  end,  the 
water  will  in  a  few  hours  rise  to  a  considerable  height  in  the  tube, 
owing  to  the  contraction  of  the  intestinal  walls.  It  is  still  better  shown 
in  the  arteries,  of  which  all  that  have  muscular  coats  contract  after 
death,  and  thus  present  the  roundness  and  cord-like  feel  of  the  arteries 
of  a  limb  lately  removed,  or  those  of  a  body  recently  dead.  Subsequently 
they  relax,  as  do  all  the  other  muscles,  and  feel  lax  and  flabby,  and  lie 
as  if  flattened,  and  with  their  walls  nearly  in  contact. 

Action  of  the  Voluntary  Muscles. 

The  greater  part  of  the  voluntary  muscles  of  the  body  act  as  sources 
of  power  for  moving  levers, — the  latter  consisting  of  the  various  bones  to 
which  the  muscles  are  attached. 

Examples  of  the  three  orders  of  levers  in  the  Human  Body. — All  levers  have 
been  divided  into  three  kinds,  according  to  the  relative  position  of  the  power. 
the  weight  to  be  removed,  and  the  axis  of  notion  or  fulcrum.  In  a  lever  of 
the  first  kind  the  power  is  at  one  extremity  of  the  lever,  the  weight  at  the  other, 


MITSCLE-NEEVB  PHYSIOLOGY. 


523 


and  the  fulcrum  between  the  two.  If  tlie  initial  letters  only  of  the  jiower, 
weight,  and  fulcrum  be  used,  the  arrangement  will  stand  thus :— P.  F.  W.  A 
poker  as  ordinarily  used,  or  the  bar  in  fig.  334,  may  be  cited  as  an  example  of 
this  variety  of  lever ;  while,  as  an   instance  in  which  the  bones  of  the  human 


Fig.  3:J4. 

skeleton  are  used  as  a  lever  of  the  same  kind,  may  be  mentioned  the  act  of 
raising  the  body  from  the  stooping  posture  by  means  of  the  hamstring  muscles 
attached  to  the  tuberosity  of  the  ischium  (lig.  334) . 

In  a  lever  of  the  second  kind,  the  arrangement  is  thus : — P.  W.  F.  ;  and  this 
leverage  is  employed  in  the  act  of  raising  the  handles  of  a  wheelbarrow,  or  in 
stretching  an  elastic  band,  as  in  fig.  335.  In  the  human  body  the  act  of  open- 
ing the  mouth  by  depressing  the  lower   jaw  is  an  example  of   the  same  kind — 


ElasticRQano 


Fig.  335. 

the  tension  of  the  muscles  which  close  the  jaw  representing  the  weight 
(fig.   335). 

In  a  lever  of  the  third  kind  the  arrangement  is— F.  P.  W. ,  and  the  act  of 
raising  a  pole,  as  in  fig.  336,  is  an  example.  In  the  human  body  there  are 
numerous  examples  of  the  employment  of  this  kind  of  leverage.  The  act  of 
bending  the  fore-arm  may  be  mentioned  as  an  instance  (fig.  33G).  The  act  of 
biting  is  another  example. 

At  the  ankle  we  have  examples  of  all  three  kinds  of  lever.  1st  kind— Ex- 
tending the  foot.  3d  kind— Flexing  the  foot.  In  both  these  cases  the  foot 
represents  the  weight :  the  ankle  joint  the  fulcrum,  the  power  being  the  calf 
muscles  in  the  first  case  and  the  tibialis  anticus  in  th«  second  case.     2d  kind— 


624 


fiAJfrDBOOK   Off   PHYSlOLOftf. 


When  the  body  is  raised  on  tiptoe.  Here  the  ground  is  the  fulcrum,  the 
weight  of  the  body  acting  at  the  ankle  joint  the  weight,  and  the  calf  muscles 
the  power. 

In  the  human  body,  levers  are  most  frequently  used  at  a  disadvantage  as 
regards  power,  the  latter  being  sacrificed  for  the  sake  of  a  greater  range  of 
motion.  Thus  in  the  diagrams  of  the  first  and  third  kinds  it  is  evident  that 
the  power  is  so  close  to  the  fulcrum,  that  great  force  must  be  exercised  in  order 
to  produce  motion.     It  is  also  evident,  howevei",  from  the  same  diagrams,  that 


Fig.  338. 

by  the  closeness  of  the  power  to  the  fulcrum  a  great  range  of  movement  can 
be  obtained  by  means  of  a  comparatively  slight  shortening  of  the  muscular 
fibres. 

The  greater  number  of  the  more  important  muscular  actions  of  the 
human  body — those,  nameh^  which  are  arranged  harmoniously  so  as  to 
subserve  some  definite  purpose  or  other  in  the  animal  economy — are  de- 
scribed in  various  parts  of  this  work,  in  the  sections  which  treat  of  the 
physiology  of  the  processes  by  which  these  muscular  actions  are  resisted 
or  carried  out.  There  are,  however,  one  or  two  very  important  and 
somewhat  complicated  muscular  acts  which  may  be  best  described  in 
this  place. 

Walking. — In  the  act  of  walking,  almost  every  voluntary  muscle  in  the  body 
is  brought  into  play,  either  directly  for  purposes  of  progression,  or  indirectly 
for  the  proper  balancing  of  the  head  and  trunk.  The  muscles  of  the  arms  are 
least  concerned ;  but  even  these  are  for  the  most  part  instinctively  in  action  to 
some  extent. 

Among  the  chief  muscles  engaged  directly  in  the  act  of  walking  are  those  of 
the  calf,  which,  by  pulling  up  the  heel,  pull  up  also  the  astragalus,  and  with  it, 
of  course,  the  whole  body,  the  weight  of  which  is  transmitted  through  the 
tibia  to  this  bone  (fig.  337),  When  starting  to  walk,  say  with  the  left  leg, 
this  raising  of  the  body  is  not  left  entirely  to  the  muscles  of  the  left  calf,  but 
the  trunk  is  thrown  forward  in  such  a  way,  that  it  would  fall  prostrate  were 
it  not  that  the  right  foot  is  brought  forward  and  planted  on  the  ground  to  sup- 
port it.  Thus  the  muscles  of  the  left  calf  are  assisted  in  their  action  by  those 
muscles  on  the  front  of  the  trunk  and  legs  which,  by  their  contraction,  pull  the 
body  forward  ;  and,  of  course,  if  the  trunk  form  a  slanting  line,  with  the  in- 
clination forward,  it  is  plain  that  when  the  heel  is  raised  by  the  calf-muscles, 


HU8CLE-NEKVE    PHYSIOLOGY. 


535 


the  whole  body  will  be  raised,  and  pushed  obliquely  forward  and  upward. 
The  successive  acts  in  taking  the  first  step  in  walking  are  represented  in 
fig    337,  1,  2,  3. 

Now  it  is  evident  that  by  the  time  the  body  has  assumed  the  position  No.  3, 
it  is  time  that  the  right  leg  should  be  brought  forward  to  support  it  and  pre- 
vent it  from  falling  prostrate.  This  advance  of  the  other  leg  (in  this  case  the 
right)  is  effected  partly  by  its  mechanically  swinging  forward,  pendulum- 
wise,  and  partly  by  muscular  action  ;  the  muscles  used  being — 1st,  those  on  the 
front  of  the  thigh,  which  bend  the  thigh  forward  on  the  pelvis,  especially  the 
rectus  femoris,  with  the  psoas  and  the  iliacus ;  2cUy,  the  hamstring  muscles, 
which  slightly  bend  the  leg  on  the  thigh ;  and,  3dly,  the  muscles  on  the 
front  of  the  leg,  which  raise  the  front  of  the  foot  and  toes,  and  so  prevent  the 
latter  in  swinging  forward  from  hitching  in  the  ground. 

The  second  part  of  the  act  of  walking,  which  has  been  just  described,  is 
sliown  in  the  diagram  (4,  fig.   337). 

When  the  right  foot  has  reached  the  ground  the  action  of  the  left  leg  has  not 
ceased.  The  calf-muscles  of  the  latter  continue  to  act,  and  by  pulling  u^i  the 
heel,  throw  the  body  still  more  forward  over  the  right  leg,  now  bearing  nearly 
the  whole  weight,  until  it  is  time  that  in  its  turn  the  left  leg  should  swing 
forward,  and  the  left  foot  be  planted  on  the  ground  to  prevent  the  body  from 
falling  prostrate.  As  at  first,  while  the  calf-muscles  of  one  leg  and  foot  are 
preparing,  so  to  speak,  to  push  the  body  forward  and  upward  from  behind 
by  raising  the  heel,  the  muscles  on  the  front  of  the  trunk  and  the  same  leg 
(and  of  the  other  leg,  except  when   it  is  swinging  forward)    are  helping  the 


act  by  p?<ZZi??.7  the  legs  and  trunk,  so  as  to  make  them  incline  forward,  the 
rotation  in  the  inclining  forward  being  effected  niainlj-  at  the  ankle  joint. 
Two  main  kinds  of  leverage  are,  therefore,  employed  in  the  act  of  walking, 
and  if  this  idea  be  firmly  grasped,  the  details  will  be  understood  with  com- 
parative ease.  One  kind  of  leverage  employed  in  Avalking  is  essentially  the 
same  with  that  employed  in  pulling  forward  thC'pole,  as  in  fig.  336.  And  the 
other,  less  exactly,  is  that  employed  in  raising  the  handles  of  a  wheelbarrow. 
Now,  supposing  the  lower  end  of  the  pole  to  be  placed  in  the  barrow,  we 
should  have  a  very  rough  and  inelegant,  but  not  altogether  bad  representation 
of  the  two  main  levers  employed  in  the  act  of  walking.  The  hoAy  is.  pulled 
forward  bj'  the  muscles  in  front,  mncli  in  the  same  way  that  the  pole  might  be 
by  the  force  applied  at  P.,  while  the  raising  of  the  heel  and  pushing  forward 
of  the  trunk  by  the  calf-muscles  is  rouglilv  represented  on  rnising  the  handles 
of  the  barrow.  The  manner  in  which  tliese  actions  are  performed  alternately 
by  each  leg,  so  that  one  after  the  other  is  swung  forward  to  support  the 
trunk,  which  is  at  the  same  time  jvished  and  pulled  forward  oy  the  muscles 
of  the  other,  may  be  gathered  from  the  the  previous  descriptiou. 


526 


HANDBOOK   OP    PHYSIOLOGY. 


There  is  one  more  thing  to  be  especially  noticed  in  the  act  of  walking.  In- 
asmuch as  the  body  is  being  constantly  supported  and  balanced  on  each  leg 
alternately,  and  therefore  on  only  one  at  the  same  moment,  it  is  evident  that 
there  must  be  some  provision  made  for  throwing  the  centre  of  gravity  over  the 
line  of  support  formed  bj'  the  bones  of  each  leg,  as,  in  its  turn,  it  supports  the 
weight  of  the  body.  This  may  be  done  in  various  ways,  and  the  manner  in 
which  it  is  effected  is  one  element  in  the  differences  which  exist  in  the  walk- 
ing of  different  people.  Thus  it  may  be  done  by  an  instinctive  slight  rotation  of 
the  pelvis  on  the  head  of  each  femur  in  turn,  in  such  a  manner  that  the  centre 
of  gravity  of  the  body  shall  fall  over  the  foot  of  this  side.  Thus  when  the  body 
'=!  pushed  onward  and  upward  by  the  raising,  say,  of  the  right  heel,  as  in  fig. 
337,  3,  the  pelvis  is  instinctively  by  various  muscles  made  to  rotate  on  the 
iiead  of  the  left  femur  at  the  acetabulum,  to  the  left  side,  so  that  the  weight 
may  fall  over  the  line  of  support  formed  by  the  left  leg  at  the  time  that  the 


Fig.  338. 


right  leg  is  swinging  forward,  and  leaving  all  the  work  of  support  to  fall  on 
its  fellow.  Such  a  ''i-ocking"  movement  of  the  trunk  and  pelvis,  however,  is 
accompanied  by  a  movement  of  the  whole  trunk  and  leg  over  the  foot  which 
is  being  planted  on  the  ground  (fig.  338)  :  the  action  being  accompanied  with 
a  compensatory  outward  movement  at  the  hip,  more  easily  appreciated  by 
looking  at  the  figure  (in  which  this  movement  is  shown  exaggerated)  than 
described. 

Thus  the  body  in  walking  is  continually  rising  and  swaying  alternately 
from  one  side  to  the  other,  as  its  centre  of  gravity  has  to  be  brought  alternately 
over  one  or  other  leg ;  and  the  curvatures  of  the  spine  are  altered  in  corre- 
spondence with  the  varying  position  of  the  weight  which  it  has  to  support.  The 
extent  to  which  the  body  is  raised   or  swayed  differs  much  in  different  people. 

In  walking,  one  foot  or  the  other  is  always  on  the  ground.  The  act  of  leaping 
or  jumping,  consists  in  so  sudden  a  raising  of  the  heels  by  the  sharp  and  strong 
contraction  of  the  calf-muscles,  that  the  body  is  jerked  off  the  ground.  At  the 
same  time  the  effect  is  much  increased  by  first  bending  the  thighs  on  the  pel- 


MDSCLE-NEKVE   PHYSIOLOGY,  527 

vis,  and  the  legs  on  the  tliighs,  and  then  suddenly  straightening  out  the  angles 
thus  formed.  The  share  which  this  action  has  in  producing  the  effect  may  be 
easily  known  by  attempting  to  leap  in  the  upright  posture,  with  the  legs  quite 
straight. 

Running  is  performed  by  a  series  of  rapid  low  jumps  with  each  leg  alter- 
nately ;  so  that,  during  each  complete  muscular  act  concerned,  there  is  a  moment 
when  both  feet  are  off  the  ground. 

In  all  these  cases,  however,  the  description  of  the  manner  in  which  any 
given  effect  is  produced,  can  give  but  a  very  imperfect  idea  of  the  infinite 
number  of  combined  and  harmoniously  arranged  muscular  contractions  which 
are  necessary  for  even  the  simplest  acts  of  locomotion. 

Action  of  the  Involuntary  Muscles. — The  involuntary  muscles 
are  for  the  most  part  not  attached  to  bones  arranged  to  act  as  levers,  but 
enter  into  the  formation  of  such  hollow  parts  as  require  a  diminution  of 
their  calibre  by  muscular  action,  under  particular  circumstances.  Ex- 
amples of  this  action  are  to  be  found  in  the  intestines,  urinary  bladder, 
heart  and  blood-vessels,  gall-bladder,  gland-ducts,  etc. 

The  difference  in  the  manner  of  contraction  of  the  striated  and  non- 
striated  fibres  has  been  already  referred  to  (p.  529) ;  and  the  peculiar 
vermicular  or  jjeristaltic  action  of  the  latter  fibres  has  also  been  described. 

Electrical  Cuerents  ik  Nerves. 

The  electrical  condition  of  nerves  is  so  closely  connected  with  the 
phenomena  of  muscular  contraction,  that  it  will  be  convenient  to  con- 
sider it  in  the  present  chapter. 

If  a  piece  of  nerve  be  removed  from  the  body  and  subjected  to  exami- 
nation in  a  way  similar  to  that  adopted  in  the  case  of  muscle,  which  has 
been  described,  electrical  currents  are  found  to  exist  which  correspond 
exactly  to  the  natural  muscle  currents,  and  which  are  called  natural 
nerve  currents  or  currents  of  rest,  according  as  one  or  other  theory  of 
their  existence  be  adopted,  as  in  the  case  with  muscle.  One  point 
(equator)  on  the  surface  being  positive  to  all  other  points  nearer  to  the 
cut  ends,  and  the  greatest  deflection  of  the  needle  of  the  galvanometer 
taking  place  when  one  electrode  is  applied  to  the  equator  and  the  other 
to  the  centre  of  either  cut  end.  As  in  the  case  of  muscle,  these  nerve 
currents  undergo  a  negative  variation  when  the  nerve  is  stimulated,  the 
variation  being  momentary  and  in  the  opposite  direction  to  the  natural 
currents;  and  are  similarly  known  as  the  currents  of  action.  The  cur- 
rents of  action  arc  propagated  in  both  directions  from  the  point  of  the 
application  of  the  stimulus,  and  are  of  momentary  duration. 

Rheoscopic  Frog. — Tliis  negative  variation  may  be  demonstrated  by  means  of 
the  following  experiment.  The  new  current  produced  by  stimulating  the  nerve 
of  one  nerve-muscle  preparation  may  be  used  to  stimulate  the  nerve  of  a  second 
perve-muscle  preparation.     The  foreleg  of  a  frog  with  the  nerve  going  to  the 


528  HAifDBOOK   Ol"    PHYSIOLOGY. 

gastrocnemius  cut  long  is  placed  upon  a  glass  plate,  and  arranged  in  such  way 
that  its  nerve  touches  in  two  places  the  sciatic  nerve,  exposed  but  preserved^ 
171  situ  in  the  opposite  thigh  of  the  frog.  The  electrodes  from  an  induction 
coil  are  placed  behind  the  sciatic  nerve  of  the  second  preparation,  high  up. 
On  stimulating  it  with  a  single  induction  shock,  the  muscles  not  only  of  the 
same  leg  are  found  to  undergo  a  twitch,  but  also  those  of  the  first  preparation, 
although  this  is  not  near  the  electrodes,  and  so  the  stimulation  cannot  be  due 
to  an  escape  of  the  current  into  the  first  nerve.  This  experiment  is  known 
under  the  name  of  the  rheoscopic  frog. 

Nerve-stimuli. — Nerve-fibres  require  to  be  stimulated  before  they  can 
manifest  any  of  their  properties,  since  they  have  no  power  of  themselves 
of  generating  force  or  of  originating  impulses.  The  stimuli  which  are 
capable  of  exciting  nerves  to  action  are,  as  in  the  case  of  muscle,  very 
diverse.  They  are  very  similar  in  each  case.  The  mechanical,  chem- 
ical, thermal,  and  electric  stimuli  which  may  be  used  in  the  one  case 
are  also,  with  certain  differences  in  the  methods  employed,  efficacious  in 
the  other.  The  chemical  stimuli  are  chiefly  these:  withdrawal  of  water, 
as  by  drying,  strong  solutions  of  neutral  salts  of  potassium,  sodium,  etc., 
free  inorganic  acids,  except  phosphoric;  some  organic  acids;  ether, 
chloroform,  and  bile  salts.  The  electrical  stimuli  employed  are  the 
induction  and  continuous  currents  concerning  which  the  observations  in 
reference  to  muscular  contraction  should  be  consulted.  Weaker  elec- 
trical stimuli  will  excite  nerve  than  will  excite  muscle ;  the  nerve  stimuli 
appears  to  gain  strength  as  it  descends,  and  a  weaker  stimulus  applied 
far  from  the  muscle  will  have  the  same  effect  as  a  stronger  one  applied 
to  the  nerve  near  the  muscle. 

It  will  be  only  necessary  here  to  add  some  account  of  the  efect  of  a 
constant  current,  such  as  that  obtained  from  a  Daniell's  battery,  upon  a 
nerve.  This  effect  may  be  studied  with  the  apparatus  described  before. 
A  pair  of  electrodes  is  placed  behind  the  nerve  of  the  nerve-muscle  prep- 
aration, with  a  Du  Bois  Keymond's  key  arranged  for  short  circuiting 
the  battery  current,  in  such  a  way  that  when  the  key  is  opened  the  cur- 
rent is  sent  into  the  nerve,  and  when  closed  the  current  is  cut  off.  It 
will  be  found  that  with  a  current  of  moderate  strength  there  will  be  a 
contraction  of  the  muscle  both  at  the  opening  and  at  the  closing  of  the 
key  (called  respectively  mahing  and  hrealcing  contractions),  but  that 
during  the  interval  between  these  two  events  the  muscle  remains  flaccid, 
provided  the  battery  current  continues  of  constant  intensity.  If  the 
current  be  a  very  weak  or  a  very  strong  one  the  effect  is  not  quite  the 
same;  one  or  other  of  the  contractions  may  be  absent.  Which  of  these 
contractions  is  absent  depends  upon  another  circumstance,  viz.,  the 
direction  of  the  current.  The  direction  of  the  current  may  be  ascending 
or  descending:  if  ascending,  the  anode  or  positive  pole  is  nearer  the 
muscle  than  the  cathode  or  negative  pole,  and  the  current  to  return  to 


MUSCLE-KERVE    PHYSIOLOGY.  529 

the  battery  has  to  ])ass,  up  the  nerve;  if  descending,  the  position  of  tht 
electrodes  is  reversed.  It  will  be  necessary  before  considering  this  ques- 
tion further  to  return  to  the  apparent  want  of  effect  of  the  constant 
current  during  the  interval  between  the  make  and  break  contraction :  to 
all  appearances  no  change  is  produced,  but  in  reality  a  very  important 
alteration  of  the  irritability  is  brought  about  in  the  nerve  by  the  passage 
of  this  constant  (polarizing)  current.  This  may  be  shown  in  two  ways, 
first  of  all  by  the  galvanometer.  If  a  piece  of  nerve  be  taken,  and  if  at 
either  end  an  arrangement  be  made  to  test  the  electrical  condition  of 
the  nerve  by  means  of  a  pair  of  non-polarizable  electrodes  connected  with 
a  galvanometer,  while  to  the  central  portion  a  pair  of  electrodes  con- 
nected with  a  Daniell's  battery  be  applied,  it  will  be  found  that  the 
natural  nerve-currents  are  profoundly  altered  on  the  passage  of  the  con- 
stant current  in  the  neighborhood.  If  the  polarizing  current  be  in  the 
same  direction  as  the  latter  the  natural  current  is  increased,  but  if  in 
the  direction  opposite  to  it,  the  natural  current  is  diminished.  This 
change,  produced  by  the  continual  passage  of  the  battery-current  through 
a  portion  of  the  nerve,  is  to  be  distinguished  from  the  negative  varia- 
tion of  the  natural  current  to  which  allusion  has  been  already  made,  and 
which  is  a  momentary  change  occurring  on  the  sudden  application  of 
the  stimulus.  The  condition  produced  by  the  passage  of  a  constant 
current  is  known  by  the  name  of  Electrotonus. 

A  second  way  of  showing  the  effect  of  the  polarizing  current  is  by 
taking  a  nerve-muscle  preparation  and  applying  to  the  nerve  a  pair  of 
electrodes  from  an  induction  coil,  while  at  a  point  further  removed  from 
the  muscle,  electrodes  from  a  Daniell's  battery  are  arranged  with  a  key 
for  short  circuiting  and  an  apparatus  (reverser)  by  which  the  battery 
current  may  be  reversed  in  direction.  If  the  exact  point  be  ascertained 
to  which  the  secondary  coil  should  be  moved  from  the  primary  coil  in 
order  that  a  minimum  contraction  be  obtained  by  the  induction  shock, 
and  the  secondary  coil  be  removed  slightly  further  from  the  primary, 
the  induction  current  cannot  now  produce  a  contraction;  but  if  the 
polarizing  current  be  sent  in  a  descending  direction,  that  is  to  say,  with 
the  cathode  nearest  the  other  electrodes,  the  induction  current,  which 
was  before  insufficient,  will  prove  sufficient  to  cause  a  contraction; 
whereby  indicating  that  with  a  descending  current  the  irritability  of 
the  nerve  is  increased.  By  means  of  a  somewhat  similar  experiment  it 
may  be  shown  that  an  ascending  current  will  diminish  the  irritability 
of  a  nerve.  Similarly,  if  instead  of  applying  the  induction  electrodes 
below  the  other  electrodes  they  are  applied  between  them,  like  effects 
are  demonstrated,  indicating  that  in  the  neighborhood  of  the  cathode 
the  irritability  of  the  nerve  is  increased  by  the  passage  of  a  constant 
current,  and  in  the  neighborhood  of  the  anode  diminished.  This  in- 
34 


530 


HANDBOOK    OF   PHYSIOLOGY. 


crease  in  irritability  is  called  katelectrotonus,  and  similarly  the 
decrease  is  called  anelectrotonus.  As  there  is  between  the  electrodes 
both  an  increase  and  a  decrease  of  irritability  on  the  passage  of  a  po- 
larizing current,  it  must  be  evident  that  the  increase  must  shade  ojffinto 
the  decrease,  and  that  there  must  be  a  neutral  point  where  there  is 
neither  increase  nor  decrease  of  irritability.  The  position  of  this 
neutral  point  is  found  to  vary  with  the  intensity  of  the  polarizing  cur- 
rent— when  the  current  is  weak  the  point  is  nearer  the  anode,  when 


-^s; 


£ 


5 


Fig.  339.  — Diagram  iUustrating  the  effects  of  various  intensities  of  the  polarizing  currents, 
n,  11',  nerve ;  a,  anode :  fc,  kathode ;  the  curves  above  indicate  increase,  and  those  below  decrease 
of  irritability,  and  when  the  current  is  small  the  increase  and  decrease  are  botli  small,  with  the 
neutral  point  near  a,  and  so  on  as  the  current  is  increased  in  strength. 

strong  nearer  the  kathode  (fig.  339) ;  when  a  constant  current  passes 
into  a  nerve,  therefore,  if  a  contraction  result,  it  may  be  assumed  that 
it  is  due  to  the  increased  irritability  produced  in  the  neighborhood  of 
the  kathode,  but  the  breaking  contraction  must  be  produced  by  a  rise 
in  irritability  from  a  lowered  state  to  the  normal  in  the  neighborhood 
of  the  anode.  The  contractions  produced  in  the  muscle  of  a  nerve- 
muscle  preparation  by  a  constant  current  have  been  arranged  in  a  table 
which  is  known  as  Pfiiiger's  Law  of  Contractions.  It  is  really  only  a 
statement  as  to  when  a  contraction  may  be  expected : — 


Strength  op  Current  uskd. 

Descending  Current. 

Ascending  Current. 

Make. 

Break. 

Make. 

Break. 

Very  Weak 

Weak 

Yes. 
Yes. 
Yes. 
Yes. 

No. 
No. 
Yes. 
No. 

No. 
Yes. 
Yes. 

No. 

No. 
No. 

IModerate 

Yes. 

Strong 

Yes. 

The  difficulty  in  this  table  is  chiefly  intheeifect  of  a  weak  ascending 
current,  but  the  following  statement  may  remove  it.  The  increase  of 
irritability  at  the  kathode  when  the  current  is  made  is  more  potent  to 
produce  a  contraction  than  the  rise  of  irritability  at  the  anode  when  the 
current  is  broken;  and  so  with  weak  currents  the  only  effect  is  a  con- 
traction at  the  make  of  botli  currents.     The  descending  current  is  more 


MUSCLE-NERVE    PHYSIOLOGY.  531 

notent  than  the  ascending  (and  with  still  weaker  currents  is  the  only 
one  which  produces  any  effect),  since  the  kathode  is  near  the  muscle. 
In  the  case  of  the  ascending  current  the  stimulus  has  to  pass  through  a 
district  of  diminished  irritability,  which  with  a  very  strong  current 
acts  as  a  block,  being  of  considerable  amount  and  extent,  but  with  a 
weak  current  being  less  considerable  both  in  intensity  and  extent,  only 
slightly  affects  the  contraction.  As  the  current  is  stronger  however, 
recovery  from  anelectrotonus  is  able  to  produce  a  contraction  as  well 
as  katelectrotonus ;  a  contraction  occurs  both  at  the  make  and  the 
break  of  the  current.  The  absence  of  contraction  with  a  very  strong 
current  at  the  break  of  the  ascending  current  maybe  explained  by  sup- 
posing that  the  region  of  fall  in  irritability  at  the  kathode  blocks  the 
stimulus  of  the  rise  in  irritability  at  the  anode. 

Thus  we  have  seen  that  two  circumstances  influence  the  effect  of  the 
constant  current  upon  a  nerve,  viz.,  the  strength  and  direction  of  the 
current.  It  is  also  necessary  that  the  stimulus  should  be  applied  s?<f/- 
denlij  and  not  gradually,  and  that  the  irn'tabilifi/  of  the  nerve  sliould  he 
normal;  not  increased  or  diminished.  Sometimes  (when  the  prepara- 
tion is  specially  irritable?)  instead  of  a  simple  contraction  a  tetanus 
occurs  at  the  make  or  break  of  the  constant  current.  This  is  especially 
liable  to  occur  at  the  break  of  a  strong  ascending  current  Avhich  has 
been  passing  for  some  time  into  the  preparation;  this  is  called  Ritter's 
tetanus,  and  may  be  increased  by  passing  a  current  in  an  opposite  di- 
rection or  stopped  by  passing  a  current  in  the  same  direction. 

The  Effect  of  Battery  Currents  on  Normal  Human  Nerves. 

The  following  account  is  condensed  from  Lombard  in  "An  American 
Text-book  of  Physiology." 

As  an  electric  current  cannot  be  applied  to  living  human  nerves  di- 
rectly, it  is  applied  to  the  skin  along  tiie  course  of  the  nerve.  The  cur- 
rent passes  from  the  anode  or  positive  pole  through  the  skiu,  and  spreads 
out  in  the  tissues  much  as  the  bristles  of  a  brush;  it  then  gradually 
concentrates  and  leaves  the  skin  at  the  kathode  or  negative  pole. 

In  addition  to  the  physical  anode  and  kathode  of  the  battery,  there 
are  what  are  called  physiological  anodes  and  kathodes.  There  is  a 
physiological  anode  at  every  2^oint  where  the  current  enters  a  nerve,  and 
a  physiological  kathode  at  every  point  where  it  leaves  it. 

Generally  when  the  current  is  applied  to  nerves  through  the  skin, 
only  part  of  it  flows  longitudinally  along  the  nerves;  most  of  it  passes 
diagonally  through  them  to  the  tissues  below.  Thus  it  happens  that  in 
that  part  of  the  nerve  beneath  either  the  physical  anode  or  kathode, 
grouj^s  of  physiological  anodes  and  kathodes  are  found. 


532  HANDBOOK    OF   PHYSIOLOGY. 

The  contraction  "which  occurs  ■uhen  the  current  is  closed  (closing  con- 
traction) represents  irritation  at  the  physiological  kathode,  while  the 
opening   contraction   rej)resents   irritation   at  the   ph3'siological  anode. 


Fig.  340.— Diagram  of  skin  and  subjacent  nerve.  A,  the  positive  electrode  or  physical  anode; 
B,  the  negative  electrode  or  physical  kathode.  Signs +,  physiological  anodes;  signs  — ,  physio- 
logical kathodes.     (After  Waller.) 

Since  there  are  physiological  anodes  and   kathodes  beneath  each  elec- 
trode, one  or  more  of  four  conditions  may  arise: 

1.  Anodic  closing  contraction,  i.e.,  the  effect  of  the  change  developed 
at  the  physiological  kathode,  beneath  the  physical  anode  (positive  pole). 

2.  Anodic  opening  contraction,  i.e.,  the  effect  of  the  change  developed 
at  the  physiological  anode,  beneath  the  physical  anode  (positive  pole). 

3.  Kathodic  closing  contractioji,  i.e.,  the  effect  of  the  change  devel- 
oped at  the  physiological  kathode,  beneath  the  physical  kathode  (nega- 
tive pole). 

4.  Katliodic  ojMning  contraction,  i.e.,  the  effect  of  the  change  devel- 
oped at  the  physiological  anode,  beneath  the  physical  kathode  (negative 
pole). 

The  following  abbreviations  of  these  contractions  are  used:  ACC, 
AOC,  KCO,  KOC. 

The  closing  contractions,  KCO  and  ACC,  are  stronger  than  the 
opening  contractions,  KOC  and  AOC.  Of  the  closing  contractions, 
KCO  is  stronger  than  ACC.  Of  the  o^iening  contractions,  AOC  is 
stronger  than  KOC.  These  facts  are  also  shown  in  a  table  of  the  effects 
of  gradually  increasing  the  strength  of  the  current. 


Weak  currents. 

Medium  currents. 

strong  currents 

KCC 

KCC 

KCO 

ACC 

ACC 

AOC 

AOC 

KOC 

Sometimes  AOC  is  stronger  than  ACC. 

In  diseases  which  cause  degeneration  of  the  nerves  going  to  a  muscle, 
stimulation  causes  results  different  from  the  above,  and  we  get  what  is 
known  as  the  reaction  of  degeneration. 


JIUSCLE-NEKVE    PHYSIOLOGY. 


533 


MUSCULAK   AND   NERVOUS   METABOLISM. 

The  question  of  the  metabolism  of  muscle  both  in  a  resting  and  in  an 
active  condition  has  for  many  years  occupied  the  attention  of  physiolo- 
gists. It  cannot  be  said  even  now  to  be  thoroughly  understood.  Most 
of  the  facts  with  reference  to  the  subject  have  been  already  mentioned. 
We  may  shortly  recapitulate  them  here: — First,  muscle  during  rest  ab- 
sorbs oxygen  and  gives  out  carbon  dioxide.  This  has  been  shown  by  an 
analysis  of  the  gases  of  the  blood  going  to  and  leaving  muscles.  During 
activity,  e.  g.,  during  tetanus,  the  same  interchange  of  gases  takes  place, 
but  the  quantities  of  the  oxygen  absorbed  and  of  the  carbon  dioxide 
given  up  are  increased,  and  the  proj)ortion  between  them  is  altered  thus : — 


Venous  Blood. 

O,  less  than  Arterial 
Blood. 

COj,  more  than  Arterial 
Blood. 

Of  resting  muscle 

9  per  cent. 

6.71  per  cent. 

Of  active  muscle 

12.26  per  cent. 

10.79  per  cent. 

There  is  then  a  greater  proportion  of  carbon  dioxide  produced  in 
muscle  during  activity  than  during  rest. 

During  rigor  mortis  there  is  also  an  increased  production  of  carbon 
dioxide. 

Second,  muscle  duriug  rest  i^roduces  nitrogenous  crystallizable  sub- 
stances, such  as  kreatiu,  from  the  metabolism  which  is  constantly  going 
on  in  it  during  life;  in  addition  there  is  in  all  probability  sarcolactic 
acid  formed  and  other  nou-uitrogenoas  matters. 

During  activity  the  nitrogenous  substances,  such  as  kreatin,  undergo 
very  slight,  if  any,  increase — about  the  amount  produced  during  rest — 
but  the  sarcolactic  acid  is  distinctly  increased;  sugar  (glucose)  is  also 
increased,  whereas  the  glycogen  is  diminished. 

During  rigor  mortis  the  s.-.rcolaetic  acid  is  also  increased,  and  in  ad- 
dition myosin  is  formed. 

From  these  data  it  is  assumed  thr.t  the  processes  which  take  jilace  in 
resting  and  active  muscle  are  somewhat  different,  at  any  rate  in  degree. 
From  actively  contracting  muscle,  also,  there  are  obtained  an  increased 
amount  of  heat  and  mechanical  work,  more  potential  is  converted  into 
kinetic  energy. 

Many  theories  have  been  proposed  to  explain  the  facts  of  muscular 


534  HANDBOOK    OF    PHYSIOLOGY. 

energy.  It  has  been  suggested  by  Herman  that  muscular  activity  de- 
pends upon  the  splitting  up  and  subsequent  re-formation  of  a  complex 
nitrogenous  body,  called  by  him  Inogen.  When  this  body  so  splits  up 
there  result  from  its  decomposition,  carbon  dioxide,  sarcolactic  acid, 
and  a  gelatino-albuminous  body.  Of  these  the  carbon  dioxide  is  carried 
away  by  the  blood  stream;  the  albuminous  substance  and  possibly  the 
acid,  at  any  rate  in  part,  go  to  re-form  the  inogen.  The  other  materials 
of  which  the  inogen  is  formed  are  supplied  by  the  blood ;  of  these  mate- 
rials we  know  that  some  carbohydrate  substance  and  oxygen  form  a  part. 
The  decomposition,  although  taking  place  in  resting  muscle,  reaches  a 
climax  in  active  muscle,  but  in  that  condition  the  destruction  of  inogen 
largely  exceeds  restoration,  and  so  there  must  be  a  limit  to  muscular 
activity.  But  this  is  not  the  only  change  going  on  in  muscle,  there  are 
others  which  affect  the  nitrogenous  elements  of  the  tissue,  and  from 
them  result  the  nitrogenous  bodies  of  which  kreatin  is  the  chief;  these 
changes  may  be  unusually  large  during  severe  exercise. 

It  has  been  further  suggested  that,  as  myosin  is  undoubtedly  formed 
in  rigor  mortis,  when  the  muscle  becomes  acid  and  gives  off  carbon 
dioxide,  that  myosin  is  also  formed  when  muscle  contracts,  and  that,  in 
other  Avords,  contraction  is  a  condition  akin  to  partial  death.  The 
electrical  reaction  appears  to  justify  this;  both  contracted  and  dead 
muscle  are  negative  to  living  muscle,  when  at  rest.  What  happens  to 
the  myosin  which  is  formed  when  muscle  contracts,  if  this  view  be  the 
correct  one,  is  unknown.  Halliburton  suggests  that  the  myosin  which 
can  be  made  to  clot  and  unclot  easily  enough  outside  the  body,  is  able 
to  do  the  same  thing  in  the  body.  It  is  possible  that  the  clotting  of 
myosinogen  which  is  supposed  to  occur  during  contraction,  is  not  of  the 
same  intensity  or  extent  as  that  which  occurs  post  mortem.  The  rela- 
tion of  the  hypothetical  inogen  to  the  rest  of  the  muscle-fibre  is  unde- 
termined. It  may  be  that  the  inogen  is  formed  by  the  activity  of  the 
muscle-protoplasm,  and  stored  up  within  itself,  and  that  during  rest  of 
muscle  it  is  gradually  used  up,  whereas  in  activity  it  is  suddenly  and 
explosively  decomposed.  In  the  rest  of  the  fibre  the  nitrogenous  meta- 
bolism continues  much  the  same  during  rest  as  during  activity. 

Again,  histologically,  the  question  as  to  which  is  the  contractile  and 
which  is  the  non-contractile  part  of  muscle,  has  been,  as  we  have  seen 
(p.  86  et  seq.),  a  matter  of  much  controversy. 

As  regards  nervous  metabolism,  we  have  little  knowledge  of  anything 
except  the  electrical  phenomena  which  have  been  already  considered. 
For  the  maintenance  of  nervous  irritability,  oxygen  is  required ;  to  form 
this,  it  has  been  suggested  that  the  nervous  impulse  is  the  result  of 
processes  of  an  oxidative  character,  etc.     The  chief  seat  of  the  metabo- 


JtUSCLE-NERYE    PHYSIOLOGY.  535 

lism  is  no  doubt  the  axis-cylinder.  The  question  whether  a  nervous 
impulse  is  jjossibly  au  electrical  change,  as  has  been  asserted  by  some, 
cannot  be  at  present  settled,  but  if  it  be  so,  at  any  rate  it  differs  essenti- 
ally from  an  ordinary  current,  if  in  no  other  respect,  at  any  rate  in  the 
rate  of  transmission. 


CHAPTEE  XY. 

THE  PRODUCTION  OF  THE  VOICE 

Before  commencing  the  consideration  of  the  Nervous  system  and 
the  Special  Senses  it  will  be  convenient  to  consider  first  speech,  the 
production  of  the  human  voice,  and  the  physiology  of  the  Larynx 
generally. 

The  Larynx. — In  nearly  all  air-breathing  vertebrate  animals  there 
are  arrangements  for  the  production  of  sound,  or  voice,  in  some  parts  of 


_  'Tiu  Stemo-liyoidetia* 


Stemorhyoidcasa 


m.  Slemo-liyoideiid. 
jn.  Crico-thjroideua. 


Lig ;  crico-thjT.  med 

Cart:  cricoidea^- 
Lig:  erico-traeheaer  --  ^ 

Cart:  traclieale*^'-— -^ 


Fig.  341. — The  Larynx,  as  seen  from  the  front,  showing  the  cartilages  and  ligaments.     The  mus- 
cles, with  the  exception  of  one  crico-thyroid,  are  cut  oif  short.     (Stoerk.) 


the  respiratory  apparatus.  In  many  animals,  the  sound  admits  of  being 
variously  modified  and  altered  during  and  after  its  production;  and,  in 
man,  one  such  modification  occurring  in  obedience  to  dictates  of  the 
cerebrum,  is  sjyeech. 

It  has  been  proved  by  observations  on  living  subjects,  by  means  of 
the  laryngoscope  (p.  543),  as  well  as  by  experiments  on  the  larynx  taken 
from  the  dead  body,  that  the  sound  of  the  human  voice  is  the  result 
of  the  vibration  of  the  inferior  laryngeal  ligaments,   or  the  true  vocal 

536 


THE    PRODI'CTION    OF   THE    VOICE.  537 

cords  which  bound  the  glottis,  caused  by  currents  of  expired  air  impelled 
over  their  edges.  If  a  free  opening  exists  in  the  trachea,  the  sound  of 
the  voice  ceases,  but  it  returns  if  the  opening  is  closed.  An  opening 
into  the  air-passages  above  the  glottis,  on  the  contrary,  does  not  prevent 
the  voice  being  produced.  By  forcing  a  current  of  air  through  the 
larynx  in  the  dead  subject,  clear  vocal  sounds  are  elicited,  tliough  the 
epiglottis,  the  upper  ligaments  of  the  larynx  or  false  vocal  cords,  the 
ventricles  between  them  and  the  inferior  ligaments  or  true  vocal  cords, 
and  the  upper  part  of  the  arytenoid  cartilages,  be  all  removed;  provided 
the  true  vocal  cords  remain  entire,  with  their  points  of  attachment, 
and  be  kept  tense  and  so  approximated  that  the  fissure  of  the  glottis  may 
be  narrow. 

The  vocal  ligaments  or  cords,  therefore,  are  regarded  as  the  proper 
organs  for  the  production  of  vocal  sounds:  the  modifications  of  these 
sounds  being  effected,  as  will  be  presently  explained,  by  other  parts, 
viz.,  by  the  tongue,  teeth,  lips,  etc.  The  structure  of  the  vocal  cords 
is  adapted  to  enable  them  to  vibrate  like  tense  membranes,  for  they  are 
essentially  composed  of  elastic  tissue;  and  they  are  so  attached  to  the 
cartilaginous  j)arts  of  the  larynx  that  their  position  and  tension  can  be 
variously  altered  by  the  contraction  of  the  muscles  which  act  on  these 
parts. 

Thus  it  will  be  seen  that  the  larynx  is  the  organ  of  voice.  It  may 
be  said  to  consist  essentially  of  the  two  vocal  cords  and  the  various  car- 
tilaginous, muscular,  and  other  apparatus  by  means  of  which  not  only 
can  the  aperture  of  the  larynx  (rima  glottidis),  of  which  they  are  the 
lateral  boundaries,  be  closed  against  the  entrance  and  exit  of  air  to  or 
from  the  lungs,  but  also  by  means  of  which  the  cords  themselves  can  be 
stretched  or  relaxed,  brought  together  and  separated  in  accordance  with 
the  conditions  that  may  be  necessary  for  the  air  in  passing  over  them,  to 
set  them  vibrating  to  produce  the  various  sounds.  Their  action  in 
respiration  has  been  already  referred  to. 

Anatomy  of  the  Larynx. — The  principal  parts  entering  into  the  formation  of 
the  larynx  (figs.  343  and  3-13)  are — the  thyroid  cartilage  :  the  cricoid  curtilage  ; 
the  two  arytenoid  cartilages  ;  and  the  two  true  vocal  cords.  The  epiglottis 
(fig.  343) ,  has  but  little  to  do  with  the  voice,  and  is  chiefly  useful  in  protect- 
ing the  upper  part  of  the  larynx  from  the  euti'ance  of  food  and  drink  in 
deglutition.  It  also  probably  guides  mucus  or  other  fluids  in  small  amoinit 
from  the  mouth  around  the  sides  of  the  upper  opening  of  the  glottis  into  the 
pharynx  and  oesophagus :  thus  preventing  them  from  entering  the  larynx. 
The  false  vocal  cords  and  the  ventricle  of  the  larynx,  Avhich  is  a  space  between 
the  false  and  the  true  cord  of  either  side,  need  be  here  only  referred  to. 

Cartilages.  —  (o)  Tlie  thi/roid  cartilage  (fig.  842,  1  to  4)  does  not  form  a  com- 
plete ring  around  the  larynx,  but  only  covers  the  front  portion,  (h)  The 
cricoid  cartilage    (fig.    343,  5,  6),  on  the   other  hand,  is  a  complete  ring ;  the 


538 


HANDBOOK    OF    PHYSIOLOGY. 


back  part  of  the  ring  being  much  broader  than  the  front.  On  the  top  of  this 
broad  portion  of  the  cricoid  are  (c)  the  arytenoid  cartilages  (fig.  342,  7) ,  the 
connection  between  the  cricoid  below  and  arytenoid  cartilages  above  being  a  joint 
with  synovial  membrane   and  ligaments,  the  latter  permitting  tolerably  free 


Fig.  342. —Cartilages  of  the  larynx  seen  from  the  front.  1  to  4,  thyroid  cartilage;  1,  verti- 
cal ridge  or  pomum  Adami ;  2,  right  ala ;  3,  superior,  and  4,  inferior  cornu  of  the  right  side ;  5,  6, 
cricoid  cartilage ;  5,  inside  of  the  posterior  part ;  6,  anterior  narrow  part  of  the  ring ;  7,  arytenoid 
cartilages.     X  M- 

motion  between  them.  But  although  the  arytenoid  cartilages  can  move  on  the 
cricoid,  they  of  course  accompany  the  latter  in  all  its  movements,  just  as  the 
head  may  nod  or  turn  on  the  top  of  the  spinal  column,  but  must  accompany 
it  in  all  its  movements  as  a  whole. 

Joints  and  Ligaments.  — The  thyroid  cartilage  is  also  connected  with  the 
cricoid,  not  only  by  ligaments,  but  also  by  joints  with  synovial  membranes ; 
the  lower  comua  of  the  thyroid  clasping,  or  nipping,  as  it  were,  the  cricoid 
between  them,  but  not  so  tightly  but  that  the  thyroid  can  revolve,    within  a 


lifg,  Ary.-epiglott. 


Csn'fe  "Wristergii 
Cart.  Santorini 

Cai-t.  arj'ten. 

Troc.  imisciil. 

Digs  crico-aryten. 
Jjig,  cetatecrico>  post,  "sup, 

CornuinfeiT 

lag",  caiafeuico.  jjost.  Jnf , 


Cart,  traehefc 


Pill's  membraa. 


Fig.  .343.— The  larynx  as  seen  from  behind  after  removal  of  the  muscles.    The  cartilages  and  lig- 
aments only  remain.     (Stoerlc.) 


certain  range,  ai-ound  an  axis  passing  transversely  through  the  two  joints  at 
which  the  cricoid  is  clasped.  The  vocal  cords  are  attached  (behind)  to  the 
front  portion  of  the  base  of  the  arytenoid  cartilages,  and  (in  front)  to  the 
re-entering  angle  at  the  back  part  of  the  thyroid  ;  it  is  evident,  therefore,  that  all 


THE    PRODUCTION    OF    THE    VOICE. 


530 


movements  of  eitlier  of  these  cartilages  must  produce  an  effect  on  them  of 
some  kind  or  other.  Inasmuch,  too,  as  the  arytenoid  cartilages  i-est  on  the 
top  of  the  back  portion  of  the  cricoid  cartilage,  and  are  connected  with  it  by 
capsular  and  other  ligaments,  all  movements  of  the  cricoid  cartilage  must 
move  the  arytenoid  cartilages,  and  also  produce  an  effect  on  the  vocal  cords. 

Intrinsic  Muscles.- — The  intrinsic  muscles  of  the  larynx  are  so  connected 
vpith  the  laiyngeal  cartilages  that  by  their  contraction  alterations  in  the  con- 
dition of  the  vocal  cords  and  glottis  are  produced.  They  are  usually  divided 
into  four  classes  according  to  their  action,  viz.,  into  abductors,  adductors, 
sphincters,  and  tensors.  The  Abductors,  the  crico-arytenoidei,  widen  the  glottis, 
by  separating  the  cords ;  the  Adductors,  consisting  of  the  thyro-ary-epiglottici, 
the  arytenoideus  posticus  sen  transversus,  the  thyro-arytenoidei  externi,  the  crico- 
arytenoidei  laterales,  and  the  thyro-ai^jtenoidei  interni,  approximate  the  vocal 
cords,  diminish  the  rima  glottidis,  and  act  generally  as  Sphincters  and  sup- 
porters of  the  glottis.  Finally,  the  Tensors  of  the  cords  put  the  cords  on  the 
stretch,  with  or  without  elongating  them  ;  the  tensors  are  the  crico-thyroidei 
and  the  thyro-arytenoidei  interni. 

The  attachments  and  the  action  of  the  muscles  will  be  readily  understood 
from  the  following  table.  All  the  muscles  are  in  pairs  except  the  arytenoideus 
posticus. 

Table  of  the  several  Groups   of  the  Intrinsic  Muscles   of  the   Larynx 
AND  their  Attachments. 


Group. 

Muscle. 

Attachments. 

Action. 

I. 
Abductors. 

Crico-aryte- 
noidei pos- 
tici. 

This    pair    of    muscles    arises,    on 
either  side,    from   the    posterior 
surface  of  tlie  corresponding  half 
of  the  cricoid   cartilage.     From 
this    depression  their  fibres  con- 
verge on  either  side  upward   and 
outward  to    be  inserted    into  the 
outer  angle  of   the  base   of    the 
ar5'tenoid    cartilages   behind   the 
crico-arytenoid  laterales. 

Draw  inward  and 
backward  the 
outer  angle  o  f 
arytenoid  carti- 
lages, and  so  ro- 
tate outward 
the  processus  vo- 
calis  and  widen 
the  glottis. 

II.  and  III. 
Adductors 

and 
Sphincters. 

In  three  lay- 

pvg  • 

(a)     '  Outer 
layer,  Thy- 
r  o  -  a  r  y  - 
e  p  i  g  1  ot- 
tici. 

A  pair  of  muscles.     Flat  and  nar- 
row, which  arise   on  either  side 
from  the  processus  muscularis  of 
the  arytenoid  cartilage,  then  pass- 
ing   upward    and    inward    cross 
one  another  in  the  middle  line  to 
be  inserted  into  tlie  upper  half  of 
the  lateral  border  of  the  opposite 
arytenoid  cartilage  and  the  poste- 
rior   border  of    tlie    cartilage   of 
Santorini.     The    lower  fibres  run 
forward     and     downward    to    be 
inserted  into  the    thyroid    carti- 
lage  near  the   coniniissurc.      The 
lilnvs  attached  to  tlie  cartiinge  of 
Santorini  are  continued  forward 
and  upward  into  the  ary-epiglot- 
tic  fold. 

Help  to  narrow  or 
close  the  rima 
glottidis, 

540 


HANDBOOK    OF    PHYSIOLOGY. 


Group. 


Muscle. 


Attachments. 


Action. 


II.  and  III. 
Adductors 

and 
Sphincters. 
— continued. 


(b)    Middle 
layer. 
i.   A  r  y  te 
n  o  i  d  e  us 
posticus 


A  single  muscle.  Half-quadri- 
lateral, attached  to  the  borders 
of  the  arytenoid  cartilages,  its 
fibres  running  horizontally  be- 
trvveen  the  two. 


Draws  together  the 
arytenoid  carti- 
lages and  also  de- 
presses them. 
"When  the  mus- 
cle is  paralyzed, 
the  inter-carti- 
laginous part  of 
the  cords  cannot 
come  together. 


ii.  Thyro 
aryteno  i  ■ 
d  e  i  e  X  ■ 
terni. 


iii.  Crico- 
aryteno  i  - 
dei  later- 
ales. 


(c)  Inner- 
most lay- 
er,  Thyro- 
a  r  ytenoi- 
dei  in- 
tern!. 


A  pair  of  muscles.  Each  of  which 
consists  of  three  chief  portions 
— lower,  middle,  and  upper 
The  lower  and  principal  fibres 
may  be  further  divided  into  two 
layers,  internal  and  external. 
These  fibres  arise  side  by  side 
from  the  lower  half  of  the  inter- 
nal surface  of  the  thyroid  carti- 
lage, close  to  the  angle,  and  fromi 
the  fibrous  expansion  of  the  crico-l 
thyroid  ligament,  and  are  insert- 
ed into  the  lateral  border  of  the 
arytenoid  cartilage.  The  inner 
fibres  run  horizontally,  to  be  at- 
tached to  the  lower  half  of  this 
border,  and  the  outer  fibres  pass 
obliquely  outward  to  be  inserted 
into  the  upper  half,  while  some 
pass  to  the  cartilage  of  Wrisburg 
and  the  ary -epiglottic  fold. 


A  pair  of  muscles.  They  arise  on 
eithar  side  from  the  middle  third 
of  the  upper  border  of  the  cricoid 
cartilage  and  are  inserted  into  the 
whole  anterior  margin  of  the  base 
of  the  arytenoid  cartilage.  Some 
of  their  fibres  join  the  thyroid 
ary-epigiottici. 


A  pair  of  muscles.  They  arise  on 
either  side,  internally  frona  the 
angle  of  the  thyroid  cartilage, 
internal  to  the  last  described 
muscle  (  (b),  iii.),  and  running- 
parallel  to  and  in  the  substance  of 
the  vocal  cords  are  attached  pos- 
teriorly to  the  processus  vocalis 
along  their  whole  length  and  to 
the  adjacent  part  of  the  outer 
surface  of  the  arytenoid  carti- 
lages. 


Approximate  the 
vocal  cords 
by  drawing  the 
processus  mus- 
cularis  of  the 
arytenoid  carti- 
lages forward 
and  downward 
and  so  rotate  the 
processus  vocalis 
inward. 


Render  the  vocal 
cords  tense  and 
rotate  the  aryte- 
noid cartilages 
and  approximate 
the  processus 
vocalis. 


THE    PRODUCTIOX    OF   THE   VOICE. 


541 


Group. 


IV. 
Tensors. 


Muscle. 


Crico  - 1  h  y- 
roidei. 


Attachments. 


Thyro  -  ary- 
teno  i  d  e  i 
interni. 


A  pair  of  fan -shaped  muscles  at 
tached  on  either  side  to  the  cricoid 
cartilage  below ;  from  the  mesial 
line  iu  front  for  nearly  one-half  of 
its  lateral  circumference  back- 
ward the  fibres  pass  upward  and 
outward  to  be  attached  to  the  low- 
er border  of  the  thyroid  cartilage 
and  to  the  front  border  of  its 
lower  cornea. 


The  most  posterior  part  is  almost 
a  distinct  muscle  and  its  fibres 
are  all  but  horizontal :  some- 
times this  muscle  is  described  as 
consisting  of  two  layers,  super- 
ficial Avith  cortical  fibres,  deep 
with  oblique  fibres,  described 
under  Group  III. 


The  thyroid  carti- 
lage being  fixed 
by  its  extrinsic 
muscles,  the 
front  of  the  cri- 
coid cartilage  is 
drawn  upward, 
and  its  back, 
with  the  aryte- 
noids attached, 
is  drawn  down. 
Hence  the  vocal 
cords  are  elon- 
gated a  n  t  e  r  o  - 
posteriorly  and 
put  upon  the 
stretch.  Paral- 
ysis of  these 
muscles  causes 
an  inabilitj'  to 
produce  high 
notes. 


Described  above. 


Nerve  Supply. — In  the  performance  of  the  functions  of  the  larynx  the  sensory 
filaments  of  the  superior  laryngeal  branch  of  the  vagus  supply  that  acute  sen- 
sibility by  which  the  glottis  is  guarded  against  the  ingress  of  foreign  bodies,  or 
of  irrespirable  gases.  The  contact  of  these  stimulates  the  nerve  filaments  ; 
and  the  impression  conveyed  to  the  medulla  oblongata,  whether  it  produce 
sensation  or  not,  is  reflected  to  the  filaments  of  the  recurrent  or  inferior  laryngeal 
branch,  and  excites  contraction  of  the  muscles  that  close  the  glottis.  Both  these 
branches  of  the  vagi  co-operate  also  in  the  production  and  regulation  of  the 
voice ;  the  inferior  laryngeal  determining  the  contraction  of  the  muscles  that 
vary  the  tension  of  the  vocal  cords,  and  the  superior  laryngeal  conveying  to 
the  mind  the  sensation  of  the  state  of  tliese  muscles  necessary  for  their  contin- 
uous guidance.  And  both  the  branches  co-operate  in  the  actions  of  the  larynx 
in  the  ordinary  slight  dilatation  and  contraction  of  the  glottis  in  the  acts  of 
expiration  and  inspiration,  and  more  evidently  in  those  of  coughing  and  other 
forcible  respiratoiy  movements. 

The  laryngoscope  is  an  instrument  employed  in  investigating  during  life  the 
condition  of  the  pliarynx,  larynx,  and  trachea.  It  consists  of  a  large  concave 
mirror  with  perforated  centre  and  of  a  smaller  mirror  fixed  in  a  long  handle. 
It  is  thus  used  :  the  patient  is  placed  in  a  chair,  a  good  light  (argaud  burner,  or 
lamp)  is  arranged  on  one  side  of,  and  a  little  above  his  liead.  The  operator 
fixes  the  large  mirror  round  his  head  iu  such  a  manner,  that  he  looks  through. 


542 


HAXDBOOK    OF    PHYSIOLOGY. 


the  central  aperture  with  one  eye.  He  then  seats  himself  opposite  the  patient, 
and  so  alters  the  position  of  the  mirror,  which  is  for  this  purpose  provided 
with  a  ball  and  socket  joint,  that  a  beam  of  light  is  reflected  on  the  lips  of  the 
patient. 

The  patient  is  now  directed  to  throw  his  head  slightly  backward,  and  to 
open  his  mouth ;  the  reflection  from  the  mirror  lights  up  the  cavity  of  the 
mouth,  and  by  a  little  alteration  of  the  distance  between  the  operator  and  the 
patient  the  point  at  which  the  greatest  amount  of  light  is  reflected  by  the 
mirror — in  other  words  its  focal  length — is  readily  discovered.  The  small 
mirror  fixed  in  the  handle  is  then  warmed,  either  by  holding  it  over  the  lamp, 
or  by  putting  it  into  a  vessel  of  warm  water ;  this  is  necessary  to  prevent  the 
condensation  of  breath  upon  its  surface.     The  degree  of  heat  is  regulated  by 


l,ig,ary  epigloto 

Cai-t.  ■\Vrisbei'gii> 
Cart.  Santorini- 

imi.  Arytcn.  obliqit. 

m.  Ciico-aiytenoid.  post 

Cornu  inferior 

Xag-.  ceratorcric. 

Pars.  post.  inf.  memljrani. 
Pars,  caitilag. 


Fig.  344.— The  larynx  as  seen  from  behind.    To  show  the  intrinsic  muscles  posteriorly.    (Stoerk.) 


applying  the  back  of  the  mirror  to  the  hand  or  cheek,  when  it  should  feel  warm 
without  being  painful. 

After  these  preliminaries  the  patient  is  directed  to  put  out  his  tongue,  which 
is  held  by  the  left  hand  gently  but  firmly  against  the  lower  teeth  by  means  of 
a  handkerchief.  The  warm  mirror  is  passed  to  the  back  of  the  mouth,  until 
it  rests  upon  and  slightly  raises  the  base  of  the  uvula,  and  at  the  same  time 
the  light  is  directed  upon  it  ran  inverted  image  of  the  larynx  and  trachea 
will  be  seen  in  the  mirror.  If  the  dorsum  of  the  tongue  be  alone  seen,  the 
handle  of  the  mirror  must  be  slightly  lowered  until  the  larynx  comes  into 
view ;  care  should  be  taken,  however,  not  to  move  the  mirror  upon  the  uvula, 
as  it  excites  retching.  The  observation  should  not  be  prolonged,  but  should 
rather  be  repeated  at  short  intervals. 

The  structures  seen  will  vary  somewhat  according  to  the  condition  of  the 
parts  as  to  inspiration,  expiration,  phonation,  etc.  ;  they  are  (fig.  347)  first, 
and  apparently  at  the  posterior  part,  the  base  of  the  tongue,  immediately  below 
which  is  the  accurate  outline  of  the  epiglottis,  with  its  cushion  or  tubercle. 
Then  are  seen  in  the  central  line  the  true  vocal  cords,  white  and  shining  in  their 
normal  condition.     The  cords  approximate  (in  the  inverted  image)  posteriorly ; 


THE    PRODUCTIOX    OF   THE   VOICE. 


543 


between  them  is  left  a  chink,  narrow  while  a  high  note  is  being  sung,  wide 
during  a  deep  inspiration.  On  each  side  of  the  true  vocal  cords,  and  on  a 
higher  level,    are   the  pink  false  vocal  cords.     Still  more  externally  than  the 


Fig.  345.— The  parts  of  the  Laryngoscope. 


false  vocal  cords  is  the  aryteno-epiglottklean  fold,  in  which  are  situated  upon 
each  side  three  small  elevations ;  of  these  the  most  external  is  the  cartilage  of 
Wrisherg,  the  intermediate  is  the  cartilage  of  Santorini,  while  the  summit  of 
the  arytenoid  cartilage  is  in  front,  and  somewhat  below  the  preceding,  being 


Fig.  346. —To  show  the  position  of  the  operator  and  patient  when  using  the  Larj-ngoscope. 

only  seen  during  deep  inspiration.  The  rings  of  the  trachea,  and  even  tlie 
bifurcation  of  the  trachea  itself,  if  the  patient  be  directed  to  draw  a  deep  breath, 
may  be  seen  in  the  interval  between  the  true  vocal  cords. 


544 


HAISTDBOOK    OF    PHYSIOLOGY. 


Movements  of  the  Vocal  Cords. 

In  Eesjnratio?!. — The  |)osition  of  the  vocal  cords  in  ordinary  tran- 
quil breathing  is  so  adapted  by  the  muscles,  that  the  opening  of  the 
glottis  is  wide  and  triangular  (fig.  347,  b)   becoming  a  little  wider  at 


Fig.  S47. — Three  laryngoscopic  views  of  the  superior  aperture  of  the  larynx  and  surrounding 
parts.  A,  the  glottis  during  the  emission  of  a  high  note  in  singing ;  B,  in  easy  and  quiet  inha- 
lation of  air;  C,  in  the  state  of  the  widest  possible  dilatation,  as  in  inhaling  a  very  deep  breath. 
The  diagrams  A',  B',  and  C,  show  in  horizontal  sections  of  the  glottis  the  position  of  the  vocal 
ligaments  and  arytenoid  cartilages  in  the  three  several  states  represented  in  the  other  flgui'es. 
In  all  the  figures,  so  far  as  marked,  the  letters  indicate  the  parts  as  follows,  viz. :  I,  the  base  of 
the  tongue;  e,  the  upper  free  part  of  the  epiglottis;  e',  the  tubercle  or  cushion  of  the  epiglottis; 
ph,  part  of  the  anterior  wall  of  the  pharynx  behind  the  larynx ;  in  the  margin  of  the  aryteno- 
epiglottidean  fold  w,  the  swelling  of  the  membrane  caused  by  the  cartilages  of  Wrisberg ;  s,  that 
of  the  cartilages  of  Santorini;  a,  the  tip  or  summit  of  the  arytenoid  cartilages;  c  v,  the  true 
vocal  cords  or  lips  of  the  rima  glottidis;  cvs,  the  superior  or  false  vocal  cords;  between  them 
the  ventricle  of  the  larynx ;  in  C,  tr  is  placed  on  the  anterior  wall  of  the  receding  trachea, 
and  b  indicates  the  commencement  of  the  two  bronchi  beyond  the  bifurcation  which  may  be 
brought  into  view  in  this  state  of  extreme  dilatation.     (Quain  after  Czermak.) 

each  inspiration,  and  a  little  narrower  at  each  expiration.  On  making 
a  rapid  and  deep  inspiration  the  opening  of  the  glottis  is  widely  dilated 
(fig.  347,  c),  and  somewhat  lozenge-shaped. 

In  Vocalization.' — At  the  moment  of  the  emission  of  a  note,  it  is  nar- 
rowed, the  margins  of  the  arytenoid  cartilages  being  brought  into  contact 
and  the  edges  of  the  vocal  cords  approximated  and  made  parallel,  at 
the  same  time  that  their  tension  is  much  increased.  The  higher  the  note 
produced,  the  tenser  do  the  cords  become  (fig.  347,  a);  and  the  range  of 


THE    PBODUCTIOX    OF   THE    VOICE. 


545 


a  voice  depends,  of  course,  in  the  main,  on  the  extent  to  which  the 
degree  of  tension  of  the  vocal  cords  can  be  thus  altered.  In  the  produc- 
tion of  a  high  note  the  vocal  cords  are  brought  well  within  sight,  so  as 
to  be  plainly  visible  with  the  help  of  the  laryngoscope.  In  the  utter- 
ance of  grave  tones,  on  the  other  hand,  the  epiglottis  is  depressed  and 
brought  over  them,  and  the  arytenoid  cartilages  look  as  if  they  were 
trying  to  hide  themselves  under  it  (fig.  348).     The  epiglottis,  by  being 


Fig.  348.— View  of  the  upper  part  of  the  larynx  as  seen  by  means  of  the  laryngoscope  during 
the  utterance  of  a  grave  note,  c.  Epiglottis;  s,  tubercles  of  the  cartilages  of  Santorini;  a,  aryt- 
enoid cartilages;  z,  base  of  the  tongue;  p/i,the  posterior  wall  of  the  pharynx.     (Czermak.) 

somewhat  pressed  down  so  as  to  cover  the  superior  cavity  of  the  larynx, 
serves  to  render  the  notes  deeper  in  tone  and  at  the  same  time  somewhat 
duller,  just  as  covering  the  end  of  a  short  tube  placed  in  front  of 
caoutchouc  tongues  lowers  the  tone.  In  no  other  respect  does  the 
epiglottis  appear  to  have  any  effect  in  modifying  the  vocal  sounds. 

The  degree  of  approximation  of  the  vocal  cords  also  usually  corre- 
sponds with  the  height  of  the  note  produced ;  but  probably  not  always, 
for  the  width  of  the  aperture  has  no  essential  influence  on  the  height  of 
the  note,  as  long  as  the  vocal  cords  have  the  same  tension :  only  with  a 
wide  aperture  the  tone  is  more  difficult  to  produce  and  is  less  perfect, 
the  rushing  of  the  air  through  the  aperture  being  heard  at  the  same 
time. 

No  true  vocal  sound  is  produced  at  the  posterior  part  of  the  aperture 
of  th(|  glottis,  that,  viz.,  which  is  formed  by  the  space  between  the 
arytenoid  cartilages.  For  if  the  arytenoid  cartilages  be  approximated 
in  such  a  manner  that  their  anterior  processes  touch  each  other,  but  yet 
leave  an  opening  behind  them  as  well  as  in  front,  no  second  vocal  tone 
is  produced  by  the  passage  of  the  air  through  the  posterior  opening,  but 
merely  a  rustling  or  bubbling  sound ;  and  the  height  or  pitch  of  the 
note  produced  is  the  same  whether  the  posterior  part  of  the  glottis  be 
open  or  not. 

The  Voice  in  Singing  and  Speaking. 

Varieties  of  Vocal  Sounds. — The  laryngeal  notes  may  observe  three 

different  kinds  of  sequence.     The  first  is  the  monotonous,  in  which  the 

notes  have    nearly  all    the  same    pitch  as  in  ordinary  speaking;    the 

variety  of  the  sounds  of  speech  being  due  to  articulation  in  the  mouth. 

35 


546  HAK^DBOOK    OF   PHYSIOLOGY. 

In  speaking,  however,  occasional  syllables  generally  receive  a  higher 
intonation  for  the  sake  of  accent.  The  second  mode  of  sequence  is  the 
successive  transition  from  high  to  low  notes,  and  vice  versa,  without 
intervals;  such  as  is  heard  in  the  sounds,  which,  as  expressions  of  pas- 
sion, accompany  crying  in  men,  and  in  the  howling  and  whining  of 
dogs.  The  third  mode  of  sequence  of  the  vocal  sounds  is  the  musical, 
in  which  each  sound  has  a  determinate  number  of  vibrations,  and  the 
numbers  of  the  vibrations  in  the  successive  sounds  have  the  same  relative 
proportions  that  characterize  the  notes  of  the  musical  scale. 

In  different  individuals  this  comprehends  one,  two,  or  three  octaves. 
In  singers — that  is,  in  persons  apt  for  singing — it  extends  to  two  or 
three  octaves.  But  the  male  and  female  voices  oommence  and  end  at 
different  points  of  the  musical  scale.  The  lowest  note  of  the  female 
voice  is  about  an  octave  higher  than  the  lowest  of  the  male  voice ;  the 
highest  note  of  the  female  voice  about  an  octave  higher  than  the  highest 
of  the  male.  The  compass  of  the  male  and  female  voices  taken  together, 
or  the  entire  scale  of  the  human  voice,  includes  about  four  octaves. 
The  principal  difference  between  the  male  and  female  voice  is,  therefore, 
in  theiv  pitch;  but  they  are  also  distinguished  by  their  tone, — the  male 
voice  is  not  so  soft.  The  voice  presents  other  varieties  besides  that  of 
male  and  female;  there  are  two  kinds  of  male  voice,  technically  called 
the  iass  and  te^ior,  and  two  kinds  of  female  voice,  the  contralto  and 
soprano,  all  differing  from  each  other  in  tone.  The  bass  voice  usually 
reaches  lower  than  the  tenor,  and  its  strength  lies  in  the  low  notes; 
while  the  tenor  voice  extends  higher  than  the  bass.  The  contralto 
voice  has  generally  lower  notes  than  the  soijrano,  and  is  strongest  in  the 
lower  notes  of  the  female  voice ;  while  the  soprano  voice  reaches  higher 
in  the  scale.  But  the  difference  of  compass,  and  of  power  in  different 
parts  of  the  scale,  is  not  the  essential  distinction  between  the  different 
voices;  for  bass  singers  can  sometimes  go  very  high,  and  the  contralto 
frequently  sings  the  high  notes  like  soprano  singers.  The  essential 
difference  between  the  base  and  tenor  voices,  and  between  the  contralto 
and  soprano,  consists  in  their  tone  or  timbre,  Avhich  distinguishes  them 
even  when  they  are  singing  the  same  note.  The  qualities  of  the  bary- 
tone and  mezzo-soprano  voices  are  less  marked ;  the  harytone  being  in- 
termediate between  the  bass  and  tenor,  the  mezzo-soprano  between  the 
contralto  and  soprano.  They  have  also  a  middle  position  as  to  pitch  in 
the  scale  of  the  male  and  female  voices. 

The  differences  in  the  pitch  of  the  male  and  the  female  voices 
depends  on  the  different  length  of  the  vocal  cords  in  the  two  sexes; 
their  relative  length  in  men  and  women  being  as  three  to  two.  The 
difference  of  the  two  voices  in  tone  or  timbre,  is  owing  to  the  different 
nature  and  form  of  the  resounding  walls,  which  in   the  male  larynx  are 


THE    PRODUrTIOX    OF    THE    VOICE.  547 

much  more  extensive,  jmd  ronii  ;i  more  acuU;  angle  anteriorly.  The 
flifferiuit  qnalitie.s  of  the  Imor  ami  liass,  and  of  the  alto  and  sojjrano 
voices,  pi'obably  dejimd  on  some  |iecnliai'itie.s  of  the  liuanieiits,  and  the 
membranous  and  eartilagiiions  ])arieterf  of  the  hiryngeal  eavity,  whieli 
are  not  at  present  understood,  but  of  ■\vhieli  -we  inay  form  some  idea, 
by  recollecting  that  inu.^ieal  instruments  made  of  different  materials, 
e.g.,  metallic  and  gut-strings,  maybe  tuned  to  the  same  note,  l)ut  that 
each  \\'A\  give  it  with  a  peenliar  tone  or  timhrc. 

The  boy's  larynx  resendjles  tlie  female  hirynx;  their  vocal  ronls 
before  puberty  are  not  two-thirds  the  length  of  the  adult  cords;  and 
•the  angle  of  their  thyroid  cartilage  is  as  little  prominent  as  in  tlie 
female  larynx.  Boys'  voices  are  altu  and  sopraito,  resembling  in  pitch 
those  of  women,  but  louder,  and  differing  somewhat  from  them  in  tone. 
]3ut,  after  the  larynx  has  undergone  the  change  produced  during  the 
period  of  develoiDmeut  at  puberty,  the  hoy's  voice  becomes  bass  or  teuor. 
While  the  change  of  form  is  taking  jjlace,  the  voice  is  said  to  craclc;  it 
becomes  imperfect,  frequently  hoarse  and  crowing,  and  is  unlitted  for 
singing  until  the  new  tones  are  brought  under  command  by  practice. 
In  eunuchs,  who  have  been  dej^rivedof  the  testes  before  puberty,  the  voice 
does  not  undergo  this  change.  The  voice  of  most  old  people  is  deficient 
in  tone,  unsteady,  and  more  restricted  in  extent:  the  first  defect  is 
owing  to  the  ossification  of  the  cartilages  of  the  larynx  and  the  altered 
condition  of  the  vocal  cords ;  the  want  of  steadiness  arises  from  the  loss  of 
nervous  power  and  command  over  the  muscles;  the  result  of  which  i.-^ 
here,  as  in  other  parts,  a  tremulous  movement.  These  two  causes  com- 
bined render  the  voices  of  old  peoj^le  void  of  tone,  unsteady,  bleating, 
and  Aveak. 

In  any  class  of  persons  arranged,  as  in  an  orchestra,  according  to  the 
character  of  voices,  each  would  possess,  with  the  general  characteristics 
of  a  bass,  or  tenor,  or  any  other  kind  of  voice,  some  peculiar  character 
by  which  his  voice  Avould  be  recognized  from  all  the  rest.  The  condi- 
tions that  determine  these  distinctions  are,  however,  quite  unknown. 
They  are  probably  inherent  in  the  tissues  of  the  larynx,  and  are  as 
indiscernible  as  the  minute  differences  that  characterize  men's  features; 
one  often  observes,  in  like  nuinner,  hereditary  and  family  peculiarities 
of  voice,  as  well  marked  as  those  of  the  limbs  or  face. 

Most  persons,  particularly  men,  have  the  power,  if  at  all  capable  of 
singing,  of  modulating  their  voices  through  a  double  series  of  notes  of 
different  character:  namely,  the  notes  of  the  natural  voice,  or  vhei^t- 
notes,  and  the  falsetto  )intes.  The  natural  voice,  which  alone  has  been 
hitherto  considered,  is  fuller,  ami  excites  a  distinct  sensation  of  much 
stronger  vibration  and  resonance  than  the  falsetto  voice,  which  has 
more  a  flute-like  character.      The  deeper  notes  of  the    male  voice    can 


548  HAXDBOOK    OF    PHYSIOLOGY. 

be  produced  only  with  the  natural  voice,  the  highest  with  the  falsetto 
only ;  the  notes  of  middle  pitch  can  be  produced  either  with  the  natural 
or  falsetto  voice;  the  two  registers  of  the  voice  are  therefore  not  limited 
in  such  a  manner  as  that  one  ends  when  the  other  begins,  hut  they  run 
in  part  side  by  side. 

The  natural  or  chest-notes  are,  as  we  have  seen,  produced  by  the  or- 
dinary vibrations  of  the  vocal  cords.  The  mode  of  production  of  the 
falsetto  notes  is  still  obscure. 

By  Miiller  they  were  thought  to  be  d\ie  to  vibrations  of  only  the  inner 
borders  of  the  vocal  cords.  In  the  opinion  of  Petrequin  and  Diday,  they 
do  not  result  from  vibrations  of  the  vocal  cords  at  all,  but  from  vibra- 
tions of  the  air  passing  through  the  aperture  of  the  glottis,  which  they 
believe  assumes,  at  such  times,  the  contour  of  the  emloucJiure  of  a  flute. 
Others,  considering  some  degree  of  similarity  which  exists  between  the 
falsetto  notes  and  the  peculiar  tones  called  harmonic,  which  are  pro- 
duced when,  by  touching  or  stopping  a  harp-string  at  a  particular  point, 
only  a  portion  of  its  length  is  allowed  to  vibrate,  have  supposed  that,  in 
the  falsetto  notes,  portions  of  the  cords  are  thus  isolated,  and  made  to 
vibrate  while  the  rest  are  held  still.  The  question  cannot  yet  be  settled; 
but  any  one  in  the  habit  of  singing  may  assure  himself,  both  by  the 
difficulty  of  passing  smoothly  from  one  set  of  notes  to  the  other,  and  by 
the  necessity  of  exercising  himself  in  both  registers,  lest  he  should 
become  very  deficient  in  one,  that  there  must  be  some  great  difference 
in  the  modes  in  which  their  respective  notes  are  produced. 

The  pitch  of  the  note,  which  depends  upon  the  rapidity  of  the  vibra- 
tions, is  altered  by  alterations  of  the  vocal  cords,  and  so  the  strength  of 
the  voice  is  in  proportion  {a)  to  the  degree  to  which  the  vocal  cords  can 
be  made  to  vibrate ;  and  partly  {h)  to  the  fitness  for  resonance  of  the 
membranes  and  cartilages  of  the  larynx,  of  the  parietes  of  the  thorax, 
lungs,  and  cavities  of  the  mouth,  nostrils,  and  communicating  sinuses. 
It  is  diminished  by  anything  which  interferes  with  such  capability  of 
vibration. 

The  intensity  or  loudness  of  a  given  note  with  maintenance  of  the 
same  pitch,  cannot  be  rendered  greater  by  merely  increasing  the  force 
of  the  current  of  air  through  the  glottis;  for  increase  of  the  force  of  the 
current  of  air,  cceter is  paribus,  raises  the  pitch  both  of  the  natural  and 
the  falsetto  notes.  Yet,  since  a  singer  possesses  the  power  of  increasing 
the  loudness  of  a  note  from  the  faintest  piano  to  fortissimo  without  its 
pitch  being  altered,  there  must  be  some  means  of  compensating  the 
tendency  of  the  vocal  cords  to  emit  a  higher  note  when  the  force  of  the 
current  of  air  is  increased.  This  means  evidently  consists  in  modify- 
ing the  tension  of  the  vocal  cords.  When  a  note  is  rendered  louder 
and  more  intense,  the  vocal  cords  must  be  relaxed  by  remission  of  the 


THK    PKODUCTIOX    OF   THE    VOICE.  .'540 

muscular  action,  in  proportion  as  the  force  of  the  current  of  the  breath 
through  the  glottis  is  increased.  When  a  note  is  rendered  fainter,  the 
reverse  of  this  must  occur. 

The  arches  of  the  palate  and  the  uvula  become  contracted  during  the 
formation  of  the  higher  notes;  but  their  contraction  is  the  same  for  a 
note  of  given  height,  whether  it  be  falsetto  or  not;  and  in  either  case 
the  arches  of  the  palate  may  be  touched  with  the  finger,  without  the 
note  being  altered.  Their  action,  therefore,  in  the  production  of  the 
higher  notes  seems  to  be  merely  the  result  of  involuntary  associate  ner- 
vous action,  excited  by  the  voluntarily  increased  exertion  of  the  muscles 
of  the  larynx.  If  the  palatine  arches  contribute  at  all  to  the  production 
of  the  higher  notes  of  the  natural  voice  and  the  falsetto,  it  can  only  be 
by  their  increased  tension  strengthening  the  resonance. 

The  office  of  the  ventricles  of  the  larynx  is  evidently  to  afford  a  free 
space  for  the  vibrations  of  the  lips  of  the  glottis;  they  may  be  com- 
pared with  the  cavity  at  the  commencement  of  the  mouthpiece  of  trum- 
pets, which  allows  the  free  vibration  of  the  lips. 

Speech. — Besides  the  musical  tones  formed  in  the  larynx,  a  great 
number  of  other  sounds  can  be  produced  in  the  vocal  tubes,  between 
the  glottis  and  the  external  apertures  of  the  air-passages,  the  combination 
of  which  sounds  by  the  agency  of  the  cerebrum  into  different  groups 
to  designate  objects,  properties,  actions,  etc.,  constitutes  language.  The 
languages  do  not  employ  all  the  sounds  which  can  be  produced  in  this 
manner,  the  combination  of  some  with  others  being  often  difficult. 
Those  sounds  which  are  easy  of  combination  enter,  for  the  most  part, 
into  the  formation  of  the  greater  number  of  languages.  Each  language 
contains  a  certain  number  of  such  sounds,  but  in  no  one  are  all  brought 
together.  On  the  contrary,  different  languages  are  characterized  by  the 
prevalence  in  them  of  certain  classes  of  these  sounds,  while  others  are 
less  frequent  or  altogether  absent. 

Articulate  Sounds. — The  sounds  produced  in  speech,  or  the  articu- 
late sounds,  are  commonly  divided  into  ro/rrls  and  cunsoiianis:  the  dis- 
tinction between  which  is,  that  the  sounds  for  the  former  are  generated 
by  the  larynx,  while  those  for  the  latter  are  produced  by  interruption 
of  the  current  of  air  in  some  part  of  the  air-passages  above  the  larynx. 
The  term  consonant  has  been  given  to  these  because  several  of  them  are 
not  properly  sounded,  except  ro>iso7ianth/  with  a  vowel.  Thus,  if  it  be 
attempted  to  pronounce  aloud  the  consonants  b,  d,  and  g,  or  their  modi- 
fications, p,  t,  k,  the  intonation  only  follows  them  in  their  combination 
with  a  vowel.  To  recognize  the  essential  properties  of  the  articulate 
sounds,  it  is  necessary  first  to  examine  them  as  they  are  produced  in 
whispering,  and  tlien  investigate  which  of  them  can  also  be  uttered  in 
a  modified  character  cnujoined  with  vocal  tone.      By    this   procedure  we 


550  HANDBOOK    OF    PHYSIOLOGY. 

{ind  two  series  of  sounds:  in  one  the  sounds  are  mute,  and  cannot  be 
uttered  with  a  vocal  tone;  the  sounds  of  the  other  series  can  be  formed 
independently  of  voice,  but  are  also  capable  of  being  uttered  in  con- 
junction with  it. 

All  the  vowels  can  be  expressed  in  a  whisper  without  vocal  tone^  that 
is,  viiitehj.  These  mute  vowel-sounds  differ,  however,  in  some  meas- 
ure, as  to  their  mode  of  production,  from  the  consonants.  All  the 
mute  consonants  are  formed  in  the  vocal  tube  above  the  glottis,  or  in 
the  cavity  of  the  mouth  or  nose,  by  the  mere  rushing  of  the  air  between 
the  surfaces  differently  modified  in  disposition.  But  the  sound  of  the 
vowels,  even  when  mute,  has  its  source  in  the  glottis,  though  its  vocal 
cords  are  not  thrown  into  tbe  vibrations  necessar}^  for  the  production,  of 
voice;  and  the  sound  seems  to  be  produced  by  the  passage  of  the  current 
of  air  between  the  relaxed  vocal  cords.  The  same  vowel-sound  can  be  pro- 
duced in  the  larynx  when  the  mouth  is  closed,  the  nostrils  being  open, 
and  the  utterance  of  all  vocal  tone  avoided.  The  sound,  when  the  mouth 
is  open,  is  so  modified  by  varied  forms  of  the  oral  cavity,  as  to  assume 
the  characters  of  the  vowels  a,  e,  i,  o,  u,  in  all  their  modifications. 

The  cavity  of  the  mouth  assumes  the  same  form  for  the  articulation 
of  each  of  the  mute  vowels  as  for  the  corresponding  vowel  when  vocal- 
ized; the  only  difference  in  the  two  cases  lies  in  the  kind  of  sound 
emitted  by  the  larynx.  It  has  been  pointed  out  that  the  conditions 
necessary  for  changing  one  and  the  same  sound  into  the  different  vowels, 
tire  differences  in  the  size  of  two  j)ai'ts — the  oral  canal  and  the  oral  open- 
ing; and  the  same  is  the  case  with  regard  to  the  mute  vowels.  By  oral 
canal,  is  meant  here  the  space  between  the  tongue  and  palate:  for  the 
pronunciation  of  certain  vowels  both  the  opening  of  tbe  mouth  and  the 
space  just  mentioned  are  widened;  for  the  pronunciation  of  other  vowels 
both  are  contracted;  and  for  others  one  is  wide,  the  other  contracted. 
Admitting  five  degrees  of  size,  both  of  the  opening  of  the  mouth  and  of 
the  space  between  the  tongue  and  palate,  Kempelen  thus  states  tht^ 
dimensions  of  tliese  parts  for  the  folloAving  vowel-sounds: — 

Size  of  oral  opening.  Size  of  oral  canal. 

5  ...  3 

4  ...  2 

3  ...  1 

3  ...  4 

1  ...  5 

Another  important  distinction  inarticulate  sounds  is,  that  the  utter- 
ance of  some  is  only  of  momentary  duration,  taking  place  during  a  sud- 
den change  in  the  conformation  of  the  mouth,  and  being  incapable  of 
prolongation  by  a  continued  expiration.  To  this  class  belong  b,  p,  d, 
and  the  hard  g.  In  the  utterance  of  other  consonants  the  sounds  may 
be  continuous;  they  may  be  prolonged,  ad  libitum,  as  long  as  a  particu- 
lar disposition  of  the  mouth  and  a  constant  expiration  are  maintained. 


Vowel. 
a     as 

in 

Sound. 
"  far" 

a        " 
e        " 

"  name" 
"  theme" 

o        " 
oo      " 

"Ko" 
"cool" 

THE    PRODUCTION    OF   THE   VOICE.  551 

Among  these  consonants  are  h,  m,  n,  f,  s,  r,  1.  Corresponding  differences 
in  respect  to  the  time  tliat  may  be  occupied  in  their  utterance  exist 
in  the  vowel  sounds,  and  principally  constitute  the  differences  of  long 
and  sliort  syllables.  Thus  the  a  as  in  far  and  fate,  the  o  as  in  go  and 
fort,  may  be  indefinitely  prolonged;  but  the  same  vowels  (or  more 
properly  different  vowels  expressed  by  the  same  letters),  as  in  can  and 
fact,  in  dog  and  rotten,  cannot  be  prolonged. 

All  sounds  of  the  first  or  explosive  kind  are  insusceptible  of  com- 
bination with  vocal  tone  {intonation),  and  are  absolutely  mute;  nearly 
all  the  consonants  of  the  second  or  continuous  kind  may  be  attended 
with  intonation. 

Ventriloquism. — The  peculiarity  of  speaking,  to  which  the  term 
ventriloquism  is  applied,  appears  to  consist  merely  in  the  varied  modi- 
fication of  the  sounds  produced  in  the  larynx,  in  imitation  of  the  modi- 
fications which  voice  ordinarily  suffers  from  distance,  etc.  From  the 
observations  of  Muller  and  Colombat,  it  seems  that  the  essential 
mechanical  parts  of  the  process  of  ventriloquism  consist  in  taking  a  full 
inspiration,  then  keeping  the  muscles  of  the  chest  and  neck  fixed,  and 
speaking  with  the  mouth  almost  closed,  and  the  lips  and  lower  jaw  as 
motionless  as  possible,  while  air  is  very  slowly  expired  through  a  very 
narrow  glottis ;  care  being  taken  also,  that  none  of  the  expired  air  passes 
through  the  nose.  But,  as  observed  by  Miiller,  much  of  the  ventrilo- 
quist's skill  in  imitating  the  voices  coming  from  particular  directions, 
consists  in  deceiving  other  senses  than  hearing.  We  never  distinguish 
very  readily  the  direction  in  which  sounds  reach  our  ear;  and,  when 
our  attention  is  directed  to  a  particular  point,  our  imagination  is  very 
apt  to  refer  to  that  point  whatever  sounds  we  may  hear. 

Action  of  the  Tongue  in  Speech. — The  tongue,  which  is  usually 
credited  with  the  power  of  speech — language  and  speech  being  often 
employed  as  synonymous  terms — plays  only  a  subordinate,  although  very 
important  part.  This  is  well  shown  by  cases  in  which  nearly  the  whole 
organ  has  been  removed  on  account  of  disease.  Patients  who  recover 
from  this  operation  talk  imperfectly,  and  their  voice  is  considerably 
modified ;  but  the  loss  of  speech  is  confined  to  those  letters  in  the  pro- 
nunciation of  which  the  tongue  is  concerned. 

Stammering  depends  on  a  want  of  harmony  between  the  action  of 
the  muscles  (chiefly  abdominal)  which  expel  air  through  the  larynx,  and 
that  of  the  muscles  which  guard  the  orifice  (rima  glottidis)  by  which  it 
escapes,  and  of  those  (of  tongue,  palate,  etc.)  which  modulate  the  sound 
to  the  form  of  speech. 

Over  either  of  the  groups  of  muscles,  by  itself,  a  stammerer  may 
have  as  much  power  as  other  people.  But  he  cannot  harmoniously 
arrange  their  conjoint  actions. 


CHAPTER  XYI. 

THE    NERVOUS    SYSTEM. 

The  nervous  system  consists  of  the  following  parts:  firstly,  of  large 
masses  of  nervous  matter  situated  within  the  bony  cranium  and  spinal 
column,  and  constituting  the  brain  and  spinal  cord;  secondly,  of 
smaller  masses  of  nervous  matter,  situated  for  the  most  part  in  the 
abdominal  and  thoracic  cavities,  but  also  in  the  neck  and  head,  and 
constituting  what  are  known  as  sympathetic  ganglia;  thirdly,  of  cords 
of  nerve-fibres  which  connect  the  central  nervous  system  with  the 
periphery  and  with  the  so-called  sympathetic  ganglia,  which  are  not  in 
reality  a  system  independent  of  the  brain  and  cord  as  was  formerly 
taught,  but  are  really  part  and  parcel  of  the  same  system ;  and  fourthly, 
of  peripheral  organs  in  connection  with  the  beginnings  or  endings  of  the 
nerves  at  the  periphery  of  the  body. 

It  will  be  necessary  to  consider  these  several  parts  of  the  nervous  system 
seriatim ;  it  will  be  most  useful  for  the  understanding  of  the  subject, 
however,  to  proceed  first  of  all  with  the  consideration  of  the  properties 
of  nerve-fibres,  as  this  forms  the  most  elementary  portion  of  the  subject. 

Nerve-fibres. — The  structure  of  the  diiferent  kinds  of  nerve-fibres 
has  been  already  dealt  with  (p.  91,  et  seq.) ;  their  function  remains  to  be 
considered  here. 

FUNCTIO^Sr   OF   NeEVE  FIBRES. 

The  office  of  nerve- fibres  is  to  conduct  impressions.  From  the 
account  of  nervous  action  previously  given  (p.  527  et  seq.)  it  will  be 
readily  understood,  that  nerve-fibres  may  be  stimulated  to  act  by  any- 
thing which,  with  sufficient  suddenness,  increases  their  irritability; 
they  are  incapable  of  originating  of  themselves  the  condition  necessary 
for  the  manifestation  of  their  own  energy.  The  stimulus  produces  its 
effect  upon  the  termination  of  the  nerve  stimulated,  being  conducted  to 
it  by  the  nerve-fibre.  The  effect  of  the  stimulus  upon  a  nerve  therefore 
depends  upon  the  nature  of  its  end-organ,  A  length  of  a  nerve  trunk 
when  freshly  removed  from  the  body,  if  stimulated  midway  between  its 
extremities,  will,  as  shown  by  the  deflection  of  the  needle  of  a  galvanomete''^ 
at  either  end,  conduct  the  electrical  impressions  in  either  direction,  and 
it  may  be  considered  therefore  only  an  accidental  circumstance  as  it 
were,  whether  when  in  situ  it  has  conducted  impressions  to  the  central 

552 


TTFTK    XERVOUS   SYSTEM.  553 

nervous  system  from  the  periphery,  or  from  the  central  nervous  system 
to  the  muscles  or  other  tissues.  The  same  fibre  cannot  be  used  for  the 
one  purpose  at  one  time,  and  for  the  other  at  another,  simply  because  of 
the  nature  of  its  terminal  organs.  Thus,  when  a  cerebro-spinal  nerve- 
fibre  is  irritated  in  the  living  body  as  by  pinching,  or  by  heat,  or  by 
electrifying  it,  there  is,  under  ordinary  circumstances,  one  of  two  effects, 
— either  there  is  pain,  or  there  is  twitching  of  one  or  more  muscles  to 
which  the  nerve  distributes  its  fibres.  From  various  considerations 
it  is  certain  that  pain  is  always  the  result  of  a  change  in  the  nerve- 
cells  of  the  brain.  Therefore,  in  such  an  experiment  as  that  referred 
to,  the  irritation  of  the  nerve-fibre  is  conducted  in  one  of  two  direc- 
tions, i.e.,  either  to  the  brain,  which  is  the  central  termination  of  the 
fibre,  when  there  is  pain, or  to  a  muscle,  which  is  the  peripheral  ter- 
mination, when  there  is  movement. 

The  effect  of  this  simple  experiment  is  a  type  of  what  always  occurs 
when  nerve-fibres  are  engaged  in  the  performance  of  their  functions. 
The  result  of  stimulating  them,  which  roughly  imitates  what  happens 
naturally  in  the  body,  is  found  to  occur  at  one  or  other  of  their  ex- 
tremities, central  or  peripheral,  never  at  both;  and  in  accordance  with 
this  fact,  and  because,  for  any  given  nerve-fibre,  the  result  is  always  the 
same,  nerve-fibres  have  been  commonly  classed  as  sensory  or  motor. 

This  is  not  altogether  accurate,  and  the  terms  centrifugal  or  eferent 
and  centripetal  or  afferent  are  more  properly  used,  since  the  result  of 
stimulating  a  nerve  of  the  former  kind  is  not  always  the  production  of 
pain  or  other  form  of  sensation,  nor  is  motion  the  invariable  result  of 
stimulating  the  latter. 

The  term  intercentral  is  applied  to  those  nerve-fibres  which  connect 
more  or  less  distinct  nerve-centres,  and  may,  therefore,  be  said  to  have 
no  peripheral  distribution,  in  the  ordinary  sense  of  the  term. 

Impressions  made  upon  the  terminations  or  upon  the  trunk  of  a 
centripetal  nerve  may  cause  {a)  pain,  or  some  other  kind  of  sensation ;  (b) 
special  sensation ;  or  [c)  reflex  action  of  some  kind ;  or  {d)  inhibition, 
restraint  of  action.  Similarly  impressions  made  upon  a  centrif- 
ugal nerve  may  cause  {a)  contraction  of  muscle  (motor  nerve) ;  (/;)  it 
may  influence  nutrition  (trophic  nerve) ;  or  {c)  may  influence  secretion 
(secretory  nerve) ;  or  {d)  inhibit,  augment,  or  stop  any  other  efferent 
action. 

It  is  a  law  of  action  in  all  nerve-fibres,  and  corresponds  with  the  con- 
tinuity and  simplicity  of  their  course,  that  an  impression  made  on 
any  fibre,  is  simply  and  uninterruptedly  transmitted  along  it,  without 
itself  being  imparted  or  ditt'nsed  to  any  of  the  fibres  lying  near  it.  it 
is  possible  that  the  mere  passage  of  a  nerve  impulse  along  a  nerve-fibre, 
however,    may  produce  some   effect   upon  the  neighboring  nerve-fibres. 


554  HANDBOOK    OF    PHYSIOLOGY. 

Their  adaptation  to  the  purpose  of  simple  conduction  is,  perhaps,  due 
to  the  contents  of  each  fibre  being  completely  isolated  from  those  of  ad- 
jacent fibres  by  the  myelin  sheath  in  which  each  is  inclosed,  and  which 
acts,  it  may  be  supposed,  just  as  silk,  or  other  non-conductors  of  elec- 
tricity do,  which,  when  covering  a  wire,  prevent  the  electric  condition 
of  the  wire  from  being  conducted  into  the  surrounding  medium. 

Velocity  of  a  Nervous  I7n2}2dse. — The  change  which  a  stimulus  sets  up  in 
a  nerve,  of  the  exact  nature  of  Avhich  we  are  unacquainted,  appears  to  travel 
along  a  nerve-fibre  in  both  directions  with  considerable  velocity  in  the 
form  of  a  wave.  Helmholtz  and  Baxt  have  estimated  the  average  rate 
of  conduction  in  human  jnotor  nerves  at  111  feet  (nearly  29  metres)  per 
second;  this  result  agreeing  very  closely  with  that  previously  obtained. 
It  is  probably  rather  under  than  over  the  average  velocity.  Eutherford's 
observations  agree  with  those  of  Yon  Wittich,  that  the  rate  of  transmis- 
sion in  sensory  nerves  is  about  140  feet  (42  metres)  per  second.  The 
velocity  of  the  nerve  impulse  in  motor  nerves  has  been  calculated  by  notic- 
ing the  duration  of  the  interval  between  two  contractions  of  the  same 
muscle  when  stimulated  by  means  of  two  pairs  of  electrodes,  one  placed 
behind  the  nerve  close  to  the  muscle,  and  the  second  placed  at  a  known  . 
distance  further  away  from  the  muscle.  The  contraction  ensues  when 
the  stimulus  is  applied  further  from  the  muscle  later  than  the  other 
case,  and  the  interval  between  the  two  contractions  is  occupied  by  the 
passage  of  the  impulse  down  the  nerve.  With  these  data  it  is  concluded 
that  the  velocity  of  the  passage  of  the  nerve  impulse  in  a  frog's  motor 
nerve  is  28,  to  30  metres  ipev  second.  In  the  human  motor  nerve,  cal- 
culated by  applying  the  stimulus  through  the  skin  instead  of  directly 
to  the  nerve,  the  velocity  is  greater,  viz.,  about  33  to  50  metres  per 
second.  In  sensory  nerves  the  velocity  is  said  to  be  about  30  to  33 
metres  per  second.  Various  conditions  modify  the  rate  of  transmission, 
of  which  temperature  is  one  of  the  most  important,  a  very  low  or  a  very 
high  temperature  diminishing  it ;  fatigue  of  the  nerve  acting  in  the 
same  direction,  but  increase  of  the  stimulus  up  to  a  certain  point  increas' 
ing  it,  as  does  also  the  hatelectrotonic  condition  of  the  nerve. 

The  Cerebro- Spinal  Nervous  System. — The  parts  of  which  this  sys- 
tem is  composed  are  the  following:  (a)  the  spinal  cord  and  its  nerves; 
{h)  the  brain  made  up  of  cerebrum,  crura  cerebri  and  the  ganglia  in  con- 
nection with  them,  pons  varolii,  cerebellum,  and  the  medulla  oblongata 
or  bulb  which  connects  the  upper  parts  of  the  system  with  the  spinal 
cord,  or  medulla  spinalis. 

All  of  these  parts  of  the  nervous  system  are  nerve-centres,  in  contra- 
distinction to  nerve-trunks,  and  differ  from  the  nerves  in  being  made  up 
of  nerve-cells  and  their   branchings  as  well  as  of  nerve-fibres.     As  now 


THE    NERVOUS   SYSTEM.  555 

coticeived,  the  nerve-centres  are  composed  of  neurons,  while  the  nerve- 
trunks  are  made  up  of  the  neuraxons  with  their  various  terminals.  (See 
}).  1)1  ct  scq.)  There  are  other  gangliuhesides  these,  distributed  elsewhere 
and  not  witliin  tlie  cranium  and  spinal  column,  but  these  arc,  for  the 
sake  of  convenience,  considered  apart,  under  the  head  of  the  sympathetic 
system,  as  they  jDresent  some  differences  to  the  more  central  ganglia. 

The  cerebro-spinal  centres  then  are  distinguished  from  mere  nerve- 
ti'unks  by  the  possession  of  nerve-cells;  these  are,  as  w^e  have  seen  in  a 
former  chapter  (p.  99  ei  seq.),  of  different  kinds;  they  very  possibly 
ditfer  in  function.  It  is,  however,  to  the  possession  of  ganglion-cells 
tliat  the  increase  of  the  functions  of  nerve-centres  over  that  of  nerve- 
trUuks  is  credited.  Before  turning  to  the  discussion  of  the  functions 
of  the  spinal  cord  it  will  be  as  well  to  devote  a  little  time  therefore  to 
the  question  of  the  functions  of  the  nerve-centres  in  general.  The 
ganglia  of  the  sympathetic  system  also  contain  nerve-cells,  hut  to  these 
it  is  supposed  a  different  use  is  to  be  assigned,  and  what  is  said  as  to  the 
functions  of  nerve-ganglia  in  this  place  is  only  to  be  applied  to  those 
of  the  cerebro-spinal  centres. 

FuxcTioNs   OF   Nerve-centres. 

Reflex  action. — One  of  the  chief  functions  of  nerve-cells  appears 
to  be  the  power  of  sending  out  imjaulses  to  the  periphery  along  efferent 
nerves  in  response  to  impulses  reaching  them  through  afferent  nerves. 
This  power  is  sometimes  called  the  conversion  of  an  afferent  into  an 
efferent  impulse.  If  may  be  supposed  that  an  impulse  passing  to  a 
nerve-cell  may  produce  such  a  change  in  its  metabolism  that  a  discharge 
of  energy  ensues.  This  discharge  is  in  some  way  passed  down  an  efferent 
nerve  as  stimulus,  and  effects  some  change — motor,  secretory,  or  nutri- 
tive, at  the  peripheral  extremity  of  the  latter — the  difference  in  effect 
depending  on  the  kind  of  peripheral-nerve  termination.  The  reflex  action 
may  be  limited  in  its  effect,  or  it  may  be  extensive.  Reflex  movements,  oc- 
curring quite  independently  of  sensation,  are  generally  called  excito-motor: 
those  which  are  guided  or  acompanied  by  sensation,  but  not  to  the  extent 
of  a  distinct  perception,  or  intellectual  process,  are  termed  sensor i-motor. 

{a)  For  the  manifestation  of  every  reflex  action,  these  things  an- 
necessary:  (1),  one  or  more  perfect  afferent  fibres,  to  convey  an  impres- 
sion; (2),  a  nervous  centre  for  its  reception,  and  by  which  it  may  be  re- 
flected; (3),  one  or  more  efferent  nerve-fibres,  along  which  the  impres- 
sion may  be  conducted  to  (4)  the  muscular  or  other  tissue  by  which  the 
effect  is  manifested.  Allthis  means,  in  simpler  statement,  that  for  the 
production  of  a  reflex  action  there  must  ho  two  perfect  neurons,  a  sen- 
sory or  afferent  and  a  motor  or  efferent.      This  arrangement  is  shown  in 


o56 


HANDBOOK   OF   PHYSIOLOGY. 


Fig.  349. — Showing  the  arrangement 
of  the  reflex  mechanism,  with  a  neu- 
ron intercalated  between  the  sensoi'j^ 
and  motor  neurons. 


fig.  349.     {b)  All  reflex  actions  are  essentially  involuntary,  though  most 

of  them  admit  of  being  modified,  controlled,  or  prevented  by  a  voluntary 

effort. 

(c)  Reflex  actions  performed  in  health  have,  for  the  most  part,  a  dis- 
tinct purpose,  and  are  adapted  to  secure 
some  end  desirable  for  the  •well-being  of  the 
body;  but,  in  disease,  many  of  them  are 
irregular  and  purposeless. 

(d)  Muscular  contractions  produced  by 
reflex  action  are  often  more  sustained  than 
those  produced  by  the  direct  stimulus  of 
motor  nerves  themselves.  The  irritation 
of  a  muscular  organ,  or  its  motor  nerve, 
produces  contraction  lasting  only  so  long  as 
the  irritation  continues;  but  irritation  ap- 
plied to  a  nervous  centre  through  one  of  its 
centripetal  nerves  may  excite  reflex  and 
harmonious  contractions,  which  last  sojne 
time  after  the  withdrawal  of  the  stimulus. 

Relations  heticeen  the  Stinnihis  cnul  the 
Effect    iwoduced. — Certain    rules    showing 

the  relation  between  the  resulting  reflex  action  and  the  stimulus  have 

been  drawn  up  by  Pfliiger  as  follows: — 

1.  Law  of  unilateral  reflection. — A  slight  irritation  of  the  surface 
supplied  by  certain  sensory  nerves  is  reflected  along  the  motor  nerves  of 
the  same  region.  Thus,  if  the  skin  of  a  frog's  foot  be  tickled  on  the 
rigM  side,  the  rigM  leg  is  drawn  up. 

2.  Law  of  symmetrical  reflection. — A  stronger  irritation  is  reflected, 
not  only  on  one  side,  but  also  along  the  corresponding  motor  nerves  of 
the  opposite  side. 

3.  Law  of  intensity. — In  the  above  case,  the  contractions  will  be 
more  violent  on  the  side  irritated,  but  it  must  not  be  assumed  that  the 
effect  is  always  in  proportion  to  the  strength  of  the  stimulus. 

4.  Laio  of  radiation. — If  the  irritation  (afferent  impulse)  increases, 
it  is  reflected  along  other  motor  nerves  till  at  length  all  the  muscles  of 
the  body  are  throwai  into  action. 

In  the  simplest  form  of  reflex  action  a  single  sensory  and  single  motor 
neuron  may  be  supposed  to  be  concerned,  but  in  the  majority  of  actual 
actions  many  neurons  are  probably  engaged.  The  impulse  is  carried  by 
collaterals  up  and  down  to  different  levels  of  the  spinal  cord,  and  thus 
a  number  of  groups  of  cells  are  affected  (fig.  349a). 

The  reflex  effect  produced  by  a  stimulus  applied  to  a  sensory  surface 
depends,  however,  not  only  upon  the  strength  of  the  stimulus,  but  also 
upon  other  circumstances,  the  most  important  of  which  is  the  condi- 
tion of  the  nerve-centre  itself.     Looking  upon  the  effect  produced  as 


THE   NERVOUS   SYSTEM. 


557 


the  resnlt  of  the  discharge  as  it  were  of  euergy  from  the  centre,  it  njay 
be  supposed  that  sometimes  the  centre  is  in  a  more  explosive  condition 
than  at  another;  this  is  shown  for  example  in  the  case  of  a  frog  poisoned 
by  strychnine,  when  the  slightest  stimulus  applied  to  the  ski.i  will  pro- 
duce the  most  violent  and  general  tetanic  spasms,  while  under  ordinary 
circumstances  the  contraction  of  a  few  muscles  only  would  result.  .  We 
must  also  suppose  that  the  centres  are  particularly  sensitive  tcv  articu- 
lar kinds  of  stimuli,  sometimes  producing  very  extensive  and  violent 


Fifr.  349a.— Showing  the  arrangement  of  a  simiOe  reflex  mechanism  composed  of  a  motor  and 
sensory  neiiron.  xg,  Posterior  spinal  ganglion ;  a- and  st/i,  sensory  root;  m,  motor  nerve  cell;  mtr, 
motor  root. 


muscular  actions  in  response  to  a  slight  stimulus  of  a  special  kind. 
Such  a  condition  is  illustrated  in  the  violent  and  general  muscular 
spasms  occurring  when  a  small  particle  of  food  passes  into  the  larynx, 
violent  expiratory  spasms  accompanied  by  contractions  of  other  muscles 
taking  place. 

A  nerve-centre  must  be  considered  as  capable  by  its  connections 
with  efferent  nerves  of  producing  most  extensive  muscular  movements, 
and  when  from  any  reason,  either  by  the  intensity  of  the  afferent 
stimuli  reaching  it,  or  by  the  special  nature,  extent,  or  point  of  appli- 
cation of  the  afferent  stimuli,  or  by  special  changes  in  its  own  metabol- 
ism brought  about  by  poison  or  by  some  other  means,  a  maximum  dis- 
charge takes  place,  the  resulting  movements  are  most  extensive.  Under 
ordinary  conditions,  hoAvever,  a  slight  stimulus  produces,  as  above  men- 


558  ha:n'Dbook  of  physiologt. 

tioned  only  a  moderate  discharge  from  the  centre,  the  movement  being 
centre  may  be  not  only  not  to  set  it  into  activity,  but  to  prevent  or 
stop  an  action  already  going  on.  On  the  other  hand,  the  action  of 
afferent  impulses  upon  a  nerve-centre  may  be  to  augment,  render  more 
powerful  or  extensive,  and  increase  in  a  certain  direction  an  action 
already  in  course.  Such  may  be  well  illustrated  by  the  action  of  the 
to  a  certain  extent  co-extensive  with  the  strength  of  the  stimulus. 

The  time  taken  in  a  reflex  action  has  been  found  to  be  .066  to  ,058 
second,  but  this  is  only  a  rough  and  arbitrary  estimation. 

Automatism. — A  second  function  which  appears  to  be  possessed  by 
certain  nerve-centres  and  not  by  others  is  that  of  automatic  action  or 
automatism.  By  this  is  meant  that  it  is  not  dependent  for  its  discharge 
upon  any  afferent  stimuli,  but  that  it  is  capable  of  sending  out  of  itself 
efferent  impulses  of  various  kinds.  The  centre  may  be  supposed  to  do 
this  by  the  nature  of  its  own  metabolism,  anabolism  or  building  up  of  the 
explosive  substance  being  followed  by  katabolism  or  its  discharge.  So 
that  the  centre  sends  out  its  impulses  to  muscles  rhythmically.  Such 
a  power  of  automatism  we  have  seen  is  attributed  to  the  res^oiratory  cen- 
tres in  the  bulb. 

Inhibition  and  Augmentation.— Not  only  may  movements  of 
muscles,  discharge  of  secretion  from  gland-cells  and  the  like  be  produced 
by  afferent  impulses  reaching  nerve-centres,  but  also  inhibition  of  action 
which  is  already  taking  place.  This  is  well  seen  in  the  matter  of  the 
inhibitory  action  of  the  vagus  upon  the  cardiac  contractions.  The  vagi 
convey  to  the  heart  impulses  from  the  cardio-inhibitory  centres  which 
have  a  restraining  action  upon  the  contractions  of  the  heart,  as  is  seen 
by  the  increase  in  the  frequency  of  the  heart-beats  when  the  vagi  are 
divided;  but  we  have  seen  that  appropriate  afferent  stimuli,  as,  for 
example,  when  applied  to  the  abdominal  sympathetic,  may  increase  the 
action  of  the  centre  to  such  an  extent  that  the  heart  may  be  altogether 
stopped  in  diastole.  In  such  a  case  the  result  of  the  afferent  stimuli 
upon  the  centre  has  been  to  produce  complete  inhibition  and  not  mus- 
cular contraction.  This  is  not  the  only  example  of  inhibition  which 
might  be  instanced;  the  action  of  almost  any  centre  may  be  inhibited 
by  impulses  reaching  it;  indeed  the  effect  of  afferent  impulses  upon  a 
vagi  upon  the  respiratory  centres  to  which  attention  has  been  drawn  in 
the  chapter  upon  respiration. 

Membranes  of  the  Brain  and  Spinal  Cord. — The  Brain  and  Spinal  Cord  are 
enveloped  in  three  membranes — (1)  the  Dura  Mater,  (2)  the  Arachnoid,  (8) 
the  Pia  Mater. 

(1)  The  Dura  Mater,  or  external  covering,  is  a  tough  membrane  composed  of 
bundle?  of  connective-tissue  which  cross  at  various  angles,  and  in  whose  inter- 
stices branched  connective-tissue  corpuscles  lie  :  it  is  lined  by  a  thin  elastic  mem- 
brane, and  on  the  inner  surface  and  where  it  is  not  adherent  to  the  bone,  on  the 


THI   >-ERVOUS   SYSTEM. 


559 


outer  surface  also  Is  a  layer  of  eDciothclial  cells  very  similar  to  those  found  in 
serous  membranes.  (2.)  The  Arachnoid  is  a  much  more  delicate  membrane,  very 
similar  in  structure  to  the  dura  mater,  and  lined  on  its  outer  or  free  surface  by  an 
endothelial  membrane. 


U/iftxr  Eidtre  tnity 
nf  S/xlnod  Corel 


LcwcrKxtttmUy 


U,\U 


—  \-    lit  Lainhu 
.^\    VH-tefyru. 


rip.  350.— View  of  the  cerebro-spinal  axis  of  the  nervous  system.  The  right  half  of  the 
cranium  and.trunk  of  the  body  has  been  removed  by  a  vertical  section;  the  membranes  of  the 
brain  and  spinal  cord  have  also  been  removed,  and  the  roots  and  first  part  of  the  fifth  and  ninth 
cranial,  and  of  all  spinal  nerves  of  the  riphtside,  have  been  dissected  out  and  laid  separately  on 
the  wall  of  the  skull  and  on  the  several  vertebrae  opposite  to  the  place  of  their  natural  exit  from 
the  cranio-spinal  cavity.     (After  Bourgery.) 

(3.)  The  Pia  Mater  consists  of  two  chief  layers,  between  which  numerous  blood- 
vessels ramify.  Between  the  arachnoid  and  pia  mater  is  a  network  of  fibrous- 
tissue  trabeculai  sheathed   with   endothelial  cells :   these   sub-arachnoid  trabeculea 


560  HANDBOOK    OF    PHYSIOLOGY. 

diTide  up  the  sub-arachnoid  space  into  a  number  of  irregular  sinuses.  There 
are  some  similar  trabeculee,  but  much  fewer  in  number,  traversing  the  sub-dural 
space,  i.  e. ,  the  space  between  the  dura  mater  and  arachnoid. 

Pacchionian  bodies  are  growths  from  the  sub-arachnoid  network  of  connec- 
tive-tissue trabeculse  which  project  through  small  holes  in  the  inner  layers  of 
the  dura  mater  into  the  venous  sinuses  of  that  membrane.  The  venous  sinuses 
of  the  dura  mater  have  been  injected  from  the  sub-arachnoidal  space  through 
the  intermediation  of  these  villous  outgrowths. 

The  Spinal  Cord  and  its  Nerves. 

The  Spinal  cord  is  a  cylindriform  column  of  nerve-substance  con- 
nected above  with  the  brain  through  the  medium  of  the  bulb,  and  ter- 
minating below,  about  the  lower  border  of  the  first  lumbar  vertebra,  in  a 
slender  filament  of  gray  substance,  the  filum  terminale,  which  lies  in  the 
midst  of  the  roots  of  many  nerves  forming  the  cauda  equina. 

Structure. — The  cord  is  composed  of  white  and  gray  nervous  sub- 
stance, of  which  the  former  is  situated  externally,  and  constitutes  its  chief 
portion,  while  the  latter  occupies  its  central  or  axial  portion,  and  is  so 
arranged,  that  on  the  surface  of  a  transverse  section  of  the  cord  it 
appears  like  two  somewhat  crescentic  masses  connected  together  by  a 
narrower  portion  or  isthmus  (fig.  350a).  Passing  through  the  centre  of 
this  isthmus  in  a  longitudinal  direction  is  a  minute  canal  (central 
canal),  which  is  continued  through  the  whole  length  of  tlK.  cord,  and 
opens  above  into  the  s^Dace  at  the  back  of  medulla  oblongata  and  pons 
Varolii,  called  the  fourth  ventricle.  It  is  lined  by  a  layer  of  columnar 
ciliated  epithelium. 

The  spinal  cord  consists  of  two  exactly  symmetrical  halves,  separated 
anteriorly  and  posteriorly  by  \evi\cdl  fissures  (the  posterior  fissure  being 
deeper,  but  less  wide  and  distinct  than  the  anterior),  and  united  in  the 
middle  by  nervous  matter  which  is  usually  described  as  forming  two 
commissures — an  anterior  commissure,  in  front  of  the  central  canal, 
consisting  of  medullated  nerve-fibres,  and  a  'posterior  commissure  behind 
the  central  canal  consisting  also  of  medullated  nerve-fibres,  but  witli 
more  neuroglia,  which  gives  the  gray  aspect  to  this  commissure.  The 
fibres  of  the  commissures  are  mainly  composed  of  collaterals.  Each 
luilf  of  the  spinal  cord  is  marked  on  the  sides  (obscurely  at  the  lower 
part,  but  distinctly  above)  by  two  longitudinal  furrows,  which  divide  it 
into  three  portions,  columns,  or  tracts,  an  anterior.,  lateral,  and  2^osterior. 
From  the  groove  between  the  anterior  and  lateral  columns  spring  the 
anterior  roots  of  the  spinal  nerves  (4);  and  just  in  front  of  the  groove 
between  the  lateral  and  posterior  columns  arise  the  posterior  roots  of  the 
same;  a  pair  of  roots  on  each  side  corresponding  to  each  vertebra. 

White  Matter.— The  wliite  matter  ol'  the  cord  is  seen  to  be 
made  up  of   medullated  nerve-fibre.-^,   of  different  sizes,   arranged  lougi- 


THE    NERVOUS"SYSTEM. 


^at 


tudinall}',  and  of  a  sujiporting  material  of  two  kinds,  viz. : — (i/)  ordinary 
tibrous  connective  tissue  with  elastic  fibres,  which  is  couuecteu  with 
septa  from  the  pia  mater  which  pass  into  the  cord  to  carry  the  blood 
vessels.  (/*)  Neuroglia;  this  material  is  made  up  of  the  branching  cells 
(tig.  351a),  the  bodies  of  which,  in  consequence  of  the  high  development 
of  the  branchings,  are  small.  The  processes  of  the  neuroglia-cells  are 
arranged  so  as  to  support  the  nerve-fibres  which  are  without  the  usual 
external  nerve  sheaths.  Neuroglia  was  formerly  considered  to  be  a 
kind  of  connective  tissue,  but  is  now  considered  to  be  a  distinct  material. 


15    13 


**rt 


AA 


^^ 


Fig.  350a.— Horizuiital  section  of  tlie  cord  and  its  envelopes,  at  the  middle  of  a  vertebral  body 
(Schematic).  1,  Spinal  cord  with  :.',  its  anterior  median  fissure:  3.  its  posterior  median  fissure; 
4,  anterior  roots;  5,  posterior  roots;  6,  pia  mater  (in  red);  7,  ligamentum  dentatum;  8,  connect- 
ing fibres  passing  from  the  pia  to  dura  mater;  9,  visceral  layer  and  9',  parietal  layer  of  the 
arachnoid  (in  blue);  10,  subaraclmoid  space;  11,  arachnoid  cavity;  12,  dura  mater  (in  yellow);  13, 
periosteum;  W.  external  periosteum;  14,  cellular  tissue  situated  between  the  dura  mater  and  the 
wall  of  the  vertebral  canal;  15,  common  posterior  vertebral  ligament;  16,  intra-spinal  veins;  17, 
vertebra  in  section.    (Testui.) 


It  is  derived  from  the  neural  epiblast,  and  yields  neuro-keratin.  (See-p^ 
107.) 

The  general  ri;le  respecting  the  size  of  difl'erent  parts  of  the  c<5rd 
appears  to  be,  that  each  part  is  in  direct  proportion  in  this  resj)cct  to  the 
size  and  number  of  nerve-roots  given  off  from  it,  and  has  but  little  reia- 
tion  to  the  size  or  number  of  those  given  off  below  it.  Thus  tlie  cord  is 
very  large  in  the  middle  and  lower  part  of  its  cervical  portion,  whence 
arise  the  large  nerve-roots  for  the  formation  of  the  brachial  plexuses  and 
the  supply  of  the  upper  extremities,  and  again  enlarges  at  the  lowest 
36 


562 


HANDBOOK    OF    PHYSIOLOGY. 


part  of  its  dorsal  portion  and  tlie  upper  part  of  its  lumbar,  at  the  origins 
of  the  large  nerves  which,  after  forming  the  lumbar  and  sacral  plexuses, 
are  distributed  to  the  lower  extremities.  The  chief  cause  of  the  greater 
size  at  these  parts  of  the  spinal  cord  is  increase  in  the  quantity  of  gray 
matter;  for  there  seems  reason  to  believe  that  the  white  part  of  the 
cord  becomes  gradually  and  progressively  larger  from  below  upward, 
doubtless  from  the  addition  of  a  certain  number  of  upward  passing- 
fibres  from  each  pair  of  nerves.  ■ 


Fig,  351. — From  the  lower  lumbar  cord  of  man,  after  a  preparation  by  Klonne  and  Muller.  of 
Berlin  (No.  11,153),  staiuedby  Weigrert  and  Pal's  method.  A  portion  of  the  Rray  substance  of  the 
ventral  cornu  with  the  adjoining:  portions  of  the  lateral  column  is  represented,  showing  anterior 
liorn  cells  and  the  fine  medullated  fibres  which  enter  the  gray  substance  from  the  lateral  column 
*nd  surround  tlie  nerve-cells,  which  liere  are  provided  with  fine  pigmented  granules.  High  power. 
(Koelliker.^ 


From  careful  estimates  of  the  number  of  nerve-fibres  in  a  transverse 
section  of  the  cord  toward  its  upper  end,  and  the  number  entering  or 
issuing  from  it  by  the  anterior  and  posterior  roots  of  each  pair  of  nerves, 
it  has  been  shown  that  in  the  human  spinal  cord  not  more  than  half 
of  the  total  number  of  nerve-fibres  of  all  the  spinal  nerves  are  contained 
in  a  transverse  section  near  its  uj)per  end.  It  is  obvious,  therefore,  that 
at  least  half  of  the  nerve-fibres  entering  it  must  terminate  somewhere  in 
the  cord  itself. 


THE    XEK VOL'S   SYSTEM. 


5H3 


The  gray  matter  of  the  spinal-cord  consists  of  numerous  groups  of 
nerve-cells,  of  a  close  meshwork  of  niednllated  fibres,  most  of  which  are 
very  fine  and  delicate,  and  of  an  extremely  delicate  network  of  axis- 
cylinders.  This  latter  fine  plexus  has  been  called  "  Gerlach's  network." 
Mingled  with  it  and  supporting  it,  is  the  mesh  work  of  the  neuroglia, 
which  is  finer  even,  in  its  structure,  than  that  of  the  nerve-tissue,  so 
that  except  under  proper  staining  and  illumination,  it  may  appear 
granular.  This  is  especially  developed  around  the  central  canal,  which 
is  lined  with  columnar  ciliated  epithelium,  the  cells  of  which  at  their 
outer  end  terminate  in  fine  processes,  which  join  the  neurogliar  network 
surrounding    the   canal,    and    form   the   snhstantia  geJatinosa  centralis. 


Fig:.  351a.— Different  types  of  neuroglia  cells.     fAfter  v.  Geliucliteu.)    b.  Neuroglia  cells  of  the 
white  substance,  and  c,  of  the  gray  substance  of  the  cord  of  an  embryo  calf. 

Neuroglia  was  formerly  thought  to  be  mainly  present  in  the  tip  of  the 
posterior  cornn  of  gray  matter,  forming  what  is  known  as  the  substantia 
gelatimsa  laferaJis  of  Kolando,  through  which  the  posterior  nerve-roots 
pass.  This  is  nosv  known  to  be  composed  of  very  small  nerve-cells  and 
their  processes. 

Groups  of  cells  in  fjrai/  matter. — The  multipolar  cells  are  either  scat- 
tered singly  or  arranged  in  groups,  of  which  the  following  are  to  be  dis- 
tinguished on  either  side — certain  of  the  gtoups  being  more  or  less 
marked  in  all  of  the  regions  of  the  cord,  viz.,  those  (a)  in  the  anterior 
cornu,  (b)  those  in  the  posterior  cornn,  and  (c)  intrinsic  cells  distributed 
throughout  the  gray  matter. 

(a)  The  cells  in   the  anterior  cornu   are  large  and   branching,  and 


564 


HANDBOOK    OF    PHYSIOLOGY, 


each  gives  rise  to  an  axis-cylinder  process  whicli  passes  out  in  the 
anterior  nerve-root.  These  cells  are  everywhere  conspicuous,  hut  are 
particularly  numerous  in  the  cervical  and  lumbar  enlargements.  In  these 
districts  they  may  be  divided  into  several  groups — (i.)  a  group  of  large 
cells  close  to  the  tij)  of  the  inner  part  of  the  anterior  cornu — all  the  cells 
of  the  anterior  cornu  in  the  dorsal  or  thoracic  region  are  said  to  belong 
to  this  group;  (ii.)  several  lateral  groups  (2,  «,  J,  and  c,  fig.  353)  on 
the  outer  side  of  the  gray  matter,  and  (iii.)  a  certain  number  of  cells  at 
the  base  of  the  inner  part  of  the  anterior  cornu  particularly  vi'ell  marked 
in  the  thoracic  region.  (5)  Cells  of  the  posterior  cornu— these  are  not 
numerous;  they  are  small  and  branched,  and  each  has  an  axis-cylinder 


Fig.  352.— Section  of  spinal  cord,  one  half  of  which  (left)  shows  the  tracts  of  the  white 
matter,  and  the  other  half  (right)  shows  the  position  of  the  nerve  cells  in  the  gray  matter.  7, 
10,  9  and  3  are  tracts  of  descending  degeneration,  1.  4,  6  and  8,  of  ascending  degeneration.  Semi- 
diagrammatic.     (After  Sherrington.) 

process  passing  off;  but  these  processes  do  not  pass  into  the  posterior 
nerve-roots.  The  groups  are  two  at  least  in  number,  viz.,  (i.)  in  con- 
nection with  the  edge  of  the  gray  matter  externally,  where  it  is  consider- 
ably broken  up  by  the  passage  of  bundles  of  fibres  through  it,  and  called 
the  lateral  reticular  formation;  and  (ii.)  in  connection  with  a  similar 
reticular  formation,  more  at  the  tip  of  the  gray  matter  of  the  posterior 
cornu  ;  this  is  known  as  the  posterior  reticular  formation. 

A  group  of  cells  (No  3,  fig.  352)  is  situated  at  the  base  and  me- 
dian side  of  the  posterior  cornu.  It  is  formed  of  fairly  large  cells,  fusi- 
form in  shape,  and  constitutes  the  posterior  vesicular  column,  or  Clarke's 
column.  It  extends  from  the  upper  lumbar  to  the  lower  cervical  region. 
On  the  outer  portion  of  the  gray  matter,  midway  between  the  anterior 
and  posterior  cornua,  is  a  group  of  cells,  known  as  the  cells  of  the  lateral 
gray  column.     These  are  small  and  spindle-shaped,  and  are  more  or  less 


THE    NERVOUS    SYSTEM.  565 

marked  in  tlie  lumbar  region,  as  Avell  as  in  the  thoracic  region  (No. 
5,  fig.  532). 

((■)  Besides  these  gronpt;,  which  have  their  names  largely  on  ac- 
count of  their  location,  there  are  distributed  throughout  the  gray 
matter  a  very  large  number  of  other  cells,  which  are  known  as  intrinsic 
cells.  These  send  out  neuraxons  which  pass  into  the  white  matter 
of  the  same  or  the  opposite  side,  pass  up  and  down  the  cord,  enter  the 
gray  matter  again,  and  connect  there  by  their  end-brushes  with  cells  at  a 
different  level  of  the  cord.  The  intrinsic  cells  are,  therefore,  in  the 
main,  commissural  in  their  function,  that  is  to  say,  they  unite  the  two 
sides  or  different  levels  of  the  cord.  They  are  also,  themselves,  in  re- 
lation with  the  fibres  and  cells  of  the  anterior  and  posterior  cornua. 

Culnnms  and  tracts  in  the  white  vtatter  of  the  spinal  C07'd. — In  addition 
to  the  columns  of  the  white  matter  which  are  marked  out  by  the  points 
from  which  the  nerve-roots  issue,  and  which  are  the  anterior,  the  lateral 
and  posterior,  the  posterior  is  further  divided  by  a  septum  of  the  pia 
mater  into  two  almost  equal  parts,  constituting  the  postero-exte)'7ial 
column,  or  column  of  Burdach  (fig.  353,  2),  ^m^ihe poster o-median,  or 
colunin  of  Goll  (fig.  353,  1).  In  addition  to  these  columns,  however,  it 
has  been  shown  that  the  white  matter  can  be  still  fiirther  subdivided. 
This  subdivision  has  been  accomplished  by  evidence  of  several  kinds, 
that  the  parts  or,  as  they  are  called,  tracts  in  the  white  matter,  perform 
different  functions  in  the  conduction  of  impulses. 

The  methods  of  observation  are  the  following : — 

{a)  The  emhryological  method.  It  has  been  found  that  if  the  develop- 
ment of  the  spinal  cord  be  carefully  observed  at  different  stages  that  cer- 
tain groups  of  the  nerve-fibres  put  on  their  myelin  sheath  at  earlier  peri- 
ods than  others,  and  that  the  different  groups  of  fibres  can  therefore  be 
traced  in  various  directions.      This  is  known  as  the  method  of  Flechsig. 

{b)  Waller ian  or  degeneration  method. — This  method  depends  upon 
the  fact  that  if  a  nerve-fibre  is  separated  from  its  nerve-cell,  it  wastes  or 
degenerates.  It  consists  in  tracing  the  course  of  tracts  of  degenerated 
fibres,  which  result  from  an  injury  to  any  part  of  the  central  nervous 
system.  When  fibres  degenerate  below  a  lesion  the  tract  is  said  to  be 
of  descending  degeneration,  and  when  the  fibres  degenerate  in  the  oppo- 
site direction  the  tract  is  one  of  ascending  degeneration.  By  modern 
methods  of  staining  of  the  central  nervous  system  it  has  proved  com- 
paratively easy  to  distinguish  degenerated  parts  in  sections  of  the  cord 
iind  of  other  portions  of  the  central  nervous  system.  Degenerated 
fibres  have  a  different  staining  reaction  when  the  sections  are  stained 
by  what  are  called  Weigcrt's  and  Marchi's  methods.  Accidents  to  the 
central  nervous  system  in  man  have  given  us  much  information  upon 
this  subject,  but  this  has  of  late  years  been  supplemented  and  largely 
extended   by  the  experiments  on  animals,   particularly  upon  monkeys; 


566  HANDBOOK    OF    PHYSIOLOGY. 

and  considei'iible  light  has  been  by  these  means  shed  upon  the  condnction 
of  impulses  to  and  from  the  nervous  system  by  the  study  of  the  results  of 
section  of  different  parts  of  the  central  nervous  system,  and  of  the  spinal 
nerve-roots.  Thus  we  have  not  only  embryologieal  evidence  mapping 
out  different  tracts,  but  also  confirmatory  pathological  and  experimental 
observations. 

The  tracts  which  have  been  made  out  are  the  following : — 

(a)  Of  descending  degeneration. 

(1.)  The  crossed  pyramidal  tract  (fig.  352,7). — This  tract  is  situated 
to  the  outer  part  of  the  posterior  cornu  of  gray  matter.  It  is  found 
throughout  the  whole  length  of  the  spinal  cord;  at  the  lower  part  it  ex- 
tends to  the  margin  of  the  cord,  but  higher  up  it  becomes  displaced 
■from  this  position  by  the  interpolation  of  another  tract  of  fibres,  to  be 
presently  described,  viz.,  the  direct  cerebellar  tract.  The  crossed 
•pyramidal  tract  is  large,  and  may  touch  the  tip  of  gray  matter  of  the 
posterior  cornu,  but  is  separated  from  it  elsewhere.  In  shape  on  cross- 
section  it  is  somewhat  like  a  lens,  but  varies  in  different  regions  of  the 
cord,  and  diminishes  in  size  from  the  cervical  region  downward. 
The  tract  is  particularly  well  marked  out,  both  by  the  degeneration  and 
the  embryologieal  methods.  The  fibres  are  supposed  to  pass  off  as  they 
descend,  and  to  join  the  various  local  nervous  mechanisms  of  nerve  cells 
'and  their  branchings  which  are  represented  in  the  cord.  The  tract  of 
degeneration  may  be  traced  upward  beyond  the  cord,  in  a  way  to  be 
presently  described.  The  fibres  of  which  this  tract  is  composed  are 
moderately  large,  but  are  mixed  with  some  that  are  smaller. 

(ii.)  The  direct  or  uncrossed  jiyramidal  tract  (fig.  352,  10). — This 
tract  is  situated  in  the  anterior  column  by  the  sides  of  the  anterior 
fissure.  It  is  smaller  than  (i.),  and  is  not  present  in  all  animal^, 
though  conspicuous  in  the  human  cord  and  in  that  of  the  monkey.  It 
can  be  traced  upward  to  the  cerebral  cortex,  and  downward  as  far  as 
the  mid  or  lower  thoracic  region,  where  it  ends. 

(iii.)  Antero-lateral    descending   tract    (fig.   352,9). — An    extensive 
tract,  elongated  but  narrow,  and  reaching  from  the  crossed  to  the  direct 
■pyramidal  tract.     It  is  a  mixed  tract,  since  not  all  of  its  fibres  degenerate 
below  the  lesions. 

(iv.)  Comma  tract  (fig.  352,  3)  is  a  small  tract  of  fibres  which  degen- 
erate below  section  or  injury  of  the  cord.  Its  presence  has  been  demon- 
strated in  the  cervical  and  thoracic  regions.  It  is  supposed  to  consist  of 
the  descending  collaterals  of  the  posterior  nerve-roots  as  they  pass  into 
the  postero-external  columns. 

{V)  Of  ascending  degeneration. 

(i.)  Foste?-o-media7i,  column  {^g.  352,1). — This  tract  degenerates  up- 
ward on  injury  or  on  section  of  the  cord,  as  well  as  on  section  of  the 
posterior  nerve  roots.  It  exists  throughout  the  whole  of  the  cord  from 
below  up,  and  can  be  traced  into  the  bulb.     It  consists  of  fine  fibres. 


THE   NERVOUS   SYSTEM.  567 

(ii.)  Direct  cerebellar  tract  (fig.  352,  6). — This  tract  is  situated  on  the 
outer  part  of  the  cord  between  the  crossed  pyramidal  tract  and  the  mar- 
gin. It  is  found  in  tlie  cervical,  thoracic  and  upper  lumbar  regions  of 
the  cord,  and  increases  in  size  from  below  upward.  It  degenerates  on 
injury  or  section  of  the  cord  itself,  hut  not  on  section  of  the  posterior 
nerve-roots.  As  its  name  implies  it  is  believed  to  jiass  up  into  the  cere- 
bellum.    Its  fibres  are  coarse, 

(iii.)  J  /lie  ro-Iaf  end  ascend  in(/  fra<t  [Tract  of  Goicers  and  Tootli)  (fig. 
352,  8). — Tliis  tract  has  been  shown  on  injury  to  the  spinal  cord;  it  is 
situated  at  the  margin  of  the  cord  outside  of  the  corresponding  descend- 
ing tract.  It  is  traceable  throughout  the  whole  length  of  the  cord.  Its 
fibres  are  composed  of  mixed,  fine  and  coarse,  elements. 

(iv.)  Tract  of  Lissaner,  or  posterior  marginal  zone  (fig.  352,  4). — A 
small  tract  of  fine  white  fibres,  situated  at  the  apex  of  the  jiosterior 
horn,  is  made  up  of  fibres  from  the  posterior  nerve-roots  which  enter  the 
column  and  pass  up  and  down  for  a  short  distance,  finally  entering  the 
posterior  horn  where  they  terminate  in  fine  end-brushes  around  the  cells 
of  the  posterior  horn. 

It  will  thus  be  seen  that  the  white  matter  of  the  spinal-cord  has  three 
general  divisions,  into  the  anterior,  the  lateral,  and  posterior  columns. 
These  columns  are  subdivided  into  columns  in  which  the  fibres  degener- 
ate upward,  those  in  which  the  fibres  degenerate  downward,  and  other 
columns  in  which  the  fibres  do  not  degenerate  either  way  when  the  cord  is 
cut  across.  These  parts  of  the  cord  are  composed  of  commissural  fibres 
which  connect  different  levels  of  the  cord.  These  commissural  columns 
are  the  antero-lateral  columns,  the  lateral  limiting  layer,  and  the  column 
of  Burdach.  The  arrangement  of  these  columns  is  shown  well  in  the 
figure  (fig.  352). 

Spinal  Nerves. — Thespinal  nrrvcs consist  of  tliirty-one  pairs,  issuing 
from  the  sides  of  the  whole  length  of  the  cord,  their  number  correspond- 
ing with  the  intervertebral  foramina  through  which  they  pass.  Eacli 
nerve  arises  by  two  roots,  an  anterior  and  posterior,  the  latter  being  the 
larger.  The  roots  emerge  through  separate  apertures  of  the  sheath  of 
dura  mater  surrounding  the  cord;  and  directly  after  their  emergence, 
where  the  roots  lie  in  the  intervertebral  foramen,  a  ganglion  is  found 
on  the  posterior  root.  The  anterior  root  lies  in  contact  with  the  anterior 
surface  of  the  ganglion,  but  none  of  its  fibres  intermingle  with  those  in 
the  ganglion  (fig.  350,  4).  But  immediately^  beyond  the  ganglion  the 
two  roots  coak'seo,  and  by  the  mingling  of  their  fibres  form  a  compound 
or  mixed  spinal  nerve,  which,  after  issuing  from  the  intervertebral 
canal,  gives  off  anterior  and  posterior  or  ventral  and  dorsal  branches, 
each  containing  fibres  from  both  the  roots  (fig.  350),  as  well  as  a  third 
or  visceral  branch,  ramus  communicans,  to  the  sympathetic. 

The  anterior  root  of  each  spinal  nerve  arises  by  numerous  separate 


568 


HANDBOOK    OF    PHYSIOLOGY. 


and  couverging  bundles  from  the  anterior  column  of  the  cord;  the  pos- 
terior root  by  more  numerous  parallel  bundles,  from  the  posterior  column, 
or,  rather,  from  the  posterior  part  of  the  lateral  column  (fig.  350),  for 
if  a  fissure  be  directed  inward  from  the  groove  between  the  middle  and 
posterior  columns,  the  posterior  roots  will  remain  attached  to  the  former. 
The  anterior  roots  of  each  spinal  nerve  consist  chiefly  of  efferent  fibres; 
the  posterior  exclusively  of  afferent  fibres. 

Course  of  the  Fibres  of  the  Spinal  Nerve- Roots. —{a)  The  Anterior 
roots  enter  the  cord  in  several  bundles,  which  may  be  called: — (1) 
Internal;  (2)  Middle;  (3)  External;  all  being  more  or  less  connected  with 
the  groups  of  multipolar  cells  in  the  anterior  cornua.  1.  The  internal 
fibres  are  partly  connected  with   internal    group   of   nerve-cells  of  the 


Fig.  353a.— Section  of  the  spinal  cord,  showing-  the  arrangement  of  the  white  and  gray  matter. 
1,  Direct  pyramidal  tract;  8,  3,  antero-lateral  column;  4,  ascending  lateral  colnnm;  5,  crossed 
pyramidal  tract;  6,  direct  cerebral  tract;  7,  column  of  Burdach;  8.  column  of  Goll;  7,  posterior 
median  fissure;  10,  anterior  median  fissure;  11,  13.  anterior  horn  cells;  13,  Clarke's  column ;  L.  R., 
Lissauer's  column ;  rp,  posterior  root;  r  a,  anterior  root. 

anterior  cornu  of  the  same  side;  but  some  fibres  send  collaterals  through 
the  anterior  commissure  to  end  in  the  anterior  cornu  of  opposite  side, 
probably  in  the  internal  group  of  cells.  3,  The  middle  fibres  are  partly 
in  connection  with  the  lateral  group  of  cells  in  anterior  cornu,  and  in 
part  pass  backward  to  the  posterior  cornu,  having  no  immediate  connec- 
tion with  cells.  3.  The  exteriial  fibrea  are  partly  in  connection  with  the 
lateral  group  of  cells  in  the  anterior  cornu,  but  some  fibres  proceed  di- 
rect into  the  lateral  column  without  connection  with  cells,  and  pass 
upward  in  it. 

Besides  these  fibres,  there  are  some  which  do  not  appear  to  have  any 
connection  with  the  anterior  horn  cells,  but  pass  directly  through  to 


THE    NERVOrS    SYSTEM, 


560 


connect  with  groups  of  iiitiiiKsic  rells  in  the  median  or  posterior  portion 
of  the  gray  matter  of  tlie  cord. 

(Jj)  The  posterior  roots  enter  tiie  s[tiiial  cord  to  tlie  inner  or  me- 
dian side  of  the  posterior  cornu.  The  fibres,  as  soon  as  they  reach  the 
cord,  divide  in  a  fork-like  fashion,  one  branch  passing  down  a  short  dis- 
tance (only  abont  three  centimetres),  the  other  branch  passing  np  for  a 
longer  or  shorter  distance.  This  upper  branch  sometimes  reaches  nearly 
the  whole  extent  of  the  cord,  but  generally  it  extends  over  only  one  or 
two  segments  of  the  cord.  These  divisions  of  the  posterior  root  fibres 
give  off  in  their  course  numerous  collaterals.  The  nerve-fibres  of  the 
]iosterior  roots  are  divided   into  two  sets,  an  internal  or  median,  an  ex- 


Fig.  353. — Section  of  the  spinal  cord  showing  the  grouping  of  nerve-cells  and  tlie  course  of  nerve- 
fibres  entering  in  posterior  and  anterior  roots. 


ternal  or  lateral.  The  lateral  set  consists  mostly  of  small  fibres,  and  it 
enters  the  cord  opposite  the  tip  of  the  posterior  horn.  The  fibres  pass 
in  part  to  the  marginal  column  of  Liasauer,  where  they  ascend  and  de- 
scend;  in  part  they  penetrate  the  posterior  horn,  and  come  in  relation 
with  its  cells.  T'he  median  set  sends  some  fibres  which  pass  to  Clarke's 
column  of  cells,  others  pass  by  way  of  the  posterior  commissure  to  the 
median  cells  of  the  other  side.  Some  others  pass  through  the  median 
gray  matter  to  the  anterior  horn  cells  of  the  same  side.  Thus  the  pos- 
terior root-fibres  are  connected  with  all  the  cell  groups  of  the  posterior 
horn,  of  the  anterior  horn  of  the  same  side,  and  the  cells  of  the  median 
gray  of  the  opposite  side.     Besides  this,  they  are  connected  through  col- 


670  HANDBOOK    OF   PHYSIOLOGY. 

laterals  with  the  intrinsic  cells  of  the  gray  matter  at  different  levels  of 
the  cord.  One  can  realize  that  each  nerve-root  has,  in  this  way,  an 
effective  grip  npon  a  large  extent  of  the  cord.  This  is  seen  well  by 
studying  figs.  352a  and  353. 

The  Peculiarities  of  different  regions  of  the  Spinal  Cord. — The  outline  of  the 
gray  matter  and  the  relative  proportion  of  the  white  matter  varies  in  different 
regions  of  the  spinal  cord,  and  it  is,  therefore,  possible  to  tell  approximately 
from  what  region  any  given  transverse  section  of  the  spinal  cord  has  been 
taken.  The  white  matter  increases  in  amount  from  below  upward.  The 
amount  of  gray  matter  varies  ;  it  is  greatest  in  the  cervical  and  lumbar  enlarge- 
ments, viz. ,  at  and  about  the  5th  lumbar  and  6th  cervical  nerve,  and  least  in  the 
thoracic  region.  The  greatest  development  of  gray  matter  corresponds  with 
greatest  number  of  nerve-fibres  passing  from  the  cord. 

In  the  cervical  enlargement  th-e  gray  matter  occupies  a  large  px'oportion  of  the 
section,  the  gray  commissure  is  short  and  thick,  the  anterior  horn  is  blunt,  while 
the  posterior  is  somewhat  tapering.  The  anterior  and  posterior  roots  run  some 
distance  through  the  white  matter  before  they  reach  the  periphery. 

In  the  dorsal  region  the  gray  matter  bears  only  a  small  relation  to  the  white, 
and  the  posterior  roots  in  particular  run  a  long  course  through  the  white  matter 
before  they  leave  the  cord  ;  the  gray  commissure  is  thinner  and  narrower  than 
in  the  cervical  region.     The  tractus  intermedio-lateralis  is  here  most  marked. 

In  the  lumbar  enlargement  the  gray  matter  again  bears  a  very  large  propor- 
tion to  the  whole  size  of  the  transverse  section,  but  its  posterior  cornua  are 
shorter  and  blunter  than  they  are  in  the  cervical  region.  The  gray  commis- 
sure is  short  and  extremely  narrow. 

At  the  upper  part  of  the  eonus  medullaris,  which  is  the  portion  of  the  cord 
immediately  below  the  lumbar  enlargement,  the  gray  substance  occupies 
nearly  the  whole  of  the  transverse  section,  as  it  is  only  invested  by  a  thin 
layer  of  white  substance.  This  thin  layer  is  wanting  in  the  neighborhood  of 
the  posterior  nerve-roots.     The  great  commissure  is  extremely  thick. 

At  the  level  of  the  fifth  sacral  vertebra  the  gray  matter  is  again  in  excess,  and 
the  central  canal  is  enlarged,  appearing  T-shaped  in  section ;  while  in  the 
upper  portion  of  the  filum  terminale  the  gray  matter  is  uniform  in  shape  without 
any  central  canal. 

The  shape  of  the  cord  changes  from  the  sacral  and  lumbar  region 
where  it  is  circular  to  the  thoracic  where  it  is  oval,  and  to  the  cervical 
where  the  lateral  diameter  considerably  exceeds  the  antero-posterior  j 
the  change  in  shape  is  due  to  a  gradual  increase  of  the  lateral  columns. 
The  Spinal  Cord  and  Nerve-Koots  a  Mass  of  Nerve-Units. — 
We  have,  in  the  foregoing,  described  the  spinal  cord  as  being  composed 
of  white  and  gray  matter,  and  these  substances,  in  turn,  being  composed 
of  nerve-fibres  and  nerve-cells,  and  a  supporting  substance  called  neurog- 
lia. From  the  physiologist's  point  of  view,  the  spinal  cord  is  considered 
■to  be  composed  of  a  mass  of  nerve-units  or  neurons.  These  are  divided 
into  three  great  classes:  the  motor  neurons,  the  sensory  neurons,  and 
the  intermediate  neurons.  The  motor  neurons  make  up  the  larger  part 
of  the  nerve-tissue   in  the  anterior   horns;    their  neuraxons   pass    out 


THK    NERVOUS    SYSTEM.  571 

into  the  anterior  roots.  The  sensory  neurons  have  tlieir  cells  or  start- 
ing-points in  the  posterior  spinal  ganglia,  these  being  large  gang- 
lionic masses  which  lie  npon  the  posterior  roots.  These  cells  have 
a  process  which  runs  spineward  through  the  posterior  roots  into  the 
spinal  cord,  and  another  which  runs  peripherally,  forming  the  sen- 
sory nerve.  The  intermediate  neurons  have  their  cells  of  origin  in  the 
posterior  horus  and  median  part  of  the  gray  matter,  and,  to  a  slight  ex- 
tent, in  the  anterior  horns.  Their  cells  form  the  intrinsic  cells  of  the 
spinal  cord,  and  also  assist  in  the  conduction  of  sensory  and  other  afier- 
eut  impulses.  For  example,  the  neurons,  starting  with  the  cells  lying 
in  Clarke's  column,  send  their  processes  up  into  the  cerebellum,  and 
thus  continue  afferent  impulses  brought  to  the  neurons  through  the  pos- 
terior roots.  On  the  other  hand,  other  groups  of  cells  lie  in  the  lateral 
part  of  the  gray  matter  and  give  rise  to  processes  which  jjass  out  into  the 
lateral  columns  and  then  enter  the  gray  matter  again,  to  connect  with 
cells  at  different  levels.  These  are  the  intermediate  neurons  which  are 
commissural  in  their  functions. 

Functions  of  the  Spinal  Nerve-Koots. 

The  anterior  sjjinal  nerve-roots  are  efferent  in  function :  the  posterior 
are  afferent.  The  fact  is  proved  in  various  ways.  Division  of  the 
anterior  roots  of  one  or  more  nerves  is  followed  by  complete  loss  of  mo- 
tion in  the  parts  supplied  by  the  fibres  of  such  roots;  but  the  sensation 
of  the  same  parts  remains  perfect.  Division  of  the  posterior  roots 
destroys  the  sensibility  of  the  parts  supplied  by  their  fibres,  while  the 
power  of  motion  continues  unimpaired.  Moreover,  irritation  of  the 
ends  of  the  distal  portions  of  the  divided  anterior  roots  of  a  nerve  excites 
muscular  movements;  irritation  of  the  ends  of  the  proximal  portions, 
which  are  still  in  connection  with  the  cord,  is  followed  by  no  appreciable 
eff-ect.  It  must  be  remembered,  however,  that  in  the  anterior  or  efferent 
nerves  other  besides  motory  are  contained,  e.g.,  vaso-motor,  secretory, 
heat  fibres,  and  it  may  be  supposed  that  when  the  distal  end  of  a  divided 
nerve  is  stimulated,  the  effects  would  be  exercised  not  only  upon  mus- 
cles, but  upon  glands,  blood-vessels,  etc.  Irritation  of  the  distal  portions 
of  the  divided  posterior  roots,  on  the  other  hand,  produces  no  muscular 
movements  and  no  manifestations  of  pain;  for,  as  already  stated,  sen- 
sory nerves  convey  impressions  only  toward  the  nervous  centres:  but 
irritation  of  the  proximal  portions  of  these  roots  elicits  signs  of  intense 
suffering.  Occasionally,  under  this  last  irritation,  muscular  movements 
also  ensue;  but  these  are  either  voluntary,  or  the  result  of  the  irritation 
being  reflected  from  the  sensory  to  the  motor  fibres.  Occasionally,  too, 
irritation  of  the  distal  ends  of  divided  anterior  roots  elicits  signs  of  pain. 


5T2  HANDBOOK    OF    PHYSIOLOGY. 

as  well  as  producing  muscular  movements:  the  pain  thus  excited  is  prob- 
ably the  result  either  of  cmmj-)  or  of  so-called  recurrent  sensibility. 

Recurrent  Sensil)iUtij.—\f  the  anterior  root  of  a  spinal  nerve  be 
divided,  and  the  peripheral  end  be  irritated,  not  only  movements  of  the 
muscles  supplied  by  the  nerve  take  place,  but  also  of  other  muscles,  indic- 
ative of  pain.  If  the  main  trunk  of  the  nerve  (after  the  coalescence  of 
the  roots  beyond  the  ganglion)  be  divided,  and  the  anterior  root  be 
irritated  as  before,  the  general  signs  of  pain  still  remain,  although  the 
contraction  of  the  muscles  does  not  occur.  The  signs  of  pain  disappear 
when  the  posterior  root  is  divided.  From  these  experiments  it  is  be- 
lieved that  the  stimulus  passes  down  the  anterior  root  to  the  mixed 
nerve,  and  returns  to  the  central  nervous  system  through  the  posterior 
root  by  means  of  certain  sensory  fibres  from  the  posterior  root,  which 
loop  back  into  the  anterior  root  before  continuing  their  course  into  the 
mixed  nerve-trunk.  These  fibres  degenerate  when  the  posterior  nerve- 
root  is  divided  beyond  the  ganglion. 

Functions  of  the  Ganglia  on  Poster ior  Roots. — The  cells  of  the  pos- 
terior ganglia  act  as  centres  for  the  nutrition  of  the  nerve-fibres  given  off 
from  them.  When  these  are  cut,  the  parts  of  the  nerves  so  severed  de- 
generate, while  the  parts  which  remain  in  connection  with  the  cells  do 
not.  Thus  on  section  of  the  posterior  nerve-root  beyond  the  ganglion 
the  peripheral  part  wastes  and  the  central  does  not,  and  on  section  of 
the  root  between  the  ganglion  and  the  cord  the  central  part  to  a  great 
extent  wastes  and  the  peripheral  remains  unaffected. 


Functions  of  the  Spinal  Coed. 

The  power  of  the  spinal  cord,  as  a  nerve-centre,  may  be  arranged 
under  the  heads  of  (1)  Conduction;  (2)  Reflex  action. 

(1)  Conduction. — The  functions  of  the  spinal  cord  in  relation  to 
conduction  may  be  best  remembered  by  considering  its  anatomical  con- 
nections with  other  parts  of  the  body.  From  these  it  is  evident  that 
there  is  no  way  by  which  nerve-impulses  can  be  conveyed  from  the  trunk 
and  extremities  to  the  brain,  or  vice  versa,  other  than  that  formed  by 
the  spinal  cord.  Through  it,  the  impressions  made  upon  the  peripheral 
extremities  or  other  parts  of  the  spinal  sensory  nerves  are  conducted  to 
the  brain,  where  alone  they  can  be  perceived.  Through  it,  also,  the 
stimulus  of  the  will,  conducted  from  the  brain,  is  capable  of  exciting  the 
action  of  the  muscles  supplied  from  it  with  motor  nerves.  And  for  all 
these  conductions  of  impressions  to  and  fro  between  the  brain  and  the 
spinal  nerves,  the  perfect  state  of  the  cord  is  necessary;  for  when  any 
part  of  it  is  destroyed,  and  its  communication  with  the  brain  is  inter- 
rupted, impressions  on   the  sensory  nerves  given  off  from  it  below  the 


THE  NERVOUS  syst?:m.  57'S 

seat  of  injury,  cease  to  be  propagated  to  the  brain,  and  the  brain  loses 
the  power  of  voluntarily  exciting  the  motor  nerves  proceeding  from  the 
portion  of  cord  isolated  from  it.  Illustrations  of  this  are  furnished  by 
various  examples  of  paralysis,  but  by  none  better  than  by  the  common 
paraplegia,  or  loss  of  sensation  and  voluntary  motion  in  the  lower  part  of 
the  body,  in  consequence  of  destructive  disease  or  injury  of  a  portion, 
including  the  whole  thickness,  of  the  spinal  cord.  Such  lesions  destroy 
the  communication  between  the  brain  and  all  parts  of  the  spinal  cord 
below  the  seat  of  injury,  and  consequently  cut  off  from  their  connection 
with  the  brain  the  various  organs  supplied  with  nerves  issuing  from 
those  parts  of  the  curd. 

It  is  Jiot  piobable  ihat  the  conduction  of  motor  or  sensory  impulses  is 
effected  under  ordinary  circumstances  (to  any  great  extent),  as  was  for- 
merly supposed,  through  the  gray  substance,  i.e.,  through  tne  nerve- 
corpuscles  and  filaments  connecting  them.  AH  parts  of  the  cord  are  not 
alike  able  to  conduct  all  impressions;  and  as  there  are  separate  nerve- 
fibres  for  motor  and  for  sensory  impressions,  so  in  the  cord,  separate  and 
determinate  tracts  serve  to  conduct  always  the  same  kind  of  impres- 
sion. The  sensations  of  touch,  temperature,  and  pain,  however,  do  not 
appear  to  have  such  sharply  limited  tracts  as  the  inotor  impulses. 

Experimental  and  other  observations  point  to  the  following  conclu- 
sions regarding  the  conduction  of  sensory  and  motor  impressions  through 
the  spinal  cord.  Many  of  these  conclusions  must,  however,  be  received 
with  considerable  reserve. 

a.  Sensory  Impressions. — By  sensory  impressions  are  here  meant 
the  sensations  of  touch  and  pain,  of  heat  and  cold,  and  of  muscular  sense. 
These  impressions  are  conveyed  to  the  spinal  cord  by  the  posterior  nerve- 
roots.  Part  of  them  are  then  carried  directly  into  the  postero-median 
column  on  the  same  side,  and  thence  up  to  the  nucleus  of  this  column 
in  the  medulla.  It  is  mainly  the  impulses  of  muscle  sense  that  are  thus 
carried.  Other  sensations  are  carried  by  the  posterior  root-fibres  to  the 
cells  of  the  column  of  Clarke.  From  there  the  impulses  are  conveyed  to 
the  direct  cerebellar  tract  on  the  same  side,  and  thence  up  to  the  cere- 
bellum. These  are  mainly  sensations  that  subserve  the  sense  of  equili- 
brium, and  are  closely  connected  in  function  with  those  which  pass  up 
the  column  of  Coll  to  its  nucleus.  The  impressions  of  touch  and  pain, 
and  of  heat  and  cold,  are  conveyed  to  the  nerve-cells  in  the  posterior 
cornua  of  the  same  side  in  jjart,  and  in  part  to  the  nerve-cells  in  the 
posterior  cornua  and  median  gray  of  the  opposite  side.  From  this  point, 
the  impulse  is  taken  up  again  by  intermediary  neurons  and  conveyed 
through  the  anterior  and  lateral  columns  of  the  cord,  in  the  ascending 
tract  of  Cowers  and  Tooth,  to  the  brain.  By  reason  of  the  great  number 
of  collaterals  and  the  interpolation  in  the  course  of  the  sensory  impulse 
of  many  intermediary  neurons,  no  very  sharply  defined  tract  has  yet 
been  satisfactorily  made  out  in  the  spinal   cord   for  the  conduction  of 


574  HANDBOOK    OF    PHYSIOLOGY. 

these  sensations  of  temperature,  pain,  and  touch.  If  one  set  of  fibres  ia 
destroyed  by  disease,  others  seem  able,  through  the  collaterals,  to  take 
up  its  function.  We  can  only  say  that  most  of  these  sensory  impressions 
pass  up  in  the  lateral  and  anterior  columns.  It  is  probable,  also,  that 
pain  and  temperature  sensations  cross  over  at  once,  to  a  considerable  ex- 
tent, and  pass  up  in  the  opposite  side  of  the  cord  to  which  they  enter., 
Touch  and  pressure  sensations,  as  well  as  muscle-sense  impressions,  and 
sensations  of  equilibrium,  pass  up  largely  upon  the  same  side  until  they 
reach  the  medulla  or  cerebellum. 

The  direct  cerebellar  tract  is  believed  to  commence  in  the  cells  of  the 
posterior  vesicular  column  of  Clarke  of  the  same  side;  it  goes  chiefly  to 
the  cerebellum,  through  the  restiform  body,  but  is  said  also  to  contain 
fibres  which  pass  up  as  far  as  the  corpora  quadrigemina  and  then  turn 
backward  and  lying  near  the  brachium  pass  to  the  cerebellum.  The 
fibres  of  the  antero-lateral  ascending  tract  are  believed  to  arise  from 
the  gray  matter  of  the  posterior  cornu.  In  the  case  of  the  ascending 
tracts,  with  the  exception  of  the  posterior  median  column,  the  connec- 
tion with  the  posterior  nerve-roots  is  not  direct. 

h.  Motor  Impressions. — Motor  impressions  are  conveyed  down- 
ward from  the  brain  along  tlie  pyramidal  tracts,  viz.,  the  direct  or  an- 
terior, and  tlie  crossed  or  lateral,  chiefly  in  the  latter.  Generally 
speaking,  the  impressions  pass  down  on  the  side  opposite  to  which  they 
originate,  having  undergone  decussation  in  the  medulla;  but  some  im- 
pressions do  not  cross  in  the  medulla,  btit  lower  down,  in  the  cord,  being 
conveyed  by  the  anterior  or  uncrossed  pyramidal  fibres,  and  decussate  in 
the  anterior  commissure.  The  motor-fibres  for  the  legs  joar^m//?/  pass 
downward  in  the  lateral  columns  of  the  same  side.  This  is  also  probably 
the  case  with  the  bilateral  muscles,  i.e.,  muscles  of  the  two  sides  acting, 
together,  such  as  the  intercostal  muscles  and  other  muscles  of  the  trunk, 
as  well  as  the  costo-bumeral  muscles. 

It  is  quite  certain,  as  was  just  now  pointed  out,  that  the  fibres  of  the 
anterior  nerve-roots  are  more  numerous  than  the  fibres  proceeding  down- 
ward from  the  brain  in  the  pyramidal  tracts,  or  the  so-called  pyramidal 
fibres.  This  is  because  each  pyramidal  fibre  is  really  a  very  long  nerve 
process  or  neuraxon,  and  is  supplied  in  its  course  with  a  large  number 
of  collaterals,  which  gooff  at  difiierent  points,  and  thus  put  it  in  relation 
with  different  groups  of  nerve-cells  in  the  anterior  cornua  at  various 
levels.  Each  nerve-fibre  of  the  pyramidal  tract,  by  means  of  its  col- 
laterals, can  control  a  number  of  nerve-cells,  and  can  thus  co-ordinate 
the  action  of  impulses  sent  out  through  the  anterior  roots  to  a  number 
of  groups  of  muscles.  In  other  words,  the  gray  matter  of  the  anterior 
cornua  contains  an  apparatus  with  various  complicated  co-ordinating 
powers,  which  apparatus  is  under  the  control  of  the  neurons  whose 
cells  of  origin  are  in  the  cortex  of  the  brain.  This  apparatus  is  also  re- 
flexly  influenced  by  sensory  impressions  passing  to  the  cord. 


THE    NERVOUS    SYSTEM.  575, 

Division  of  the  anterior  pyramids  of  the  medulla  at  the  point  of 
decussation  is  followed  by  paralysis  of  motion,  never  quite  absolute,  in 
all  parts  below.  Disease  or  division  of  any  part  of  the  cerebro-spinal 
axis  above  the  seat  of  decussation  is  followed  by  imjiaired  or  lost  power 
of  motion  on  the  opposite  side  of  the  body;  while  a  like  injury  inflicted 
below  this  part  induces  similar,  never  quite  absolute  no  doubt,  on  the 
corresponding  side. 

When  one  half  of  the  spinal  cord  is  cut  through  in  monkeys,  the 
following  results  follow  (Mott) : — Motor  paralysis  of  the  muscles  of  the 
same  side  (never  complete  of  muscles  used  in  bilateral  associated  action), 
followed  by  gradual  recovery  of  muscular  movement,  except  of  the  finer 
movements  of  the  hand  and  foot ;  wasting  and  flabbiness  of  the  muscles ; 
sensory  paralvsis  of  the  same  side  (temperature,  touch,  pain  and  pres- 
sure) ;  temjDorary  vaso-motor  i:)aralysi3  on  came  side.  The  temperature  of 
the  affected  side  was  depressed  1  to  3°  (F.). 

Reflex  Action. — In  man  the  spinal  cord  is  so  much  under  the  control 
of  the  higher  nerve-centres,  that  its  own  individual  functions  in  rela- 
tion to  reflex  action  are  apt  to  be  overlooked;  so  that  the  result  of 
injury,  by  which  the  cord  is  cut  off  completely  from  the  influence  of  the 
encephalon,  is  apt  to  lessen  rather  than  increase  our  estimate  of  its 
importance  and  individual  endowments.  Thus,  when  the  human 
spinal  cord  is  divided,  the  lower  extremities  fall  into  any  position  that 
their  weight  and  the  resistance  of  surrounding  objects  combine  to  give 
them;  and  if  the  body  is  irritated,  they  do  not  move  toward  the  irrita- 
tion; and  if  they  are  touched,  the  consequent  reflex  movements  are 
disorderly  and  purposeless;  all  power  of  voluntary  movement  is  absolutely 
abolished.  In  other  mammals,  however,  e.g. ,  in  the  rabbit  or  dog,  after 
recovery  from  the  shock  of  the  operation,  which  takes  some  time,  reflex 
action  will  occur  in  the  parts  below  after  the  spinal  cord  has  been  divided, 
a  very  feeble  irritation  being  followed  by  extensive  and  co-ordinate 
movements.  In  the  case  of  the  frog,  and  many  other  cold-blooded 
animals,  in  which  experimental  and  other  injuries  of  the  nerve-tissues 
are  better  borne,  and  in  which  the  lower  nerve-centres  are  less  subor- 
dinate in  their  action  to  the  higher,  the  reflex  functions  of  the  cord  are 
still  more  clearly  shown.  When,  for  example,  a  frog's  head  is  cut  off, 
its  limbs  remain  in,  or  assume  a  natural  position;  they  resume  it  when 
disturbed;  and  when  the  abdomen  or  back  is  irritated,  the  feet  are 
moved  with  the  manifest  purpose  of  pushing  away  the  irritation.  The 
main  difference  in  the  cold-blooded  animals  being  that  the  reflex  move- 
ments are  more  definite,  complicated,  and  effective,  although  less  ener- 
getic than  in  the  case  of  mammals.  It  might  indeed  be  thought,  on 
superficial  examination,  that  the  mind  of  the  animal  was  engaged  in 
the  acts;  and  yet  all  analogy  would  lead  us  to  the  belief  that  the  spinal 
cord  of  the  frog  has  no  different  endowment,  in  kind,  from  those  which 


576  HANDBOOK    OF    PHYSIOLOGY. 

belong  to  tlie  cord  of  the  higher  vertebrata:  the  diifereuce  is  only  in 
degree.  And  if  this  be  granted,  it  may  be  assumed  that,  in  man  and 
the  higher  animals,  many  actions  are  performed  as  reflex  movements 
occurring  through  and  by  means  of  the  spinal  cord,  although  the  latter 
cannot  by  itself  initiate  or  even  direct  them  independently. 

Cutaneov.s  and  Muscle  Reflexes. — In  the  human  subject  two  kinds  of 
reflex  actions  dependent  upon  the  spinal  cord  are  usually  distinguished, 
the  alterations  of  which,  either  in  the  direction  of  increase  or  of  diminu- 
tion, are  indications  of  some  abnormality,  and  are  used  as  a  means  of 
diagnosis  in  nervous  and  other  disorders.  They  are  termed  respectively 
{(i.)  cutaneous  reflexes,  and  {b.)  muscle  reflexes,  {a.)  Cutaneous  reflexes 
are  set  up  by  a  gentle  stimulus  applied  to  the  skin.  The  subjacent 
muscle  or  muscles  contract  in  response.  Although  these  cutaneous 
reflex  actions  may  be  demonstrated  almost  anywhere,  yet  certain  of  such 
actions  as  being  most  characteristic  are  distinguished,  e.g.,  plantar 
reflex;  glutear  reflex,  i.e.,  a  contraction  of  the  gluteus  maximus  when 
the  skin  over  it  is  stimulated ;  cremaster  reflex,  retraction  of  the 
testicle  when  the  skin  of  the  inside  of  the  thigh  is  stimulated,  and  the 
like.  The  ocular  reflexes,  too,  are  important.  They  are  contraction 
of  the  iris  on  exposure  to  light,  and  its  dilatation  on  stimulating  the  skin 
of  the  cervical  region.  All  of  these  cutaneous  reflexes  are  true  reflex 
actions.  They  differ  in  different  individuals,  and  are  more  easily  elicited 
in  the  young.  Muscle  reflexes,  or  as  they  are  often  termed,  tendon 
reflexes,  consist  of  a  contraction  of  a  muscle  under  conditions  of  more  or 
less  tension,  when  its  tendon  is  sharply  tapped.  The  so-called  patellar- 
tendon-reflex  is  the  most  well-known  of  this  variety  of  reflexes.  If  one 
kuee  be  slightly  flexed,  as  by  crossing  it  over  the  other,  so  that  the 
quadriceps  femoris  is  extended  to  a  moderate  degree,  and  the  patella 
tendon  be  tapped  with  the  fingers  or  the  earpiece  of  a  stethoscope,  the 
muscle  contracts  and  the  foot  is  jerked  forward. 

Another  variety  of  the  same  jihenomenon  is  seen  if  the  foot  is  flexed  so 
as  to  stretch  the  calf  muscles  and  the.tendo  Achillis  is  tapped;  the 
foot  is  extended  by  the  contraction  of  the  stretched  muscles.  It  appears, 
however,  that  the  tendon  reflexes  are  not  exactly  what  their  name  im- 
plies. The  interval  between  the  tap  and  the  contraction  is  said  to  be 
too  short  for  the  production  of  a  true  reflex  action.  It  is  suggested 
that  the  contraction  is  caused  by  local  stimulation  of  the  muscle,  but 
that  this  would  not  oQCur  unless  the  muscle  had  been  reflexly  stimulated 
previously  by  the  tension  applied,  and  placed  in  a  condition  of  excessive 
irritability.  It  is  further  probable  that  the  condition  on  which  it 
depends  is  a  reflex  spinal  irritability  of  the  muscle  or  (exaggerated) 
muscular  tone,  which  is  admitted  to  be  a  reflex  phenomenon — or  an  ex- 
ample of  automatism — in  the  spinal  cord. 


TTTK    XEKVOUS   SYSTEM.  577 

Inhibition  nf  Reflex  Action.'^. — Movements  such  as  are  produced  by 
irritating  the  skin  of  the  lower  extremities  in  the  human  subject,  after 
division  or  disorganization  of  a  part  of  the  spinal  cord,  do  not  follow 
the  same  irritation  when  the  cerebrum  is  active  and  the  connection 
between  the  cord  and  the  brain  is  intact.  This  is,  probably,  due  to 
the  fact  that  the  mind  ordinarily  perceives  the  irritation  and  instantly 
inhibits  or  controls  the  action;  for,  even  when  the  cord  is  perfect,  such 
involuntary  movements  may  follow  an  irritation,  applied  when  the  cere- 
brum is  inactive.  When,  for  example,  one  is  anxiously  thinking,  even 
slight  stimuli  may  produce  involuntary  and  reflex  movements.  So,  also, 
during  sleep,  such  reflex  movements  may  be  observed,  when  the  skin  is 
touched  or  tickled;  for  example,  when  one  touches  with  the  finger  the 
palm  of  the  hand  of  a  sleeping  child,  the  finger  is  grasped — the  im- 
pression on  the  skin  of  the  palm  producing  a  reflex  movement  of  the 
muscles  which  close  the  hand.  But  when  the  child  is  awake,  no  such 
effect  is  produced. 

Further,  many  reflex  actions  are  capable  of  being  more  or  less  con- 
trolled or  even  altogether  prevented  by  the  will :  thus  an  inhibitory  action 
tnay  be  exercised  by  the  cerebrum  over  reflex  functions  of  the  cord 
and  the  other  nerve-centres.  The  following  may  be  quoted  as  familiar 
examples  of  this  action : — 

To  prevent  the  reflex  action  of  crying  out  when  in  pain,  it  is  often 
sufficient  firmly  to  clench  the  teeth  or  to  grasp  some  object  and  hold  it 
tight.  When  the  feet  are  tickled  we  can,  by  an  effort  of  will,  prevent 
the  reflex  action  of  jerking  them  up.  So,  too,  the  involuntary  closing 
of  the  eyes  and  starting,  when  a  blow  is  aimed  at  the  head,  can  be 
similarly  restrained. 

Darwin  has  mentioned  an  interesting  example  of  the  way  in  which, 
on  the  other  hand,  such  an  instinctive  reflex  act  may  override  the 
strongest  effort  of  the  will.  He  placed  his  face  close  against  the  glass 
of  the  cobra's  cage  in  the  Eeptile  House  at  the  Zoological  Gardens,  and 
though,  of  course,  thoroughly  convinced  of  his  perfect  security,  could 
not  by  any  effort  of  the  will  prevent  himself  from  starting  back  when 
the  snake  struck  with  fury  at  the  glass. 

It  has  been  found  by  experiment  that  in  a  frog  the  optic  lobes  and 
optic  tJialamihoNQ  Skdiistiuci  action  in  inhibiting  or  delaying  reflex  ac- 
tion, and  also  that  more  generally  any  afferent  stimulus,  if  sufficiently 
strong,  may  inhibit  or  modify  any  reflex  action  even  in  the  absence  of 
these  centres. 

On  the  whole,  therefore,  it  may,  from  these  and  like  facts,  be  con- 
cluded that  reflex  acts,  performed  under  the  influence  of  the  reflecting 
power  of  the  spinal  cord,  are  essentially  independent  of  the  brain  and  may 
be  performed  perfectly  when  the  brain  is  separated  from  the  cord:  that 
37 


578  HANDBOOK    OF    PHYSIOLOGY. 

these  include  a  much  larger  number  of  the  natural  and  purposive  move- 
ments of  the  lower  animals  than  of  the  warm-blooded  animals  including 
man:  and  that  over  nearly  all  of  them  the  mind  may  exercise,  through 
the  higher  nerve-centres,  some  control;  determining^  directing^  hinder- 
ing, or  modifying  them,  either  by  direct  action,  or  by  its  power  over 
associated  muscles. 

To  these  instances  of  spinal  reflex  action,  some  add  yet  many  more, 
including  nearly  all  the  acts  which  seem  to  be  performed  unconsciously, 
such  as  those  of  walking,  running,  writing,  and  the  like:  for  these  are 
really  involuntary  acts.  It  is  true  that  at  their  first  performances  they 
are  voluntary,  that  they  require  education  for  their  perfection,  and  are 
at  all  times  so  constantly  performed  in  obedience  to  a  mandate  of  the 
will,  that  it  is  difficult  to  believe  in  their  essentially  involuntary  nature. 
But  the  will  really  has  only  a  co7itrolling  power  over  their  performance ; 
it  can  hasten  or  stay  them,  but  it  has  little  or  nothing  to  do  with  the 
actual  carrying  out  of  the  effect.  And  this  is  proved  by  the  circum- 
stance that  these  acts  can  be  performed  during  complete  mental  abstrac- 
tion :  and,  more  than  this,  that  the  endeavor  to  carry  them  out  entirely 
by  the  exercise  of  the  will  is  not  only  not  beneficial,  but  positively  in- 
terferes with  their  harmonious  and  perfect  performance.  Any  one  may 
convince  himself  of  this  fact  by  trying  to  take  each  step  as  a  voluntary 
act  in  walking  downstairs,  or  to  form  each  letter  or  word  in  writing  by 
a  distinct  exercise  of  the  will. 

These  actions,  however,  will  be  again  referred  to. 

Morlid  reflex  actions. — The  relation  of  the  reflex  action  to  the  strength 
of  the  stimulus  is  the  same  as  was  shown  generally  to  occur  in  nerve- 
centres,  a  slight  stimulus  producing  a  slight  movement,  and-  a  greater, 
a  greater  movement,  and  so  on;  but  in  instances  in  which  we  must 
assume  that  the  cord  is  morbidly  more  irritable,  i.  e. ,  apt  to  issue  more 
nervous  force  than  is  proportionate  to  the  stimulus  applied  to  it,  a  slight 
impression  on  a  sensory  nerve  produces  extensive  reflex  movements. 
This  appears  to  be  the  condition  in  the  disease  called  tetanus,  in 
which  a  slight  touch  on  the  skin  may  throw  the  whole  body  into 
convulsions. 

Special  Centres. — It  may  seem  to  have  been  implied  that  the  spinal 
cord  as  a  single  nerve-centre,  reflects  alike  from  all  parts  all  the  impres- 
sions conducted  to  it.  This,  however,  is  not  the  case,  and  it  should  be 
regarded  as  we  have  indicated,  as  a  collection  of  nervous  centres  united 
in  a  continuous  column.  This  is  well  illustrated  by  the  fact  that  seg- 
ments of  the  cord  may  act  as  distinct  nerve-centres,  in  which  special 
co-ordinated  muscular  actions  are  represented,  and  excite  muscular  action 
in  the  parts  supplied  with  nerves  given  off  from  them ;  as  well  as  by  the 
analogy  of    certain  cases  in  which  the   muscular  movements  of  single 


THE    NERVOUS    SYSTEM^  579 

organs  are  uuder  the  control  of  certain  circumscribed  portions  of  tlie 
cord.     The  special  centres  are  the  following  (on  each  side  ) : — 

(n.)  The  JJefcBcation,  or  Ano- Spinal  centre. — Tlie  mode  of  actioji  of 
the  ano-spinal  centre  apjjears  to  be  this.  The  mucous  membrane  of  the 
rectum  is  stimulated  by  the  presence  of  fseces  or  of  gas  in  the  bowel. 
The  stimulus  passes  up  by  the  afferent  nerves  of  the  haemorrhoidal  and 
inferior  mesenteric  jilexus  to  the  centre  in  the  cord,  situated  in  the 
lumbar  enlargement,  and  is  reflected  through  the  pudendal  plexus  to 
the  anal  sphincter  on  the  one  hand,  and  on  the  other  to  the  muscular 
tissue  in  the  wall  of  the  lower  bowel.  In  this  way  is  produced  a  relaxa- 
tion of  the  first  and  a  contraction  of  the  second,  and  expulsion  of  the 
contents  of  the  bowel  follows.  The  centre  in  the  spinal  cord  is  par- 
tially under  the  control  of  the  will,  so  that  its  action  may  be  either 
inhibited  or  augmented.  The  action  may  be  helped  by  the  abdominal 
muscles  which  are  under  the  control  of  the  will,  although  under  a  strong 
etimulus  they  may  also  be  compelled  to  contract  by  reflex  action. 

(Jj.)  The  Micturition,  or  the  Vesica- Spinal  centre. — The  vesico-sj)inal 
centre  acts  in  a  very  similar  way  to  that  of  the  ano-spinal.  The  centre 
is  also  in  the  lumbar  enlargement  of  the  cord.  It  may  be  stimulated  to 
action  by  impulses  descending  from  the  brain,  or  reflexly  b}'  the  pres- 
ence of  urine  in  the  bladder.  The  action  of  the  brain  may  be  voluntary, 
or  it  may  be  excited  to  action  by  the  sensation  of  distention  of  the  bladder 
by  the  urine.  The  sensory  fibres  concerned  are  the  posterior  roots  of  the 
lower  sacral  nerves.  The  action  of  the  centre  thus  stimulated  is  double, 
or  it  may  bo  supposed  that  the  centre  consists  of  two  parts,  one  which  is 
usually  in  action  and  maintains  the  tone  of  the  sjihincter,  and  the  other 
which  causes  contraction  of  the  bladder  and  otlier  muscles.  When  evacu- 
ation of  the  bladder  is  to  occur,  impulses  are  sent  to  one  part  of  the 
centre  on  the  one  liand,  and  from  it  to  tlie  bladder  and  to  certain  other 
muscles  which  cause  their  contraction,  and  on  the  other  to  the  other 
part  of  the  centre,  inhibiting  its  action  on  the  spliincter  urethra^  whicli 
procures  its  relaxation.  The  way  having  been  opened  by  the  relaxation  of 
the  sphincter,  the  urine  is  expelled  by  the  combined  action  of  the  blad- 
der and  accessory  muscles.  The  cerebrum  may  act  not  only  in  the  way  of 
stimulating  the  centre  to  action,  but  also  in  the  way  of  inhibiting  its 
action.  Tlic  ab(lo7ninal  muscles  may  be  called  into  action  as  in  dcfa-- 
c;i,tion. 

(c.)  The  Emission  of  Senien^  or  Genito-Spinal  centre. — The  centre 
situated  in  the  lumbar  enlargement  of  the  spinal  cord  is  stimulated  to 
action  by  sensory  impressions  from  the  glans  penis.  Efferent  impulses 
from  the  centre  excite  the  successive  and  co-ordinate  contractions  of  tlie 
muscular  fibres  of  the  vasa  deferentia  and  vesiculse  seminales,  and  of  the 
accelerator  urina?  and  other  muscles  of  the  urethra;  and  a  forcible  expul- 


580  HANDBOOK    OF    PHYSIOLOGY. 

si  on  of  semen  takes  place,  over  which  the  mind  has  little  or  no  control, 
and  which,  in  cases  of  paraplegia,  may  be  unfelt. 

(d.)  The  Erection  of  the  Penis  centre. — This  centre  is  also  situated 
in  the  lumbar  region.  It  is  excited  to  action  by  the  sensory  nerves  of 
the  penis.  Efferent  impulses  produce  dilatation  of  the  vessels  of  the  penis, 
which  also  appears  to  be  in  part  the  result  of  a  reflex  contraction  of  the 
muscles  by  which  the  veins  returning  the  blood  from  the  penis  are  com- 
pressed. 

(e.)  Parturition  centre. — The  centre  for  the  expulsion  of  the  con- 
tents of  the  uterus  in  parturition  is  situated  in  the  lumbar  spinal  cord 
rather  higher  up  than  the  other  centres  already  enumerated.  The 
stimulation  of  the  interior  of  the  uterus  by  its  contents  may,  under 
certain  conditions,  excite  the  centre  to  send  out  impulses  which  produce 
a  contraction  of  the  uterine  walls  and  expulsion  of  the  contents  of  the 
cavity.  The  centre  is  independent  of  the  will  since  delivery  can  take 
place  in  paraplegic  women,  and  also  while  a  patient  is  under  the  influ- 
ence of  chloroform.  Again,  as  in  the  cases  of  defajcation  and  micturi- 
tion, the  abdominal  muscles  assist;  their  action  being  for  the  most 
part  reflex  and  involuntary. 

(/■.)  The  Centre  for  the  Movements  of  Lymphatic  Hearts  of  Frog. — 
Volkmann  has  shown  that  the  rhythmical  movements  of  the  anterior  pair 
of  lymphatic  hearts  in  the  frog  depend  upon  nervous  influence  derived 
from  the  portion  of  spinal  cord  corresponding  to  the  third  vertebra,  and 
those  of  the  posterior  pair  on  influence  supplied  by  the  portion  of  cord 
opposite  the  eighth  vertebra.  The  movements  of  the  heart  continue, 
though  the  whole  of  the  cord,  except  the  above  portions,  be  destroyed ;  but 
on  the  instant  of  destroying  either  of  these  portions,  though  all  the  rest  of 
the  cord  be  untouched,  the  movements  of  the  corresponding  hearts  cease. 

(//.)  The  Centre  for  the  Tone  of  Muscles. — ^The  influence  of  the  spinal 
cord  on  tlie  sphincter  ani  and  spliincter  urethra  has  been  already  men- 
tioned (see  above).  It  maintains  these  muscles  in  permanent  contrac- 
tion. The  condition  of  these  sphincters,  however,  is  not  altogether 
exceptional.  It  is  the  same  in  kind,  though  it  exceeds  in  degree  that 
condition  of  muscles  which  has  been  called  tone,  or  passive  contraction; 
a  state  in  which  they  always  when  not  active  appear  to  be  during  health, 
and  in  which,  though  called  inactive,  they  are  in  slight  contraction,  and 
certainly  are  not  relaxed,  as  they  are  soon  after  death,  or  when  the  spinal 
cord  is  destroyed.  This  tone  of  all  the  muscles  of  the  trunk  and  limbs 
depends  on  the  spinal  cord,  just  as  the  contraction  of  the  sphincters 
does.  If  an  animal  be  killed  by  injury  or  removal  of  the  brain,  the 
muscles  retain  their  tone;  but  if  the  spinal  cord  be  destroyed,  the 
sphincter  ani  relaxes,  and  all  the  muscles  feel  loose,  flabby,  and  atonic, 
remaining  so  till  rigor  mortis  commences. 


THK    XKKVOUS    SYSTEM.  oSl 

This  kind  of  tone  must  be  distinguished  from  that  mere  firmness  and 
tension  which  it  is  customary  to  ascribe,  under  the  name  of  tone,  to 
all  tissues  that  feel  robust  and  not  flabby,  as  well  as  to  muscles.  The 
tone  peculiar  to  muscles  has  in  it  a  degree  of  vital  contraction:  that  of 
other  tissues  is  only  due  to  their  being  well  nourished,  and  therefore  com- 
pact and  tense. 

All  the  foregoing  examples  illustrate  the  fact  that  the  spinal  cord  is 
a  collection  of  reflex  centres,  upon  which  the  higher  centres  act  by  send- 
ing down  impulses  to  set  in  motion,  modify  or  control  them.  The 
movements  or  other. phenomena  of  reflex  action  are,  as  it  were,  the  func- 
tion of  the  ganglion  cells  to  which  an  afferent  impression  is  conveyed  by 
the  posterior  nerve-trunks  in  connection  with  them.  The  extent  of  the 
movement  depends  upon  the  strength  of  the  stimulus,  the  position  in 
which  it  is  apjjlied  as  well  as  the  condition  of  the  nerve-cells;  the  con- 
nection between  the  cells  being  so  intimate  that  a  series  of  co-ordinated 
movements  may  result  from  a  single  stimulation.  Whether  the  cells 
possess  as  well  the  power  of  originating  impulses  (automatism)  is  doubt- 
ful, but  this  is  jDossible  in  the  case  of  (Ji)  vaso-motor  centres  which  are 
situated  in  the  cord  (p.  246),  and  of  (i)  sivectting  centres  which  must  be 
closely  related  to  them,  and  possibly  in  the  case  of  (/)  the  centres  for 
maintaining  the  tone  of  muscles. 

The  Nvtrition  (a)  of  the  muscles  appears  to  be  under  the  control  of 
the  spinal  cord.  When  the  nerve-cells  of  the  anterior  cornu  are  diseased 
the  muscles  atrophy.  In  the  same  way  (b)  the  bones  and  (c)  joints  are 
seriously  affected  when  the  cord  is  diseased.  The  former  when  the 
anterior  nerve-cells  are  implicated,  do  not  grow,  and  the  latter  are  dis- 
organized in  some  eases  when  the  posterior  columns  are  affected,  {(t) 
The  skin,  too,  is  evidently  only  maintained  in  a  healthy  condition  as 
long  as  the  cord  and  its  nerves  are  intact.  Ko  doubt  part  of  this  influ- 
ence which  the  cord  exercises  over  nutrition  is  due  to  the  relationship 
which  it  bears  to  the  vaso-motor  nerves. 

Within  the  cord  are  contained,  for  some  distance,  fibres  (a)  which 
regulate  the  dilatation  of  the  pupil,  (b)  which  have  to  do  with  the  glyco- 
genic function  of  the  liver,  {c)  which  control  the  nerve-supply  of  the 
vessels  of  the  face  and  head,  {d)  which  produce  acceleration  of  the 
heart's  action,  and,  {e)  have  a  termotaxic  action  on  the  muscles,  etc. 

Tfte  Relations  of  the  Different  Parts  of  the  Braik, 

Before  considering  the  parts  of  tlie  brain  separately,  it  will  be  best  for 
the  comprehension  of  thej^lanof  its  construction  to  take  a  general  survey 
of  the  whole.  The  brain  on  superficial  examination  presents  four 
distinct  parts,  viz.   (a.)   The    largo   and    prominent    masses  of    nervous 


582 


HANDBOOK    OF    PHYSIOLOGY. 


matter  divided  by  fissures  into  convolutions  (fig.  354),  and  covering  to  a 
large  extent  the  other  parts,  separated  from  one  another  by  a  deep 
fissure  running  from  front  to  back.  These  constitute  the  cerebral 
hemispheres  or  cerebrum,  (b)  On  the  under  or  central  surface  of  the 
brain  can  be  seen  a  broad  mass  rounded  on  the  surface  more  or  less 
quadrilateral  in  shape;  this  is  the  pons  Varolii  (fig.   354,   VI.).     An- 


Fig.  354.— Base  of  the  brain.  1,  superior  longitudinal  fissure;  2,  2',  2",  anterior  cerebral 
lobe;  3,  fissure  of  Sylvius,  between  anterior  and  4,  4',  4",  middle  cerebral  lobe;  5,  5',  posterior 
lobe ;  6,  medulla  oblongata.  The  figure  is  in  the  right  anterior  pyramid ;  7,  8,  9,  10,  the  cerebellum ; 
-(-,  the  inferior  verimf  orm  process.  The  figures  from  I.  to  IX.  are  placedagainst  the  corresponding 
cerebral  nerves;  III.  is  placed  on  the  right  cms  cerebri.  VI.  and  VII.  on  the  pons  Varolii;  X. 
the  first  cervical  or  suboccipital  nerve.     (Allen  Thomson.)    J^. 

teriorly  it  is  seen  to  branch  off  into  two  strands,  which  are  the  crura 
cerebri;  and  posteriorly  it  joins  with  a  narrower  portion,  which  is  the 
medulla  oblongata  or  bulb.  This  latter  is  continuous  with  the  sj)inal  cord. 
In  connection  with  the  buLb  and  pons  are  seen  many  nerve-trunks  pass- 
ing off;  these  are  the  chief  part  of  the  cranial  nerves.  Two  of  the 
cranial  nerves,  however,  are  more  interior,  and  one,  the  optic  (fig.  354, 
2),  is  seen  to  send  off  abroad  band  of  fibres  which  apparently  passes 
into  the  substance  of  the  cerebrum.  The  most  anterior  nerve-root  on 
either  side,  viz.,  the  olfactory  (fig.  354,  1),  extends  for  some  distance 
upon  the  under  surface  of  each  cerebral  hemisphere,  (c.)  The  pons  is 
seen  to  be  connected  laterally  with  a  large  mass  of  nervous  matter,  upon 
which  in  the  position  of  the  brain  turned  upward,  the  bulb  also  rests j 


THE    NERVOUS    SYSTEM,  583 

this  is  the  cerebellum^  and  {d.)  When  the  brain  is  viewed  in  the  normal 
position  at  tlie  bottom  of  the  fissure,  between  the  hemispheres  is  seen  a 
broad  baud  of  white  matter  connecting  one  hemisphere  with  its  fellow, 
the  main  commissure  or  corpus  callosum  (fig.  357).  Such  parts  of  the 
brain  are  evident  even  on  superficial  examination.  On  dissection,  it  is 
found  that  the  central  nervous  system  is  not  a  solid  mass  of  nerve  mate- 
rial; it  incloses  certain  cavities,  the  cerebral  ventricles.  Forming  the 
walls  and  boundaries  of  these  ventricles  are  very  important  masses  of 
nervous  matter.  The  cerebrum  proper  incloses  a  large  central  cavity, 
the  lateral  ventricle^  but  separated  by  a  median  partition  into  two.  Into 
the  cavity  of  each  lateral  ventricle  (fig.  355)  projects  a  rounded  mass  of 
gray  matter  anteriorly,  which  is  the  caudate  nucleus  of  an  important 
structure  known  as  the  corpus  striatu7n,  the  more  external  part  of  which, 
the  lenticular  nucleus,  is  embedded  in  the  mass  of  the  cerebral  hemi- 
sphere. Below,  or  more  posterior  to  the  caudate  nucleus,  and  also  pro- 
jecting into  the  lateral  ventricle,  is  a  second  mass  of  gray  matter,  called 
the  optic  thalamus;  the  upper  part  of  this  only,  however,  is  seen  in  the 
lateral  ventricle,  the  lower  and  more  internal  part  approaching  its  fellow 
in  the  middle  line  leaves  a  space  which  on  vertical  section  is  more  or  less 
triangular,  called  the  third  ventricle.  The  lateral  ventricles  are  sepa- 
rated from  one  another  by  means  of  a  partition  made  of  two  layers  of 
white  matter,  the  septum  lucidum.  On  section  the  septum  is  seen  to  be 
more  or  less  triangular,  and  between  the  two  layers  there  is  the  space  of 
the  fifth  ventricle  filled  with  fluid. 

At  the  posterior  part  of  the  septum  lucidum,  and  joining  with  it,  is 
the  fornix.  This  is  a  longitudinal  commissure;  it  is  arched  and  its 
edge  is  seen  in  the  lateral  ventricle  on  either  side.  Between  its  edge 
and  the  upper  part  of  the  optic  thalamus  projects  a  fringe  of  blood- 
vessels, which  is  the  upper  part  of  the  septum  of  the  vascular  pia  mater, 
which  passes  into  the  interior  of  the  brain,  and  which  is  called  the  cho- 
roid p)lex  us  ;  the  whole  of  the  projection  forming  a  roof  for  the  third 
ventricle  is  called  the  velum  interpositum. 

The  fornix  (fig.  355,  e)  is  made  up  of  two  strands  anteriorly,  called 
the  anterior  pillars,  and  of  two  similar  pillars  posteriorly;  the  middle 
portion  called  the  body  consists  of  the  parts  of  the  two  pillars  wliich  are 
joined  together  in  the  middle  line.  The  body  of  the  fornix  is  triangular 
in  shape,  broad  and  flat  behind,  where  it  is  connected  with  the  corpus 
callosum,  and  narrow  in  front  where  it  is  connected  to  the  septum  luci- 
dum. The  anterior  pillars  pass  downward,  separated  from  one  another 
on  either  side  of  the  third  ventricle  in  front  of  the  foramen,  by  which 
the  lateral  communicates  with  the  third  ventricle,  called  the  foramen 
of  Monro;  each  pillar  then  passes  forward  and  down,  and  twisting  upon 
itself  forms  the  corpus  albicans,  and  then  passes  in  part  to  join  the  optic 


584  HAliTDBOOK    OF    PHYSIOLOGY. 

thalamus.  The  posterior  pillars  pass  down  and  out  and  form  part  of 
the  interior  of  that  part  of  the  lateral  A^entricle  which  descends  into  tlie 
posterior  lobe  of  the  cerebrum.  Thus,  when  the  fornix  is  reflected  from 
the  front,  first  of  all  the  velum  interpositum  is  seen,  and  when  that  is 
removed  the  third  ventricle  comes  into  sight. 

The  third  ventricle  terminates  at  its  posterior  extremity  in  the  pineal 
body.     From  this  ventricle  a  short   narrow  passage,  the  iter  a  tertio  ad 


Fig.  365.— Dissection  of  brain,  from  above,  exposing  the  lateral  fourth  and  fifth  ventricles 
with  the  surrounding  parts.  J^.  a.  Anterior  part,  or  genu  of  corpus  callosum ;  6,  corpus  stria- 
tum ;  t»',  the  corpus  striatum  of  left  side,  dissected  so  as  to  expose  its  gray  substance ;  c,  points 
by  a'  line  to  the  taenia  semicircularis ;  d,  optic  thalamus;  e,  anterior  pillars  of  fornix  divided; 
below  they  are  seen  descending  in  front  of  the  third  ventricle,  and  between  them  is  seen  part  of 
the  anterior  commissure;  in  front  of  the  letter  e  is  seen  the  slit-like  fifth  ventricle,  between  the 
two  laminaB  of  the  septum  lucidum ;  /,  soft  or  middle  commissure ;  g  is  placed  in  the  posterior 
part  of  the  third  ventricle;  immediately  behind  the  latter  are  the  posterior  commissure  (just 
visible)  and  the  pineal  gland,  the  two  crura  of  which  extend  forward  along  the  inner  and  up- 
per mar-gins  of  the  optic  thalami ;  h  and  ?',  the  corpora  quadrigemina ;  fc,  superior  crus  of  cere- 
bellum; close  to  fc  is  the  valve  of  Vieussens,  which  nas  been  divided  so  as  to  expose  the  fourth 
ventricle ;  i,  hippocampus  major  and  corpus  flmbriatum,  or  taenia  hippocampi ;  m,  hippocampus 
minor;  n  e'minentia  collateralis;  o,  fourth  ventricle;  p,  posterior  surface  of  medulla  oblongata; 
r  section  of  cerebellum;  s,  upper  part  of  left  hemisphere  of  cerebellum  exposed  by  the  removal 
o'f  part  of  the  posterior  cerebral  lobe.     ("Hirschfield  and  Leveillfi.) 

quartum  ventriculum,  or  aqueduct  of  Sylvius,  passes  through  the  next 
portion  of  the  brain  called  the  mid-brain.  This  part  is  covered  in  by 
two  pairs  of  nerve-ganglia,  the  anterior  and  the  posterior  corpora  qua- 
drigemina,  and  the  floor  is  formed  by  tlie  crura  cerebri.  The  aqueduct 
of  Sylvius  opens  at  the  upper  angle  of  a  lozenge-shaped  cavity,  the 
fourth  ventricle,  which  is  situated  on  the  dorsal  aspect  of  the  pons  and 
bulb.     The  fourth  ventricle  has  no  roof  of  its  own  beyond  a  layer  of 


TTfK    XHUVOTS    RV8TEM. 


oKo 


epithelium,  but  it  is  covered  in  by  the  cerebellum,  the  superior  jjedun- 
cles  of  which,  convergiug  forward,  form  its  anterior  limits,  uiid  the 
inferior  peduncles  form  its  posterior  boundaries  on  either  side. 

The  lateral,  third  and  fourth  ventricles  communicate,  and  through 
the  last  with  the  central  canal  of  the  spinal  cord.  They  are  all  lined 
with  columnar  ciliated  epithelium,  beneath  which  is  a  develo^jmeut  of 
neuroglia.  This  lining  so  formed  is  called  the  cpendyma  of  the  ven- 
tricles. Where  the  superior  peduncles  of  the  cerebellum  are  approach- 
ing each  other  at  the  upper  part  of  the  fourth  ventricle,  the  interval 
betwoen  them  is  bridged  over  by  a  thin  layer  of  gray  matter  called  the 
valve  of  Vieussens. 

The  portions  of  the  central  nervous  system  are  thus  classified : — 

(i.)  Cerebral  hemispheres  with  the  corpora  striata,  developed  from 
the  cerebral  vesicles — and  enclosing  the  lateral  ventricles. 

(ii.)  Fore-brain,  formed  of  the  parts,  including  the  optic  thalami, 
which  inclose  the  third  ventricle. 

(iii.)  Mid-hrain,  consisting  of  the  parts  inclosing  the  aqueduct  of 


Fig.  356. — Plan  in  outline  of  the  encephalon,  as  seen  from  the  right  side.  }^.  The  parts  are 
represented  as  separated  from  one  another  somewhat  moi-e  than  natural,  so  as  to  show  their 
connections.  A,  Cerebrum;  /,  q,  h,  its  anterior,  middle,  and  posterior  lobes;  e,  fissure  of  Syl- 
vius; B,  cerebellum;  C,  pons  Varolii;  D,  medulla  oblongata:  a,  peduncles  of  the  cerebrum; 
6,  c,  d,  superior,  middle,  and  inferior  peduncles  of  the  cerebellum.     (From  Quain.  ) 


Sylvius,  viz.,  the  corpora  quadrigemina,  which  form   the  roof,  and   the 
crura  cerebri  which  form  the  floor. 

(iv.)  Hind-hrain,  the  pons  Varolii  and  the  cerebellum  form  respec- 
tively the  floor  and  roof  of  the  fore-part  of  the  hind-brain,  and  the  bulb 
the  floor  of  the  back  part  of  tlie  hind -brain,  the  roof  being  practically 
absent. 


586 


HANDBOOK    OF    PHYSIOLOGY. 


This  division  of  the  brain  into  the  four  parts  is  justified  by  a  consid- 
eration of  its  development.  As  will  be  seen  later  on,  the  brain  consists 
originally  of  three  cerebral  vesicles,  the  dilated  extremity  of  the  neural 


Fig.  357. — View  of  the  Corpus  Callosum  from  above.  ]/^. — The  upper  surface  of  the  corpus 
callosum  has  been  fully  exposed  by  separating  the  cerebral  hemispheres  and  throwing  them  to 
the  side ;  the  gyrus  fornicatus  has  been  detached,  and  the  transverse  fibres  of  the  corpus  callo- 
sum traced  for  some  distance  into  the  cerebral  medullary  substance.  1,  the  upper  surface  of  the 
corpus  callosum;  2,  median  furrow  or  raphe;  3,  longitudinal  striae  bounding  the  furrow;  4, 
swelling  formed  by  the  transverse  bands  as  they  pass  into  the  cerebrum ;  5,  anterior  extremity 
or  knee  of  the  corpus  callosum :  6,  posterior  extremity ;  7,  anterior,  and  8,  posterior  part  of  the 
mass  of  fibres  proceeding  from  the  corpus  callosum ;  9,  margin  of  the  swelling ;  10,  anterior  part 
of  the  convolution  of  the  corpus  callosum;  11,  hem  or  band  of  union  of  this  convolution;  12,  in- 
ternal convolutions  of  the  parietal  lobe ;  13,  upper  surface  of  the  cerebellum.  (Sappey  after 
Foville.) 


canal,  and  these  consist  of  fore-,  mid-,  and  hind-brain.  From  the  fore- 
brain  there  is  first  of  all  budded  off  on  either  side  a  new  vesicle,  the 
optic  vesicle  from  which  is  developed  the  optic  nerve  and  retina,  and 
afterward  a  large  vesicle,  the  cerebral  vesicle,  which  grows  rapidly, 
becomes  divided  by  a  central  partition  into  two,  each  of  which  incloses 
the  lateral  ventricle.  The  cerebral  vesicles  grow  so  quickly  as  to  cover 
both  the  fore-  and  the  mid-brain.  The  parts  of  which  the  fore-,  mid-, 
and  hind-brains  are  made  up  are  developed  from  the  corresponding  cere- 
bral vesicles. 

It  will  be  as  well  here  to  indicate  briefly  the  structure  of  the  brain. 
It  consists  of  white  and  gray  matter  differently  arranged  in  different 
districts. 


THE   KERVOUS   SYSTEM,  587 

Distribution  of  the  Gray  Matter. 

(i.)  In  the  bulb^  at  the  lower  part  the  distribution  of  gray  matter  fol- 
lows that  which  prevails  in  the  cord.  Higher  up  the  chief  part  is  found 
toward  the  posterior  or  dorsal  aspect,  surrounding  the  central  canal. 
When  the  central  canal  opens  out  into  the  fourth  ventricle  the  gray 
matter  comes  to  that  surface  chiefly,  and  is  found  to  consist  more  par- 
ticularly, on  either  side,  of  the  nuclei  of  origin  of  the  cranial  nerves, 
viz.,  the  12th,  11th,  10th,  9th,  and  8th,  and  more  externally  of  the 
nucleus  gracilis  and  nucleus  cuneatus  (w.^. ,  n.c,  figs.  361,  302).  In 
addition  to  these  masses  of  gray  matter,  there  are  the  olivary  bodies  (o, 
figs.  361,  362)  toward  the  ventral  surface  with  the  accessory  olives  (o'), 
and  the  external  arcuate  {n.ar.  in  figs.)  nuclei,  placed  at  the  tip  of  the 
anterior  fissure  on  either  side  on  the  ventral  surface  of  the  anterior 
pyramids. 

(ii.)  In  the  2}ons  Varolii. — In  addition  to  the  origins  of  nerves  in 
the  floor  of  the  fourth  ventricle  on  the  dorsal  aspect  of  the  pons,  viz. , 
of  the  7th,  6th,  and  5th  nerves,  there  are  several  masses  of  gray  matter, 
viz.,  in  the  back  part,  the  siqjerior  olive  (fig.  362),  and  in  the  front 
part  the  locus  cmrideus,  as  well  as  small  amounts  of  the  same  material 
mixed  with  fibres  in  the  more  ventral  surface. 

(iii.)  In  the  mid-brain,  the  gray  matter  preponderates  in  the  optic 
thalami,  corpo7-a  quadrigeryiina,  and  corpora  geniculata.  It  is  also  found 
surrounding  the  aqueduct  of  Sylvius,  and  in  other  parts  of  the  crura, 
notably  such  masses  as  the  red  nucleus  (fig.  363),  locus  niger  (fig.  365). 

(iv.)  In  the  cerebral  hemispheres,  the  cerebral  cortex  is  made  up  of 
gray  matter  which  incloses  white  matter,  and  the  corpus  striatum  is 
made  up  more  or  less  of  the  same  material. 

(v.)  In  the  cerebellum,  the  gray  matter  forms  the  incasing  material. 
In  the  interior  too  there  are  masses  of  gray  matter  forming  the  corpora 
dentata. 

This  then  roughly  indicates  the  localities  in  which  gray  matter  is 
found ;  the  arrangement  of  the  fibres  and  their  relationship  to  the  gray 
matter  will  be  dealt  with  later  on. 

The  Bulb  or  Medulla  Oblongata. 

The  medulla  oblongata  (figs.  358,  359),  is  a  column  of  gray  and 
white  matter  formed  by  the  prolongation  upward  of  the  spinal  cord  and 
connecting  it  with  the  brain. 

Structure. — The  gray  substance  which  it  contains  is  situated  in  the 
interior  and  variously  divided  into  masses  and  laminae  by  the  white  or 
fibrous  substance  which  is  arranged  partly  in  external  columns,  and 


.188 


HAifDBOOK    OF    PHYSIOLOGY. 


partly  in  fasciculi  traversing  the  central  gray  matter.  The  medulla 
oblongata  is  larger  than  any  part  of  the  spinal  cord.  Its  columns  are 
pyriform,  enlarging  as  they  proceed  toward  the  brain,  and  are  continu- 
ous with  those  of  the  spinal  cord.  Each  half  of  the  medulla,  therefore, 
may  be  divided  into  three  columns  or  tracts  of  fibres,  continuous  with 
the  three  tracts  of  which  each  half  of  the  spinal  cord  is  made  up, — the 
columns  more  prominent  than  those  of  the  spinal  cord,  and  separated 
from  each  other  by  deeper  grooves.  The  anterior,  continuous  with  the 
anterior  columns  of  the  cord,  are  called  the  antei'ior  pyramids,  and  the 


Fig.  359. 

Fig.  358.  —Ventral  or  anterior  surface  of  the  pons  Varolii,  and  meduUa  oblongata,  o,  a,  an- 
terior pjramids;  b,  their  decussation;  c,  c,  olivarv  bodies;  d,  d,  restiform  bodies;  e,  arciform 
fibres;  /.  fibres  passing  from  the  anterior  column  of  the  cord  to  the  cerebellum;  gr,  anterior  col- 
umn of  the  spinal  cord;  /i,  lateral  column;  p,  pons  Varolii;  i,  its  upper  fibres;  5,  5,  roots  of  the 
fifth  pair  of  nerves. 

Fig.  3.yj.— Dorsal  or  posterior  surface  of  the  pons  Varolii,  corpora  quadrigemina,  and  me- 
dulla oblongata.  The  peduncles  of  the  cerebellum  are  cut  short  at  the  side,  a,  a,  the  upper 
pair  of  corpora  quadrigemina;  6,  6,  the  lower;  /,  /,  superior  jjeduncles  of  the  cerebellum;  c. 
eminence  connected  with  the  nucleus  of  the  hypoglossal  nerve;  e,  that  of  the  glosso-pharyngeal 
nerve;  i,  that  of  the  vagus  nerve;  d,  d,  restiform  bodies;  p,  p,  posterior  pyramids;  v,  v,  groove 
in  the  middle  of  the  fourth  ventricle,  ending  below  in  the  calamus  scriptorius;  7,  7,  roots  of  the 
auditory  nerves. 

postero-median  and  postero-external  columns  are  also  represented  at  the 
posterior  or  dorsal  aspect  of  the  cord  as  the  fasciculus  gracilis  and  the 
fasciculus  cuneatus.  The  posterior  pyramids  of  the  medulla  which  in- 
clude these  two  columns  of  white  matter  soon  become  much  increased 
in  width  by  the  addition  of  a  new  column  of  white  matter  outside  the 
other  two  which  is  known  as  the  fasciculus  of  Rolando.  The  lateral  col- 
umns of  the  cord  undergo  considerable  change  and  are  scarcely  repre- 
sented as  such  in  the  bulb. 

It  may  be  said  then  that  the  bulb  at  its  commencement  differs  only 
slightly  in  size  from  the  cord   with  which  it  is  continuous.     It  soon 


THK    NERVOUS   SYSTEM, 


589 


becomes  larger  both  laterally  and  antero-posteriorly,  and  after  a  time 
opens  out  on  the  dorsal  surface  into  a  space  which  is  known  as  the  fourth 
ventricle,  and  from  being  a  cylinder  with  a  central  canal,  it  is  flattened 
out  on  one  surface  by  the  gradual  approach  of  the  central  canal  to  that 


jTj 


y-^ 


Fig.  360.— DofBal  or  posterior  view  of  the  meduUa,  fourth  ventricle,  and  mesencephalon 
(natural  size),  ji.  n. ,  line  of  the  posterior  roots  of  the  spinal  nerves;  p.m.f.,  posterior  median 
fissure; /..(/.,  funiculus  gracilis;  c?. ,  its  clava;  f.c.  funiculus  cuni-atus";  /.A'.,  funiculus  of 
Rolando;  r.  6. ,  restifomi  body;  c.  .s. ,  calamus  scriptorius:  ?,  section  of  ligula  or  tjpnia;  part  of 
choroid  plexus  is  seen  lieneath  it;  /.r. ,  lateral  recess  of  the  ventricle;  str.^  striiK  acusticae;  i.f., 
inferior  fossa;  s.f..  posterior  fossa;  between  it  and  the  median  sulcus  is  tlie  fasciculus  teres'; 
chl.^  cut  surface  of  the  cerebellar  hemisphere;  nd..  central  or  gray  matter;  s.m.v.,  superior 
medullary  velum ;  Inci.,  ligula;  s.c.  p.,  superior  cerebellar  peduncle  cut  longitudinally;  cr., 
combined  section  of  the  three  cerebellar  peduncles;  c.q.s.,  c.q.i..  corpora  quadrigeniina  (su- 
perior and  inferior):  fr.,  fra?nulum;  /. ,  fibres  of  the  fillet  seen  on  the  surface  of  the  tegmen- 
tum; c. ,  crusti;  '..'/..  lateral  groove;  c.g.i.,  corpus  geniculum  internus;  th.,  posterior  part  of 
thalamus;  p.,  pineal  body.  The  Roman  numbers  indicate  the  corresponding  cranial  nerves 
(E.  A.  Schiifer.) 


surface.     The  central  canal  of  the  cord,  therefore,  is  directly  continuous 
with  the  fourth  ventricle. 

If  the  bulb  be  examined  on  its  anterior  or  ventral  surface  it  is  found 
that  the  anterior  fissure,  which  is  a  continuation  of  the  same  fissure  in 
the  cord,  is  occupied  at  the  most  posterior  part  by  fibres  Avhich  are 
crossing  from  one  side  to  the  other;  the  central  canal  being  pushed  now 
toward  the  i)osterior  surface.  This  is  what  is  known  as  the  anferivr 
decussation  of  the  medulla  oblongata.  It  is  formed  of  the  fibres  which 
in  the  cord  occujiy  the  postero-lateral  region  and  are  called  the  crossed 
pyramidal  fibres.  Tlio  lateral  })yramidal  fibres  of  either  side  after  cross- 
ing ill  the  middle  line  in  this  way  become  part  of  the  anterior  pyramid 


590-  HAXDBOOK    OF    PHYSIOLOaY. 

of  the  opposite  side ;  the  rest  of  the  pyramid  being  made  up  of  the  fibres 
from  the  anterior  cohimn  of  the  cord  known  as  the  direct  or  uncrossed 
pyramidal  fibres.  These  two  pyramidal  strands  of  fibres  are  those  which 
degenerate  on  lesions  of  certain  parts  of  the  cerebrum  which  are  known 
as  the  motor  areas  of  the  cortex.  They  can  therefore  be  traced  downward 
on  such  lesions  as  tracts  of  degeneration.  They  are  the  fibres  of  commu- 
nication between  the  cerebral  cortex  and  the  different  segments  of  the 
spinal  cord.  The  anterior  pyramids  of  the  bulb  are  marked  out  by  the 
exit  from  that  part  of  the  nervous  axis  to  the  outside  of  them,  of  a 
nerve,  the  12th  or  hypoglossal.  More  laterally  than  this  nerve,  there 
soon  becomes  very  prominent  on  either  side  a  rounded  elevation  or  col- 
umn which  is  known  as  the  olivary  iody.  It  is  not  seen  at  the  begin- 
ning of  the  bulb  at  its  junction  with  the  cord,  but  begins  at  a  lower 
level  than  the  opening  of  the  fourth  ventricle.  On  the  further  side  of 
the  olivary  body  is  seen  the  line  of  origin  of  fibres  of  the  11th,  10th,  and 
9th  nerves,  and  from  this  to  the  posterior  fissure  is  the  posterior  pyramid. 

The  whole  of  that  part  of  the  medulla  which  is  situated  laterally 
between  the  olivary  body  and  the  posterior  fissure  is  known  as  the  resti- 
form  hocly;  it  is  continued  forward  on  either  side  as  the  inferior  peduncle 
of  the  cerebellum. 

The  changes  which  are  noticed  by  the  study  of  series  of  sections  of 
the  bulb  from  below  upward  may  be  summarized  thus:  In  the  dorsal  or 
posterior  region,  the  jDOsterior  cornua  are  pushed  more  to  each  side,  and 
the  substance  of  Rolando  is  increased  and  becomes  rounded,  reaching 
almost  to  the  surface  of  the  bulb  on  each  side,  a  small  tract  of  longitu- 
dinal fibres  of  the  ascending  root  of  the  oth  nerve  only  intervening. 
There  is  a  great  increase  of  the  reticular  formation  around  the  central 
canal,  and  the  lateral  approaches  the  anterior  coruu.  Then  at  the  ven- 
tral or  anterior  aspect  the  decussation  of  the  lateral  fibres  begins.  By 
this  crossing  over  of  the  fibres,  the  tip  of  the  gray  anterior  cornu  is  cut 
off  from  the  rest  of  the  gray  matter.  The  central  canal  is  pushed  further 
toward  the  posterior  surface,  first  of  all  by  the  decussation  of  the  anterior 
pyramids  just  mentioned,  and  later  on,  i.e.,  above,  by  another  decussa- 
tion of  fibres  more  dorsal.  These  fibres  of  the  second  decussation  as 
they  cross-form  a  median  raphe  and  also  help  to  break  up  the  remaining 
gray  matter  into  what  is  called  a  reticular  formation.  There  has  been 
some  little  doubt  as  to  the  origin  of  these  descussating  fibres,  but  the 
best  authorities  now  consider  them  to  be,  at  any  rate  in  part,  the  fibres 
from  the  nuclei  of  the  fasciculus  gracilis  and  fasciculus  cuneatus  of 
either  side,  and  look  upon  them  as  a  sensory  decussation.  At  the  pos- 
terior part  soon  there  appear  in  the  columns  of  white  matter  of  the 
fasciculus  gracilis  and  fasciculus  cuneatus  new  masses  of  gray  matter. 
The  lateral  norn  approaches  the  anterior;  but  soon  the  latter  is  pushed 


THE    NERVOUS    SYSTEM. 


591 


further  and  further  toward  the  centre,  while  the  lateral  horn  remains 
near  the  lateral  surface.  The  anterior  gray  matter  becomes  broken  up 
and  merged  into  the  reticular  formation.  There  is  also  a  similar  reticu- 
lar formation  both  toward  the  centre  and  also  laterally  in  the  dorsal 
region.  At  the  level  where  the  central  canal  opens  into  the  4th  ventri- 
cle, the  posterior  pyramids  diverging  to  form  the  lower  and  outside 
boundaries,  and  inclosing  a  space,  the  calamus  scriptorius,  between 
them,  there  are  to  be  made  out  various  masses  of  gray  matter  in  addi- 
tion to  the  reticular  formation,  viz.,  the  nuclei  of  the  fasciculus  gracilis 


fm.f.   M    -n.g 


Figr.  361.— Anterior  or  dorsal  section  of  the  medulla  oblougata  in  the  regrion  of  the  superior 
pyramidal  decussation,  a.  >»./.,  anterior  median  fissure;  f.a.,  siiperficial  arciform  fibres 
emerging  from  the  fissure;  py.,  pyramid;  n.ar.,  nuclei  of  arciform  filires;  f.a.,  deep  arciform 
becoming  superficial;  o,  lower  end  of  olivary  nucleus;  m.7.  ,  nucleus  lateralis;  /.  r. ,  formatio 
reticularis;  f.a.^,  arciform  fibres  proceeding  from  the  formatio  reticularis;  g.,  substantia  ge- 
latinosa  of  Rolando;  a.  V.,  ascending  root  of  fifth  nerve;  n.c.  nucleus  cuneatus;  n.c. ',  external 
cuneate  nucleus ;  n.g.,  nucleus  gracilis;  /.(/.,  funiculus  gracilis;  p.m.f.,  posterior  median  fis- 
sure; c.c,  central  canal  surrounded  by  gray  matter,  in  wliich  are  n.A'/. ,  nucleus  of  the  spinal 
accessory,  and  n.XIL,  nucleus  of  tne  hypoglossal;  s. d.,  superior  pyramidal  decussation. 
(Modified  from  Schwalbe.) 


and  fasciculus  cuneatus  (361,  n.g.  and  n.c.).,  which  are  at  this  level, 
however,  already  diminishing  and  are  lost  at  a  level  of  the  pons  Varolii. 

The  olivary  bodies  extend  forward  almost  to  the  level  of  the  pons. 
They  consist  of  gray  and  white  matter.  The  gray  matter  consists  of  a 
plicated  thinnish  strand  containing  small  nerve-cells,  folded  upon  itself 
in  the  form  of  a  loop,  with  the  ends  turned  inward  and  slightly  dorsal 
(Fig,  362,  o).  The  gray  loop  is  filled  with  and  covered  by  white  matter, 
part  of  the  fibres  passing  through  the  gray. 

Internal  to  the  olivary  body  on  either  side  are  two  small  masses  of 
gray  matter,  one  more  ventral  to  the  other,  called  accessory  olives,  ex- 
ternal and  internal,  and  on  the  surface  of  the  anterior  pyramid  on  either 


592 


HANDBOOK    OF    PHTSIOLOGT. 


side  a  small  mass  of  gray  matter,  external  arcuate  nucleus;  laterally 
another  mass  of  the  same  material,  the  representative  of  the  lateral  nu- 
cleus of  the  cord,  is  seen,  viz.,  the  antero-lateral  nucleus,  which  gives 
origin  to  the  spinal  accessory  nerve. 

It  will  be  necessary  to  follow  as  shortly  as  possible  the  fibres  of  the 
spinal  cord  upward  into  the  bulb  and  beyond : — 

The  crossed  and  direct  pyramidal  tracts  have  already  been  described. 
JN'othing  definite  is  known  of  the  antero-lateral  descending  tracts.  The 
cerebellar  tracts  pass  laterally  into  the  restiform  bodies  and  go  to  the 


Fig.  362.— Section  of  the  medulla  oblongata  at  about  the  middle  of  the  olivary  bodj'.  f.l.a., 
anterior  median  Assure;  n.ar.,  nucleus  arciformis;  p.,  pyramid;  XII. ,  bundle  of  hypoglossal 
nerve  emerging  from  the  surface;  at  6,  it  is  seen  coursing  between  the  pyramid  and  the  olivary 
nucleus,  o.  ; /.a. e.,  external  arciform  fibres;  n.l.,  nucleus  lateralis;  a.,  arciform  fibres  passing 
toward  restitorm  body,  partly  through  the  substantia  gelatinosa,  g. ,  partly  superficial  to  the 
ascending  root  of  the  fifth  nerve,  a,V.  ;  X,  bundle  of  vagus  root  emerging;  /.?•.,  formatio  retic- 
ularis; c.r.,  corpus  restiform,  beginning  to  be  formed,  chiefly  by  arciform  fibres,  superficial 
and  deep;  n.c,  nucleus  cuneatus;  n.g.,  nucleus  gracilis;  t,  attachment  of  the  ligula;  f.s.,  funi- 
culus solitarius;  n.X.,  n.X.',  two  parts  of  the  vagus  nucleus ;  n.XIL,  hypoglossal  nucleus;  71. t., 
nucleus  of  the  funiculus  teres;  n.am.,  nucleus  ambiguus;  ?•. ,  raphe;  A.,  continuation  of  the 
anterior  column  of  cord;  o',  0",  accessory  olivary  nucleus;  p.o.,  pedunculus  olivae.  (Modified 
from  Schwalbe.) 


cerebellum.  The  antero-lateral  ascending  tracts  appear  to  have  the 
same  destination  and  pass  directly  or  indirectly  into  the  cerebellum. 
The  fibres  of  the  postero-median  and  postero-external  columns  end  in 
the  nuclei  of  the  fasciculus  gracilis  and  cuneatus  respectively,  either  in 
or  about  the  cells  contained  in  those  nuclei ;  at  any  rate,  ascending  de- 
generation of  these  columns  cannot  be  traced  above  these  nuclei. 

The  rest  of  the  fibres  of  the  cord  appear  to  end  in  the  reticular  for- 
mation of  the  bulb.  The  bundle  of  fibres  constituting  the  ascending 
root  of  the  5th  nerve  appears  to  correspond  with  the  tract  of  Lissauer. 

Connections  of  the  bulb  with  the  cerebrum  and,  cerebellum. — In  addition 


THE    NERVOUS    SYSTEM.  593 

to  the  pyramidal  tracts  connecting  the  bulb  with  the  cerebrum  and  the 
direct  cerebellar  and  the  antero-lateral  ascending  tract  connecting  it 
with  the  cerebellum,  there  are  other  connections  of  the  bulb  with  the 
cerebrum,  and  with  the  cerebellum,  not  actually  direct. 

(1.)  Fibres  from  the  nucleus  gracilis  and  nucleus  cuneatus,  which, 
as  we  have  said,  are  the  bulbar  endings  of  the  fibres  of  the  postero- 
median and  postero-external  columns  of  the  cord,  pass  in  sets  as  it  were 
in  the  following  manner: — 

(a.)  Infernal  arcuate  fiires. — Some  pass  down  and  inward  to  the  other 
side  in  the  reticular  formation,  forming  in  part  the  superior  or  sensory 
decussation,  and  in  the  inter-olivary  region  become  longitudinal  in  a 
band  of  fibres  called  the  fillet,  which  passes  upward.  These  fibres  are 
jDrobably  augmented  by  the  addition  of  fibres  from  the  anterior  columns 
of  the  cord. 

(b.)  External  arcuate  fibres  also  decussate  in  the  same  way,  pass 
down  along  the  anterior  fissure,  and  then  running  outward  superficially 
over  the  anterior  pyramid  and  olivary  body,  reach  the  restiform  body 
and  pass  to  the  side  of  the  cerebellum  opposite  to  their  nuclei  of  origin. 
These  fibres  appear  to  have  some  relation  with  the  external  arcuate  nu- 
clei. They  connect  one  side  of  the  spinal  cord  with  the  opposite  side  of 
the  cerebellum  through  the  gracile  and  cuneate  nuclei. 

(c.)  Direct  lateral  fibres  pass  to  the  restiform  body  and  so  to  the  same 
side  of  the  cerebellum. 

(2.)  Fibres  from  the  olivary  body  pass  to  the  opposite  side  of  the 
cerebellum  probably  through  the  reticular  formation. 

(3.)  Arciform  fibres. — Fibres  from  the  nucleus  of  the  8th  or  auditory 
nerve  in  the  floor  of  the  4th  ventricle,  pass  to  the  same  side  of  the  cere- 
bellum. 

Functions  of  the  Bulb  or  Medulla  Oblongata. 

The  functions  of  the  bulb  are  those  of ,  (a.)  conduction;  (b.)  reflex 
action;  and  (c.)  automatism. 

{a.)  Conduction. — As  a  conductor  of  impressions,  the  medulla  oblon- 
gata has  a  wider  extent  of  function  than  any  other  part  of  the  nervous 
system,  since  it  is  obvious  that  all  impressions  passing  to  and  fro  be- 
tween the  brain  and  the  spinal  cord  must  be  transmitted  through  it. 

(J.)  Reflex  Action. — As  a  nerve  centre  by  which  impressions  are 
reflected,  the  medulla  oblongata  also  resembles  the  spinal  cord ;  the  only 
difference  between  them  consisting  of  the  .fact  that  many  of  the  reflex 
actions  performed  by  the  former  are  much  more  complicated  than  any 
performed  by  the  spinal  cord. 

It  has  been  proved  by  repeated  experiments  on  the  lower  animals 
that  the  entire  brain  may  be  gradually  cut  away  in  successive  portions, 


594  HANDBOOK    OF    PHYSIOLOGY. 

and  yet  life  may  continue  for  a  considerable  time,  and  the  respiratory 
movements  be  uninterrupted.  Life  may  also  continue  when  the  spinal 
cord  is  cut  away  in  successive  portions  from  below  upward  as  high  as 
the  point  of  origin  of  the  phrenic  nerve.  In  amphibia,  the  brain  has 
been  all  removed  from  above,  and  the  cord,  as  far  as  the  medulla  oblon- 
gata, from  below;  and  so  long  as  the  medulla  oblongata  was  intact, 
respiration  and  life  were  maintained.  But  if,  in  any  animal,  the  me- 
dulla oblongata  is  wounded,  particularly  if  it  is  wounded  in  its  central 
part,  opposite  the  origin  of  the  vagi,  the  respiratory  movements  cease, 
and  the  animal  dies  asphyxiated.  And  this  effect  ensues  even  when  all 
parts  of  the  nervous  system,  except  the  medulla  oblongata,  are  left  intact. 
Injury  and  disease  in  men  prove  the  same  as  these  experiments  on 
animals.  Numerous  instances  are  recorded  in  which  injury  to  the  me- 
dulla oblongata  has  produced  instantaneous  death;  and,  indeed,  it  is 
through  injury  of  it,  or  of  the  part  of  the  cord  connecting  it  with  the 
origin  of  the  phrenic  nerve,  that  death  is  commonly  produced  in  frac- 
tures attended  by  sudden  displacement  of  the  upper  cervical  vertebrse. 

Special  Centres. 

In  the  medulla  are  contained  a  considerable  number  of  centres  which 
preside  over  many  important  and  complicated  co-ordinated  movements 
of  muscles.  Tha  majority  of  these  centres  are  (a.)  reflex  centres  simply, 
which  are  stimulated  by  afferent  or  by  voluntary  impressions.  Some  of 
them  are  (b.)  automatic  centres^  being  capable  of  sending  out  efferent 
impulses,  generally  rhythmical,  without  previous  stimulation  by  afferent 
or  by  voluntary  impressions.  The  automatic  centres  are,  however,  gen- 
erally influenced  by  reflex  or  by  voluntary  impulses.  Some  again  of  the 
centres,  whether  reflex  or  automatic,  are  (c.)  control  centres^  by  which 
subsidiary  spinal  centres  are  governed.  Finally  the  action  of  some  of  the 
centres  is  (cZ.)  tonic^  i.e.,  they  exercise  their  influence  either  directly  or 
through  another  apparatus,  continuously  and  uninterruptedly  in  main- 
taining a  regular  action. 

Simple  Reflex  centres. 

(1.)  Bilateral  centres  for  the  co-ordinated  movements  of  Mastication^ 
the  afferent  and  efferent  nerves  of  which  have  been  already  enumerated 
(p.  326). 

(2.)  Bilateral  centres  for  the  movements  of  Deglutition.  The  medulla 
oblongata  appears  to  contain  the  centre  whence  are  derived  the  motor 
impulses  enabling  the  muscles  of  the  palate,  pharynx,  and  oesophagus  to 
produce  the  successive  co-ordinate  and  adapted  movements  necessary  to 
the  act  of  deglutition  (p.  353).  This  is  proved  by  the  persistence  of 
swallowing  in  some  of  the  lower  animals  after  destruction  of  the  cerebral 


THE    XEKVOUS    SYSTEM.  595 

hemispheres  and  cenjbclhim;  its  existence  in  iinencephalons  monsters; 
the  power  of  swallowing  possessed  by  the  marsupial  embryo  before  the 
l)ruin  is  developed;  and  by  the  complete  arrest  of  the  ])ower  of  swallow- 
ing when  the  medulla  oblongata  is  injured  in  experiments. 

{■).)  J3ilateral  centres  for  the  combined  muscular  movements  of 
Suckiuy,  the  motor  nerves  concerned  being  the  facial  for  tlie  lips  and 
mouth,  the  hypoglossal  for  the  tongue,  and  the  inferior  maxillary  divi- 
sion of  the  5th  for  the  muscles  of  the  jaw. 

(4.)  Bilateral  centi-es  for  tlie  Secretion  of  Saliva^  which  have  been 
already  mentioned  (p.  333). 

(o.)   Bilateral  centres  for  YoihU'ukj  (p.  36'.»). 

(G.)  ]iilateral  centres  for  CoiKjliimj^  whicli  are  said  to  be  independent 
of  the  respiratory  centre,  being  situated  above  the  inspiratory  part  of 
that  centre. 

(7.)  Bilateral  centres  for  Snceziiiy,  connected  no  doubt  with  the 
respiratory  centre. 

(8.)  Bilateral  centres  for  the  Dilatatio)i  of  the  impil,  the  fibres  from 
which  pass  ont  partly  in  the  third  nerve  and  jiartly  through  the  spinal 
cord  (through  the  last  two  cervical  and  two  upper  dorsal  nerves?)  into  the 
cervical  sympathetic. 

{b.)  Automatic  centres. 

(1.)  Resjjiriitonj  centres. — The  action  of  the  respiratory  centre  has 
been  already  discussed.  It  is  only  necessary  to  repeat  here  that  although 
it  can  be  influenced  by  afEerent  impulses,  it  is  also  automatic  in  its 
action,  being  capable  of  direct  stimulation,  as  by  the  condition  of  the 
blood  circulating  within  it.  It  is  also  bilateral.  It  probably  consists  of 
an  inspiratory  part  and  of  an  expiratory  part.  The  centre  is  capable  of 
being  influenced  both  reflexly  and  to  a  certain  extent  also  by  voluntary 
impulses.  The  vagus  influence  is  probably  constant  in  the  direction  of 
stimulating  the  ins23iratory  portion  of  the  centre,  whereas  the  influence 
of  the  superior  laryngeal  is  not  always  in  action,  and  is  inhibitory. 

(2.)  Car dio- Inhibitory  centres.  The  action  of  these  centre  in  main- 
taining the  proper  rhythm  of  the  heart  through  the  vagus  fibres,  which 
terminate  in  a  local  intrinsic  mechanism,  has  been  already  discussed. 
The  centre  can  be  directly  stimulated,  as  by  the  condition  of  the  blood 
circulating  within  it,  and  also  indirectly  by  afferent  stimuli,  especially 
by  stimulating  the  abdominal  sympathetic  nerves,  but  also  by  stimulat- 
ing any  sensory  nerve,  including  the  vagus  itself. 

(3.)  Accelerator  centres  for  the  heart.  The  centres  from  which  arise 
the  accelerator  fibres  of  the  heart,  in  the  medulla.  They  are  automatic 
but  not  tonic  in  action. 

(4.)  Vaso-niotor  centres,  which  control  the  uustri})e(l  muscle  of  the 
arteries,  are  also  situated  in  the  medulla.      Like  the  respiratory  centrej 


596  HANDBOOK    OF    PHYSIOLO&Y. 

tliey  are  bilateral.  As  has  already  been  j)ointecl  out,  these  centres  may 
be  directly  or  reliexly  stimulated,  as  well  as  by  impressions  conveyed 
downward  from  the  cerebrum  to  the  medulla.  The  condition  of  the 
l.lood  circulating  in  them  is  the  direct  stimulus.  Its  influence  is  no 
doubt  a  touic  or  else  a  rhythmic  one.  It  is  also  suj)posed  that  there  is 
in  the  medulla  a  special  vasO'dilator  centre  not  acting  tonically,  stimu- 
lation of  which  produces  vascular  dilatation.  The  diabetic  centre  is 
probably  a  part  of  the  vaso-motor  centre,  at  any  rate  stimulation  of  it 
causes  dilatation  of  the  vessels  of  the  liver. 

(5.)  Bilateral  chief  centres  for  the  secretion  of  Sweat  exist  in  the 
medulla.  The  centres  on  either  side  control  the  subsidiary  spinal  sweat 
centres.  They  may  be  excited  unequally  so  as  to  produce  unilateral 
sweating.     They  are  probably  automatic  and  reflex. 

(6.)  Bilateral  Sjjasm  centres  are  said  to  be  present  in  the  medulla, 
on  the  stimulation  of  which,  as  by  suddenly  produced  excessive  venosity 
of  the  blood,  general  spasms  of  the  muscles  of  the  body  are  produced. 

(c. )  Control  centres.  These  are  centres  whose  influence  may  be 
directed  to  controlling  the  action  of  subsidiary  centres.      They  are — 

(1.)  The  Respiratory  centres,  which  probably  control  the  action  of 
other  subordinate  centres  in  the  spinal  cord. 

(2.)  The  Cardio-Inhihitori)  centres,  which  act  upon  a  local  ganglionic 
mechanism  in  the  heart. 

(3.)  The  Accelerator  centres,  if  they  exist,  probably  act  through  a 
local  mechanism  in  the  heart. 

(4.)  The  Vaso-motor  centres  control  spinal  as  well  as  local  tonic 
centres. 

(5.)   The  medullary  Sioeat  centres  control  the  spinal  sweat  centres. 

{d.)  Tonic  centres.  Of  the  centres  whose  action  is  tonic  or  con- 
tinuous up  to  a  certain  degree,  may  be  cited  the  vaso-motor  and  the  car- 
dio-inhibitori/. 

It  should  not  be  forgotten  that  in  the  medulla  are  the  centres  for 
the  special  senses.  Hearing  and  Taste,  and  that  other  special  centres  are 
supposed  to  be  localized  there,  of  which  may  be  mentioned  one,  the 
hypothetical  Inhibitory  heat  centre,  which  controls  the  production  of 
heat  by  the  tissues,  independently  of  the  vaso-motor  centre. 

The  Cranial  Nerves. 

The  cranial  nerves  consist  of  twelve  pairs;  they  appear  to  arise  (su- 
perficial origin)  from  the  base  of  the  brain  in  a  double  series,  which 
extends  from  the  under  surface  of  the  anterior  part  of  the  cerebrum  to 
the  lower  end  of  the  medulla  oblongata.  Traced  into  the  substance  of 
the  brain  and  medulla,  the  roots  of  the  nerves  are  found  to  take  origin 
from  various  masses  of  gray  matter. 


THE    NERVOUS    SYSTEM. 


597 


The  roots  of  the  hrst  or  olfactory  and  of  the  second  or  optic  nerves 
will  be  mentioned  elsewhere.  The  third  and  fourth  nerves  arise  from 
gray  matter  beneath  the  corpora  quadrigemina;  and  the  roots  of  origin 
of  the  remainder  of  the  cranial  nerves  can  be  traced  to  gray  matter  in 
the  floor  of  the  fourth  ventricle,  and  in  the  more  central  part  of  the 
medulla,  around  its  central  canal,  as  low  down  as  the  decussation  of  tlie 
pyramids. 

According  to  their  several  functions  the  cranial  nerves  may  be  thus 
arranged : — 

a.  Nerves  of  special  sense 


b.  Nerves  of  common  sensation 

c.  Nerves  of  motion 

d.  Mixed  nerves 


Olfactory,  Optic,  Auditory,  part  of  the 

Glosso-pharyngeal,    and    part    of    the 

Fifth. 
The  greater  portion  of  the  Fiftli. 
Third,    Fourth,    lesser  division  of    the 

Fifth,  Sixth,  Facial,  and  Hypoglossal. 
Crlosso-pharyngeal,  Vagus,    and    Spinal 

accessory. 

The  physiology  of  the  First,  Second,  and  Eighth  will  be  considered 
with  the  organs  of  Special  sense. 

The  Ilird  Nerve  {Motor  Ocidi). 

Origin. — The  third  nerve  arises  in  three  distinct  bauds  of  fibres  from 
the  gray  matter  surrounding  the  aqueduct  of  Sylvius  near  the  middle 
line  ventral  to  the  canal.     The  nucleus  of  origin  consists  of  large  multi- 


/LC'-J 


Fig.  363.— Section  throufrh  anterior  corpus  quadrigeminum  and  part  of  optic  thalamus,  s., 
Aqueduct  of  Sylvius;  yr. ,  gray  matter  of  the  aqueduct;  c.q.s.,  quadrigeniinal  eminence;  /., 
stratum  lemnisci;  o. ,  stratum  opticum;  c. ,  stratum  cinereum;  Th.,  pulvinate  of  optic  thala- 
mus: c.y.e.,  v.g.i.,  lateral  aud  median  corpora  geniculata;  br.s..  br.L,  superior  and  inferior 
brachia;/.,  fillet;  p.i..  posterior  longitudinal  bundle:  )■.,  raphe;  ///.,  third  nerve,  and  n.III., 
its  nucleus;  l.p.p.,  posterior  iierf orated  space;  x.n.,  substantia  nigra,  above  this  is  the  tegmen- 
tum with  the  circular  area  of  the  red  nucleus;  cr.,  crusta;  //. ,  optic  tract:  M..  medullary  centre 
of  hemisphere;  ji.c. ,  nucleus  caudatus;  .<it.,  stria  terminalis.     (After  Quain,  from  Meynert.) 

polar  ganglion-cells,  and  extends  to  the  back  part  of  the  tliird  ventricle 
as  far  as  the  level  of  the  anterior  corpus  quadrigeminuni.  The  fibres 
pass  from  their  origin  partly  through  the  red  nucleus  to  their  superficial 


598 


HANDBOOK    OF    PHYSIOLOGY. 


origin  in  front  of  the  pons,  at  the  median  side  of  each  crus.  They  de- 
cussate with  their  fellows  in  the  middle  raphe.  The  nerve  is  connected 
with  the  optic  nerve. 

Function. — It  supplies  the  levator  palpebrge  superioris  muscle,  and 
all  of  the  muscles  of  the  ej^eball,  except  the  superio?-  oblique  to  which 


Fig.  364. —Diagram  of  a  longitudinal  section  through  the  pons,  showing  the  relation  of  the 
nuclei  for  the  ocular  muscles,  cq,  corpora  quadrigemina;  3,  third  nerve;  in,  its  nucleus;  4, 
foujth  nerve;  iv,  its  nucleus,  the  posterior  part  of  the  third;  6,  sixth  nerve.  The  probable 
position  of  the  centre  and  nerve  fibres  for  accommodation  is  shown  at  a  and  a',  for  the  reflex 
action  of  iris,  at  6,  and  b' ;  for  the  external  rectus  muscles,  at  c,  c'.  The  lines  beneath  the 
floor  of  the  fourth  ventricle  indicate  fibres,  which  connect  the  nuclei.     (Gowers.) 

the  fourth  nerve  is  appropriated,  and  the  rectus  externus  which  receives 
the  sixth  nerve.  Through  the  medium  of  the  ophthalmic  or  lenticular 
ganglion,  of  which  it  forms  Avhat  is  called  the  short  root,  it  also  supplies 
motor  filaments  to  the  iris  and  ciliary  muscle.  The  fibres  which  sub- 
serve the  three  functions,  accommodation,  contraction  of  the  pupil,  and 
nerve-supply  to  the  external  ocular  muscles,  arise  from  three  distinct 
groups  of  cells. 

AVhen  the  third  nerve  is  irritated  within  the  skull,  all  those  muscles 
to  which  it  is  distributed  are  convulsed.  When  it  is  paralyzed  or  divided 
the  following  effects  ensue: — (1)  the  upper  eyelid  can  be  no  longer 
raised  by  the  levator  palpebr^,  but  droops  {ptosis)  and  remains  gently 
closed  over  the  eye,  under  the  unbalanced  influence  of  the  orbicularis 
palpebrarum,  which  is  supplied  by  the  facial  nerve :  (2)  the  eye  is  turned 
outward  and  downward  [extet^nal  strabismus)  by  the  unbalanced  action 
of  the  rectus  externus  and  superior  oblique  to  which  the  sixth  nerve  is 
appropriated;  and  hence,  from  the  irregularity  of  the  axes  of  the  eyes, 
double  sight,  diplopia.,  is  often  experienced  when  a  single  object  is  within 
view  of  both  the  eyes:  (3)  the  eye  cannot  he  moved  either  upivard,  dotvn- 
ward.,  ox  inivard:  (4)  tlie pupil  becomes  dilated  (mydriasis):  (5)  the  eye 
cannot  accommodate  for  short  distances. 


The  IVth  Nerve  {TrocMearis) . 

Origin. — The  IVth  nerve  arises  from  a  nucleus  consisting  of  large 
multipolar  ganglion  cells  situated  below,  i.e.,  ventral  to  the  aqueductus 
of  Sylvius,  which  extends  from  the  back  part  of  the  nucleus  of  the 
third  nerve  to  the  hind  level  of  the  posterior  corpus  quadrigeminum. 
The  fibres  from  either  side  sweep  round  the  central  gray  matter,  and 


THE   NERVOUS   SYSTEM, 


599 


reach  the  valve  of  Viensseus,  where  they  decussate  in  the  middle  line 
and  appear  at  the  front  of  the  pons  at  the  lateral  edge  of  the  cms.     The 


Fig.  365.— Fourth  ventricle  with  the  medulla  oblongata  and  the  corpora  quadrigemina.  The 
reman  numbers  indicate  superficial  origins  of  the  cranial  nerves,  while  the  other  numbers  in- 
dicate their  deep  origins,  or  the  position  of  their  central  nuclei.  8.  8',  8",  8'",  auditory  nuclei 
nerves;  t,  funiculus  teres;  A.,  B,  corpora  quadrigemina ;  e.g.  corpus  geniculatum;  p.  c,  pedun- 
culus  cerebri;  hi,  c,  p.  middle  cerebellar  peduncle;  s,  c,  p,  superior  cerebellar  peduncle;  2,  c,  p, 
Inferior  cerebellar  peduncle;  ?,  c,  locus  caeruleus;  e,  t,  eminentia  teres;  o,  c,  alacinerea;  a,  »i, 
accessory  nucleus;  o,  obex;  c.  clava;  /,  c.  funiculus  cuneatus;  /,  <7,  funiculus  gracilis. 

nucleus  of  the  fourth  nerve  on  either  side  is  connected  with  those  of  the 
third  and  sixth  nerves. 

Functions. — The  IVth  nerve  is  exclusively  motor,  and  supplies  only 
the  trochlearis  or  obliquus  superior  muscle  of  the  eyeball. 


The  Vth  Nerve  (Trigeminus). 

Origin. — The  Yth  or  Trigeminal  nerve  resembles,  as  already  stated, 
the  spinal  nerves,  in  that  its  branches  are  derived  through  two  roots; 
namely,  the  larger  or  sensory,  in  connection  with  which  is  the  Gasserian 
ganglion,  and  the  smaller  or  motor  root  which  has  no  ganglion,  and 
which  passes  under  the  ganglion  of  the  sensory  root  to  join  the  third 
branch  or  division  which  ensues  from  it.  The  fibres  of  origin  of  the 
fifth  nerve  come  from  the  floor  of  the  fourth  ventricle.  The  motor  root 
to  the  inside  of  the  sensory,  about  the  middle  of  each  lateral  half.  The 
sensory  fibres,  however,  can  be  traced  down  in  the  medulla  oblongata  as 
far  as  the  upper  part  of  the  cord.  From  the  motor  nucleus  there 
stretches  forward  as  far  as  the  anterior  corpus  quadrigeminum  a  bundle 
of  long  fibres  termed  the  descending  root,  which  has  attached  to  it  sparse 
spheroidal  nerve-cells.  It  is  also  connected  with  the  locus  caeruleus. 
The  sensory  nucleus  outside  the  motor  has  connected  with  it  a  tract  of 


600 


HAifDEOOK   OF    PHYSIOLOGY. 


fibres  from  the  cord  as  low  as  the  second  cervical  nerve,  and  this  forms 
a  tract  at  the  tip  of  the  posterior  cornu,  between  it  and  the  restiform 
body.  No  nerve  cells  are  connected  with  it.  The  roots  can  be  traced 
obliquely  through  the  pons  Varolii,  beneath  the  floor  of  the  front  part 
of  the  fourth  ventricle.  The  motor  root  is  in  a  position  median  to 
sensory.  The  nerve  appears  at  the  ventral  surface  of  the  pons  near  its 
front  edge,  at  some  distance  from  the  middle  line. 

Function. — The  first  and  second  divisions  of  the  nerve,  which  arise 
wholly  from  the  larger  root,  are  purely  sensory.  The  third  division 
being  joined,  as  before  said,  by  the  motor  root  of  the  nerve,  is  of  course 
both  motor  and  sensory. 

(a.)  Motor. — Through  branches  of  the  lesser  or  non-ganglionic  por- 
tion of  the  fifth,  the  muscles  of  mastication,  namely,  the  temporal,  mas- 
seter,  two  pterygoid,  anterior  part  of  the  digastric,  and  mylohyoid, 
derive  their  motor  nerves.  Filaments  are  also  supplied  to  the  tensor 
tympani  and  tensor  palati.  The  motor  function  of  these  branches  is 
proved  by  the  violent  contraction  of  all  the  muscles  of  mastication  in 
experimental  irritation  of  the  third  or  inferior  maxillary  division  of  the 
nerve;  by  paralysis  of  the  same  muscle,  when  it  is  divided  or  disorgan- 


jivm 


rig.  366.  — Section  across  the  pons,  about  the  middle  of  the  fourth  ventricle,  py. ,  pyramidal 
bundles:  730.,  transverse  fibres  passing  poj,  behind,  and po^,  in  front  of  py. ;  ?-.,  raph6;  o.s.,  su- 
perior olive;  a.V.,  bundles  of  ascending  root  of  V.  nerve  inclosed  in  a  prolongation  of  the  sub- 
stance of  Rolando;  VI.,  the  sixth  nerve,  nF/. ,  its  nucleus;  VII.,  facial  nerve;  VII. a.,  in- 
termediate portion,  n.  F//. ,  its  nucleus;  VIII.,  auditory  nerve,  nVIII.,  lateral  nucleus  of  the 
auditory.     (After  Quain.) 


ized,  or  from  any  reason  deprived  of  power;  and  by  the  retention  of  the 
power  of  these  muscles,  when  all  those  supplied  by  the  facial  nerve  lose 
their  power  through  paralysis  of  that  nerve.  The  last  instance  proves 
best,  that  though  the  buccinator  muscle  gives  passage  to,  and  receives 


THE    NERVOUS   SYSTEM. 


601 


some  filaments  from,  a  buccal  branch  of  the  inferior  division  of  the  fifth 
nerve,  yet  it  derives  its  motor  power  from  the  facial,  for  it  is  paralyzed 
together  with  the  other  muscles  that  are  supplied  by  the  facial,  but 
retains  its  power  Avhen  the  other  muscles  of  mastication  are  paralyzed. 
Whether,  however,  the  branch  of  the  fifth  nerve  which  is  supplied  to 
the  buccinator  muscle  is  entirely  sensory,  or  in  part  motor  also,  must 
remain  for  the  present  doubtful.  From  the  fact  that  this  muscle,  he- 
sides  its  other  functions,  acts  in  concert  or  harmony  with  the  muscles  of 


FiK-  367.— General  plan  of  the  branches  of  the  fifth  pair,  i^.— 1,  lesser  root  of  the  fifth 
pair;  2,  greater  root  passing  forward  into  tlie  Gasseriaii  ganglion:  3,  placed  on  the  bone  above 
the  ophthalmic  nerve,  which  is  seen  dividing  into  the  supra-orbital,  lachrymal,  and  nasal 
iirancnes,  the  latter  connected  with  the  ophthalmic  ganglion;  4.  placed  on  the  bone  close  to  the 
foramen  rotundum,  marks  the  superior  maxillary  division,  whicn  is  connected  below  with  the 
spheno-palatine  ganglion,  and  passes  forward  to  tin'  infra-orbital  foramen;  5,  placed  on  the  bone 
over  the  foramen  ovale,  nuarks  the  inferior  maxillary  nerve,  giving  off  the  anterior  auricular 
arid  muscular  branches,  and  continued  li\  the  infei'ior  dental  to  the  lower  jaw,  and  by  the  gus- 
tajtory  to  the  tongue;  «,  the  sul)niaxillary  gland,  tlie  submaxillary  ganglion  placed  above  it  in 
connectiou  with  the  gustatory  nerve;  0,  the  chorda  tyuipani;  7,  the  facial  nerve  issuing  from 
tl^g  stylomastoid  foramen.     (Charles  Bell.) 

mastication,  in  keeping  the  food  between  the  teeth,  it  might  be  sup- 
posed from  analogy,  that  it  would  have  a  motor  branch  from  the  same 
nerve  that  supplies  tlioiii.  There  can  be  no  doubt,  however,  that  the 
so-called  buccal  branch  of  the  fifth  is,  in  the  main,  sensory ;  although 
it  is  not  quite  certain  that  it  does  not  give  a  few  motor  filaments  to  the 
buccinator  muscle. 

(b.)   Sensory. — Through  the  branches  of  the  greater  or  ganglionic 
portion  of  the  fifth  nerve,  all  the  anterior  and  antero-lateral  parts  of  the 


602  HANDBOOK    OF    PHYSIOLOGY. 

face  and  head,  with  the  exception  of  the  skin  of  the  parotid  region 
(which  derives  branches  from  the  cervical  spinal  nerves) ,  acquire  com- 
mon sensibility;  and  among  these  parts  may  be  included  the  organs  of 
special  sense,  from  which  common  sensations  are  conveyed  through  the 
fifth  nerve,  and  their  special  sensations  through  their  several  nerves  of 
special  sense.  The  muscles,  also,  of  the  face  and  lower  jaw  acquire 
muscular  sensibility,  through  the  filaments  of  the  ganglionic  portion  of 
the  fifth  nerve  distributed  to  them  with  their  proper  motor  nerves.  The 
sensory  function  of  the  branches  of  the  greater  division  of  the  fifth  nerve 
is  proved,  by  all  the  usual  evidences,  such  as  their  distribution  in  parts 
that  are  sensitive  and  not  capable  of  muscular  contraction,  the  exceeding 
sensibility  of  some  of  these  parts,  their  loss  of  sensation  when  the  nerve 
is  paralyzed  or  divided,  the  pain  without  convulsions  produced  by  mor- 
bid or  experimental  irritation  of  the  trunk  or  branches  of  the  nerve, 
and  the  analogy  of  this  portion  of  the  fifth  to  the  posterior  root  of  the 
spinal  nerve. 

Other  Functions. — In  relation  to  muscular  movements,  the  branches 
of  the  greater  or  ganglionic  portion  of  the  fifth  nerve  exercise  a  mani- 
fold infiuence  on  the  movements  of  the  muscles  of  the  head  and  face 
and  other  parts  in  which  they  are  distributed.  They  do  so,  in  the  first 
place  (a),  by  providing  the  muscles  themselves  with  that  sensibility 
without  which  the  mind,  being  unconscious  of  their  position  and  state, 
cannot  voluntarily  exercise  them.  It  is,  probably,  for  conferring  this 
sensibility  on  the  muscles,  that  the  branches  of  the  fifth  nerve  commu- 
nicate so  frequently  with  those  of  the  facial  and  hypoglossal,  and  the 
nerves  of  the  muscles  of  the  eye ;  and  it  is  because  of  the  loss  of  this 
sensibility  that  when  the  fifth  nerve  is  divided,  animals  are  always  slow 
and  awkward  in  the  movement  of  the  muscles  of  the  face  and  head,  or 
hold  them  still,  or  guide  their  movements  by  the  sight  of  the  objects 
toward  which  they  wish  to  move. 

{h.)  Again,  the  fifth  nerve  has  an  indirect  influence  on  the  muscular 
movements,  by  conveying  sensations  of  the  state  and  position  of  the  skin 
and  other  parts :  which  the  mind  perceiving,  is  enabled  to  determine 
appropriate  acts.  Thus,  when  the  fifth  nerve  or  the  infra-orbital  branch 
is  divided,  the  movement  of  the  lips  in  feeding  may  cease,  or  be  imper- 
fect. 

(c.)  An  intimate  connection  with  muscular  movements  through  the 
many  reflex  acts  of  muscles  of  which  it  is  the  necessary  excitant.  Hence, 
when  it  is  divided  and  can  no  longer  convey  impressions  to  the  nervous 
centres  to  be  thence  reflected,  the  irritation  of  the  conjunctiva  produces 
no  closure  of  the  eye,  the  mechanical  irritation  of  the  nose  excites  no 
sneezing. 

{d.)  Through  its  ciliary  branches  and  the  branch  which  forms  the 


THE   N-EllYOT-S    SYSTE^^r.  603 

long  root  of  tlie  ciliary  or  ophthalmic  ganglion,  it  exercises  also  some 
influence  on  the  movements  of  the  iris.  When  the  trunk  of  the  oph- 
thalmic portion  is  divided,  the  pupil  becomes,  according  to  Valentin, 
contracted  iu  men  and  rabbits,  and  dilated  in  cats  and  dogs;  but  in  all 
cases,  becomes  immovable  even  under  all  the  varieties  of  the  stimulus  of 
light.  How  the  fifth  nerve  thus  affects  the  iris  is  unexplained;  it  has 
been  ingeniously  suggested  the  influence  of  the  fifth  nerve  on  the  move- 
ments of  the  iris  may  be  ascribed  to  the  affection  of  vision  in  consequence 
of  the  disturbed  circulation  or  nutrition  in  the  retina,  when  the  normal 
influence  of  the  fifth  nerve  is  disturbed.  In  such  disturbance,  increased 
circulation  making  the  retina  more  irritable  might  induce  extreme  con- 
traction of  the  iris. 

Tvophic  infl.ue)icc. — The  morbid  effects  which  division  of  the  fifth 
iK'rv(^  produces  in  the  organs  of  special  sense,  make  it  probable  that,  in 
the  normal  state,  the  fifth  nerve  exercises  some  sj)ecial  or  tropldc  influ- 
ence on  the  nutrition  of  all  these  organs;  although,  in  jiart,  the  effect 
of  the  section  of  the  nerve  is  only  indirectly  destructive  by  abolishing 
sensation,  and  therefore  the  natural  safeguard  which  leads  to  the  pro- 
tection of  parts  from  external  injury.  Thus,  after  such  division,  within 
a  period  varying  from  twenty-four  hours  to  a  week,  the  cornea  begins  to 
be  opaque;  then  it  grows  completely  white;  a  low  destructive  inflamma- 
tory process  ensues  in  the  conjunctiva,  sclerotica,  and  interior  jDarts  of 
the  eye;  and  within  one  or  a  few  weeks,  the  whole  eye  may  be  quite 
disorganized,  and  the  cornea  may  slough  or  be  penetrated  by  a  large 
ulcer.  The  sense  of  smell  (and  not  merely  that  of  mechanical  irritation 
of  the  nose),  may  be  at  the  same  time  lost  or  gravely  impaired;  so  may 
the  hearing,  and  commonly,  whenever  the  fifth  nerve  is  jiaralyzed,  the 
tongue  loses  the  sense  of  taste  in  its  anterior  and  lateral  parts,  and  ac- 
cording to  Gowers  in  the  posterior  part  as  well. 

In  relation  to  Taste. — The  loss  of  tactile  sensibility  as  well  as  the 
sense  of  taste,  is  no  doubt  due  («)  to  the  lingual  branch  of  the  fifth  nerve 
being  a  nerve  of  tactile  sense,  and  also  because  with  it  runs  the  chorda 
tympani,  which  is  one  of  the  nerves  of  taste;  partly,  also,  it  is  due  (/»), 
to  the  fact  that  this  branch  supplies,  in  the  anterior  and  lateral  parts  uf 
the  tongue,  a  necessary  condition  for  the  proper  nutrition  of  that  part; 
while  (c),  it  forms  also  one  chief  link  in  the  nervous  circle  for  reflex 
action,  in  the  secretion  of  saliva.  But,  deferring  this  question  until 
the  glosso-pharyngeal  nerve  is  to  be  considered,  it  may  be  observed  that 
in  some  brief  time  after  complete  paralysis  or  division  of  the  fifth  nerve, 
the  power  of  all  the  organs  of  the  special  senses  may  be  lost;  they  may 
lose  not  merely  their  sensibility  to  common  impressions,  for  which  they 
all  depend  directly  on  the  fifth  nerve,  but  also  their  sensibility  to  their 
several  peculiar   impressions  for  the  reception  and  conduction  of  which 


604:  SAI<rDBOOK   OF   PHYSIOLOGY. 

they  are  purposely  constructed  and  supplied  witli  special  nerves  besides 
the  fifth.  The  facts  observed  in  these  cases  can,  perhaps,  be  only  ex- 
plained by  the  influence  which  the  fifth  nerve  exercises  on  the  nutritive 
processes  in  the  organs  of  the  special  senses.  It  is  not  unreasonable  to 
believe,  that,  in  paralysis  of  the  fifth  nerve,  their  tissues  may  be  the 
seats  of  such  changes  as  are  seen  in  the  laxity,  the  vascular  congestion, 
oedema,  and  other  affections  of  the  skin  of  the  face  and  other  tegumen- 
tary  parts  which  also  accompany  the  paralysis ;  and  that  these  changes, 
which  may  appear  unimportant  when  they  affect  external  parts,  are 
sufficient  to  destroy  that  refinement  of  structure  by  which  the  organs  of 
the  special  senses  are  adapted  to  their  functions. 

The  Vlth  Nerve  (Abducens). 

Origin. — The  Vlth  nerve  arises  from  a  compact  oval  nucleus,  situ- 
ated somewhat  deeply  at  the  back  part  of  the  pons  near  the  middle  of 
the  floor  of  the  fourth  ventricle.  The  eminentia  teres  marks  its  posi- 
tion. It  contains  moderately  large  nerve-cells  with  distinct  axis  cylin- 
der processes.  It  is  connected  (fig.  364)  with  the  nuclei  of  the  third, 
fourth,  and  seventh  nerves.  It  is  nearer  the  middle  line  than  the  nuclei 
of  the  fifth  and  seventh.  The  root  is  thin,  and  passes  ventrally  and 
laterally  through  the  reticular  formation,  to  the  surface,  which  it  reaches 
at  the  hind  end  of  the  pons  opposite  the- front  end  of  anterior  pyramid. 

Functions. — The  sixth  nerve  is  exclusively  motor,  and  supplies  only 
the  rectus  externus  muscle  of  the  eye. 

The  rectus  externus  is  convulsed,  and  the  eye  is  turned  outward, 
when  the  sixth  nerve  is  irritated ;  and  the  muscle  is  paralyzed  when  the 
nerve  is  divided.  In  all  such  cases  of  paralysis,  the  eye  squints  inward, 
and  cannot  be  moved  outward. 

In  its  course  through  the  cavernous  sinus,  the  sixth  nerve  forms 
larger  communications  with  the  sympathetic  nerve  than  any  other  nerve 
within  the  cavity  of  the  skull  does.  But  the  import  of  these  communi- 
cations with  the  sympathetic,  and  the  subsequent  distribution  of  its 
filaments  after  joining  the  sixth  nerve,  are  quite  unknown. 

The  Vllth  Nerve  (Facial). 

Origin. — The  facial,  or  portio  dura  of  the  seventh  pair  of  nerves, 
arises  from  the  floor  of  the  central  part  of  the  fourth  ventricle  behind 
and  in  line  with  the  motor  nucleus  of  the  fifth,  to  the  outside  of  and 
deeper  down  than  the  nucleus  of  the  sixth.  The  nucleus  is  narrower  in 
front  than  behind,  and  consists  of  large  cells  with  well  marked  axis 
cylinder-processes,  which  are  gathered  up  at  the  dorsal  surface  of  the 
nucleus  to  form  a  root.     The  root  describes  a  loop  round  the  nucleus  of 


THE    NERVOUS   SYSTElf.  605 

tTie  sixth  nerve,  running  forward  for  some  little  distance  dorsal  to  the 
nucleus,  then  descending  vertically,  passing  to  outside  of  its  own  nucleus 
between  it  and  the  ascending  root  of  fifth  nerve.  It  emerges  at  the 
hinder  margin  of  the  2)ons  lateral  to  the  sixth  nerve,  opposite  the  front 
edge  of  the  groove  between  the  olivary  and  restiform  bodies.  It  may  ho 
connected  with  the  hypoglossal  nucleus.  There  are  two  roots;  the  lower 
and  smaller  is  called  the  portio  intermedia. 

Functions. — The  seventh  nerve  is  the  motor  nerve  of  all  the  muscles 
of  the  face,  including  the  platysma,  but  not  including  any  of  the  mus- 
cles of  mastication  already  enumerated;  it  supplies,  also,  the  parotid 
gland,  and  through  the  connection  of  its  trunk  with  the  Vidian  nerve, 
by  the  petrosal  nerves,  some  of  the  muscles  of  the  soft  palate,  probably 
the  levator  palati  and  azygos  uvulfe.  By  its  tympanic  branches  it  sup- 
plies the  stapedius  and  laxator  tympani ;  and  through  the  optic  ganglion, 
the  tensor  tympani ;  tln-ough  the  cliorda  tympani  it  sends  branches  to 
the  submaxillary  gland  and  to  the  lingualis  and  some  other  muscular 
fibres  of  the  tongue,  and  to  the  mucous  membrane  of  its  anterior  two- 
thirds;  and  by  branches  given  oif  before  it  comes  upon  the  face,  it  sup- 
plies the  muscles  of  the  external  ear,  the  posterior  part  of  the  digas- 
tricus,  and  the  stylo-hyoideus. 

Beside  its  motor  influence,  the  facial'  is  also,  by  means  of  the  fibres 
which  are  supplied  to  the  submaxillary  and  jaarotid  glands,  a  secretory 
nerve.  For,  through  the  last-named  branches,  impressions  may  be  con- 
veyed which  excite  increased  secretion  of  saliva. 

Paralysis  of  Facial  Nerve. — When  the  facial  nerve  is  divided,  or  in 
any  other  way  paralyzed,  the  loss  of  power  in  the  muscles  which  it  sup- 
plies, while  proving  the  nature  and  extent  of  its  functions,  displays  also 
the  necessity  of  its  perfection  for  the  perfect  exercise  of  all  the  organs 
of  the  special  senses.  Thus,  in  paralysis  of  the  facial  uerve,  the  orbicu- 
laris palpebrarum  being  powerless,  the  eye  remains  open  through  the 
unbalanced  action  of  the  levator  palpebral;  and  the  conjunctiva,  thus 
continually  exposed  to  the  air  and  the  contact  of  dust,  is  liable  to  re- 
peated inflammation,  which  may  end  in  thickening  and  opacity  of  the 
cornea.  These  changes,  however,  ensue  much  more  slowly  than  those 
which  follow  paralysis  of  the  fifth  nerve,  and  never  bear  the  same  de- 
structive character. 

The  sense  of  hearing,  also,  is  impaired  in  many  cases  of  paralysis  of 
the  facial  nerve;  not  only  in  such  as  are  instances  of  simultaneous  dis- 
ease in  the  auditory  nerves,  but  in  such  as  may  be  explained  by  the  loss 
of  power  in  the  muscles  of  the  internal  ear.  The  sense  of  smell  is  com- 
monly at  the  same  time  impaired  through  the  inability  to  draw  air 
briskly  toward  the  up})er  partof  the  nasal  cavities  in  which  part  alone 
the  olfactory  nerve  is  distributed;  because,  to  draw  the  air  perfectly  in 


606  HAXDBOOK    OP    PSTSTOLOGY. 

this  direction,-  the  action  of  the  diki,tors  and  compregsors  of  the  nos- 
trils should  be  perfect. 

Lastly,  the  sense  of  taste  is  inijiaired,  or  may  be  Avholly  lost  iu  paral- 
ysis of  the  facial  nerve,  provided  the  source  of  the  paralysis  be  in  some 
part  of  the  nerve  between  its  origin  and  the  giving  oU  of  the  chorda  tym- 
pani.  This  result,  which  has  been  observed  in  many  instances  of  disease 
of  the  facial  nerve  in  man,  appears  explicable  on  the  supposition  that  the 
chorda  tympani  is  the  nerve  of  taste  to  the  anterior  two-thirds  of  the 
tongue,  its  fibres  being  distributed  with  the  so-called  gustatory  or  lingual 
branch  of  the  fifth.  Some  look  upon  the  chorda  as  partly  or  entirely 
made  up  of  fibres  from  the  fifth  nerve,  and  not  strictly  speaking  as  a 
branch  of  the  facial;  others  consider  that  it  receives  its  taste  fibres  from 
communications  with  the  glosso-pharyngeal. 

Together  with  these  effects  of  jDaralysis  of  the  facial  nerve,  the  mus- 
cles of  the  face  being  all  poAverless,  the  countenance  acquires  on  the 
paralyzed  side  a  characteristic,  vacant  look,  from  the  absence  of  all  ex- 
pression: the  angle  of  the  mouth  is  lower,  and  the  paralyzed  half  of  the 
mouth  looks  longer  than  that  on  the  other  side;  the  eye  has  an  unmean- 
ing stare.  All  these  ]3eculiarities  increase,  the  longer  the  paralysis 
lasts;  and  their  appearance  is  exaggerated  when  at  any  time  the  muscles 
of  the  opposite  side  of  the  face  are  made  active  in  any  expression,  or  in 
any  of  their  ordinary  functions.  In  an  attempt  to  blow  or  whistle,  one 
side  of  the  mouth  and  cheeks  acts  properly,  but  the  other  side  is  mo- 
tionless, or  flaps  loosely  at  the  impulse  of  the  expired  air ;  so  in  trying 
to  suck,  one  side  only  of  the  mouth  acts;  in  feeding,  the  lij)s  and  cheeks 
are  powerless,  and  on  account  of  paralysis  of  the  buccinator  muscle  food 
lodges  between  the  cheek  and  gums. 

The  Vlllth  Nerve  {Auditory). 

Origin. — The  Vlllth  nerve  arises  from  two  nuclei,  median  and  lat- 
eral., in  the  floor  of  the  fourth  ventricle,  in  the  anterior  part  of  the 
bulb  in  front  and  to  the  side  of  the  twelfth  nerve ;  it  extends  from  the 
middle  line  to  the  outside  margin  of  the  ventricle.  There  is  also  an 
accessory  nucleus  situated  on  the  ventral  surface  of  the  restiform  body. 
The  nerve  leaves  the  surface  of  the  brain  from  the  ventral  surface  of  the 
fore-part  of  the  restiform  body  at  the  hind  margin  of  the  pons  in  two 
roots.  One  winds  round  the  restiform  body  dorsal  to  it  and  the  other 
passes  median  to  it.  The  former  is  called  the  dorscd  root.  The  latter 
is  called  the  ventral  root.  Most  of  the  fibres  of  the  dorsal  root  {cochlear) 
end  in  cells  of  the  accessory  nucleus,  but  fibres  emerging  from  this  im- 
cleus  pass  inward  to  the  bulb,  superficially,  forming  the  stricB  acusticce 
in  the  floor  of  the  fourth  ventricle  and  end  in  the  median  nucleus.     Most 


tHE  NERrots  sfsttsii.  607 

of  the  fibres  of  the  ventral  root  {cestibidar)  end  in  cells  of  the  lateral 
nucleus.  The  cells  of  the  median  nucleus  are  small,  those  of  the  lateral 
nucleus  large. 

lunctiun.s. — The  cochlear  branch  is  the  auditory  nerve  proper,  and 
the  vestibular  is  distributed  to  the  semicircular  canals,  the  utricule  and 
saccule,  parts  of  the  internal  ear  not  directly  concerned  with  hearing. 

The  IXth  Nerve  {Glosso- Pharyngeal). 

Origin. — The  glosso-pharyngeal  nerves  (ix.,  fig.  304),  iu  the  enume- 
ration of  the  cerebral  nerves  by  numbers  according  to  the  position  in 
which  they  leave  the  cranium,  are  considered  as  divisions  of  the  eighth 
pair  of  nerves,  the  vagus  and  spinal  accessory  nerves  being  included  with 
them.  The  union  of  the  nuclei  is  indeed  so  intimate  that  it  will  be  as 
well  to  take  the  origins  of  the  ninth,  tenth,  and  eleventh  nerves  together. 

These  three  nerves  emerge  from  the  bulb  and  spinal  cord  in  their 
numerical  order  from  above  downward,  the  lulbar  portion  from  the  lat- 
eral aspect  of  the  bulb  in  a  line  between  the  olivary  and  restiform  bodies; 
and  the  spinal  portion  from  a  line  intermediate  between  the  anterior  and 
posterior  nerve  roots  as  far  down  as  the  sixth  or  seventh  cervical. 

The  combined  glosso-pharyngeal-accessory-vagus  nucleus  appears  to 
consist  of  two  parts,  viz. ,  one  median  or  common  origin,  having  con- 
spicuous nerve-cells  of  moderate  size,  and  three  lateral  origins.,  having 
but  few  cells  of  small  size.  These  are — i.  the  nucleus  amhiguus,  which 
lies  on  the  lateral  side  of  the  reticular  formation  and  is  the  origin  of  the 
vagus;  ii.  the  fasciculus  solitarius,  situated  in  the  bulb,  ventral  and  a 
little  lateral  to  the  combined  nucleus,  is  also  called  the  ascending  root 
of  the  glosso-pharyngeal  nerve  or  the  respiratory  bundle ;  and  iii.  the 
spifial  jjortion  which  takes  origin  from  a  group  of  cells  lying  in  the  ex- 
treme lateral  margin  of  the  anterior  cornu.  This  is  the  origin  of  the 
spinal  accessory ;  it  corresponds  to  the  antero-lateral  nucleus  of  the  bulb, 
and  the  lateral  part  of  the  gray  matter  of  the  spinal  cord. 

The  fibres  of  the  spinal  origin  of  the  nerve  pass  from  these  cells 
through  the  lateral  column  to  the  surface  of  the  cord. 

The  fibres  from  the  comhined  nucleus,  chiefly  from  the  median  part, 
pass  in  a  ventral  and  lateral  direction  through  the  reticular  formation, 
then  ventral  to  or  through  the  gelatinous  substance  and  strand  of  fibres 
connected  with  the  fifth  nerve,  to  the  surface  of  bulb. 

The  fibres  from  the  nucleus  amhiguus  join  the  combined  nerve,  but 
especially  the  vagus. 

The  bundles  of  fibres  of  the  fasciculus  solitarius  at&rt  iu  the  lateral 
gray  matter  of  the  cervical  cord  and  higher  in  the  reticular  formation 
of  the  bulb,  run  longitudinally  forward  to  pass  into  the  roots  of  the  ninth 
nerve. 


608  HANDBOOK    OF    PHYSIOLOGY. 

IXth  Nerve. — Distrihution. — The  glosso-pharyiigeal  nerve  gives  fila- 
ments through  its  tympanic  branch  (Jacobson's  nerve),  to  the  fenestra 
ovalis  and  fenestra  rotunda,  and  the  Eustachian  tube,  parts  of  the  mid- 
dle ear;  also,  to  the  carotid  plexus,  and  through  the  petrosal  nerve,  to 
the  spheno-palatine  ganglion.  After  communicating,  either  within  or 
without  the  cranium,  with  the  vagus,  and  soon  after  it  leaves  the  cra- 
nium, with  the  sympathetic,  digastric  branch  of  the  facial,  and  the 
accessory  nerve,  the  giosso-pharyngeal  nerve  parts  into  the  two  principal 
divisions  indicated  by  its  name,  and  supplies  the  mucous  membrane  of 
the  posterior  and  lateral  walls  of  the  upper  part  of  the  pharynx,  the 
Eustachian  tube,  the  arches  of  the  palate,  the  tonsils  and  their  mucous 
membrane,  and  the  tongue  as  far  forward  as  the  foramen  caecum  in  the 
middle  line,  and  to  near  the  tip  at  the  sides  and  inferior  part. 

Functions. — The  giosso-pharyngeal  nerve  contains  some  motor  fibres, 
together  with  those  of  common  sensation  and  the  sense  of  taste. 

1.  Motor  fibres  are  distributed  to  the  palato-pharyngeus,  the  stylo- 
pharyngeus,  palato-glossus,  and  constrictors  of  the  pharynx. 

2.  Sensory  fibres  in  the  parts  which  it  supplies,  and  a  centripetal 
nerve  through  which  impressions  are  conveyed  to  be  reflected  to  the  ad- 
jacent muscles. 

3.  Fibres  for  the  special  nerve  of  taste  (from  its  fibres  derived  from 
the  fifth,  Gowers),  in  all  the  parts  of  tlie  tongue  and  palate  to  which  it  is 
distributed.  After  many  discussions,  the  question,  Which  is  the  nerve 
of  taste? — the  chorda  tympani,  the  gustatory,  or  the  giosso-pharyngeal? 
— may  be  most  probably  answered  by  stating  that  they  are  not  them- 
selves, strictly  speaking,  nerves  of  this  special  function,  but  through 
their  connection  with  the  fifth  nerve.  For  very  numerous  experiments 
and  cases  have  shown  that  when  the  trunk  of  the  fifth  nerve  is  paralyzed 
or  divided,  the  sense  of  taste  is  completely  lost  in  the  superior  surface 
of  the  anterior  and  lateral  parts' of  the  tongue,  at  the  back  of  the  tongue, 
and  on  the  soft  palate  and  palatine  arches.  The  loss  is  instantaneous 
after  division  of  the  nerve,  and,  therefore,  cannot  be  ascribed  wholly  to 
the  defective  nutrition  of  the  part,  though  to  this,  perhaps,  may  be 
ascribed  the  more  complete  and  general  loss  of  the  sense  of  taste  when 
the  whole  of  the  fifth  nerve  has  been  paralyzed. 

The  Xth  Nerve  {Vagus  or  Pneumogastric) . 

The  origin  of  the  Vagus  nerve  is,  as  we  have  just  seen,  situated  in 
the  lower  half  of  the  calamus  scriptorins  in  the  ala  cinerea  (fig.  365). 
Its  nucleus  is  said  to  represent  the  cells  of  Clarke's  (posterior  vesicular) 
cohmm  of  the  spinal  cord.  In  origin  it  is  closely  connected  with  the 
ninth,   eleventh,   and  the  twelfth.      The  combined  glosso-pharyngea,l- 


THE    NERVOUS    SYSTEM.  609 

vago-accessory  nuclei  lie  outside  of,  close  to,  and  jiarallel  with  the  nucleus 
of  the  twelfth. 

Distribution. — It  supplies  sensory  branches,  which  accompany  the 
sympathetic  on  the  middle  meningeal  artery,  and  others  which  sujiply 
the  back  part  of  the  meatus  and  the  adjoining  part  of  the  external  ear. 
It  is  connected  with  the  jietrous  ganglion  of  the  glosso-pharyngeal,  by 
means  of  fibres  to  its  jugular  ganglion;  with  the  spinal  accessory  which 
supplies  it  with  its  motor  fibres  for  the  larger  and  upper  portion  of  the 
oesophagus,  and  with  its  inhibitory  fibres  for  the  heart;  also  with  the 
twelfth;  with  the  superior  cervical  ganglion  of  the  sympathetic;  and 
with  the  cervical  plexus.  It  has,  of  all  the  nerves,  the  most  varied  dis- 
tribution and  functions,  either  through  its  own  filaments,  or  through 
those  which,  derived  from  other  nerves,  are  mingled  in  its  branches. 
The  parts  supplied  by  the  branches  of  the  vagus  are  as  follows: — 

(1.)  By  its  2)Jia7'i/ngeal  branches,  wdiich  enter  the  jiharyngeal  plexus, 
a  large  portion  of  the  mucous  membrane,  and,  jDrobably,  all  the  muscles 
of  the  pharynx. 

(2.)  By  the  si/jjei'ior  laryngeal  nerve,  the  raucous  membrane  of  the 
under  service  of  the  epiglottis,  the  glottis,  and  the  greater  jiart  of  the 
larynx,  and  the  crico-thyroid  muscle. 

(3.)  By  the  inferior  laryngeal  nerve,  the  mucous  membrane  and  mus- 
cular fibres  of  the  trachea,  the  lower  j)art  of  the  pharynx  and  larynx, 
and  all  the  muscles  of  the  larynx  except  the  crico-thyroid. 

(4.)  By  its  (Bsopliageal  branches,  the  mucous  membrane  and  muscular 
coats  of  the  oesophagus. 

(5.)  Through  the  cardiac  nerves,  moreover,  the  branches  of  the  vagus 
form  a  large  portion  of  the  supply  of  nerves  to  the  heart  and  the  great 
arteries. 

(G.)  Through  the  anterior  and  the  posterior  jmlmonary  plexuses  to  the 
lungs. 

(7.)  Through  its  ^r/s/'/'iV;  branches  to  the  stomach;  and  to  the  intes- 
tines, and  kidneys,  by  its  terminal  branches. 

(8.)  Through  its  liepatic  and  splenic  branches,  the  liver  and  the  spleen 
are  partly  supplied  with  nerves. 

Functions. — Throughout  its  whole  course,  the  vagus  contains  both 
sensory  and  motor  fibres.  To  summarize  the  many  functions  of  this 
nerve,  which  have  been  for  the  most  part  considered  in  the  preceding 
chapters,  it  may  be  said  that  it  supplies  (1)  motor  influence  to  the 
pharynx  and  oesophagus,  stomach  and  intestines,  to  the  larynx,  trachea, 
bronchi,  and  lung;  ('2)  sensory  and,  in  part,  (3)  vaso-motor  influence, 
to  the  same  regions;  (4)  inhibitory  influence  to  the  heart;  (5)  inhibi- 
39 


GIO 


HAXDBOOK    OF    PHYSIOLOGY. 


tory  afferent  impulses  to  the  vaso-motor  centre ;  (6)  excito-secretory 

to  the  salivary  glands;  (7)  excito-motor  in  coughing,  vomiting,  etc. 
Effects  of  Section. — Division  of  both  vagi,  or  of  both  their  recurrent 


Fig.  368. — View  of  the  nerves  IX,  X,  and  XI,  their  distribution  and  connections  on  the  left 
side.  2-5. — 1,  Pneumogastric  nerve  in  the  neck;  2,  ganglion  of  its  trunli;  3,  its  union  with  the 
spinal  accessory;  4,  its  union  witli  the  hypoglossal;  5,  pharyngeal  branch;  6,  superior  laryn- 
geal nerve;  7,  external  laryngeal;  8,  laryngeal  plexus;  9,  inferior  or  recurrent  laryngeal ;  10, 
superior  cardiac  branch;  11,  middle  cardiac;  12,  plexiform  part  of  the  nerve  in  the  thorax;  13, 
posterior  pulmonary  plexus;  14,  lingual  or  gustatory  nerve  of  the  inferior  maxillary;  15,  hypo- 
glossal, passing  into  the  muscles  of  the  tongue,  giving  its  thyro-hyoid  branch,  and  uniting  with 
twigs  or  the  lingual;  16,  glosso-pharyngeal  nerve;  17,  spinal  accessory  nerve,  uniting  by  its 
inner  branch  with  the  pneumogastric,  and  by  its  outer,  passing  into  the  sterno-mastoid  muscle; 
18,  second  cervical  nerve;  19,  third;  20.  fourth;  21,  origin  of  the  phrenic  nerve,  22,  2;^,  fifth,  sixth, 
seventh,  and  eighth  cervical  nerves,  forming  with  the  first  dorsal  the  brachial  plexus;  24,  su- 
perior cervical  ganglion  of  the  sympathetic;  25,  middle  cervical  ganglion;  26,  inferior  cervical 
ganglion  united  with  the  first  dorsal  ganglion ;  27,  28,  29,  30,  second,  third,  fourth,  and  fifth 
dorsal  ganglia.     (From  Sappey  after  Hirschfeld  and  Leveill6.) 

branches,  is  often  very  quickly  fatal  in  young  animals;  but  in  old  ani- 
mals the  division  of  the  recurrent  nerve  is  not  generally,  and  that  of 
both  the  vagi  is  not  always,  fatal,  and,  when  it  is  so,  death  ensues  slowly. 


THE    XERVOUS    SYSTE:iI.  611 

This  difference  is,  that  the  yielding  of  the  cartilages  of  the  larynx  in 
young  animals  permits  the  glottis  to  be  closed  by  the  atmospheric  pres- 
sure in  insi^iration,  and  so  they  are  quickly  suffocated  unless  tracheotomy 
be  performed.  In  old  animals,  the  rigidity  and  prominence  of  the  aryt- 
enoid cartilages  prevent  the  glottis  from  being  completely  closed  by  the 
atmospheric  pressure;  even  when  all  the  muscles  are  paralyzed,  a  por- 
tion at  its  posterior  part  remains  open,  and  through  this  the  animal 
continues  to  breathe. 

In  the  case  of  slower  death,  after  division  of  both  the  vagi,  the  lungs 
are  commonly  found  gorged  with  blood,  oedematous,  or  nearly  solid, 
from  a  kind  of  low  pneumonia,  and  the  bronchial  tubes  full  of  frothy 
bloody  fluid  and  mucus,  to  which,  in  general,  the  death  may  be  ascribed. 
These  changes  are  due,  in  j^art,  to  the  passage  of  food  and  of  the  various 
secretions  of  the  mouth  and  fauces  through  the  glottis,  which,  being 
deprived  of  its  sensibility,  is  no  longer  stimulated  or  closed  in  conse- 
quence of  their  contact. 

The  Xlth  Nerve  (Spinal  Accessory). 

Origin  and  Connectio7is. — The  nerve  arises  by  two  distinct  origins — 
one  from  a  centre  in  the  floor  of  the  fourth  ventricle,  partly  but  chiefly 
in  the  medulla,  and  connected  with  the  glosso-pharyngeal-vagus-nucleus; 
the  other,  from  the  outer  side  of  the  anterior  cornu  of  the  spinal  cord 
as  low  down  as  the  fifth  or  sixth  cervical  nerve.  The  fibres  from  the 
two  origins  come  together  at  the  jugular  foramen,  but  separate  again 
into  two  branches,  the  inner  of  which,  arising  from  the  medulla,  joins 
the  vagus,  to  which  it  supplies  its  motor  fibres,  consisting  of  small  me- 
dullated  or  visceral  nerve-fibres,  while  the  outer  consisting  of  large 
medullated  fibres,  supplies  the  trapezius  and  sterno-mastoid  muscles. 
The  small-fibred  branch  is  said  to  arise  from  a  nucleus  corresponding  to 
the  posterior  vesicular  column  of  Clarke. 

The  principal  branch  of  the  accessory  nerve,  its  external  branch, 
then  su2:)plies  the  sterno-mastoid  and  trajiezius  muscles;  and,  though 
pain  is  produced  by  irritating  it,  is  composed  almost  exclusively  of 
motor  fibres.  The  internal  branch  of  the  accessory  nerve  supplies  chiefly 
viscero-motor  filaments  to  the  vagus.  The  muscles  of  the  larynx,  all  of 
which,  as  already  stated,  are  supplied,  apparently,  by  branches  of  the 
vagus,  are  said  to  derive  their  motor  nerves  from  the  accessory;  and 
{which  is  a  very  significant  fact)  Vrolik  states  that  in  the  chimpanzee 
the  internal  branch  of  the  accessory  does  not  join  the  vagus  at  all,  but 
goes  direct  to  the  larynx. 

Among  the  roots  of  the  accessory  nerve,  the  lower  or  external,  aris- 
ing from  the  spinal  cord,  appears  to  be  composed  exclusively  of  motor 


612  HAXDBOOK    OF    PHYSIOLOGT. 

fibres,  and  to  be  destined  entirely  to  the  trapezius  and  extending  from 
the  back  of  the  fourth  ventricle  to  the  level  of  the  olivary  bodies  close 
to  the  middle  line,  inside  the  combined  nucleus  of  the  ninth,  tenth,  and 
eleventh  nerves. 

The  Xllth  Nerve  {Hypoglossal). 

Origin  and  Connections. — The  nerve  arises  from  a  large-celled  and 
very  long  nucleus  in  the  bulb,  extending  from  the  back  of  the  fourth 
ventricle  to  the  level  of  the  olivary  bodies  close  to  the  middle  line,  inside 
the  combined  nucleus  of  the  ninth,  tenth,  and  eleventh  nerves.  Fibres 
from  this  nucleus  run  from  the  ventral  surface  through  the  reticular 
formation  in  a  series  of  bundles  passing  between  the  olivary  nucleus  lat- 
erally and  the  anterior  jDyramid  and  accessory  olive  medially,  to  gain 
the  surface.  The  nerve  emerges  from  a  groove  between  the  anterior 
pyramid  and  olivary  body.  The  fibres  of  origin  are  continuous  with 
the  anterior  roots  of  the  spinal  nerves.  It  is  connected  with  the  vagus, 
the  superior  cervical  ganglion  of  the  sympathetic  and  with  the  upper 
cervical  nerves. 

Distribution. — This  nerve  is  the  motor  nerve  to  the  muscles  con- 
nected with  the  hyoid  bone,  including  those  of  the  tongue.  It  supplies 
through  its  descending  branch  [descendens  noni),  the  sterno-hyoid, 
sterno-thyroid,  and  omo-hyoid;  through  a  special  branch,  the  thyro- 
hyoid, and  through  its  lingual  branches,  the  genio-hyoid,  stylo-giossus, 
hyo-glossus,  and  genio-hyo-glossus  and  linguales. 

Functions. — The  function  of  the  hypoglossal  is  exclusively  motor. 
As  a  motor  nerve,  its  influence  on  all  the  muscles  enumerated  above  is 
shown  by  their  convulsions  when  it  is  irritated,  and  by  their  loss  of 
power  when  it  is  paralyzed.  The  effects  of  the  paralysis  of  one  hypo- 
glossal nerve  are,  however,  not  very  striking.  Often,  in  cases  of  hemi- 
plegia involving  the  functions  of  the  hypoglossal  nerve,  it  is  not  possible 
to  observe  any  deviation  in  the  direction  of  the  protruded  tongue;  prob- 
ably because  the  tongue  is  so  compact  and  firm  that  the  muscles  on  either 
side,  their  insertion  being  nearly  parallel  to  the  median  line,  can  push 
it  straight  forward  or  turn  it  for  some  distance  toward  either  side. 

The  Pons  Varolii. 

The  pons  Varolii  is  generally  spoken  of  as  a  great  commissure  of 
fibres;  of  fibres  which  connect  the  two  halves  of  the  cerebellum  and  of 
fibres  which  connect  the  bulb  and  spinal  cord  with  the  upper  part  of  the 
brain.  Although  this  is  true  it  must  not  be  forgotten  that  the  pons 
contains  several  masses  of  gray  matter,  and  also  in  addition  smaller  col- 
lections of  nerve-cells.     It  is  found  that  on  section  the  following  parts 


THE   NEKYOUS    SYSTEM.  613 

may  be  made  out  in  its  structure,  beginning  from  the  anterior  or  ven- 
tral surface. 

(a.)  Transverse  or  commissural  fibres  connecting  the  one  side  of  the 
cerebellum  with  the  other,  forming  the  middle  peduncle.  These  fibres 
emerge  from  the  lateral  parts  of  the  white  substance  of  the  hemispheres, 
having  come  from  the  superficial  gray  matter  of  the  whole  surface,  from 
the  median  vermis,  and  from  the  lateral  hemispheres.  Some  of  these 
fibres  are  truly  commissural  and  probably  connect  the  same  points  on 
the  surfaces  of  the  two  halves;  some  end  in  the  gray  matter  of  the  same 
side  of  the  pons  on  the  ventral  surface,  and  others  cross  to  the  opposite 
side  of  the  pons  ami  then  become  longitudinal,  passing  on  to  the  teg- 
7nentum,  a  system  of  fibres  and  gray  matter  to  be  immediately  described. 

{b.)  Fibres  longitudinal  in  direction  which  are  arranged  in  larger  or 
smaller  bundles  separated  by  gray  matter;  some  of  these  fibres  are  what 
are  called  the  pyramidal  fibres,  which  pass  down  to  the  anterior  pyra- 
mids of  the  bulb. 

(c.)  The  dorsal  portion  of  the  pons  is  made  up  to  a  considerable  ex- 
tent of  the  reticular  formation  of  the  tegmental  region  together  with 
one  or  two  distinct  bundles  of  longitudinal  fibres:  i.,  the  chief,  situated 
toward  the  junction  of  the  ventral  two  thirds  with  the  dorsal  third,  is 
the fllef,  which  consists  of  two  portions,  outer  and  median;  and  ii.,  the 
second,  a  bundle  of  similar  fibres,  posterior  longitudinal  iundles,  is  situ- 
ated between  the  two  divisions  of  the  fillet  below  the  lateral  and  to  the 
outer  side  of  the  median. 

(d.)  In  the  fore  part  of  the  pons,  a  mass  of  gray  matter  containing 
pigment,  the  locus  coeruleus,  ^jossibly  forming  the  origin  of  the  fifth  nerve, 
and  in  the  back  part  a  second  mass  of  gray  matter,  the  superior  olive. 

The  Crura  Cerebri. 

The  crura  cerebri  (iii,  fig.  354)  diverge  from  the  anterior  edge  of 
the  pons  Varolii  and  pass  upward  on  either  side  toward  the  cerebral 
hemispheres.  At  their  anterior  termination  each  of  them  appears  to 
have  upon  its  dorsal  surface,  to  the  inner  and  outer  sides  respectively, 
two  large  masses  of  gray  matter  which  have  been  already  spoken  of,  viz., 
the  optic  thalamus  and  the  corpus  striatum.  These  bodies  are  not  only 
as  it  were  placed  upon  the  surface  of  each  crus,  but  are  also  deeply  em- 
bedded in  its  substance. 

The  cms  is  found  to  be  made  up  of  two  principal  parts: — 

(«.)  The  one,  the  tegmentum,  situated  for  the  most  part  on  the  dorsal 
aspect,  is  composed  chiefly  of  gray  matter  and  some  longitudinal  fibres. 

And  (b.)  the  other,  the  cnista,  situated  toward  the  other  surface,  is 
composed  almost  entirely  of  longitudinal  fibres.     It  is  known  also  as  the 


614 


HAIS'DBOOK   OF   PHYSIOLOGY. 


pes.     Separating  these  two  parts,  is  a  mass  of  gray  matter  of  the  shape 
of  a  lens,  called  the  locus  or  nucleus  niger  or  substantia  nigra. 

The  tegmentum  situated  dorsally  ends  for  the  most  part  in  the 
neighborhood  of  the  optic  thalamus  and  the  parts  beneath.  In  conse- 
quence of  this  the  fibres  of  the  pes  are  allowed  to  come  dorsally  and  to 
proceed  between  the  optic  thalamus  and  the  more  posterior  part  (the 
lenticular  nucleus)  of  the  corpus  striatum,  on  their  course  to  the  cere- 
bral cortex.  When  in  this  situation  they  form  a  compact  mass  of  fibres. 
As  they  pass  more  dorsally  the  fibres  spread  out  in  the  form  of  a  fan. 
and  this  arrangement  is  called  the  corona  radiata.     The  fibres  of  the  pes 


Fig.  369. —Diagram  of  the  motor  tract  as  shown  in  a  diagrammatic  horizontal  section 
through  the  cerebral  hemispheres,  Crura,  Pons,  and  Medulla.  Fr. ,  Frontal  lobe ;  Oc. ,  occipital 
lobe;  AF. ,  ascending  frontal,  AP. ,  ascending  parietal  convolutions;  PCF. ,  pre-central  fissure, 
in  front  of  the  ascending  frontal  convolution ;  FR. ,  fissure  of  Rolando ;  IPF. ,  inter-parietal  fis- 
sure, a  section  of  crus  is  lettered  on  the  left  side.  SN. ,  Substantia  nigra;  Py.,  pyramidal  motor 
fibre,  which  on  the  right  is  shown  as  continuous  lines  converging  to  pass  through  the  posterior 
limb  of  IC.  internal  capsule  (the  knee  or  elbow  of  which  is  shown  thus  *)  upward  into  the 
hemisphere  and  downward  through  the  pons  to  cross  the  medulla  in  the  anterior  pyramids. 
(Gowers.) 


are  found  to  stretch  not  only  between  the  optic  thalamus  and  the  len- 
ticular nucleus,  but  also  more  anteriorly  between  the  former  and  the 
caudate  nucleus  of  the  cor2)us  striatum  which,  as  we  have  seen,  is  to  be 
seen  in  the  floor  of  the  lateral  ventricle.  The  fibres  of  the  pes  thus 
spread  out,  have  the  form  of  a  fan  bent  upon  itself  as  they  rise  to  pass 
into  the  cerebral  hemisphere.  This  constitutes  the  internal  capsule,  and 
that  portion  of  it  which  forms  the  angle  at  which  the  fibres  are  bent  is 
called  the  genu  of  the  capsule,  that  in  front  of  it  being  the  front,  and 
that  behind,  the  hind  limb.  The  fibres  constituting  the  internal  cap- 
sule are  distributed  to  different  districts  of  the  cerebral  cortex.  They 
are  made  up  of  fibres  not  only  constituting  the  pyramidal  system,  but 


THE    XEKVOUS   SYSTEM.  015 

also  of  others  which  end  in  the  masses  of  gray  matter  in  the  pons  or  crus 
itself;  but  the  function  of  all  of  the  fibres  is  believed  to  be  to  carry  im- 
pulses downward  from  the  cerebrum  either  to  the  spinal  cord  and  so  to 
the  cranial  nerves,  or  to  the  cerebellum. 

The  tegmentum  of  either  side,  on  the  other  hand,  is  supposed  to  be 
concerned,  for  the  most  part  at  any  rate,  with  afferent  impulses.  It  is 
made  ujd  to  a  very  considerable  extent  of  collections  of  gray  matter,  the 
most  important  of  which  are  (a)  the  locus  or  nucleus  niger,  separating 
the  pes  and  tegmentum;  {h)  the  nucleus  ruber,  which  is  a  rounded  mass 
situated  more  toward  the  aqueduct  of  Sylvius;  this  extends  from  the 
third  ventricle  to  the  anterior  corpus  quadrigeminum.  The  locus  niger 
extends  back  as  far  as  the  posterior  corpus  quadrigeminum.  (c)  A  third 
mass  of  gray  matter  is  situated  beneath  the  optic  thalamus,  and  is  the 
corjnis  sithtlialamicum.  Posteriorly  the  tegmentum  is  made  up  chiefly 
of  the  reticular  material  so  often  spoken  of,  and  in  the  pons  consists 
almost  entirely  of  that  kind  of  structure,  but  with  the  two  additional 
masess  of  gra}"  matter  already  indicated,  viz.,  the  locus  coeruleus  and 
superior  olive. 

It  will  be  as  well  here  to  indicate  briefly  the  other  collections  of  gray 
matter  in  the  neighborhood  of  the  crura,  viz.,  tlie  corpus  striata,  optic 
thalami,  corpora  quadrigemina,  corpora  geuiculata,  and  the  corpora 
dentata  of  the  cerebelhim. 

Corpora  Striata. — The  corpora  striata  are  situated  in  front  and  to 
the  outside  of  the  optic  thalami,  partly  within  and  jDarth'  without  the 
lateral  ventricle. 

Each  corpus  striatum  consists  of  two  parts: — 

{a.)  An  intraventricular  portion  {caudate  nucleus)  which  is  conical  in 
shape,  with  tlie  base  of  the  cone  forward;  it  consists  of  gray  matter, 
with  white  substance  in  its  centre,  {b.)  An  extraventricular  jiortion 
{lenticular  nucleus),  which  is  separated  from  the  other  portion  by  a  layer 
of  white  material,  which  forms  a  portion  of  the  internal  capsule, — the 
anterior  limb.  The  lenticular  nucleus  is  seen,  on  a  horizontal  section  of 
the  hemisphere,  to  consist  of  three  jiarts  (the  two  internal  called  globus 
2Xillidus,  major  and  minor,  and  the  outer  called  the  pufamen),  separated 
from  one  another  by  white  matter,  of  which  the  smallest  of  the  three  is 
inside.  Each  jiart  somewhat  resembles  a  wedge  in  shape.  The  upper 
and  internal  surface  is  in  relation  with  the  caudate  nucleus,  being  sepa- 
rated from  it  by  the  anterior  limb  of  the  internal  capsule.  The  remain- 
der of  the  internal  surface  is  in  relation  to  the  optic  thalamus,  being 
separated  from  it  by  the  -posterior  limb  of  the  internal  capsule.  The 
horizontal  section  is  wider  in  the  centre  than  at  the  ends.  On  the  out- 
side is  the  gray  lamina  (claustrum)  separated  by  a  thin  white  layer — 
external  capsule — from  the  lenticular  nucleus. 


616  HANDBOOK    OF    PHYSIOLOGY. 

The  cells  of  the  eorpora  striata  are  evenly  distributed,  and  not 
^ronped  in  nuclei.  Their  neuraxons  pass,  for  the  most  part,  into  the 
internal  capsule.  The  corpora  striata  are  connected  with  the  cerebellum 
through  these  fibres.  It  is  doubtful  if  these  ganglia  have  any  anatomical 
relations  with  the  cortex  of  the  brain. 

Optic  Thalami. — The  optic  thalami  are  oval  in  shape,  and  rest 
upon  the  inner  and  dorsal  surfaces  of  the  crura  cerebri.  The  upper  sur- 
face of  each  thalamus  is  free,  and  of  white  substance;  it  projects  into 
the  lateral  ventricle.  The  posterior  surface  is  also  white.  The  inner 
sides  of  the  two  optic  thalami  form  the  outer  borders  of  the  third 
ventricle,  are  in  partial  contact,  and  are  composed  of  gray  material  un- 
covered by  white  and  are,  as  a  rule,  connected  together  by  a  transverse 
portion. 

The  optic  thalamus  is  composed  of  several  collections  of  gray  matter, 
forming  somewhat  indistinctly  defined  masses  separated  by  white  fibres. 
These  masses  of  gray  matter  are  known  as  the  nuclei  of  the  thalamus, 
and  they  are  six  in  number.  They  are  called  the  anterior  tubercle,  the 
median  nucleus,  the  lateral  nucleus,  the  ventral  nucleus,  the  pulvinar, 
and  the  posterior  nucleus.  The  anterior  tubercle  is  composed  of  large 
nerve-cells  whose  neuraxons  pass  down  to  the  corpora  mammillaria  at  the 
base  of  the  brain.  There  they  meet  the  fibres  of  the  fornix  which  con- 
nect this  tubercle  of  the  thalamus  with  the  hippocampal  convolution. 
The  median  nucleus  is  connected  by  its  neuraxons  with  the  cortex  of  the 
Island  of  Eeil  and  the  second  and  third  convolutions.  The  lateral  nu- 
cleus is  quite  large  and  lies  against  the  internal  capsule,  into  which  it 
sends  fibres.  It  is  connected  with  the  central  convolutions.  The  ven- 
tral nucleus  lies  beneath  the  preceding;  it  is  small  in  size.  It  is  con- 
nected wnth  the  cortex  of  the  frontal  lobe  and  with  the  operculum,  the 
central  convolutions,  and  the  supramarginal  gyrus.  The  fifth  nucleus, 
known  as  the  2mlvi7iar,  forms  the  posterior  tip  of  the  thalamus,  and  is 
connected  with  the  optic  tract.  The  posterior  nucleus,  lying  just  below 
the  pulvinar,  is  a  small  mass  and  is  connected  with  the  cortex  of  the  in- 
ferior parietal  convolution.  The  cells  of  the  optic  thalamus  are  thus 
seen  to  be  connected  with  a  large  area  of  the  cerebral  cortex.  They  are 
also  connected  with  the  sensory,  and  probably,  to  some  extent,  with  the 
motor  tracts  coming  from  below. 

Corpora  Quadrigemina. — There  are  two  on  each  side,  anterior 
and  posterior;  they  form  prominences  on  the  dorsal  surface  of  the  pons 
and  crura  above  the  aqueduct  of  Sylvius.  They  are  composed  of  alter- 
nate layers  of  white  and  gray  matter.  The  posterior  bodies  receive 
fibres  from  the  eighth  nerve  and  the  sensory  tract,  known  as  tlie 
pief.  They  send  fibres  out  to  the  temporal  region  of  the  brain.  Tiiey 
are  closely  associated  with  the  lateral  corpora  geniculata.  The  anterior 
corpora  quadrigemina  are  connected  by  fibres  with  the  optic  nerve  and 


THE    XERVOUS    SYSTEM. 


617 


also  the  fillet,  aiul  send  fibres  to  the  occipital  cortex  of  the  braiu.  They 
are  closely  associated  with  the  median  corpora  geniculata. 

Corpora  Geniculata. — These  are  two  on  either  side,  lateral  or 
outer  and  median  or  inner;  the  former  is  developed  from  the  fore-brain, 
the  latter  from  the  mid-brain.  The  lateral  corpus  geniculatum  is  at  the 
side  of  the  cms  and  appears  to  be  a  swelling  on  the  lateral  division  of 
the  optic  tract.  Similarly  the  median  appears  to  be  the  termination  of 
the  median  division  of  the  oj)tic  tract.  They  both  contain  gray  matter 
(fig.  363). 

Corpora  Dentata  are  plicated  areas  of  gray  matter  in  the  interior 
pf  the  cerebellum,  not  unlike  the  olivary  body  of  the  bulb.  The  fibres 
from  each  pass  chiefly  to  the  superior  peduncle  of  its  own  side. 

The  Cerebrum. — For  convenience  of  description,  the  surface  of 
the  brain  has  been  divided  iutofve  lobes  (Gratiolet). 


tanjkM, 


Fig.  3V0.— Lef t  hemisi)here,  from  without.     CAfterEberstaller.) 


1.  Frontal  (fig.  370),  limited  behind  by  the  fissure  of  Rolando 
(central  fissure),  and  beneath  by  the  fissure  of  Sylvius.  Its  surface  con- 
sists of  three  main  convolutions,  which  are  aj^proximately  horizontal  in 
direction,  and  are  broken  up  into  numerous  secondary  gyri.  They  are 
termed  the  superior,  middle,  and  inferior  frontal  convolutions.  In  ad- 
<lition,  the  frontal  lobe  contains,  at  its  posterior  part,  a  convolution 
which  runs  upward  almost  vertically  {ascending  fronted),  and  is  bounded 
in  front  by  a  fissure  termed  the  praccntral,  behind  by  that  of  Kolando. 

2  Parietal.  This  lobe  is  bounded  in  front  by  the  fissure  of 
Rolando,  behind  by  the  external  perpendicular  fissure  (parieto-occipital), 
and  below  by  the  fissure  of  Sylvius.  Behind  the  fissure  of  Rolando  is 
the  ascending  parietal  convolution,  which  swells  out  at  its  upper  end 
into  what  is  termed  the  superior  parietal  lobule.  The  superior  parietal 
lobule  is  separated  from  the  inferior  parietal  lobule  by  the  intra-parietal 


618 


HANDBOOK   OP   PHYSIOLOGY. 


sulcus.  The  inferior  parietal  lobule  (pli  courbe)  is  situated  at  the  pos- 
terior and  upper  end  of  the  fissure  of  Sylvius;  it  consists  of  (a)  an 
anterior  part  (supra-marginal  convolufioti)  which  hooks  round  the  end 
of  the  fissure  of  Sylvius,  and  joins  the  superior  temporal  convolution, 
and  a  posterior  part  {!))  (angular  gyrus)  which  hooks  round  into  the 
middle  temporal  convolution. 

3.  Temporal  contains  three  well-marked  convolutions,  parallel  to 
each  other,  termed  the  superior,  middle,  and  inferior  temporal.  The 
superior  and  middle  are  separated  by  the  parallel  fissure. 

4.  Occipital.      This  lobe   lies   behind   the  external    perpendicular 


pronial  p^^ 


Fig.  371. — The  cerebrum,  from  above.    (After  Eberstaller.) 

or  parieto-occipital  fissure,  and  contains  three  convolutions,  termed  th& 
superior,  middle,  and  inferior  occipital.  They  are  often  not  well  marked. 
In  man,  the  external  parieto-occipital  fissure  is  only  to  be  distinguished 
as  a  notch  in  the  inner  edge  of  the  hemisphere;  below  this  it  is  quite- 
obliterated  by  the  four  annectant  gyri  (plis  de  passage)  which  run  nearly 
horizontally.  The  upper  two  connect  the  parietal,  and  the  lower  two 
the  temporal  with  the  occipital  lobe. 

5.  Central  lobe,  or  island  of  Eeil,  which  contains  a  number  of  radiat- 
ing convolutions  (gyri  operti). 

The  fig.  372  shows  the  following  gyri  and  sulci: — 

Gyrus  fornicatus,  a  long  curved  convolution,  parallel  to  and  curving^ 


THE    XERYOUS   SYSTEM. 


G19 


round  the  corpus  callosum,  and  swelling  out  at  its  hinder  and  upper  end 

into  the  quadrate  lobule  (prajcuneus),  which  is  continuous  with  the 
superior  parietal  lobule  on  the  external  surface.  Marginal  convolution 
runs  parallel  to  the  preceding,  and  occupies  the  space  between  it  and 
the  edge  of  the  longitudinal  fissure.  The  two  convolutions  are  separated 
by  the  calloso-marginal  fissure.  The  internal  perpendicular  fissure  is  well 
marked,  and  runs  downward  to  its  junction  with  the  calcarine  fissure : 
the  wedge-shaped  mass  intervening  between  these  two  is  termed  the 
cuneus.  The  calcarine  fissure  corresponds  to  the  projection  into  the  pos- 
terior cornn  of  the  lateral  ventricle,  termed  the  Hippocamjms  minor. 
The  teynporal  lobe  on  its  internal  aspect  is  seen  to  end  in  a  hook  (unci- 
nate gyrus).  The  notch  round  which  it  curves  is  continued  up  and 
back  as  the  dentate  or  hippocampal  sulcus:  this  fissure  underlies  the 


Fig.  87'2.— Right  hemisphere,  from  within.    (After  Eberstaller.) 

projection  of  the  hippocampus  major  within  the  brain.  There  are  three 
internal  temporo-occipital  convolutions,  of  which  the  superior  and  infe- 
rior ones  are  usually  well  marked,  the  middle  one  generally  less  so. 

The  collateral  fissure  (corresponding  to  the  eminentia  coUateralis) 
forms  the  lower  boundary  of  the  superior  temporo-occipital  convolution. 

All  the  above  details  will  be  found  iutlicated  in  the  diagrams  (figs. 
371,  372). 

iStructure. — The  cerebrum  is  constructed  like  the  other  chief  di- 
visions of  the  cerebro-spiual  system,  of  //my  and  tvhite  matter',  and,  a? 
in  the  case  of  the  Cerebellum  (and  unlike  the  spinal  cord  and  medulla 
oblongata)  the  gray  matter  (carter)  is  external,  and  forms  a  capsule  or 
covering  for  the  white  substance.  For  the  evident  purpose  of  increasing 
its  amount  without  undue  occupation  of  space,  the  gray  matter  is  vari- 
ously infolded  so  as  to  form  the  cerebral  convolutions. 


620  HANDBOOK   OF  PHYSIOLOGY. 

The  cortical  gray  matter  of  the  cerebral  cortex  has  an  average 
thickness  of  ahont  ^  inch  (3  mm.),  beiug  thin  in  the  occipital  lobe,  -^ 
inch  (2  mm.),  and  thick  in  the  pre-central,  \  inch  (4  mm.).  The  cells 
of  "which  the  substance  is  composed  are  of  diflereut  kinds:  (a)  The 
apical  process  is  very  long  and  reaches  np  often  nearly  to  the  surface. 
It  gives  off  lateral  branches,  and  is  studded  along  its  course  "with  little 
projections  called  gemmules.  This  process  is  a  protoplasmic  process  or 
dendrite;  the  cell  has  other  dendrites  given  off  from  the  angles  of  the 
body  of  the  cell.  It  always  has  an  axis-cylinder  process  or  neuraxon 
"which  passes  off  usually  from  about  the  middle  of  the  base.  There  are, 
besides  these  large  pyramidal  cells,  others  practically  of  the  same  shape 
and  structure  but  smaller.     They  are  the  small  pyramidal  cells. 

(Z>)  In  the  superficial  layer  of  the  cortex  there  is  a  peculiar  type  of 
cell,  first  described  by  Cajal.  Most  of  these  bodies  are  fusiform  in  shape, 
"with  the  long  axis  parallel  to  the  surface  of  the  convolution.  They  give 
off  usually  two  neuraxons  which  run  along  parallel  to  the  surface  and 
send  down  numerous  fine  collaterals  at  right  angles.  Another  form  of 
Cajal  cell,  triangular  or  quadrangular  in  shape,  is  also  seen.  Both 
forms  have,  as  a  rule,  more  than  one  neuraxon.  Their  collaterals  pass 
in  a  horizontal  direction,  forming  a  fine  band  of  fibres,  known  as  tan- 
gential -fihres. 

(c)  A  third  type  of  cell  is  the  fusiform  ov  ^JoIyjnoiyJious.  Some  of 
these  are  strictly  fusiform  in  shape  and  lie  with  their  axis  parallel  to  the 
surface  of  the  convolution.  They  give  off  protoplasmic  processes  which 
pass  down  toward  the  white  matter,  some  of  them  turning  to  run  in  a 
horizontal  direction.  The  fusiform  and  ]3olymorphous  cells  are  grouped 
in  the  same  layer,  and  are,  therefore,  described  together. 

(cI)  Besides  these  cells  we  find  scattered  through  the  cortex  a  consid- 
erable number  of  the  neuroglia-cells.  The  character  and  position  of 
these  are  shown  in  fig.  373. 

The  general  arrangement  of  the  layers  of  the  cortex  is  described  very 
differently  by  different  authors,  and  it  differs  in  different  parts  of  the 
brain.  The  simplest  and  most  rejiresentative  type,  however  of  the  ar- 
rangement is  that  in  which  the  cortex  is  divided  into  four  layers.  The 
outermost,  or  superficial,  known  as  the  molecular  layer,  contains  rela- 
tively few  cells.  It  is  composed  of  neuroglia  tissue,  embedded  in  which 
are  a  number  of  cells  of  the  Cajal  type,  which  have  just  been  described. 
There  are  also  in  this  layer  many  neuroglia-cells.  In  the  superficial  part 
of  the  layer  of  some  areas  of  the  cortex  are  many  tangential  fibres.  The 
second  layer  is  composed  of  small  pyramidal  cells.  In  parts  of  the  brain 
there  are  here  interposed  what  are  known  as  the  vertical  fusiform  cells. 
The  third  layer  is  composed  of  large  pyramidal  cells,  in. which,  however, 
one  sees  many  small  pyramids  also.  The  fourth  layer  is  composed  of  the 
fusiform  and  polymorphous  cells,  and  beneath  this  is  the  white  sub- 


THE    NERYOrS    SYSTEM. 


621 


stance.  This  arrangement  is  shown  in  the  accomioanying  figures  (373 
and  373a).  The  gra}-- matter  of  the  brain  contains,  however,  not  only 
these  layers  and  cells,  but  an  infinitely  rich  mass  of  fibres,  which  can  be 
shown  by  yarious  stains  to  have  a  certain  definite  arrangement.  Some 
of  the  fibres  aro  vertical  in  direction,  passing  directly  np  to  the  most 
superficial  layers  of  cells;  others  have  a  horizontal  direction,  dividing 


Fig.  373. — The  principal  constituent  elements  of  the  gray  cortical  layer  of  the  anterior 
cerebrum.    (Afier  Ramon  y  Cajal.) 


the  gray  matter  into  dilTercnt  layers.  These  layers  of  fibres  have  re- 
ceived different  names.  They  vary  somewhat  in  accordance  with  the 
area  of  the  cortex  examined.  A  typical  arrangement  is  shown  in  fig. 
374.     The  most  conspicuous  aro  certain   large  triangular  or  pyramidal 


^22 


HANDBOOK   OF   PHYSIOLOGY. 


fi 


JLlj 


^-A 


(4 


n 


^^i 


SL 


Tangential  fibres. 


Striae  of  Bechterew  and  de 
Kaes. 


Superradiaiy  network  (of  the 
)      second  and  third  layers). 


/ 


Striae  of  Baillarger. 


\      Interradiary  network  (of  the 
^        third  and  fourth  layers). 


Meynert's  intracortical 
association  fibres. 


Subcortical  association 
fibres. 


y73A. 


Fig.  374. 


Fig.  873a. — Schematic  diagram  of  the  different  layers  of  the  cerebral  cortex.  (After  Ramon  y 
Oajal,  1890.  ~)  The  tangential  fibres,  Vicqd'Azyr's  ribbon,  Baillargers  internal  and  external  striae, 
and  the  white  substance  are  stained  red ;  M,  molecular  layer;  pPij.  layer  of  small  pyramidal  cells; 
gPy,  layer  of  large  pyramidal  cells;  Pm,  layer  of  polymorphous  cells. 

Fig.  374.— Schematic  diagram  sliowing  the  arrangement  of  the  nerve  fibres  in  the  cerebral 
■cortex.    The  dotted  lines  separate  the  four  cellular  layers  of  Cajal.    Sb,  white  substance. 


THE   NERVOUS   SYSTEM. 


623 


cells,  granular  or  fibrillated,  with  large  aud  distinct  nuclei,  arranged 
with  their  apices  toward  the  surface. 

Chemical  Compositmi. — The  chemistry  of  nerves  and  nerve-cells  has 
been  chiefly  studied  in  the  brain  and  spinal  cord.  Nerve  matter  con- 
tains several  albuminous  and  fatty  bodies  (cerebrin,  lecithin,  and  some 
others),  also  fat  matter  which  can  be  extracted  by  ether  (including  cho- 
lesterin)  and  various  salts,  especially  Potassium  and  Magnesium  phos- 
phates, which  exist  in  larger  quantity  than  those  of  Sodium  and  Calcium. 

Arrangement  of  the  parts  of  the  cerebrum. — The  great  relative  and 
absolute  size  of  the  Cerebral  hemispheres  in  the  adult  man,  masks  to  a 


Fig.  375.— Diagrammatic  horizontal  section  of  a  vertebrate  brain.  The  figures  serve  both 
for  this  and  the  next  diagram.  Mb,  mid-brain:  what  lies  in  front  of  this  is  the  fore-,  and  what 
lies  behind,  the  hin<l-braiu;  Lt,  lamina  terminalis;  Olf,  olfactory  lobes:  Hmp,  hemispheres; 
Th.  E.  thalanienieiiliahin;  Pn.  pineal  gland;  Py,  pituitary  bodj' ;  F.M.  foramen  of  Munro;  cs, 
corpus  striatum :  77i,  optic  thalamus;  CC\  crura  cerebri :  t"he  mass  lying  above  the  canal  rep- 
resents the  corjiora  quaih-igemina;  C6,  cerebellum;  I— IX,  the  nine  pairs  of  cranial  nerves;  1, 
olfactory  ventricle;  ~',  lateral  ventricle;  3,  third  ventricle;  4,  fourth  ventricle;  +,  iter  a  tertio 
ad  quartum  ventriculum.     (Huxley.) 


great  extent  the  real  arrangement  of  the  several  parts  of  the  brain,  which 
is  illustrated  in  the  two  accompanying  diagrams  (figs.  375,  376). 

From  these  it  is  apparent  that  the  parts  of  the  brain  are  disposed  in 
Hi  linear  series,  as  follows  (from  before  backward) :  olfactory  lobes,  cere- 


624 


HAJTDBOOK    OF    PHYSIOLOGY. 


bral  hemispheres,  optic  thalami,  and  third  ventricle,  corpora  quadri- 
gemina,  or  optic  lobes,  cerebellum, medulla  oblongata. 

This  linear  arrangement  of  parts  actually  occurs  in  the  human  foetus ;. 
and  it  is  jDermanent  in  some  of  the  lower  Vertebrata,  e.g.^  Fishes,  in 
which  the  cerebral  hemispheres  are  represented  by  a  pair  of  ganglia 
intervening  between  the  olfactory  and  the  optic  lobes,  and  considerably 
smaller  than  the  latter.  In  Amphibia  the  cerebral  lobes  are  f  urthei 
developed,  and  are  larger  than  any  of  the  other  ganglia. 

In  reptiles  and  birds  the  cerebral  ganglia  attain  a  still  further  devel- 
opment, and  in  mammalia  the  cerebral  hemispheres  exceed  in  weight 
all  the  rest  of  the  brain.  As  we  ascend  the  scale,  the  relative  size  of  the 
cerebrum  increases,  till  in  the  higher  apes  and  man  the  hemispheres, 
which  commenced  as  two  little  lateral  buds  from  the  anterior  cerebral 
vesicle,  have  grown  upward  and  backward,  completely  covering  in  and 
hiding  from  view  all  the  rest  of  the  brain.     At  the  same  time  the  smooth 


Fig.  376.  — Longitudinal  and  vertical  diagrammatic  section  of  a  vertebrate  brain.  Letters 
as  before.  Lamina  terminalis  is  represented  by  the  strong  black  line  joining  Pn  and  Py. 
(Huxley,  j 

surface  of  the  brain,  in  many  lower  mammalia,  such  as  the  rabbit,  is 
replaced  by  the  labyrinth  of  convolutions  of  the  human  brain. 

Weight  of  the  Brain. — The  brain  of  an  adult  man  weighs  from  48  to  50  oz. — 
or  about  3  lbs.  (about  1550  gi-ms. ) .  It  exceeds  in  absolute  weight  that  of  all  the 
lower  animals  except  the  elephant  and  whale.  Its  weight,  relatively  to  that  of 
the  body,  is  only  exceeded  by  that  of  a  few  small  birds,  and  some  of  the 
smaller  monkeys.     In  the  adult  man  it  ranges  from  -^q — -V  of  the  body  weight. 

Variations.  Age. — In  a  new-born  child  the  brain  (weighing  10  to  14  oz. )  is 
■^^  of  the  body  weight.  At  the  age  of  7  years  the  weight  of  the  brain  already 
averages  40  oz. ,  and  about  14  years  the  brain  not  infrequently  reaches  the 
weight  of  48  oz.  Beyond  the  age  of  forty  years  the  weight  slowly  but  steadily 
declines  at  the  rate  of  about  1  oz.  in  10  years. 

Sex. — The  average  weight  of  the  female  brain  is  less  than  the  male  :  and  this 
difference  persists  from  birth  throughout  life.  In  the  adult  it  amounts  to 
about  5  oz.     Thus  the  average  weight  of  an  adult  woman's  brain  is  about  44  oz. 

Intelligence. — The  brains  of  idiots  are  generally  much  below  the  average, 
some  weighing  less  than  16  oz.  Still  the  facts  at  present  collected  do  not  war- 
rant more  than  a  very  general  statement,  to  which  there  are  numerous  excep- 
tions, that  the  brain  weight  corresponds  to  some  extent  with  the  degree  of 
intelligence.     There  can  be  little  doubt  that  the  complexity  and  depth  of  the 


THE   XEKVOUS   SYSTEM. 


625 


convolutions,  which  indicate  the  area  of  the  gray  matter  of  the  cortex,  corre- 
spond with  the  degree  of  intelligence. 

Weight  of  the  Spinal  Cord. — Tlie  spinal  cord  of  man  weighs  from  1 — 1^  oz.  ; 
its  weight  relatively  to  the  brain  is  about  1  :  36.  As  we  descend  the  scale, 
this  ratio  constantly  increases  till  in  the  mouse  it  is  1  :  4.  In  cold-blooded 
animals  the  relation  is  reversed,  the  spinal  cord  is  the  heavier  and  the  more 
important  organ.     In  the  newt,  2:1;    and  in  the  lamprey,  75  :  1. 

Distinctive  Characters  of  the  Human  Brain. — The  following  characters  dis- 
tinguisli  the  brain  of  man  and  apes  from  tliose  of  all  other  animals,  (a.)  The 
rudimentary  condition  of  the  olfactorj^  lobes.  (6.)  A  perfectly  defined  fissure 
of  Sylvius,  (e.)  A  posterior  lobe  completely  covering  the  cerebellum,  (d.) 
The  presence  of  posterior  comua  in  the  lateral  ventricles. 

The  most  distinctive  points  in  the  human  brain,  as  contrasted  with  that  of 
apes,  are: — (1.)  The  much  greater  size  and  weight  of  the  whole  brain.  The 
brain  of  a  full-grown  gorilla  weighs  only  about  15  oz.  (450  grms.),  which  is 
less  than  J  the  weight  of  the  human  adult  male  brain,  and  barely  exceeds  that 
of  the  human  infant  at  birth.  (2.)  The  inuch  greater  complexity  of  the  con- 
volutions, especially  the  existence  in  the  human  brain  of  tertiary  convolutions 


yo.  * 


Fig.  377.— Brain  of  the  Orang,  %  natural  size,  showing  the  arrangement  of  the  convolutions. 
9y,  fissure  of  Sylvius;  R,  fissure  of  Rolando;  E P,  ext<?rnal  perpendicular  fissure;  07/,  olfactory 
lobe;  C6,  cprehplluni ;  PV.  pons  Varolii;  3/ O,  medulla  oblongata.  As  contrasted  with  the 
human  brain,  tlu'  fnmtal  lobe  is  short  and  small  relatively,  the  fissure  of  Sylvius  is  oblique, 
the  temporo-splu'iKiulal  lobe  very  prominent,  and  the  external  perpendicular"  fissure  very  well 
marked.     (.Gratiolet.; 

in  the  sides  of  the  fissures.  (3. )  The  greater  relative  size  and  complexitj',  and 
the  blunted  quadrangular  contour  of  the  frontal  lobes  in  man,  which  are 
relatively  both  broader,  longer,  and  higher,  than  in  apes.  In  apes  the  frontal 
lobes  project  keel -like  (rosti'um)  between  the  olfactory  bulbs.  (4.)  The  much 
greater  prominence  of  the  temporo-sphenoidal  lobes  in  apes.  (5.)  The  fissm-e 
of  Sylvius  is  nearly  horizontal  in  man,  while  in  apes  it  slants  considerably  up- 
ward. (6.)  The  distinctness  of  the  external  perpendicular  fissure,  which  in 
apes  is  a  well-defined  almost  vertical  "slash,"  while  in  man  it  is  almost 
obscured  by  the  annectent  gyri. 

Most  of  the  above  points  are  shown  in  the  accompanying  figure  of  the  brain 

of  the  Orang. 

40 


636 


HANDBOOK    OF    PHYSIOLOGY. 


The  Motor  areas  of  the  Cerebral  Cortex. 

The  experiments  upon  the  brains  of  various  animals  by  means  of 
electrical    stimulation    have  demonstrated  that    there   are   definite  re- 


Fig.  378. 


Figs.  378  and  379. — Brain  of  dog,  viewed  from  above  and  in  profile.  F,  frontal  fissure  some- 
times termed  crucial  sulcus,  corresponding  to  the  fissure  of  Rolando  in  man.  S,  fissure  of 
Sylvius,  around  which  the  foiu'  longitudinal  convolutions  are  concentricallj'  arranged;  1,  flexion 
of  head  on  the  neck,  in  the  median  line;  2,  flexion  of  head  on  the  neck,  with  rotation  toward 
the  side  of  the  .stimulus ;  3,  4,  flexion  and  extension  of  anterior  limb ;  .5,  6,  flexion  and  extension 
of  posterior  limb;  7,  8,  9,  contraction  of  orbicularis  oculi,  and  the  facial  nnuscles  in  general. 
The  unshaded  part  is  that  exposed  by  opening  the  skull.     (Dalton.) 


gions  of  the  cerebral  cortex  the  stimulation  of  which  produces  definite 
movements  of  co-ordinated  groups  of  muscle  of  the  opposite  side  of 
the  body.     Fritsch  and  Ilitzig  were   the  first  to  .show  that  the  cere- 


THE    NERVOUS    SYSTEM.  '  (527 

bral  cortex  responded  to  electric  irritation.  They  employed  a  weak  con- 
stant current  in  their  experiments,  applying  a  pair  of  fine  electrodes  not 
more  than  -^^  in.  apart  to  different  parts  of  the  cerebral  cortex.  The 
results  thus  obtained  have  been  confirmed  and  extended  by  Ferrier  and 
many  others,  chiefly  with  induction  currents. 

The  fundamental  phenomena  observed  in  all  these  cases  may  be  thus 
epitomized : — 

(1).  Excitation  of  the  same  spot  is  always  followed  by  the  same 
movement  in  the  same  animal.  (2).  The  area  of  excitability  for  any 
given  movement  is  extremely  small,  and  admits  of  very  accurate  defini- 
tion. (3).  In  different  animals  excitations  of  anatomically  corresponding 
si)ots  produce  similar  or  corresponding  results. 

The  various  definite  movements  resulting  from  the  electric  stimulation 
of  circumscribed  areas  of  the  cerebral  cortex,  are  enumerated  in  the  de- 
scription of  the  accompanying  figures  of  the  dog  and  monkey's  brain. 

In  the  case  of  the  dog,  the  results  obtained  are  summed  up  as  fol- 
lows, by  Hitzig: — 

[a.)  One  portion  (anterior)  of  the  convexity  of  the  cerebrum  is 
motor;  another  portion  (posterior)  is  non-motor,  [h.)  Electric  stimu- 
lation of  the  motor  portion  produces  co-ordinated  muscular  contraction 
on  the  opposite  side  of  the  body.  (c. )  With  very  weak  currents,  the 
contractions  produced  are  distinctly  limited  to  particular  groups  of 
muscles;  with  stronger  currents  the  stimulus  is  communicated  to  other 
muscles  of  the  same  or  neighboring  parts.  {(I.)  The  portions  of  the 
brain  intervening  between  these  motor  centres  are  in  excitable  by  similar 
means. 

Motorial  area  of  the  Monl-eifs  Brain.  — According  to  the  observations 
of  Ferrier,  confirmed  and  extended  by  later  experimenters,  stimulation 
of  various  parts  of  the  monkey's  brain,  as  indicated  by  the  numbers  in 
figs.  380,  381,  produces  movements  of  definite  muscles,  thus: — 

Stimulation  of  the  district  marked  1,  causes  movement  of  hind 
foot:  of  2,  chiefly  adduction  of  the  foot;  of  3,  movements  of  hind  foot 
and  tail;  of  4,  of  latissimus  dorsi ;  of  5,  extension  forward  of  arm;  a, 
i,  c,  d,  movements  of  hand  and  wrist;  of  G,  suj^ination  and  flexion  of 
forearm ;  of  7,  elevation  of  the  upper  lip ;  of  8,  conjoint  action  of  eleva- 
tion of  upper  lip  and  depression  of  lower;  of  9,  opening  of  mouth  and 
protrusion  of  tongue;  of  10,  retraction  of  tongue;  of  11,  action  of 
platysma;  of  12,  elevation  of  eyebrows  and  eyelids,  dilatation  of  pupils, 
and  turning  head  to  opposite  side;  of  13,  eyes  directed  to  opposite  side 
and  upward,  Avith  usually  contraction  of  the  pupils;  of  13',  similar 
action,  but  eyes  usually  directed  downward;  of  14,  retraction  of  oppo- 
site ear,  head  turns  to  the  opposite  side,  the  eyes  widely  opened,  and 
pupils  dilated;  of  15,  stimulation  of  this  region,  which  corresponds  to 


628 


HAKDBOOK    OF    PHYSIOLOGY. 


the  tip  of  the  uncinate  convohitiou,  causes  torsion  of  the  hp  and  nostril 
oi  the  same  side. 

It  is  thus  seen  that  the  motor  areas  chiefly  correspond  with  the 
ascending  frontal  and  ascending  parietal  convolutions,  and  that  the 
movements  of  the  leg  are  represented  at  the  upper  part  of  these  con- 
volutions, then  follow  from  above  downward  the  centres  for  the  arms, 
the  face,  the  lips,  and  the  tongue. 

According  to  the  further  researches  of  Schafer  and  Horsley,  electrical 
stimulation  of  the  marginal  convolution  internally  at  the  i^arts  corre- 
sponding with  the  ascending   frontal  and  parietal   convolutions,   from 


Fig.  380.  Fig.  381. 

Figs.  380  and  381. —Diagrams  of  monkey's  brain  to  show  the  effects  of  electric  stimulation  of  cer- 
tain spots.     (According  to  Ferrier.) 

before  backward,  produces  movements  of  the  arm,  of  the  trunk,  and 
of  the  leg. 

A  good  deal  of  doubt  was  thrown  upon  the  experiments  of  Ferrier 
by  Goltz  and  other  observers,  from  the  results  of  excising  the  so-called 
motor  areas  of  the  dog's  brain.  It  was  found  that  the  part  might  be 
sliced  away  or  washed  away  with  a  stream  of  water,  but  that  no  perma- 
nent paralysis  ensued. 

More  extensive  observations  however,  have  confirmed  Ferrier 's  original 
statement,  at  any  rate  with  regard  to  the  monkey's  brain.  Destruction 
of  the  motor  areas  for  the  arm  produces  at  any  rate  some  permanent 
paralysis  of  the  arm  of  the  opposite  side,  and  similarly  of  that  for  the 
leg,  paralysis  of  the  opposite  leg.  If  both  areas  are  destroyed  permanent 
hemiplegia  ensues.     Paralysis  of  so  extensive  and  permanent  character 


THE    XEiiVOL'S    SYSTEM. 


629 


does  not,  however,  appear  the  rule  when  the  brain  of  a  dog  is  used 
instead  of  that  of  the  monkey.  It  is  suggested  that  in  the  animal  lower 
in  the  scale,  the  functions  which  in  the  monkey  are  discharged  by  the 
cortical  centres  may  be  subserved  by  the  basal  ganglia. 

Motorial  Areas  of  the  Human  Brain. — It  is  naturally  of  great  impor- 
tance to  discover  how  far  the  result  of  experiments  upon  the  dog  and 
monkey  hold  good  with  regard  to  the  human  brain.  Evidence  furnished 
by  diseased  conditions  is  not  wanting  to  support  the  general  idea  of  the 
existence  of  cortical  motorial  centres  in  the  human  brain  (fig.  382). 


Fig.  382.— The  Cortical  Centres.     (Daua.) 

So  far,  however,  it  has  been  possible  to  localize  motor  functions  in 
the  frontal  and  ascending  parietal  convolutions  only,  to  the  convolutions 
which  bound  the  fissure  of  Rolando,  and  to  those  on  the  inner  side  of 
the  hemispheres  which  correspond  thereto,  and  possibly  to  the  frontal 
lobe  in  front  of  the  ascending  convolution. 

The  position  of  the  centres  is  probably  much  the  same  as  in  the  mon- 
key's brain — those  for  the  leg  above,  those  for  the  arm,  face,  lips,  and 
tongue  from  above  downward.  Destruction  of  these  parts  causes  pa- 
ralysis, corresponding  to  the  district  aflfected,  and  irritation  causes  con- 
vulsions of  the  muscles  of  the  same  part.  Again,  a  number  of  cases 
are  on  record  in  which  aphasia.,  or  the  loss  of  power  of  expressing  ideas 
in  words,  lias  been  associated  with  disease  of  the  posterior  part  of  the 
lower  or  third  frontal  convolution  on  the  left  side.  This  condition  ia 
usually  associated  with  paralysis  of  the  right  side  (right  hemiplegia)."' 

This  district  of  the  brain  is  now  generally  known  as  the  motor  area; 
und  there  seems  no  doubt  whatever  that  from  this  area  pass  the  nerve- 


630 


HANDBOOK    OF    PHYSIOLOGY. 


fibres  which  proceed  to  the  spinal  cord,  and  are  there  represented  as 
the  pyramidal  tracts. 

This  is  the  reason,  no  doubt,  that  movements  are  produced  on  stimu- 
lation of  the  white  matter  after  the  superficial  gray  matter  of  the 
animal's  brain  has  been  sliced  off. 

Motor  tracts  in  the  brain. — These  motor  fibres  are  connected  with  the 
pyramidal  cells  of  the  cortex,  and  are  indeed  their  continuations. 

It  will  be  necessary,  therefore,  to  trace  them  from  the  cortex  down- 
ward.    From  the  motor  area  of  the  cortex  they  converge  to  the  inter- 


Fig.  383. —Diagram  to  show  the  connecting  of  the  Frontal  Occipital  Lobes  with  the  Cere- 
bellum, etc.  The  dotted  lines  passing  in  the  crusta  (too),  outside  the  motor  fibres,  indicate  the 
connection  between  the  temporo-occipital  lobe  and  the  cerebellum,  f.  c.  ,  the  f ronto-cerebellar 
fibres,  which  pass  internally  to  the  motor  tract  in  the  crusta ;  i.  f.  ,  fibres  from  the  caudate 
nucleus  to  the  pons,  fb.,  frontal  lobe;  Oc,  occipital  lobe;  af.,  ascending  frontal;  ap.,  ascend- 
ing parietal  convolutions;  pcf.,  precentral  fissure  in  front  of  the  ascending  frontal  convolution; 
FR. ,  fissure  of  Rolando ;  iff.  ,  interparietal  fissure,  a  section  of  crus  is  lettered  on  the  left  side. 
SN. ,  substantia  nigra;  py. ,  pyramidal  motor  fibre,  which  on  the  right  is  shown  as  continuous 
lines  converging  to  pass  tlarough  the  posterior  limb  of  ic.  internal  capsule  (the  knee  or  elbow 
of  which  is  shown  thus  *)  upward  into  the  hemisphere  and  downward  through  the  pons  to  cross 
at  tiie  medulla  in  tlie  anterior  pyramids.     (Gowers.) 


nal  capsules,  and  pass  down  to  the  crusta  of  the  crus  in  the  way  already 
indicated. 

In  the  internal  capsule  the  fibres  which  pass  onward  and  downward 
to  the  pyramidal  tracts  of  the  spinal  cord  do  not  occupy  more  than  a 
small  section,  namely,  that  part  known  as  the  knee,  and  the  anterior 
two-thirds  of  the  posterior  segment  (fig.  384).  In  this  district  the 
fibres  for  the  face,  arm,  and  leg,  are  in  this  relation:  those  for  the  face 
and  tongue  are  just  at  the  knee,  and  below  or  behind  them  come  first 
the  fibres  for  the  arm  and  then  those  for  the  leg. 

The  more  accurate  arrangement  of  these  fibres  in  the  monkey's  brain 
from  above  down  are  those  for  the  eye,  head,  tongue,  mouth,  shoulder, 


THE    XERYOUS    SYSTEM. 


G31 


elbow,  digits,  abdomen,  li}!,  knee,  digits.  These  fibres  come  for  the 
most  part  from  the  part  of  tlie  cortex  on  either  side  of  the  fissure  of 
Rolando,  hence  called  the  7?nh/)uJir  area  on  either  side.     But  the  areas 


Fig.  384. — Diagram  to  show  the  relative  po.sitious  of  the  several  motor  tracts  in  their  course 
from  the  cortex  to  the  crus.  The  section  through  the  convolution  is  vertical ;  that  through  the 
internal  capsule,  I,  C,  horizontal ;  that  through  the  crus  again  vertical.  C,  N,  caudate  nucleus ; 
O,  TH,  optic  thalamus;  L2  and  L.3,  middle  and  outer  part  of  lenticular  nucleus:  /.  a.  I.  face, 
arm,  and  leg  fibres.    The  words  in  italic  indicate  corre.si)onding  cortical  centres.     (Gowers.) 

for  the  head  and  eyes  lie  more  anterior  in  the  frontal  lobe,  to  the  front 
of  the  precentral  sulcus,  that  for  the  head  above  that  for  the  e3''es,  and 
an  area  for  the  trunk  (not  indicated  in  the  fig.  383),  is  situated  more 
toward  the  middle  line  of  the  hemisphere,  internal  to  that  for  the  leg. 

But  there  are  other  fibres  which  are  arranged  in  front  of  the 
pyramidal  fibres  in  tlie  front  limb  of  the  capsule,  as  well  as  others  behind 
them  in  the  hind  limb  of  the  capsule.  Those  in  front  are  from  the 
anterior  ])art  of  the  frontal  lobe,  and  these  in  passing  into  the  crus  are 
found  on  the  median  side  of  the  pyramidal  fibres  (fig.  383).  They 
appear  to  end  in  the  gray  matter  of  the  pons,  and  there  to  be  connected 
with  fibres  from  the  middle  peduncle  of  the  opposite  side  of  the  cere- 
bellum. Those  behind  the  pyramidal  fibres  in  the  hind  limb  of  the  cap- 
sule are  from  the  te»)j)oraI-occipital  lobe.  These  fibres  pass  into  the  crus 
to  the  outer  side  of  the  pyramidal  fibres  (fig.  383),  they  probably  also 
end  in  the  gray  matter  in  the  same  way.  There  are  other  fibres  from  the 
corpus  striatum,  from  both  nuclei,  but  particularly  from  the  caudate 
nucleus,  which  pass  to  the  crus,  and  are  situated  between  the  pyramidal 
tract  and  the  locus  niger  (fig.  383),  some  of  which  terminate  in  that 
nucleus,  while  others  terminate  in  the  ])ons.  Besides  the  above  fibres, 
all  of  which  are  believed  to  be  efferent  fibres,  and  are  at  any  rate  fibres 
of  descending  degeneration,  there  are  fibres  which  pass  from  the  cortex 
to  the  optic  thalamus  and  tegmentum,  fibres  of  ascending  degeneration 


632 


HANDBOOK    OF    PHYSIOLOGY. 


found  in  the  internal  capsule,  viz. ,  those  from  the  frontal  lobes  are 
situated  at  the  extreme  tip  of  the  front  limb,  in  front  of  the  motor  fibres 
from  the  same  district,  and  others  from  the  temporal-occipital  district 
converge  to  the  posterior  part  of  the  hind  limb.  Those  passing  between 
the  occipital  lobe  and  the  optic  thalamus  are  believed  to  be  concerned 
with  vision,  and  are  called  fibres  of  the  ojjHc  radiation. 

It  may  be  as  well  to  mention  here  that  some  other  fibres  from  the 
temporo-occipital  lobe  pass  into  the  optic  thalamus,  without  forming  a 
part  of  the  internal  capsule. 

The  optic  thalamus  then  receives  fibres  from  nearly  all  parts  of  the 
cerebral  cortex,  some  of  which  are  not  found  in  the  internal  capsule. 
The  tegmentum,  the  afferent  or  sensory  tract  of  the  crus  to  a  great  ex- 
tent ends  in  the  optic  thalamus,  and  is,  therefore,  connected  through  it 
with  nearly  all  parts  of  the  cortex,  indirectly.  It  is  also  more  directly 
connected  with  cortex  [a)  by  fibres  of  the  optic  radiation  which  do  not 
go  to  the  optic  thalamus,  {b)  by  fibres  from  the  frontal  and  parietal 
lobes,  which  pass  through  the  lenticular  nucleus,  and  (c)  by  fibres  from 
both  the  lenticular  and  caudate  nuclei  of  the  corpus  striatum. 

In  the  tegmentum  the  longitudinal  fibres  may  be  thus  enumerated : — 

{a. )  The  fillet,  which  consists  of  fibres  from  the  sensory  decussation  of 


T/lzr 


Fig.  385.— Vertical  section  through  the  cerebrum  and  basic  ganglia  to  show  the  relations  of 
the  latter,  co,  cerebral  convolutions ;  c,c,  corpus  callosum;  v.  I.,  lateral  ventricle;  y,  fornix; 
vlIL,  third  ventricle;  n.c,  caudate  nucleus;  th,  optic  thalamus;  n.l.,  lenticular  nucleus;  c.i. , 
internal  capsule;  c.l.,  claustrum;  c.e.,  external  capsule;  m,  corpus  mammillare;  t.o.,  optic 
tract;  s.t.t.,  stria  terminalis ;  n.a.,  nucleus  amygdalae ;  cm,  soft  commissure.     (Schwalbe.) 

the  bulb,  which  becomes  longitudinal  in  the  inter-olivary  region,  and  in 
its  course  upward,  from  masses  of  gray  matter,  such  as  the  superior 
olive;  it  divides  into  two  bundles,  (i.)  Lateral,  ends  in  gray  matter 
of  posterior  corpus  quadrigeminum  and  in  white  matter  beneath  the 
anterior,  and  (ii.)  median,  ends  in  anterior  corpus  quadrigeminum  and 


THE   XERVOUS   SYSTEM.  633 

in  the  corpus  subtlialamicum,  thence  to  the  optic  thalamus  and  the  cere- 
bral cortex. 

(b.)  Posterior  longihcdinal  bundles. — A  bundle  of  fibres  which  appear 
to  begin  the  bulb  as  certain  fibres  of  the  anterior  column  of  the  cord, 
which  are  the  short  longitudinal  commissures  between  segments  of  the 
cord.  It  is  traceable  upward  as  far  as  the  nucleus  of  the  third  nerve. 
It  is  supposed  to  connect  the  nuclei  of  the  fourth  and  sixth  nerves  with 
the  third,  and  with  the  anterior  corpus  quadrigemiuum. 

(c.)  Superior  peduncle  of  the  cerebellum. — This  arises  on  either  side 
from  the  superficial  gray  matter,  but  chiefly  from  the  corpus  dentatum, 
and  passes  forward  outward  beneath  the  posterior  corpus  quadrigeminum, 
and  beneath  it  and  the  anterior  corpus  quadrigeminum  decussates  with 
its  fellow;  the  fibres  then  pass  forward  in  the  anterior  district  of  the 
tegmentum  and  end  in  the  red  nucleus. 

{d.)  Fibres  from  the  corpora  quadrigemina. — From  each  corpus  quad- 
rigeminum passes  forward  and  downward  a  tract  called  the  brachium. 
The  anterior  brachium  goes  to  the  lateral  corpus  geniculatum,  and  then 
to  the  optic  tract,  other  fibres  pass  into  the  tegmentum,  and  thence 
directly  to  the  occipital  cortex.  The  posterior  brachium  goes  to  the 
median  corpus  geniculatum,  thence  to  the  tegmentum,  and  through  it 
possibly  to  the  temporal  region  of  the  cerebral  cortex. 

Commissural  fibres. — In  addition  to  the  fibres  of  the  corpus  callosum, 
which  connect  all  parts  of  the  hemispheres,  and  fornix,  there  are  three 
other  commissures,  the  anterior  white  commissure,  and  the  posterior 
white  commissure  in  the  third  ventricle  connect  by  white  fibres  the  two 
sides  of  the  brain.  The  fibres  in  the  anterior  come  from  the  temporo- 
sphenoidal  convolution  chiefly,  but  a  few  are  part  of  the  olfactory  tract. 
The  posterior  connects  the  optic  thalami  and  tegmenta.  The  middle 
is  chiefly  composed  of  gray  matter,  but  also  contains  some  transverse 
fibres. 

Functions  of  the  Cerebrum. 

Speaking  in  the  most  general  way,  and  for  the  present  omitting 
the  accumulating  evidence  in  favor  of  the  direct  representation  of  the 
various  co-ordinated  movements  of  the  muscles  of  the  body  in  ganglia 
situated  in  diiferent  parts  of  the  cerebral  cortex,  it  may  be  said  that : — 
(1.)  The  cerebral  hemispheres  are  the  organs  by  which  are  perceived 
those  clear  and  more  impressive  sensations  which  can  be  retained,  and 
regarding  which  we  can  judge.  (2.)  The  cerebrum  is  the  organ  of  the 
will,  in  so  far  at  least  as  each  act  of  the  w'ill  requires  a  deliberate,  how- 
ever quick  determination.  (3.)  It  is  the  means  of  retaining  impressions 
of  sensible  things,  and  reproducing  them  in  subjective  sensations  and 
ideas.     (4.)  It  is  the  medium  of  all  the  higher  emotions  and  feelings,  and 


634  HANDBOOK    OF    PHYSIOLOGY. 

of  the  faculties  of  judgment,  understanding,  memory,  reflection,  induc- 
tion, imagination  and  the  like. 

Evidence  regarding  the  physiology  of  the  cerebral  hemispheres,  has 
been  obtained,  as  in  the  case  of  other  parts  of  the  nervous  system,  from 
the  study  of  Comparative  Anatomy,  from  Pathology,  and  from  Experi- 
ments on  the  lower  animals.  The  chief  evidences  regarding  the  func- 
tions of  the  cerebral  hemispheres  derived  from  these  various  sources,  are 
briefly  these: — 1.  Any  severe  injury  of  them,  such  as  a  general  concus- 
sion, or  sudden  pressure  by  apoplexy,  may  instantly  deprive  a  man  of  all 
power  of  manifesting  externally  any  mental  faculty.  2.  In  the  same 
general  proportion  as  the  higher  mental  faculties  are  developed  in  the 
Vertebrate  animals,  and  in  man  at  different  ages  and  in  different  indi- 
viduals, the  more  is  the  size  of  the  cerebral  hemispheres  developed  in 
comparison  with  the  rest  of  the  cerebro-spinal  system.  3.  No  other  part 
of  the  nervous  system  bears  a  corresponding  proportion  to  the  develop- 
ment of  the  mental  faculties.  4.  Congenital  and  other  morbid  defects 
of  the  cerebral  hemisphere  are,  in  general,  accompanied  by  correspond- 
ing deficiency  in  the  range  or  power  of  the  intellectual  faculties  and  the 
higher  instincts.  5.  Eemoval  of  the  cerebral  hemispheres  in  one  of  the 
lower  animals  produces  effects  corresponding  with  what  might  be  antici- 
pated from  the  foregoing  facts. 

Effects  of  the  Removal  of  the  Cereirimi.  — The  removal  of  the  cere- 
brum in  the  lower  animals  appears  to  reduce  them  to  the  condition  <.if  a 
mechanism  without  spontaneity. 

In  the  case  of  the  frog,  when  the  cerebral  lobes  have  been  removed, 
the  animal  appears  similarly  deprived  of  all  power  of  spontaneous  move- 
ment. But  it  sits  up  in  a  natural  attitude,  breathing  quietly;  when 
pricked  it  jumjDS  away;  when  thrown  into  the  water  it  swims;  when 
placed  upon  the  palm  of  the  hand  it  remains  motionless,  although,  if 
the  hand  be  gradually  tilted  over  till  the  frog  is  on  the  point  of  losing 
his  balance,  he  will  crawl  up  till  he  regains  his  equilibrium,  and  comes 
to  be  perched  quite  on  the  edge  of  the  hand.  This  condition  contrasts 
with  that  resulting  from  the  removal  of  the  entire  brain,  leaving  only 
the  spinal  cord ;  in  this  case  only  the  simpler  reflex  actions  can  take 
place.  The  frog  does  not  breathe,  he  lies  flat  on  the  table  instead  of 
sitting  up;  when  thrown  into  a  vessel  of  water  he  sinks  to  the  bottom; 
when  his  legs  are  pinched  he  kicks  out,  bvit  does  not  leap  away. 

A  pigeon  from  which  the  cerebrum  has  been  removed  will  remain 
motionless  and  apparently  unconscious  unless  disturbed.  When  dis- 
turbed in  any  way  it  soon  recovers  its  former  position;  when  thrown 
into  the  air  it  flies. 

In  mammals  it  is  difficult  to  remove  the  cerebral  hemispheres,  but  in 
those  animals  in  which  the  operation  has  been  carried  out,  as  for  example 


THE   NERVOUS   SYSTEM.  035 

in  tlio  rabbit  and  rat,  a  result  very  similar  to  those  observed  in  the  case  of 
the  frog  and  pigeon  has  been  obtained.  The  animal  is  able  to  maintain  its 
equilibrium,  to  run  or  jump,  and  in  fact  carry  out  all  the  most  compli- 
cated co-ordinated  movements,  but  it  is  unable  to  originate  them  without 
stimulation.  In  the  case  of  the  dog,  however,  it  has  been  found  im2_)os- 
sible  to  remove  the  whole  brain,  but  when  it  has  been  removed  piece- 
meal the  animal  may  be  kept  alive  for  some  time,  and  can  carry  out  co- 
ordinated movements  well,  and  even  manifest  intelligence. 

It  is  quite  evident,  therefore,  that  the  apparatus  for  carrying  out  co- 
ordinated movements  is  in  these  animals  not  localized  either  in  the  cere- 
brum or  in  the  spinal  cord,  and  must  therefore  be  connected  in  some 
way  with  the  parts  of  the  brain  below  the  cerebrum  and  above  the 
cord.  There  is  no  reason  Avhysuch  an  arrangement  may  not  be  supposed 
to  exist  in  the  human  brain. 

We  must  look  upon  the  cerebrum,  however,  for  the  orii>iiuitor  of  vol- 
untary movements. 

As  regards  the  theory  of  the  localization  of  different  movements  in 
different  parts  of  the  cerebral  cortex  which  as  we  have  seen  has  received 
so  mucli  sup2)ort  from  observation  on  animals  such  as  the  dog  and  the 
monkey,  at  any  rate,  we  may  say  that  certain  parts  of  the  cerebral  cortex 
appear  to  be  highly  sensitive  to  electrical  stimuli,  particularly  the 
Rolandic  area  and  the  frontal  lobe  in  front  of  it.  Stimulation  of  cer- 
tain other  regions,  viz.,  of  the  occipital  region,  of  the  parietal  and  tem- 
poral region,  and  of  the  gyrus  fornicatus  and  the  frontal  region  in  front 
of  the  motor  area,  does  not  give  rise  to  such  movements.  Such  observa- 
tions as  it  has  been  possible  to  make  on  man  show  that  the  localization 
of  movement  on  the  human  cerebral  cortex  is,  if  anything,  superior 
to  that  observed  in  monkeys.  We  have,  of  course,  but  few  data  upon 
which  to  base  our  conclusion,  except  such  as  have  been  obtained  from 
the  observation  of  the  symptoms  of  disease,  but  with  the  help  of  these 
we  may  assume  that  in  the  cerebral  cortex  the  co-ordinated  movements 
of  the  body  in  some  way  are  represented.  The  cases  which  have  given 
us  most  of  our  knowledge  upon  the  subject  are  those  in  which  haMuorrhages 
have  occurred  in  different  jmrts  of  the  brain,  followed  by  paralysis  of 
the  opposite  side  of  the  body.  These  haemorrhages  chiefly  occur  in 
the  neighborhood  of  the  corpus  striatum.  T'he  paralysis  of  the  extremities 
is  practically  permanent,  although,  as  a  rule,  the  muscles  connected  with 
the  trunk  are  not  jiaralyzed.  This  means  that  some  interruption  has 
taken  place  between  the  cerebral  cortex  and  the  paralyzed  nmscles,  and  if 
the  lesion  is  a  destroying  one, the  connection  is  never  re-established.  In  the 
case  of  the  animals,  such  as  the  dog,  this  is  not  the  case,  as  the  paralysis 
is  tempor;iry.  It  is  supposed  that  in  man  not  only  the  more  highly 
skilled   movements  but  all    voluntary  movements  of    the   inusck\«   are 


636  HAXDBOOK    OF    PHYSIOLOGY. 

actually  represented  in  the  cortical  areas,  and  that  the  pyramidal  tracts 
are  actually  essential  for  voluntary  movements.  If  the  pyramidal 
tracts  be  partially  or  wholly  destroyed,  anywhere  in  their  course,  a 
paralysis  corresponding  with  the  amount  destroyed  invariably  follows. 
In  the  dog  experiments  have  shown  that  this  is  not  the  case,  and  the 
conduction  of  voluntary  impulse  to  muscles  may  take  place,  for  example, 
in  other  parts  of  the  cord  besides  the  pyramidal  tract,  after  hemisection. 

The  pyramidal  tracts  in  man,  however,  must  be  considered  also  as 
the  only  path  connecting  the  cortical  centres  with  the  co-ordinated 
centres  lower  down  in  the  brain,  as,  for  example,  in  the  bulb.  The 
impulses  which  pass  down  from  the  cortex,  whatever  they  may  be,  are 
not  however  of  necessity  connected  with  consciousness,  and  many  volun- 
tary movements  of  a  complicated  nature  may  take  place  really  better  with- 
out consciousness  than  with  it.  This  is  shown  in  such  co-ordinated 
movements  as  writing,  walking,  marching,  and  the  like,  all  of  which  are 
acquired  with  time  and  much  labor,  but  when  once  perfect  in  the 
individual,  can  best  be  performed  without  voluntary  effort.  Such 
movements  must  be  represented  by  impulses  passing  in  the  pyramidal 
tracts,  for  if  they  are  interrupted,  the  movements  are  no  longer  per- 
formed. 

What  actually  originates  a  voluntary  action,  or  one  performed  by 
an  effort  of  the  will,  we  are  unable  to  say.  No  doubt  impulses  from  the 
periphery  conducted  to  the  cerebral  cortex  along  all  kinds  of  afferent 
channels  must  have  something  to  do  with  it;  directly  or  indirectly, 
sooner  or  later.  In  the  human  cortex  it  would  seem  that  the  apparatus 
for  performing  all  manner  of  possible  co-ordinated  movements  which  may 
result  in  speech  or  action,  are  stored.  This  apparatus  is  capable  of 
being  set  in  action  either  in  the  absence  of  consciousness  by  afferent 
stimuli  of  some  kind  directly,  or  by  what  may  be,  indirectly  or  remotely, 
in  some  way  the  result  of  afferent  stimuli,  viz.,  the  will.  It  is  also  prob- 
able that  the  will  of  another  may  take  the  place  of  the  man's  own  will, 
and  may  call  for  the  movements,  actions,  and  speech,  all  of  which  are, 
as  it  were,  ready  to  be  called  forth  by  a  stimulus  of  some  kind.  It  may 
be  supposed  that  the  condition  of  development  of  the  brain  inherited  by 
the  individual  has  something  to  do  both  with  the  potentialities  of  the 
apparatus  for  co-ordinated  acts,  which  he  receives  at  birth,  and  with  the 
way  in  which  the  apparatus  is  set  in  motion. 

Unilateral  Action. — Respecting  the  mode  in  which  the  brain  dis- 
charges its  functions,  there  is  no  evidence  whatever.  But  it  appears 
that,  for  all  but  its  highest  intellectual  acts,  one  of  the  cerebral  hemi- 
spheres is  sufficient.  For  numerous  cases  are  recorded  in  which  no 
mental  defect  was  observed,  although  one  cerebral  hemisphere  was  so 
disorganized  or  atrophied  that  it  could  not  be  supposed  capable  of  dis- 


THE    NERVOUS   SYSTEM.  637 

charging  its  I'uuctious.  The  remaining  hemisphere  was,  in  these  cases, 
adequate  to  the  functions  generally  discharged  by  both;  but  the  mind 
does  not  seem  in  any  of  these  cases  to  have  been  tested  in  very  high 
intellectual  exercises ;  so  that  it  is  not  certain  that  one  hemisphere  will 
suffice  for  these.  In  general,  the  brain  combines,  as  one  sensation,  the 
impressions  which  it  derives  from  one  object  through  both  hemisi^heres, 
and  the  ideas  to  which  the  two  such  impressions  give  rise  are  single.  In 
relation  to  common  sensation  and  the  efforts  of  the  will,  it  must  always 
be  remembered  that  the  impressions  to  and  from  the  hemispheres  of  the' 
brain  are  carried  across  the  middle  line ;  so  that  in  destruction  or  com- 
pression of  either  hemisphere,  whatever  effects  are  produced  in  loss  of 
sensation  or  voluntary  motion,  are  observed  on  the  side  of  the  body 
opposite  to  that  on  which  the  brain  is  injured. 

Sleep. — All  parts  of  the  body  which  are  the  seat  of  active  change  require- 
periods  of  rest.  The  alternation  of  work  and  rest  is  a  necessary  condition  of 
their  maintenance,  and  of  the  healthy  performance  of  their  functions.  These 
alternating  periods,  however,  differ  much  in  duration  in  different  cases ;  but, 
for  any  individual  instance,  they  preserve  a  general  and  rather  close  uniformitj'. 
Thus,  as  before  mentioned,  the  periods  of  rest  and  Avork,  in  the  case  of  the 
heart,  occupy,  each  of  them,  about  half  a  second ;  in  the  case  of  the  ordinary 
respiratory  muscles  the  periods  are  about  four  or  five  times  as  long.  In  many 
cases,  again  (as  of  the  voluntary  muscles  during  violent  exercise) ,  while  the 
periods  during  active  exertion  alternate  very  frequently,  yet  the  expenditure 
goes  far  ahead  of  tlie  repair,  and,  to  comijeusate  for  this,  an  after  repose  of 
some  hours  becomes  necessary  ;  the  rhythm  being  less  perfect  as  to  time,  than 
in  the  case  of  the  muscles  concerned  in  circulation  and  respiration. 

Obviouslj%  it  would  be  impossible  that,  in  the  case  of  the  brain,  there 
should  be  short  jjeriods  of  activity  and  repose,  or  in  other  words,  of  conscious- 
ness and  unconsciousness.  The  repose  must  occur  at  long  intervals ;  and  it 
must  therefore  be  proportionatelj'  long.  Hence  the  necessitj- for  that  condition 
which  we  call  Sleep;  a  condition  which  seeming  at  first  s-ight  exceptional,  is 
only  an  unusually  perfect  example  of  what  occurs,  at  varying  intervals,  in 
every  actively  working  portion  of  oiir  bodies. 

A  temporarj^  abrogation  of  the  functions  of  the  cerebrum  imitating  sleep, 
may  occur,  in  the  case  of  injury  or  disease,  as  the  consequence  of  two  appar- 
ently widely  different  conditions.  Insensibility  is  equally  jiroduced  by  a 
deficient  and  an  excensii-e  quantity  of  blood  within  the  cranium  (coma)  ;  but  it 
was  once  supi)osed  that  the  latter  offered  the  truest  analogj'  to  the  normal  con- 
dition of  the  brain  in  sleep,  and  in  the  absence  of  any  proof  to  the  contrary, 
the  brain  was  said  to  be  during  sleep  congested.  Direct  experimental  inquiry 
has  led,  however,  to  the  opposite  conclusion. 

By  exposing,  at  a  circumscribed  spot,  the  surface  of  the  brain  of  living 
animals,  and  protecting  the  exposed  part  by  a  watch-glass,  Durham  was  able 
to  prove  that  the  brain  becomes  visibly  paler  (anaemic)  during  sleep ;  and  the 
anaemia  of  the  optic  disc  during  sleep,  observed  by  Hughlings  Jackson,  may 
be  taken  as  a  strong  confirmation,  by  analogy,  of  the  same  fact. 

A  very  little  consideration  will  show  that  these  experimental  results  corre- 
spond exactly  with  what  might  have  been  foretold  from  the  analogy  of  other 


638  HAXDBOOK    OF    PHYSIOLOGY. 

physiological  conditions.  Blood  is  supplied  to  the  brain  for  two  partly  dis- 
tinct purposes.  (1.)  It  is  supplied  for  mere  nuti'ition's  sake.  (2.)  It  is  neces- 
saiy  for  bringing  supplies  of  potential  or  active  energy  {i.  e. ,  comhustible  matter 
or  heat)  which  may  be  transformed  by  the  cerebral  corpuscles  into  the  various 
manifestations  of  nerve-force.  During  sleep  blood  is  requisite  for  only  the  first 
of  these  pui-poses ;  and  its  supply  in  greater  quantity  would  be  not  only 
useless,  but  by  supplying  an  excitement  to  work,  when  rest  is  needed,  would  be 
positively  harmful.  In  this  respect  the  varying  circulation  of  blood  in  the 
brain  exactly  resembles  that  which  occurs  in  all  other  energy -transforming 
parts  of  the  body  ;  e.g.,  glands  or  muscles. 

At  the  same  time,  it  is  necessary  to  remember  that  the  normal  anaemia  of 
the  brain  which  accompanies  sleep  is  probably  a  result,  and  not  a  cause  of  the 
quiescence  of  the  cerebial  functions.  What  the  immediate  cause  of  this 
periodical  partial  abrogation  of  functions  is,  however,  we  do  not  know. 

Somnambulism  and  Dreams. — What  we  term  sleep  occurs  often  in  very  differ- 
ent degrees  in  different  parts  of  the  nervous  system  ;  and  in  some  parts  the 
expression  cannot  be  used  in  the  ordinary  sense. 

The  phenomena  of  dreams  and  somnambidism  are  examples  of  differing 
degrees  of  sleep  in  different  parts  of  the  cerebro- spinal  nervous  system.  In  the 
former  case  the  cerebrum  is  still  partially  active ;  but  the  mind-products  of  its 
action  are  no  longer  corrected  by  the  reception,  on  the  part  of  the  sleeping 
sensorium,  of  impressions  of  objects  belonging  to  the  outer  world  ;  neither  can 
the  cerebrum,  in  this  half -awake  condition,  act  on  the  centres  of  reflex  action 
of  the  voluntary  muscles,  so  as  to  cause  the  latter  to  contract — a  fact  within 
the  painful  experience  of  all  who  have  suffered  from  nightmare. 

In  somnambulism  the  cerebrum  is  capable  of  exciting  that  train  of  reflex 
nervous  action  which  is  necessary  for  progression,  while  the  nerve-centre  of 
musctdar  sense  (in  the  cerebellum?)  is,  presumably,  fully  awake ;  but  the  .se?i- 
sorium  is  still  asleep,  and  impressions  made  on  it  are  not  sufficiently  felt  to 
rouse  the  cerebrum  to  a  comparison  of  the  difference  between  mere  ideas  or 
memories  and  sensations  derived  from  external  objects. 

The  centres  for  7iuiscular  co-ordinations. — In  asserting  that  the  co- 
ordination of  complicated  muscular  movements  is  connected  with  the 
middle  parts  of  the  brain  below  the  cerebrum  and  above  the  bulb,  we 
were  stating  a  fact  deduced  from  experiments  upon  animals.  It  is  diffi- 
cult to  understand  the  exact  way  in  which  these  parts  of  the  brain  are 
concerned.  It  appears,  however,  that  co-ordinated  movements  such  as 
standing,  walking,  and  the  maintenance  of  the  equilibrium  generally, 
require  to  be  guided  and  governed  by  afferent  impulses,  which  tell  of 
the  condition  of  the  body  and  of  its  relations  to  its  environment  ("  its 
position  in  space").  The  afferent  impulses  are ^^ns^/^y  visual  and  tactile 
sensations,  secondly  sensations  by  which  we  appreciate  the  condition  of 
our  muscles  (muscular  sense),  and  tliirdly,  as  appears  from  experiments 
on  pigeons  and  other  animals,  sensations  produced  by  the  pressure,  in 
different  directions,  of  the  fluid  in  the  semicircular  canals  of  the  in- 
ternal ear. 

Experiments  show  that  when    the   horizontal  semicircular  canal   is 


THE   XERVOUS    SYSTEM.  630 

divided  iii  a  pigeou,  iuco-ordination  occurs,  with  a  constant  movement 
of  the  head  from  side  to  side,  and  simihirly,  when  one  of  the  vertical 
canals  is  operated  upon,  up  and  down  movements  of  the  head  are  ob- 
served. The  bird  is  unable  to  fly  in  an  orderly  manner,  flutters  and 
falls  when  thrown  into  the  air,  and,  moreover,  is  able  to  feed  with 
difficulty.  Hearing  remains  unimpaired.  So  tliat  inco-ordination 
depends  upon  deficiency  or  disorder  of  normal  ampullar  influences.  It 
will  be  recollected  that  the  semicircular  canals  are  supplied  with  a 
nerve,  the  vestibular  branch  of  the  auditory,  which  is  connected  with  the 
bulb. 

It  is  probable  that  the  various  afferent  impulses  upon  w/iich  co-ordina- 
tion and  the  maintenance  of  the  equilibrium  depend  are  gathered  uj),  as 
it  were,  in  the  tegmental  system  from  the  bulb  upward,  since  this 
region  is  so  intimately  connected  with  the  bulb  and  cord  posteriorly, 
and  with  the  optic  thalamus  and  corpora  quadrigemina  anteriorly.  In 
addition  to  the  tegmentum,  however,  the  cerebellum  and  pons  are  in 
some  way  concerned,  because  of  their  intimate  connection  with  the 
spinal  cord  and  bulb,  the  cerebellum  being  further  connected  with  the 
auditory  nerve  en  the  one  hand,  and  with  the  gray  matter  in  connection 
with  the  tegmentum  on  the  other  hand. 

Sensory  Centres, 

There  is  evidence  that  fibres  from  the  nerves  of  special  sense  are 
specially  connected  with  definite  and  distinct  parts  of  the  cerebrum. 

Visual  or  Optic  Centre. — The  termination  of  the  optic  nerve  in  each 
eye,  the  retina,  to  the  structure  of  which  we  shall  return  when  treating 
of  the  eye,  is  so  arranged  that  when  we  look  at  an  object  with  both 
eyes  symmetrical  parts  of  each  retina  are  used.  For  example,  if  w^e  look 
at  an  object  to  the  left,  an  image  of  that  object  is  focussed  upon  the 
right  half  of  both  retina?,  viz.,  upon  the  temporal  side  of  the  right 
retina,  and  upon  the  nasal  side  of  the  left  retina.  The  optic  nerve- 
fibres  of  these  symmetrical  parts  of  the  retina  are  gathered  together 
behind  where  the  optic  nerves  decussate,  viz.,  in  the  optic  chiasma. 
The  fibres  which  come  from  the  right  side  of  both  eyes  are  contained  in 
the  optic  tract  of  the  same  side,  viz.,  the  right,  those  from  the  right  eye 
being  outside  of  the  others.  In  the  same  way  the  left  optic  tract  con- 
tains internally  fibres  from  the  left  side  of  the  right  eye  and  externally 
those  from  the  left  side  of  the  left  eye.  On  the  inner  border  of  the  optic 
chiasma  and  tract  there  are  also  commissural  fibres  which  pass  from  one 
side  of  the  brain  to  the  other;  these  are  fibres  which  connect  one  median 
corpus  geniculatum  with  the  other.  They  are  called  the  inferior  or 
arcuate  commissure.     The  optic  tract  thus  formed  then  passes  back- 


640 


HANDBOOK    OF    PHYSIOLOGY. 


ward  and  terminates  in  three  distinct  nuclei,  viz.,  the  pulvinar  of  the 
optic  thalamus,  the  anterior  corpus  quadrigeminum  and  the  lateral 
corpus  geniculatum.  These  nuclei  waste  if  the  eyes  are  removed  from 
^n  adult  animal ;  and  if  from  a  newly  born  animal  they  do  not  develop. 
The  optic  chiasma  in  its  course  gives  off  fibres  which  are  connected  with 
the  nucleus  of  the  third  nerve. 

It  appears  that  some  of  the  fibres  of  the  optic  tract  pass  directly  into 
the  cerebral  cortex  without  joining  with  the  optic  thalamus,  corpus  quad- 
rigeminum or  corpus  geniculatum. 

It  was  shown  above  that  the  fibres  of  the  cerebral  cortex,  known  as 
the  optic  radiation,  pass  from  the  occipital  region  to  the  three  nuclei 
about  which  we  are  speaking,  viz. ,  into  the  j)ulvinar  of  the  optic  thala- 
mus, the  anterior  corpus  quadrigeminum  and  lateral  corpus  geniculatum^ 


Fig.  386.— The  Cortical  Centres. 

and  it  is  known  that  when  the  occipital  cortex  is  removed,  these  three 
waste.  It  has  been  further  shown  that  in  a  newly  born  animal  the 
removal  of  such  a  region  is  followed  by  imperfect  development  of  the 
parts  in  question. 

If  one  optic  nerve  be  divided  blindness  of  the  corresponding  eye 
results,  but  if  one  optic  tract  be  divided  there  is  a  half  blindness, 
which  is  called  liemianopsia^  hemianopia,  or  Imniopia^  right  or  left, 
according  as  the  right  or  left  field  of  vision  is  cut  off.  It  is  highly 
probable  that  the  occipital  lobe  (figs.  382,  386),  and  particularly 
the  cuneus,  is  concerned  as  a  so-called  visual  centre,  since  not  only  is 
it  connected  with  the  optic  nerves,  as  we  have  seen,  but  also  because  the 
removal  of  the  right  occipital  lobe  in  an  animal  (monkey),  is  followed 
by  left  hemiopia,  removal  of  the  left  by  right  hemiopia,  and  removal  of 
both  occipital  lobes  by  total  blindness.   Some  have  connected  the  angular 


THE    XERVOUS   SYSTEM.  6-41 

gyrus  also  with  vision  as  the  centre,  while  others  look  upon  it  merely 
as  an  accessory  centre. 

Olfactory  centre.- — ^The  olfactory  nerve  differs  from  the  other  cranial 
nerves.  In  reality  it  is  a  representative  of  the  olfactory  lobes  of  other 
animals,  which  are  part  of  the  cerebrum.  It  originates  as  an  off-shoot 
from  the  cerebral  vesicle,  the  front  part  of  which  is  developed  into  the 
bulb  of  the  olfactory  nerve,  while  the  back  forms  its  peduncle.  The 
nerve,  the  cavity  of  which  is  filled  up  in  the  fully  developed  condition 
with  neurogliar  substance,  lies  upon  the  cribriform  plate  of  the  ethmoid 
bone,  and  is  contained  in  a  groove  of  the  frontal  lobe  on  its  under  sur- 
face. On  examination  of  the  bulb  it  is  found  to  be  thus  made  up. 
Beneath  the  neurogliar  layer  is  a  layer  of  longitudinal  fibres  and  a  few 
nerve-cells,  next  to  this  is  a  layer  of  small  cells  (nuclear  layer) ,  fibres 
from  the  layer  of  nerve-fibres  passing  through  it. 

The  nuclear  layer  is  also  separated  into  groups  of  cells  by  an  inter- 
lacing of  the  fibres.  The  next  layer  is  thick  and  is  composed  of  neuroglia 
and  some  fibres,  some  of  which  are  medullated,  as  well  as  of  cells  more 
or  less  pyramidal  in  shajDe.  Below  this  layer  is  the  layer  of  olfactory 
glomeruli.  These  glomeruli  are  small  coils  of  olfactory  fibres  inclosing 
small  cells  and  granular  matter.  A  full  description  of  the  anatomy  of 
these  parts  is  given  later  (see  Olfactory  nerve). 

Fibres  of  the  olfactory  nerve  proper  are  found  below  this  layer  and 
pass  to  be  distributed  to  the  olfactory  mucous  membrane.  They  are 
thought  to  have  origin  in  the  glomeruli.  The  peduncle  of  the  nerve 
or  the  olfactory  tract  as  it  ig  sometimes  called,  is  made  up  of  longitudinal 
fibres  originating  in  the  bulb,  with  neuroglia  and  some  nerve-cells. 

The  fibres  of  the  olfactory  tract  have  been  traced  into  the  nucleus 
amygdalae  and  its  junction  with  the  hippocampal  gyrus  in  the  temporal 
lobe  (fig.  386).  The  hippocampus  must  be  in  some  way  connected  with 
smell,  since  a  lesion  of  it,  leaving  the  olfactory  tract  uninjured,  seriously 
interferes  with  that  sense. 

Taste  centre. — It  is  very  uncertain  where  the  taste  centre  is  situated, 
if  such  exist.  It  has  been  placed  in  the  temporal  lobe,  not  far  from  that 
of  smell  (fig.  386). 

Auditory  Centre. — This  centre  has  been  localized  in  the  superior 
temporal  convolution  (fig.  383).  Experiments  have  been  made  which 
connect  auditory  impulses  on  either  side  with  the  posterior  corpus  quad- 
rigeminum  and  the  median  corpus  geniculatum,  for  when  the  internal 
ear  is  destroyed  there  results  atrophy  of  these  bodies  as  well  as  of  the 
lateral  fillet  of  the  opposite  side;  and  on  the  other  hand,  destruction  of 
the  part  of  the  temporal  lobe  above  indicated  is  similarly  followed  by 
atrophy  of  the  nuclei  of  the  same  side.  If  these  results  be  confirmed  by 
additional  experiments,  it  would  make  it  plain  that  these  nuclei  bear 
much  the  same  relation  to  the  sense  of  hearing  as  do  the  anterior  corpus 
41 


642  HANDBOOK    OF    PHYSIOLOGY. 

quadrigeminum  and  the  lateral  corpus  geuiciilatum  to  the  sense  of 
sight. 

Centre  for  Cutaneous  Sensations. — Physiological  experiments,  as  well 
as  clinical  and  pathological  observations,  now  show  pretty  certainly  that 
the  cortical  centre  for  sensations  of  touch,  and  probably  of  pain  and 
temperature,  are  essentially  identical  "vvith  the  motor  areas,  that  is  to 
say,  in  the  central  convolutions.  Owing,  however,  to  the  wide  distribu- 
tion of  afferent  impulses,  through  the  multiplication  of  their  means  of 
getting  to  the  brain,  the  area  of  these  sensory  centres  is  not  as  strictly 
limited  as  that  of  other  special  centres. 

TJie  Centre  for  Muscular  Sensations. — A  great  deal  of  evidence  is  ac- 
cumulated to  show  that  the  most  important  area  in  which  these  sensa- 
tions are  brought  to  consciousness  is  in  the  inferior  parietal  lobule. 

FUNCTIOI^S    OF    CORPOEA    STRIATA    AXD    OpTIC    ThALAMI. 

The  Corpora  Striata. — The  idea  formerly  held  that  the  corpora 
striata  are  concerned  in  the  transmission  of  motor  impulses,  or  that  they 
are  the  great  motor  ganglia  at  the  base  of  the  brain,  rests  upon  insuffi- 
cient evidence.  Lesions  of  the  corpora  striata  produce  hemiplegia  only 
because  of  the  pressure-effects  they  exercise  upon  the  internal  capsule 
close  by. 

The  caudate  nucleus  is  connected  with  the  opposite  side  of  the  cere- 
bellum by  fibres  which  conduct  downward,  and  the  lenticular  nucleus  is 
connected  with  the  cerebellum  by  fibres  from  the  tegmentum  and  su- 
perior cerebellar  peduncles  which  conduct  upward.  It  is  suggested  that 
the  corjDora  striata  are  central  organs  analogous  to  the  cerebral  cortex 
itself.  "  The  analogy  to  those  parts  of  the  cortex  that  are  connected 
with  the  cerebellum  is  rendered  still  greater  by  the  fact  that  a  lesion, 
even  an  extensive  lesion,  may  exist  in  either  the  caudate  or  lenticular 
nucleus,  and  so  long  as  it  does  not  interfere  W'ith  the  functions  of  the 
motor  or  sensory  parts  of  the  internal  capsules  it  causes  no  persistent 
symptoms."     (Gowers.) 

On  the  whole,  however,  it  must  be  said  that  the  functions  of  the 
corpora  striata  are  unknown,  and  it  is  possible  that  in  man  they  are  very 
subsidiary,  if  not  even  rudimentary,  bodies. 

Tlte  Optic  Thalami. — That  the  optic  thalami  are  the  great  sensory 
centres  at  the  base  of  the  brain — which  was  a  view  held  by  many  until 
recently — does  not  seem  to  be  based  u]3on  sufficiently  accurate  observa- 
tions. The  important  relation  to  the  tegmentum  of  its  own  side  would 
make  it  appear  as  being  specially  concerned  with  the  sensory  fibres  pass- 
ing to  the  cerebrum,  for  which  it  probably  forms  a  relay. 

Its  connection  with  the  optic  nerves  has  been  commented  upon 
above.  Fibres  connect  the  optic  thalamus  too  with  the  superior  pe- 
duncle of  the  cerebellum  of  the  opposite  side. 


TIIK    XEKVOLS    SYSTEM. 


ri43 


Lesions  of  the  optic  thalamus  do  not  of  themselves  produce  entire 
loss  of  sensation.  If  such  a  symptom  follows,  it  is  due  to  pressure  upon, 
or  injury  to,  the  posterior  limb  of  the  internal  capsule.  The  optic 
thalamus  is  connected  with  visual  sensations  and  may  be  a  reflex-centre 
for  some  of  the  higher  reflex  actions. 

The  optic  thalamus  is  so  closely  connected  with  a  large  area  of  the 
cortex  that  it  undoubtedly  must  have  some  function  in  connection  with 
the  mechanical  or  muscular  movements  and  of  expression.  It  is  prob- 
able that  it  is  the  organ  to  which  automatic  activities  are  relegated  in 
states  of  partial  consciousness.     The  automatic  walking,  writing,  speak- 


Fig.  387.— Cerebellum  in  section  and  fourth  ventricle,  with  the  neighboring  parts.  1. 
Median  groove  of  fourth  ventricle,  ending  below  in  the  calamus  scripton'us,  with  the  longitu- 
dinal eminences  formed  by  the  fasciculi  teretes,  one  on  each  side;  2,  the  same  groove,  at  the 
place  where  the  white  streaks  of  "the  auditory  nerve  emerge  from  it  to  cross  the  floor  of  the  ven- 
tricle; 3,  inferior  cms  or  peduncle  of  the  cerebellum,  formed  by  the  restiform  body;  4,  posterior 
pyramid;  above  this  is  the  calamus  scriptorius;  5,  superior  cms  of  cerebellum,  or  processus  o 
cerebello  ad  cerebrum  (or  ad  testes);  6,  6,  fillet  to  the  side  of  the  crura  cerebri;  7,  7,  lateral 
grooves  of  the  crura  cerebri ;  8,  corpora  quadrigemina.  CFrom  Sappey  after  Hirschfeld  and 
Leveill6.) 

ing,  and  emotional  expressions,  for  example,  that  are  done  by  men  in 
hvpnotic  states  or  in  sleep,  are  very  jirobably  largely  under  the  control 
of  the  optic  thalamus  in  connection  with  the  cerebellum  and  associated 
ganglia. 

Of  the  functions  of  the  (wtcDud  capstde  and  of  the  cJaustnim  nothing 
definite  is  known. 


The  Cerebellum. 

The  cerebellum  (7,  8,  9,  10,  fig.  ob-^)  is  composed  of  an  elongated 
central  portion  or  lobe,  called  the  vermiform  processes,  and  two  hemi- 
spheres. Each  hemisphere  is  connected  with  its  fellow,  not  only  by 
means  of  the  vermiform  processes,  but  also  by  a  bundle  of  fibres  called 
i\\Q  7nicl(lle  cms  ov  ipeduncle  {i\\e  latter  forming  the  greater  part  of  the 


644  HANDBOOK    OF    PHYSIOLOGY. 

pons  A'arolii),  while  the  siqjerior  crura  with  the  valve  of  Vieussens  coii' 
cect  it  with  the  cerebrum  (5,  fig.  387),  and  the  inferior  crura  (formed 
by  the  prolonged  restiform  bodies)  connect  it  with  the  medulla  oblongata 
(3,  fig.  387). 

Structure. — The  cerebellum  is  composed  of  white  and  gray  matter, 
the  latter  being  external,  like  that  of  the  cerebrum,  and  like  it  infolded, 
so  that  a  larger  area  may  be  contained  in  a  given  space.  The  convolu- 
tions of  the  gray  matter,  however,  are  arranged  after  a  different  pattern, 
as  shown  in  fig.  387,  Besides  the  gray  substance  on  the  surface,  there 
is,  near  the  centre  of  the  white  substance  of  each  hemisphere,  a  small 
capsule  of  gray  matter  called  the  corjnis  dentatum  (fig.  388,  cd),  resem- 
bling very  closely  the  corpus  dentatum  of  the  olivary  body  of  the  medulla 
oblongata  (figs.  362,  388,  o). 


Fig.  388. — Outline  sketch  of  a  section  of  the  cerebellum,  showing  the  corj)us  dentatum.  The 
section  has  been  carried  through  the  left  lateral  part  of  the  pons,  so  as  to  divide  the  superior  pe- 
duncle and  pass  nearly  through  the  middle  of  the  left  cerebellar  hemisphere.  The  olivary  body 
has  also  been  divided  longitudinally  so  as  to  expose  in  section  its  corpus  dentatum.  c  r,  crus 
cereljri;  /,  fillet;  g,  corpora  quadrigemina ;  s  p,  superior  peduncle  of  the  cerebellum  divided; 
7)1  p,  middle  peduncle  or  lateral  part  of  the  pons  Varolii,  with  fibres  passing  from  it  into  the 
white  stem;  a  v,  continuation  of  the  white  stem  radiating  toward  the  arbor  vitse  of  the  folia; 
c  d,  corpus  dentatum;  o,  olivary  body  with  its  corpus  dentatum;  p,  anterior  pyramid.  (Allen 
Thomson.)    %. 

If  a  section  be  taken  through  the  gray  matter  of  the  cerebellum,  it 
will  be  found  to  be  composed  of  two  layers,  an  outer,  or  molecular,  and 
an  inner,  or  granular,  layer.  Each  of  these  layers  contains  a  large  num- 
ber of  peculiar  shaped  nerve-cells,  and  very  rich  plexuses  of  nerve-fibres. 
Eecent  studies  of  the  cortex  of  the  cerebellum  by  modern  methods  have 
revealed  a  most  complex  and  beautiful  arrangement  of  the  parts,  which 
we  shall  describe  briefly  here. 

The  molecular  layer  contains  two  kinds  of  cells,  one  large  and  known 
as  Purhinje''s  cell,  the  other  smaller  and  known  as  stellate  cells.  The 
cells  of  Purkinje  lie  along  the  internal  margin  of  the  layer,  being,  in 
fact,  practically  at  the  boundary  of  the  molecular  and  granular  layers. 
They  measure  40x30  //.,  and  have  large,  round  nuclei.  Each  cell  gives 
off  an  enormous  number  of  branching  dendrites,  "which  run  up  toward 
the  surface  of  the  cerebellum  in  the  shape  of  a  bush.  Each  little  branch 
sends  off  from  the  side  small  buds,  which  are  called  the  gemmules  or 
thorns.  These  branching  dendrites  do  not  juiss  up  altogether  like  the 
branches  of  a  round  bush,  but  are  flattened  like  a  bush  that  has  been 


THE    XKK vol's    SYSTEM. 


645 


pressed,  so  that  if  one  cuts  tlie  cell  in  one  directior!,  only  the  profile  is 
shown.  The  Purkinje  cells  are  arranged  so  that  the  axis  of  these  flat- 
tened branches  is  transverse  to  the  longitudinal  surface  of  the  convolu- 


Fig.  388a. — The  different  constituent  elements  of  tlie  gray  cortical  layer  of  the  cerebellum. 


Fig.  380.— Longitudinal  section  of  the  gray  substance  of  a  cerebellar  convolution.  Schematic, 
pr,  Qranula;  n,  its  uerv<nis  processos:  n',  divisions  of  the  latter  in  the  molecular  layer  and  eacll 
separating  into  two  lougitudinal  flue  Ilbres;  p,  cells  of  Purkinj6. 


646 


HA2<rDB00K   OF   PHYSIOLOGY. 


tion,  and  if  one  makes  a  section  down  through  tlie  centre  of  the  convo- 
lution, in  its  longitudinal  course,  a  side  view  of  the  cell  only  is  shown 
(fig.  389). 

The  cells  of  Purkinje  give  off  at  their  under  surface  a  neuraxon 
which  runs  down  into  the  white  matter  of  the  cerebellum.  Lvincr 
throughout  the  molecular  layer  are  the  stellate  cells,  wljich  are  much 
smaller  in  size,  and  which  give  off  a  number  of  dendrites  (fig.  388a). 

Each  cell  has  also  an  axis-cylinder  (neuraxon)  and  this  sends  off  col- 
laterals which  end   in   a  fine  basket-like  network  which  surrounds  the 


molecular 
ayer 


Fig.  389a.— A,  Afferent  fibre  to  basket  (stellate)  cell;  B,  neuraxon  of  Purkinjg  cell;  C,  afferent 
fibre  to  Purkinj6  cell;  D,  afferent  (mossy)  fibre  to  granule  cell. 


body  of  the  cells  of  Purkinje  (fig.  38'Ja).  On  this  account  they  are  some 
times  called  basket-cells.  There  are  other  stellate-shaped  cells  in  the 
molecular  layer  "which  lie  more  superficially,  and  do  not  have  this  partic- 
ular connection  with  the  Purkinje  cells,  but  appear,  however,  to  belong 
to  the  same  type. 

The  granular  layer  contains  a  large  number  of  very  small  granular- 
like  cells  that  Golgi  was  the  first  to  show  were  really  nerve  cells.  They 
are  only  about  5/^  in  diameter,  and  they  have  a  number  of  short  den- 
drites which  end  in  clubbed  extremities.  They  give  off  a  very  fine  axis- 
cylinder  process  (neuraxon)  which  runs  up  into  the  molecular  layer  and 
there  divides  in  a  T-shaped  fashion,  the  fibres  running  parallel  to  the 
surface  of  the  convolution  and  passing  in  between  the  branches  of  the 
cells  of  Purkinje.  There  are,  besides  these  granular  cells,  a  few  larger 
cells,  with  axis-cylinders,  that  divide  and  subdivide,  ending  in  a  finely 
ramifying  plexus.  These  are  known  as  the  cells  of  Golyi.  They  are 
iound  in  other  parts  of  the  brain. 

The  white  substance  of  the  cerebellum  consists  of  nerve-fibres,  which 


THE   NERVOUS   SYSTEM.  647 

are  of  three  kinds:  1st,  Descending  fibres,  that  are  made  up  of  the  axis- 
cylinders  of  the  cells  of  Purkinje  carrying  impulses  down  from  the  cere- 
bellar cortex.  2d,  Ascending  fibres,  which  pass  into  the  granular  layer, 
and  there  end  in  a  number  of  very  short,  finely  split  fibres,  j^resenting  a 
mossy  appearance,  so  that  these  are  known  as  the  mossy Jihres.  These 
connect  with  the  granular  cells  of  this  layer.  3d,  Ascepding  fibres,  which 
pass  up  through  the  granular  into  the  molecular  layer  and  there  break 
uj)  into  a  fine  network,  which  interlaces  with  and  coils  among  the  proto- 
plasmic branches  of  the  cells  of  Purkinje. 

It  will  be  seen  that  the  arrangements  for  the  transmission  and  difl'ii- 
sion  of  nerve-impulses  and  for  the  cooperation  of  different  cells  wiili 
each  other  are  extremely  complicated  and  delicate,  as  would  be  needed  for 
so  important  an  organ.  It  is  not  possible  to  indicate  absolutely  by  any 
scheme  the  course  of  fibres  and  the  course  of  impulses  through  the  cere- 
bellum, but,  approximately,  it  is  somewhat  like  that  in  the  accompany- 
ing figure  (fig.  389a). 

Impulses  pass  up  along  those  ascending  fibres  called  "mossy"  to  the 
granular  cells.  These  cells,  being  stimulated,  send  the  impulses  by  their 
axis-cylinders  to  the  molecular  layer,  and  through  their  T-shaped  divis- 
ions to  the  dendrites  of  the  cells  of  Purkinje.  Thence  an  impulse  is 
send  out  by  the  axis-cylinder  process  of  this  cell.  Other  ascending  im- 
pulses are  brought  up  by  those  fibres  which  pass  to  the  molecular  layer 
and  send  their  terminals  winding  around  among  the  dendrites  of  the  cells 
of  Purkinje.  Probably  impulses  pass  up  also  through  the  ascending 
fibres,  and  affect  the  stellate  cells,  and  through  them  and  their  basket- 
like terminals  the  cells  of  Purkinje. 

FUNCTIOXS   OF   THE    CEREBELLUM. 

(1.)  With  the  exception  of  its  middle  lobe,  the  cerehelhon  is  itself 
insensible  to  irritation  and  may  be  all  cut  away  without  eliciting  signs 
of  pain  (Longet).  Its  removal  or  disorganization  by  disease  is  also  gen- 
erally unaccompanied  by  loss  or  disorder  of  sensibility;  animals  from 
which  it  is  removed  can  smell,  see,  hear,  and  feel  pain,  to  all  appear- 
ances, as  perfectly  as  before  (Flourens;  Magendie).  It  cannot,  there- 
fore, bo  regarded  as  a  priucipal  organ  of  sensation.  Yet,  if  any  of  its 
crura  be  touched,  pnin  is  indicated;  and,  if  the  restiform  tracts  of  the 
medulla  oblongata  h^  irritated,  the  most  acute  suffering  ajipears  to  be 
produced. 

(2.)  Co-ordination  of  Movements. — In  reference  to  motion,  the  experi- 
ments of  Longet  and  many  others  agree  that  no  irritation  of  the  cerebel- 
lum produces  movement  of  any  kind.  Eemarkable  results,  however,  are 
produced  by  removing  parts  of  its  substance.  Flourens  (whose  experi- 
ments have  been  confirmed  by  those  of  Bouillaud,  Longet,  and  others) 
extirpated  the  cerebellum  in  birds  by  successive  layers.     Feebleness  and 


648  HANDBOOK    OF    PHYSIOLOGY. 

want  of  harmony  of  muscular  movements  were  the  consequence  of  remov- 
ing the  superficial  layers.  When  he  reached  the  middle  layers,  the  ani- 
mals became  restless  without  being  convulsed;  their  movements  were 
violent  and  irregular,  but  their  sight  and  hearing  were  perfect.  By  the 
time  that  the  last  portion  of  the  organ  was  cut  away,  the  animals  had 
entirely  lost  the  powers  of  springing,  flying,  walking,  standing,  and 
preserving  their  equilibrium.  When  an  animal  in  this  state  was  laid  upon 
its  back,  it  could  not  recover  its  former  230sture,  but  it  fluttered  its 
wings,  and  did  not  lie  in  a  state  of  stupor;  it  saw  the  blow  that  threatened 
it,  and  endeavored  to  avoid  it.  Volition  and  sensation,  therefore,  were 
not  lost,  but  merely  the  faculty  of  combining  the  actions  of  the  muscles; 
and  the  endeavors  of  the  animal  to  maintain  its  balance  were  like  those 
of  a  drunken  man. 

The  experiments  afforded  the  same  results  when  repeated  on  all  classes 
of  animals;  and  from  them  and  the  others  before  referred  to,  Flourens 
inferred  that  the  cerebellum  belongs  neither  to  the  sensory  nor  the  intel- 
lectual apparatus;  and  that  it  is  not  the  source  of  voluntary  movements, 
although  it  belongs  to  the  motor  apparatus ;  but  is  the  organ  for  the  co- 
ordination of  the  voluntary  movements,  or  for  the  excitement  of  the  corn- 
lined  action  of  muscles. 

Such  evidence  as  can  be  obtained  from  cases  of  disease  of  this  organ 
confirms  the  view  taken  by  Flourens :  and,  on  the  whole,  it  gains  sup- 
port from  comparative  anatomy;  animals  whose  natural  movements 
require  most  frequent  and  exact  combinations  of  muscular  actions  being 
those  whose  cerebella  are  most  developed  in  proportion  to  the  spinal 
cord. 

We  must  remember,  too,  that  the  cerebellum  is  connected  with  the 
posterior  columns  of  the  cord  as  well  as  with  the  direct  cerebellar  tract, 
both  of  which  probably  convey  to  the  middle  lobe  muscular  sensations. 
It  is  also  connected  with  the  auditory  nerves  and  bulb  by  the  internal  and 
external  acute  fibres;  and  with  the  tegmentum  through  the  red  nuclei. 
Its  connection  with  the  efferent  tracts  from  the  different  cerebral  lobes 
through  the  pons  is  also  highly  important.  Movements  of  the  eyes  also 
occur  on  direct  stimulation  of  the  middle  lobe.  It  seems,  therefore,  to 
be  connected  in  some  way  with  all  of  the  chief  sensory  impulses  which 
have  to  do  with  the  maintenance  of  the  equilibrium,  and  is  generally 
included  in  the  nervous  apparatus  which  is  supposed  to  govern  this  func- 
tion of  our  bodies. 

Foville  supposed  that  the  cerebellum  is  the  organ  otmiiscular  sense,  i.e.,  the 
organ  by  which  the  mind  acquires  that  knowledge  of  the  actual  state  and 
position  of  the  muscles  which  is  essential  to  the  exercise  of  the  will  upon  them  ; 
and  it  must  be  admitted  that  all  the  facts  just  referred  to  are  as  well  explained 
on  this  hypothesis  as  on  that  of  the  cerebellum  being  the  organ  for  combining 


tlUi    XKKVOUS    SYSTE^r.  64'J 

movements.  A  harmonious  combination  of  muscular  actions  must  depend  as 
mucVi  on  the  capability  of  appreciating  the  condition  of  the  muscles  with  repaid 
to  their  tension,  and  to  the  force  with  which  they  are  contracting,  as  on  the 
power  which  any  special  nerve-centre  may  possess  of  exciting  them  to  coTitrac- 
tion.  And  it  is  because  the  power  of  such  harmonious  movement  would  be 
equally  lost,  whether  the  injury  to  the  cerebellum  involved  injury  to  the  seat 
of  muscular  sense,  or  to  the  centre  for  combining  muscular  actions,  that  ex- 
periments on  the  subject  afford  no  proof  in  one  direction  more  than  the  other. 

Forced  Movements. — The  influence  of  each  half  of  the  cerebelhnn 
is  directed  to  muscles  on  the  opposite  side  of  the  body;  and  it  would 
appear  that  for  the  right  ordering  of  movements,  the  actions  of  its  two 
halves  must  be  always  mutually  balanced  and  adjusted.  For  if  one  of  its 
crura,  or  if  the  pons  on  either  side  of  the  middle  line,  be  divided,  so  as 
to  cut  off  from  the  medulla  oblongata  and  spinal  cord  the  influence  of  one 
of  the  hemispheres  of  the  cerebellum,  strangely  disordered  movements 
ensue  (forced  movements).  The  animals  fall  down  on  the  side  opposite 
to  that  on  which  the  cms  cerebelli  has  been  divided,  and  then  roll  over 
continuously  and  repeatedly;  the  rotation  being  always  round  the  long 
axis  of  their  bodies,  and  generally  from  the  side  on  which  the  injury  has 
been  inflicted.  The  rotations  sometimes  take  place  with  much  rajsidity; 
as  often,  according  to  Magendie,  as  sixty  times  in  a  minute,  and  may  last 
for  several  days.  Similar  movements  have  been  observed  in  men;  as  by 
Serres  in  a  man  in  whom  there  was  apoplectic  effusion  in  the  right  cms 
cerebelli ;  and  by  Belhomme  in  a  woman,  in  whom  an  exostosis  pressed 
vOn  the  left  crus.  They  may,  perhaps,  be  explained  by  assuming  that 
the  division  or  injury  of  the  crus  cerebelli  produces  paralysis  or  imper- 
fect and  disorderly  movements  of  the  opposite  side  of  the  body ;  the 
animal  falls,  and  then,  struggling  with  the  disordered  side  on  the 
ground,  and  striving  to  rise  with  the  other,  pushes  itself  over;  and  so 
again  and  again,  with  the  same  act,  rotates  itself.  Such  movements  cease 
when  the  other  crus  cerebelli  is  divided ;  but  probably  only  because  the 
paralysis  of  the  body  is  thus  made  almost  complete.  Other  varieties  of 
forced  movements  have  been  observed,  especially  those  named  "  circus 
movements,"  when  the  animal  operated  upon  moves  round  and  round  in 
a  circle;  and  again  those  in  which  the  animal  turns  over  and  over  in  a 
series  of  somersaults.  Nearly  all  these  movements  may  result  on  section 
of  one  or  other  of  the  following  parts;  viz.,  crura  cerebri,  medulla, 
pons,  cerebellum,  corpora  quadrigemina,  corpora  striata,  optic  thalami, 
and  even,  it  is  said,  of  the  cerebral  hemispheres. 

Functions  of  the  Corpora  Quadrigemina  and  Geniculata. 

The  corpora  quadrigemina  are  the  homologues  of  the  optic  lobes  in 
birds,  amphibia,  and  fishes.     The  anterior  pair  may  be  regarded  as  the 


650  HANDBOOK    OF    PHYSIOLOGY. 

principal  nerve-centres  for  visual  sensations,  the  posterior  possibly  with 
auditory  sensation. 

Functions. — (1)  The  experiments  show  that  removal  of  the  anterior 
corpora  quadrigemina  wholly  destroys  the  power  of  seeing;  and  diseases 
in  which  they  are  disorganized  are  usually  accompanied  by  blindness. 
Atrophy  of  them  is  also  often  a  consequence  of  removal  of  the  eyes. 
Destruction  of  one  of  the  anterior  corpora  quadrigemina  (or  of  one  optic 
lobe  in  birds)  produces  hemiopia  of  opposite  field  of  vision.  This  loss  of 
sight  is  the  only  apparent  injury  of  sensibility  sustained  by  the  removal 
of  the  corpora  quadrigemina. 

The  (2)  removal  of  one  of  them  affects  the  movements  of  the  body, 
so  that  animals  rotate,  as  after  division  of  the  crus  cerebri,  only  more 
slowly :  but  this  may  be  due  to  giddiness  and  partial  loss  of  sight. 

(3)  The  more  evident  and  direct  influence  is  that  produced  on  the 
iris.  It  contracts  when  the  anterior  corpora  quadrigemina  are  irritated: 
it  is  always  dilated  when  they  are  removed :  so  that  they  may  be  regarded, 
in  some  measure  at  least,  as  the  nervous  centres  governing  its  move- 
ments, and  adapting  them  to  the  impressions  derived  from  the  retina 
through  the  optic  nerves  and  tracts. 

(4)  The  centre  for  the  co-ordination  of  the  movements  of  the  eyes  is 
also  contained  in  them.  This  centre  is  closely  associated  with  that  for 
contraction  of  the  pupil,  and  so  it  follows  that  contraction  or  dilatation 
follows  upon  certain  definite  ocular  movements. 

As  we  have  seen,  the  lateral  corpus  geniculatum  is  associated  on 
either  side  with  the  anterior  corpus  quadrigeminum,  and  the  median 
corpus  geniculatum  with  the  posterior  corpus  quadrigeminum. 

The  Sympathetic  System. — Having  in  the  preceding  chapters  com- 
pleted the  description  of  the  Cerebro-spinal  nervous  system  proper,  there 
remains  to  be  considered  the  structure  and  functions  of  the  so-called 
Sympathetic  nervous  system,  and  to  this  it  is  now  necessary  to  direct 
attention. 

It  should,  however,  be  distinctly  borne  in  mind  that  the  cerebro- 
spinal and  sympathetic  systems  are  not  distinct  from  one  another.  The 
separation  of  the  one  from  the  other  may  be  considered  to  be  purely  for 
the  sake  of  convenience. 

Distribution. — It  consists  of:  (1)  A  double  chain  of  ganglia  and 
fibres,  which  extends  from  the  cranium  to  the  pelvis,  along  each  side  of 
the  vertebral  column,  and  from  which  branches  are  distributed  both  to 
the  cerebro-spinal  system,  and  to  other  parts  of  the  sympathetic  system. 
With  these  may  be  included  the  small  ganglia  in  connection  with  those 
branches  of  the  fifth  cerebral  nerve  which  are  distributed  in  the  neigh- 
borhood of  the  organs  of  special  sense :  namely,  the   Ophthalmic^  OtiCj 


THE    NERVOUS    SYSTEM. 


051 


Fig.  390.— Diaf^rammatic  view  of  the 
Sympathetic  cord  of  the  j-ight  side,  show- 
ing its  connections  with  tlie  jjiincipal 
cerebro-spinal  nerves  and  the  main  prae- 
aortic  plexuses.  >4.  (,From  Quain's 
Anatomy.) 

Cerebro-spinal  nerves.~Yl.,  a  portion 
of  the  sixth  cranial  as  it  passes  throuKh 
the  cavernous  sinus,  receiving  two  twigs 
from  the  carotid  ple.'^us  of  the  sympathe- 
tic nerve;  O,  ophthalmic  ganghon  con- 
nected by  a  twig  with  the  carotid  plexus; 
M,  connection  of  the  spheuo-palatiue 
ganglion  by  the  Vidian  nerve  with  the 
carotid  plexus;  C,  cervical  plexus;  Br, 
brachial  plexus;  D  0.  sixth  intercostal 
nerve;  D  Id,  twelfth;  L  3,  third  lumbar 
nerve;  S  1,  first  sacral  nerve;  S  3,  third; 
S  5,  fifth;  Cr,  anterior  crural  nerve;  Cr', 
great  sciatic ;  pn,  vagus  in  the  lower  part 
of  the  neck;  r,  recurrent  nerve  winding 
round  the  subclavian  artery. 

Sympathetic  Cord—c,  superior  cervi- 
cal ganglion;  e',  second,  or  middle;  c",in- 
ferior:  f  lom  each  of  these  ganglia  cardiac 
nerves  (all  deep  on  this  side )  are  seen  de- 
scending to  the  cardiac  plexus;  d  1. 
placed  immediately  below  the  first  dorsal 
sympathetic  ganglion;  d  6,  is  opposite 
thesi.\th;  1 1,  first  lumbar  ganglion;  c  g, 
the  terminal  or  coccygeal  ganglion. 

Prceaortic  and  Visceral  Plexuses. ^pj). 
pharyngeal,  and,  lower  down,  laryngeal 
plexus;  pi,  post-pulmonar3'  plexus 
spreading  from  the  vagus  on  the  back  of 
the  right  bronchus;  ca,  on  the  aorta,  the 
cardiac  plexus,itowardswhich,  inaddition 
to  the  cardiac  nerves  from  the  three  cer- 
vical symiiathetic  gangUa,  other  branch- 
es are  seen  descending  from  the  vagus 
and  recurrent  nerves;  co,  ri^it  or  poste- 
rior and  CO' .  left  or  ant.  coronary  plexus; 
o,  oesophageal  plexus  in  long  meshes  on 
the  gullet;  sp,  great  splanchnic  nerve 
formed  by  branches  from  the  fifth,  sixtli, 
seventh, eighth, and nintli  dorsal  ganglia; 
-|-,  small  splatichnic  from  the  ninth  and 
tenth;  +  -f,  smallest  or  third  splanchnic 
from  the  eleventh ;  the  first  and  second  of 
these  are  shown  joining  the  solar  plexus, 
s  o;  the  third  descending  to  the  renal 
plexus,  ?-e;  connecting  branches  between 
the  solar  plexus  and  the  vagi  are  also  rep- 
resented; p*i',  aiiovcthe  place  wherethe 
right  vagus  passes  to  the  lower  or  pos- 
terior surface  of  the  stomach;  2>»",  the 
left  distributed  on  the  anterior  or  upper 
sin'face  of  the  cardiac  portion  of  the  or- 
gan: from  thesolar  ])lexus  large  branch- 
es are  seen  surrounding  the  arteries  of 
the  coeliac  axis,  and  descending  to  in  s, 
the  sup.  mesenteric  ple.xus;  opposite  to 
this  is  an  indication  of  the  suprarenal 
plexus;  below  r  e  ( tlio  renal  plexus i,  the 
spermatic  plexus  is  also  indicated;  ao,  on 
the  front  of  the  aiuta.  marks  the  aortic 
plexus,  formed  by  nerves  descending 
from  the  solar  and  sup.  mesenteric  plex- 
uses and  from  the  lumliar  ganglia;  r»/, 
the  inf.  mesenteric  ple.vus  surrounding 
thecorrespondiugartery :/(//,  hv]  11  igastric 
plexus  placed  betwei'ii  the  edmrridii  Uiai 
vessels,  connected  alxive  v.itli  tlie  aoitic 
plexus,  receiving  nerves  from  tlit^  lower 
lumbar  ganglia,  and  dividing  lielmv  into 
the  right  and  left  jielvic  or  inf.  liyjiogas 
trie  piexuses;p/,  the  right  jielvic  jili  \ns, 
from  this  the  nerves  descending  ai  i  join- 
ed by  those  from  the  plexus  on  the  sup. 
hemorrhoidal  vessels,  mi',  bynervesfroni 
the  sacral  ganglia,  and  by  visceral 
nerves  from  the  third  anil  fourth  sawal 
spinal  nerves,  and  there  are  thus  formed 
the  rectal,  vesical,  and  other  plexuses,  which  ramify  upon  the  viscera,  as  towards  tr,  and  v,  the 
rectum  and  bladder. 


052  HANDBOOK    OF    PHYSIOLOGY. 

Splieno-palatine  and  Submaxillary  ganglia,  (2)  Various  ganglia  and 
plexuses  of  nerve-fibres  which  give  off  brandies  to  the  thoracic  and  ab- 
dominal viscera,  the  chief  of  such  plexuses  being  the  Cardiac,  Solar^ 
and  Hypogastric;  but  inintimate  connection  with  these  are  many  second- 
ary plexuses,  as  the  Aortic,  Spermatic,  and  Renal.  To  these  plexuses, 
fibres  pass  from  the  prsevertebral  chain  of  ganglia,  as  well  as  from  cerebro- 
spinal nerves.  (3)  Various  ganglia  and  plexuses  in  the  substance  of 
many  of  the  viscera,  as  in  the  Stomach,  Intestines,  and  Urinary  'bladder. 
These,  which  are,  for  the  most  part,  microscopic,  also  freely  communi- 
cate with  other  parts  of  the  sympathetic  system,  as  well  as,  to  some  ex- 
tent, with  the  cerebro-spinal.  (4)  By  many,  the  ganglia  on  the  Pos- 
terior roots  of  the  spinal  nerves,  on  the  Glossopharyngeal  and  Vagus,  and 
on  the  Sensory  root  of  the  Fifth  cerebral  nerve  (Gasserian  ganglion) ,  are 
also  included  as  sympathetic-nerA^e  structures. 

Classification. — Gaskell's  researches  have  suggested  a  convenient 
classification  for  the  sympathetic  ganglia  into:  (1.)  The  main  sympa- 
thetic chain,  extending  from  above  downward,  in  the  form  of  connected 
ganglia  lying  upon  the  bodies  of  the  vertebrse,  which  may  be  called 
lateral  or  vertebral  ganglia.  (2).  A  more  or  less  distinct  chain,  prsever- 
tebral in  position,  consisting  of  the  semi-lunar,  inferior  mesenteric  and 
similar  plexuses,  which  may  be  called  collateral  ganglia.  (3.)  Ganglia 
situated  in  the  organs  and  tissues  themselves,  called  terminal  ganglia. 
(4.)  The  ganglia  of  the  p)Osterior  roots  of  the  spinal  nerves. 

The  connection  between  these  parts  is  as  follows:  the  visceral  branch 
or  ramus  communicans  of  each  spinal  nerve,  which  is  one  of  the  divi- 
sions of  a  typical  spinal  nerve — the  others  being  the  dorsal  and  ventral 
— passes  first  of  all  into  the  lateral  chain ;  from  this  chain  branches, 
rami  efferentes,  joass  into  the  collateral  ganglia,  and  from  these  again 
other  branches  pass  off  into  the  orga,ns  to  end  in  the  terminal  ganglia. 
In  the  thoracic  region  the  rami  communicantes  are  composed  of  two  parts, 
white  and  gray.  The  former  can  be  traced  backward  into  both  spinal 
nerve-roots  of  their  corresponding  spinal  nerve ;  and  in  the  other  direc- 
tion partly  into  the  lateral  sympathetic  chain,  and  partly  into  the  great 
splanchnic  nerves  and  so  into  the  collateral  ganglia  without  entering 
the  lateral  chain  at  all.  The  upper  ivhite  rami  (from  the  2nd  to  the 
5th),  however,  proceed  upward  and  Join  the  superior  cervical  ganglion 
instead  of  passing  downward  into  the  splanchnics.  Other  branches  go 
downward  into  the  lumbar  and  sacral  plexuses.  The  gray  rami  of  all 
the  spinal  nerves  are  the  only  apparent  representatives  of  the  visceral 
branches  in  the  regions  above  the  2nd  thoracic  nerve-root,  and  below 
the  2nd  lumbar  nerve-root,  with  the  exception  of  the  roots  of  the  2nd 
and  3rd  sacral  nerves,  which  have  also  white  rami,  and  consist  of  non- 
medullated  fibres,  and  pass  from  the  ganglia  to  be  distributed  chiefly  to 


THE   NERVOUS   SYSTEM.  653 

the  spinal  column,  to  the  spinal  membranes  and  to  the  spinal  nerve-roots 
themselves.  We  must  look  upon  the  white  rami  then  as  the  visceral 
branches  proper. 

A  peculiarity  in  the  structure  of  these  white  medullated  visceral 
nerves  is  the  fineness  of  their  fibres.  They  are  a  third  or  a  fourth  of  the 
diameter  of  ordinary  medullated  fibres,  measuring  I.S/j.  to  2.7//  instead 
of  14.4//  to  19//.  Such  fibres  are  a  peculiarity  of  the  spinal  nerve-roots 
chiefly  in  the  thoracic  region,  but  they  are  also  found  in  the  second  and 
third  sacral  nerves,  and  constitute  there  the  nervi  erigentes  which  pass 
directly  to  the  hypogastric  plexus,  and  not  first  of  all  into  the  lateral 
chain.  From  this  plexus  branches  pass  upward  into  the  inferior, 
mesenteric  ganglia  and  downward  to  the  bladder,  rectum  and  generative 
organs.  These  nerves,  called  by  Gaskell  pelvic  splanchnio  nerves,  differ 
from  the  rami  viscerales  of  the  thoracic  region  only  in  not  communicat- 
ing with  the  lateral  ganglia;  the  branches  which  pass  upward  from  the 
thoracic  region  to  the  neck,  he  calls  cervical  sjAanchnics,  and  the 
splanchnics  proper  iibdominal  splanclinics.  The  white  rami  viscerales  of 
the  upper  cervical  and  cervico-cranial  regions  do  not  run  with  their 
corresponding  gray  rami,  but  form,  Gaskell  thinks,  the  internal  branch 
of  the  spinal  accessory  nerve,  which  contains  small  medullated  fibres 
similar  to  those  of  the  visceral  branches  in  the  thoracic  region.  This 
branch  passes  into  the  ganglion  of  the  trunk  of  the  vagus.  Small  visceral 
fibres  exist  too  in  the  roots  of  the  vagus,  and  in  those  of  the  glosso-pharyn- 
geal  in  connection  with  the  ganglion  of  the  trunk  and  ganglion  petrosum, 
as  well  as  in  the  chorda  tympani,  in  the  small  petrosal  and  in  other 
cranial  visceral  nerves. 

Functions. — The  researches  of  Gaskell  have,  however,  done  much  to 
clear  up  the  former  confusion  as  to  the  functions  of  the  sympathetic; 
and  in  the  following  account  the  description  of  the  functions,  as  given 
by  that  observer,  is  followed. 

The  efferent  nerve  fihves  of  the  sympathetic  system  supply  {a)  the 
muscles  of  the  vascular  system,  to  which  they  send  vaso-motor  fibres, 
i.e.,  vaso-constrictor  and  cardiac  angnientor  or  accelerator,  and  vaso-in- 
hibitory  fibres,  i.e.,  vaso-dilator  and  cardiac  inhibitor i/j  {!))  the  visceral 
muscles,  to  which  they  send  both  viscero-motor  and  riscero-inhibitori/ 
fibres,     (c)  The  secretory  gland-cells. 

(rt)  i.  Vaso-niotor  or  Vaso-condrictor-M\d  Cardio-augnienlor  Fibres. — 
The  vaso-motor  nerves  for  all  parts  of  the  body  come  from  the  central  ner- 
vous system,  and  pass  out  from  the  spinal  cord  in  the  white  rami  viscerales 
of  the  thoracic  region  from  the  second  thoracic  to  the  second  lumbar  nerve- 
roots  inclusive,  as  fine  medullated  fibres;  tliey  then  pass  to  the  lateral  or 
main  sympathetic  chain,  become  non-medullated,  and  are  distributed  to 
their  muscles  either  directly  or  through  terminal  ganglia.     Thus  the  aug- 


654  HANDBOOK    OF    PHYSIOLOGY. 

mentor  nerves  of  the  heart  arise  in  the  thoracic  rami,  pass  upward 
through  the  ganglion  stellatum  (first  thoracic  ganglion),  the  annulus  of 
Yieussens  and  the  inferior  cervical  ganglion,  and  are  distributed  to  the 
heart ;  the  vaso-motor  roots  of  the  brachial  plexus,  in  the  anterior  roots 
of  the  second  and  lower  thoracic  nerves,  and  reach  that  plexus  by  the 
same  ganglion ;  the  vaso-motor  nerves  of  the  foot  leave  the  spinal  cord 
high  up,  and  reach  the  sympathetic  lateral  ganglia  above  the  origin  of 
the  sciatic  nerve,  into  which  they  pass  through  the  abdominal  sympa- 
thetic. In  all  cases  the  nerves  lose  their  medulla  in  the  ganglia. 
Similarly  the  vaso-motor  nerve  supply  for  the  blood-vessels  of  the  head 
and  neck  and  of  the  abdomen  is  derived  from  the  cervical  and  abdominal 
splanchnics  respectively,  or  from  the  corresponding  rami  efPerentes  of 
the  upper  lumbar  ganglia. 

The  lateral  sympathetic  chain  Gaskell  proposes  to  call  the  cham  of 
vaso-tnotor  ganglia. 

ii.  Vaso-inhiMtory  or  Vaso-dilator,  and  Cardio-mhihitory  Fibres. — 
Of  these,  which  are  doubtless  as  widely  distributed  as  the  vaso-motor 
fibres,  we  have  distinct  proof  in  the  existence  of  fibres  separate  from 
vaso-motor,  e.g..,  in  the  inhibitory  nerve  of  the  heart,  the  cardio-vagus ; 
in  the  chorda  tympani ;  in  the  small  petrosal,  and  in  the  nervi  erigentes. 

These  nerve-fibres,  as  far  as  we  know  at  present,  leave  the  central 
nervous  system  among  the  fine  medullated  nerves  of  the  cervico-crania\ 
and  sacral  rami  communicantes,  do  not  enter  the  lateral  ganglia,  but 
pass  without  losing  their  medulla  into  the  collateral  or  terminal 
ganglia. 

(Z». )  i.  Viscero-motor  Fibres. — These  fibres,  upon  which  depend  the 
peristaltic  movements  of  the  thoracic  portion  of  the  oesophagus,  and  of 
the  stomach  and  intestines,  arise  from  the  central  nervous  system,  as 
the  fine  medullated  fibres  of  the  upper  portion  of  the  cervical  region,  not 
in  the  spinal  nerve-roots  of  that  region,  but  as  the  bundles  of  fibres 
which  may  be  called  the  rami  viscerales  of  the  vagus  and  accessory  nerves. 
They  pass  to  the  ganglion  of  the  trunk  of  the  vagus,  where  they  lose 
their  medulla. 

ii.  Viscero- Inhibitory  Fibres. — It  appears  that  the  nerve  supply  to 
the  circular  muscles  of  the  alimentary  canal  and  its  appendages,  is  con- 
tained in  the  abdominal  splanchnics,  and  consists  of  those  fibres  which 
have  not  passed  through  the  lateral  chain,  and  which  therefore  retain 
their  medulla  until  they  reach  the  proximal  or  collateral  chain. 

(c.)  Glandular  Nerve- Fibres. — A  double  nerve  supply,  in  all  proba- 
bility coinciding  with  the  supply  to  the  visceral  muscles,  has  been 
demonstrated  in  the  cases  of  the  submaxillary,  parotid,  and  lachrymal 
glands,  and  in  these  cases  the  course  of  the  fibres  is  very  similar  to 
that  of  the  corresponding  fibres  for  the  vaso-muscular  supply.     Thus 


THE    XERVOUS    SYSTEM.  655 

the  sympathetic  supply  for  these  glands  passes  along  with  the  vaso- 
motor fibres  from  the  cervical  splanchnic  (or  sympathetic  trunk),  and 
superior  cervical  ganglion;  while  the  cerebro-spinal  supply  comes  from 
the  rami  viscerales  of  the  cranial  nerves  in  conjunction  with  the  vaso- 
dilator fibres. 

Central  Origin  of  the  Rami  Viscerales. — There  appears  to  be  the 
strongest  presumption  that  the  white  rami  of  the  thoracic  region  arise 
in  the  spinal  cord  in,  or  are  connected  with,  the  cells  of  the  posterior 
vesicular  column  of  Clarke.  This  conclusion  is  based  upon  the  fact  that 
these  special  cells  are  found  in  the  three  regions  already  mentioned,  and 
in  those  only  where  the  white  rami  of  fine  medullated  fibres  exist,  viz., 
in  the  cervico-cranial  regions,  in  the  spinal  accessory,  in  the  thoracic 
region,  and  in  the  sacral  region.  But  it  is  probable  that  the  fibres  are 
also  connected  with  the  cells  of  the  lateral  horn  of  the  gray  matter  of 
the  spinal  cord,  and  its  representative  in  the  medulla,  the  antero-lateral 
nucleus  of  Clarke. 

In  a  paper  supplementary  to  his  first  account  of  the  sympathetic 
system,  Gaskell  traced  the  nerve  fibres  of  the  anterior  nerve  roots  to  the 
various  groups  of  nerve  cells  in  the  spinal  cord  thus:  (i.)  Efferent 
nerves  to  somatic  muscles  arise  from  group  of  cells  of  anterior  cornua; 
(ii.)  efferent  nerves  to  striated  splanchnic  muscles  from  cells  of  the  trac- 
tus  intermedio-lateralis.  (iii-)  Anabolic  or  inhibitory  nerves  to  glands, 
muscles  of  viscera,  and  vessels  of  splanchnic  system  from  cells  of  Clarke's 
column;  (iv.)  motor  nerves  to  visceral  muscles  from  solitary  cells  at  the 
base  of  the  posterior  cornu ;  and  (v. )  motor  or  catabolic  nerves  to  glands 
and  vascular  muscles  from  small  cells  of  the  lateral  cornu. 

Structure  and  Functions  of  the  Ganglia. — The  sympathetic 
gauglia  all  contain — (1.)  nerve-fibres  traversing  them;  (3.)  nerve-fibres 
originating  in  them,  (3.)  nerve  or  ganglion-corpuscles,  giving  origin  to 
these  fibres;  and  (4.)  other  corpuscles  that  appear  free.  In  the  sym- 
pathetic ganglia  of  the  frog,  ganglion-cells  of  a  very  complicated  struc- 
ture have  been  described  by  Beale,  and  subsequently  by  Arnold.  The 
cells  are  inclosed  each  in  a  nucleated  capsule :  they  are  pyriform  in  shape, 
and  from  the  pointed  end  two  fibres  are  given  oft",  which  gradually 
acquire  the  characters  of  nerve-fibres;  one  of  them  is  straight,  and  the 
other  (which  sometimes  arises  from  the  cell  by  two  roots)  is  spirally 
coiled  around  it. 

According  to  Gaskell  the  functions  of  the  main  sympathetic  ganglia 
are  the  following: — (1.)  They  effect  the  conversion  of  medullated  into 
non-medullated  fibres;  (2.)  They  possess  a  nutritive  infiuence  over  the 
nerves  which  pass  from  them  to  the  periphery;  (3.)  They  increase  the 
number  of  fibres  at  the  same  time  as  they  cause  the  removal  of  the 
medulla.     As  regards  their  possession  of  the  usual  properties  of  nerve- 


656  HANDBOOK    OF    PHYSIOLOGY. 

centres  little  or  nothing  is  certainly  known.  It  appears  unlikely  that 
they  possess  the  reflex  functions  of  the  spinal  centres. 

As  a  contribution  toward  the  explanation  of  the  nervous  mechanism 
of  nutrition  comes  in  Gaskell's  theory  of  kataholic  and  anabolic  nerves. 
He  supposes  that  every  tissue  is  supplied  with  two  sets  of  nerves,  the 
former  of  which  corresponds  with  the  motor  nerve,  the  viscero-motor 
and  the  cardio-augmentor,  by  the  stimulati<5n  of  which  an  increase  of 
the  metabolism  takes  place,  and  which  is  followed  by  exhaustion.  It 
may  be  accompanied  either  by  contraction  of  a  muscle  or  by  an  increase 
of  contraction.  Such  a  nerve  is  excellently  illustrated  by  the  sympa- 
thetic augmentor  or  accelerator  nerve  of  the  heart,  on  stimulation  of 
which  an  increase  in  the  force  and  frequency  of  the  heart  takes  place, 
followed  after  a  time  by  exhaustion.  A  katabolic  nerve  stimulates  the 
destructive  metabolism  which  is  always  going  on  in  a  tissue.  The 
anabolic  nerve  is  the  exact  opposite  of  the  katabolic  nerve  in  function. 
It  subserves  constructive  metabolism.  Stimulation  of  the  nerve  pro- 
duces diminished  activity,  repair  of  tissue  and  building  up.  An  exam- 
ple of  this  kind  of  nerve  is  seen  in  the  cardiac  vagus,  stimulation  of 
which  produces  inhibition.  Inhibition  must  generally  be  looked  upon 
as  an  anabolic  process. 

It  will  be  seen  that  the  results  of  stimulation  of  the  nerves  to  the 
salivary  glands,  discussed  in  a  former  chapter,  appear  to  support  the 
theory,  that  the  processes  of  constructive  and  destructive  metabolism 
are  under  the  control  of  separate  nerve-fibres.  In  the  case  of  the  sub- 
maxillary gland  for  example,  if  the  sympathetic  fibres  be  stimulated,  a 
katabolic  effect  is  produced,  and  the  materials  of  secretion  are  formed  at 
the  expense  of  the  protoplasm  (this  action  in  the  case  of  the  gland 
Heidenhain  calls  trophic) ;  if  on  the  other  hand  the  chorda  tympani  or 
the  secretory  nerve  be  stimulated,  two  things  happen,  one  being  the 
discharge  of  water  and  the  materials  of  secretion  from  the  gland  cells, 
and  the  other  the  building  up  or  reconstruction  of  the  protoplasm  of  the 
cells.  A  part  of  this  action  at  any  rate  is  anabolic,  and  similar  to  the 
action  of  inhibitory  nerves. 


CHAPTEK    XVII. 

THE    SENSES. 

General  Considerations. — Through  the  medium  of  the  nervous  sys- 
tem the  mind  obtains  a  knowledge  of  the  existence  both  of  the  various 
parts  of  the  body,  and  of  the  external  world.  This  knowledge  is  based 
upon  sensations  resulting  from  the  stimulation  of  certain  centres  in  the 
brain,  by  irritations  conveyed  to  them  by  afferent  nerves.  Under  normal 
circumstances,  the  following  structures  are  necessary  for  sensation:  [a) 
A  peripheral  organ  for  the  reception  of  the  impression ;  {h)  a  nerve  for 
conducting  it;  (c)  a  nerve-centre  for  feeling  or  perceiving  it. 

Classification  of  Sensations. — Sensations  may  be  conveniently  classed 
as  (1)  common  and  (2)  special. 

(1.)  Common  Sensations. — Under  this  head  fall  all  those  general 
sensations  which  cannot  be  distinctly  localized  in  any  particular  part  of 
the  body,  such  as  fatigue,  discomfort,  faintness,  satiety,  together  with 
hunger  and  thirst,  in  which,  in  addition  to  a  general  discomfort,  there  is 
in  many  persons  a  distinct  sensation  referred  to  the  stomach  or  fauces. 
In  this  class  must  also  be  placed  the  various  irritations  of  the  mucous 
membrane  of  the  bronchi,  which  give  rise  to  coughing,  and  also  the 
sensations  derived  from  various  viscera  indicating  the  necessity  of  ex- 
pelling their  contents;  e.g.,  the  desire  to  defecate,  to  urinate,  and,  in 
the  female,  the  sensations  which  precede  the  expulsion  of  the  foetus. 
We  must  also  include  such  sensations  as  itching,  creeping,  tickling, 
tingling,  burning,  aching,  etc.,  some  of  which  come  under  the  head  of 
pain:  they  will  be  again  referred  to  in  describing  the  tactile  sense.  It 
is  impossible  to  draw  a  very  clear  line  of  demarcation  between  many  of 
the  common  sensations  above  mentioned,  and  the  sense  of  touch,  which 
forms  the  connecting  link  between  the  general  and  special  sensations. 
Touch  is,  indeed,  usually  classed  with  the  special  senses,  and  will  be 
considered  in  the  same  group  with  them;  yet  it  differs  from  them  in 
being  common  to  many  nerves.  Among  common  sensations  some  would 
rank  the  muscular  sense,  which  has  been  already  alluded  to.  It  is  by 
means  of  this  sense  that  we  become  aware  of  the  condition  of  the  mus- 
cles, and  thus  obtain  the  information  necessary  for  their  adjustment  to 
various  purposes — standing,  walking,  grnsping,  etc.  This  muscular 
sensibility  (to  which  we  shall  again  refer)  is  shown  in  our  power  to  esti- 
4?  657 


658  HA]!TDBOOK    OF    PHYSIOLOGY. 

mate  the  difEerences  between  weights  by  the  different  muscular  efforts 
necessary  to  raise  them.  It  must  be  carefully  distinguished  from  the 
sense  of  contact  and  of  pressure,  of  which  the  skin  is  the  organ.  "When 
standing  erect,  we  can  feel  the  ground  (contact),  and  further  there  is  a 
sense  of  pressure,  due  to  our  feet  being  pressed  against  the  ground  by 
the  weight  of  the  body.  Both  these  are  derived  from  the  skin  of  the 
sole  of  the  foot.  If  now  we  raise  the  body  on  the  toes,  we  are  conscious 
(muscular  sense)  of  a  muscular  effort  made  by  the  muscles  of  the  calf, 
which  overcomes  a  certain  resistance. 

(2.)  Special  Sensations. — Including  the  sense  of  touch,  the  special 
senses  are  five  in  number — Touch,  Taste,  Smell,  Hearing,  Sight. 

The  most  important  distinction  between  common  and  special  sensa- 
tions is  that  by  the  former  we  are  made  aware  of  certain  conditions  of 
various  parts  of  our  bodies,  while  from  the  latter  we  gain  our  knowledge 
of  the  external  world  also.  This  difference  will  be  clear  if  we  compare 
the  sensations  of  pain  and  touch,  the  former  of  which  is  a  common,  the 
latter  a  special  sensation.  "  If  we  place  the  edge  of  a  sharp  knife  on 
the  skin,  we  feel  the  edge  by  means  of  our  sense  of  touch;  we  perceive 
"a  sensation,  and  refer  it  to  the  object  which  has  caused  it.  -  But  as  soon 
as  we  cut  the  skin  with  the  knife,  we  feel  pain,  a  feeling  which  we  no 
longer  refer  to  the  cutting  knife,  but  which  we  feel  within  ourselves, 
and  which  communicates  to  us  the  fact  of  a  change  of  condition  in  our 
own  body.  By  the  sensation  of  pain  we  are  neither  able  to  recognize 
the  object  which  caused  it,  nor  its  nature." 

In  studying  the  phenomena  of  sensation,  it  is  important  clearly  to 
understand  that  the  sensorium,  or  seat  of  sensation,  is  in  the  brain,  and 
not  in  the  particular  organ  through  which  the  sensor}^  impression  is  re- 
ceived. In  common  parlance  we  are  said  to  see  with  the  eye,  hear  with 
the  ear,  etc.,  but  in  reality  these  organs  are  only  adapted  to  receive 
impressions  which,  being  conducted  to  the  sensorium,  through  their  re- 
spective nerves  give  rise  to  sensation. 

Hence,  if  the  optic  nerve  is  severed,  vision  is  no  longer  possible: 
since,  although  the  image  falls  on  the  retina  as  before,  the  sensory  im- 
pression can  no  longer  be  conveyed  to  the  sensorium.  "When  any  given 
sensation  is  felt,  all  that  we  can  with  certainty  affirm  is  that  some  part 
of  the  brain  is  excited.  The  exciting  cause  may  be  some  object  of  the 
external  world,  producing  an  objective  sensation;  or  the  condition  of  the 
sensorium  may  be  due  to  some  excitement  within  the  brain  itself,  in 
which  case  the  sensation  is  termed  subjective.  The  mind  habitually  re- 
fers sensations  to  external  causes ;  and  hence,  whenever  they  are  subjec- 
tive we  can  hardly  divest  ourselves  of  the  idea  of  an  external  cause,  and 
an  illusion  is  the  result. 

Numberless  examples  of  such  illusions  might  be  quoted.     As  familiar 


THE   SENSES.  65!) 

cases  may  ^c  rnentioncd,  luiiiimiug  aud  buzzing  in  the  ears  caused  by 
some  irritation  of  tlie  auditory  nerve  or  centre,  and  even  musical  sounds 
and  voices  (sometimes  termed  auditory  spectra) ;  also  so-called  optical 
illusions:  objects  are  described  as  seen,  althougli  not  present.  Such 
illusions  are  most  strikingly  exemjilified  in  cases  of  delirium  tremens  or 
other  forms  of  deliriuiu,  and  may  take  the  form  of  cats,  rats,  creeping 
loatlisome  forms,  etc. 

Causes  of  Illusions. — One  uniform  intenial  cause,  which  nuiy  a(^t  on 
all  the  nerves  of  the  senses  in  the  same  manner,  is  capillary  congestion. 
This  one  cause  excites  in  the  retina,  while  the  eyes  are  closed,  the  sensa- 
ions  of  light  and  luminous  flashes;  in  the  auditory  nerve,  the  sensation 
of  humming  and  ringing  sounds;  in  the  olfactory  nerve,  the  sense  of 
odors;  and  in  the  nerves  of  feeling,  the  sensation  of  pain.  In  the  same 
way,  also,  a  narcotic  substance  introduced  into  the  blood,  excites  in  the 
nerves  of  each  sense  peculiar  symptoms :  in  the  optic  nerves,  the  appear- 
ance of  luminous  sparks  before  the  eyes;  in  the  auditory  nerves,  tinnitus 
aurium;  and  in  the  common  sensory  nerves,  the  sensations  of  creeping 
over  the  surface.  So,  also,  among  external  causes,  the  stimulus  of  elec- . 
tricity,  or  the  mechanical  influence  of  a  blow,  concussion,  or  pressure, 
excites  in  the  eye  the  sensation  of  light  and  colors;  in  the  ear,  a  sense 
of  a  loud  sound  or  of  ringing;  in  the  tongue,  a  saline  or  acid  taste;  and 
in  the  other  parts  of  the  body,  a  perception  of  peculiar  jarring  or  of  the 
mechanical  impression,  or  a  shock  like  it. 

Experiments  seem  to  have  proved,  however,  that  none  of  tlie  nerves 
of  special  sense  i^ossess  the  faculty  of  common  sensibility. 

PercejHions. — The  habit  of  constantly  referring  our  sensations  to  ex- 
ternal causes,  leads  us  to  interpret  the  various  modifications  whicli 
external  objects  produce  in  our  sensations,  as  properties  of  the  external, 
bodies  themselves.  Thus  we  speak  of  certain  substances  as  possessing  a 
disagreeable  taste  aud  smell;  whereas,  tlie  fact  is,  their  taste  and  smell 
are  only  disagreeable  to  vs.  It  is  evident,  however,  that  on  this  habit 
of  referring  our  sensations  to  causes  outside  ourselves  (perception),  de- 
pends the  reality  of  the  external  world  to  us;  and  nu)re  especially  is  this 
the  case  with  the  senses  of  touch  luul  sight.  By  the  co-operation  of 
these  two  senses,  aided  by  the  others,  we  are  enabled  gradually  to  at- 
tain II  knowledge  of  external  objects  which  daily  experience  confirms, 
until  we  come  to  place  unbounded  confidence  in  what  is  termed  the 
evidence  of  the  senses. 

Judgments. — AVe  must  draw  a  distinction  between  mere  sensations, 
and  the  judgments  based,  often  unconsciously,  upon  them.  Tlius,  in 
looking  at  a  near  object,  we  unconsciously  estiirmte  its  distance  and  say 
it  seems  to  be  ten  or  twelve  feet  off:  but  the  estimate  of  its  distance  is 
I'u  reality  a  judgment  based  ou  many  things  besides  the  appearance  of 


G60  HANDBOOK    OF    PHYSIOLOGY. 

the  object  itself;  among  which  may  be  mentioned  the  number  of  inter- 
vening objects,  tlie  number  of  steps  which  from  past  experience  we 
know  we  must  take  before  we  could  touch  it,  and  many  others. 

The  Special  Senses. 
I.  Touch. 

Seat. — The  sense  of  touch  is  not  confined  to  particular  parts  of  the 
body  of  small  extent,  like  the  other  senses;  on  the  contrary,  all  parts 
capable  of  perceiving  the  presence  of  a  stimulus  by  ordinary  sensation 
are,  in  a  certain  degrees,  the  seat  of  this  sense ;  but  touch  should  not  be 
considered  as  a  mere  modification  or  exaltation  of  common  sensation  or 
sensibility.  For  although  the  nerves  on  which  the  sense  of  touch  de- 
pends, are  the  same  as  those  which  confer  ordinary  sensation  on  the 
different  parts  of  the  body,  viz.,  those  derived  from  the  posterior  roots 
of  the  nerves  of  the  spinal  cord,  and  the  sensory  cerebral  nerves,  yet  it 
seems  probable  that  the  nerve-fibres  which  subserve  the  special  sense  of 
touch  are  provided  with  special  end  organs. 

All  parts  of  the  body  supplied  with  sensory  nerves  are  thus,  in  some 
degree,  organs  of  touch,  yet  the  sense  is  exercised  in  perfection  only  in 
those  parts  the  sensibility  of  which  is  extremely  delicate,  e.g. ,  the  skin, 
the  tongue,  and  the  lips,  which  are  provided  with  abundant  papilla. 
A  peculiar  and,  of  its  own  kind  in  each  case,  a  very  acute  sense  of  touch 
is  exercised  through  the  medium  of  the  nails  and  teeth.  To  a  less  extent 
the  h.-ir  may  be  reckoned  an  organ  of  touch ;  as  in  the  case  of  the  eye- 
lashes. The  sense  of  touch  renders  us  conscious  of  the  presence  of  a 
stimulus,  from  the  slightest  to  the  most  intense  degree  of  its  action,  by 
that  indescribable  something  which  we  call  feeling,  or  common  sensa- 
tion. The  modifications  of  this  sense  often  depend  on  the  extent  of  the 
parts  affected.  The  sensation  of  pricking,  for  example,  informs  us  that 
the  sensitive  fibres  are  intensely  affected  in  a  small  extent ;  the  sensation 
of  pressure  indicates  a  slighter  affection  of  the  parts  in  the  greater  ex- 
tent, and  to  a  greater  depth.  It  is  by  the  depth  to  which  the  parts  are 
affected  that  the  feeling  of  pressure  is  distinguished  from  that  of  mere 
contact. 

Varieties. — {a)  The  sense  of  touch  proper,  tactile  sensibility  or  pres- 
sure, {!))  temperature.  These  when  carried  beyond  a  certain  degree  are 
merged  in  the  sensation  of  (c)  pain. 

Touch  proper. — In  almost  all  parts  of  the  body  which  have  deli- 
cate tactile  sensibility  the  epidermis,  immediately  over  the  papillae,  is 
moderately  thin.  When  its  thickness  is  much  increased,  as  over  the 
heel,  the  sense  of  touch  is  very  much  dulled.  On  the  other  hand,  when 
it  is  altogether  removed,  and  the  cutis  laid  bare,  the  sensation  of  con- 


THE   SENSES.  fJOl 

tact  is  replaced  by  one  of  pain.  Furtlier,  in  all  highl}'  sensitive  parts, 
the  jjapillae  are  numerous  aucl  highly  vascular,  and  the  sensory  nerves 
are  connected  with  special  end-organs  which  have  been  described  p.  99 
et  seq. 

The  special  endings  of  the  nerves  Avhich  have  to  do  with  toucli  may, 
liowever,  be  here  again  mentioned.  They  are  of  two  kinds,  viz.,  (a) 
touch  rorpiiscJes,  which  are  found  chiefly  in  the  hands  and  feet,  particu- 
larly on  the  palmar  surface  of  the  hands  and  fingers,  but  also  on  the 
under  surface  of  the  forearm,  nipple,  eyelids,  lips,  and  genital  organs. 
Touch  corpuscles  are  situated  in  the  cutis  vera,  (b)  end  bulbs,  which 
are  found  in  conjunctivae  and  other  mucous  membranes,  the  lips,  genital 
organs,  tongue,  rectum,  and  elsewhere,  but  not  in  the  skin  proper.  As 
regards  the  Pacinian  corpuscles  and  similar  end-organs,  which  ai'e  so 
widely  distributed,  and  which  may  be  in  some  way  connected  with  the 
sensation,  when  they  are  found  in  the  skin  they  are  situated  very  deeply 
in  the  cutis  vera  or  in  the  subcutaneous  tissue.  They  are  extremely 
numerous  on  the  nerves  of  the  palmar  surface  of  the  fingers.  In  all  of 
these  endings,  and  iii  similar  ones  found  in  other  animals,  the  nerve 
ends,  as  in  axis  cylinder,  in  a  special  development  of  the  connective  tis- 
sue sheath.  In  addition  to  these  special  nerve-endings,  nerve-fibres 
appear  to  terminate  everywhere  in  the  skin  between  the  cells  of  the 
Malpighian  stratum  of  the  epidermis  in  the  ends,  and  in  certain  animals 
some  of  them  appear  to  end  in  special  and  rather  large  cells. 

It  is  practically  impossible  to  distinguish  between  what  is  called 
mere  contact  and  touch  in  which  the  element  of  pressure  comes  in. 
The  acuteness  of  the  sense  of  touch  depends  very  largely  on  the  cutane- 
ous circulation,  which  is  of  course  largely  influenced  by  external  temper- 
ature. Hence  the  numbness,  familiar  to  every  one,  produced  by  the 
application  of  cold  to  the  skin. 

Acuteness  of  the  Sense. — The  perfection  of  the  sense  of  touch  on 
different  parts  of  the  surface  is  proportioned  to  the  power  which  such 
parts  possess  of  distinguishing  and  isolating  the  sensations  produced  by 
two  points  placed  close  together.  This  power  depends,  at  least  in  part, 
on  the  number  of  primitive  nerve-fibres  distributed  to  the  part;  for  the 
fewer  the  primitive  fibres  which  an  organ  receives,  the  more  likely  is  it 
that  several  impressions  on  different  contiguous  points  will  act  on  onlv 
one  nervous  fibre,  and  hence  be  confounded,  and  perhaps  produce  but 
one  sensation.  Experiments  have  been  made  to  determine  tlie  tactile 
propci'ties  of  different  parts  of  the  skin,  as  measured  by  this  power  of 
distinguishing  distances.  These  consist  in  touching  the  skin,  v/hile  the 
eyes  are  closed,  with  the  points  of  a  pair  of  compasses  sheathed  with 
cork,  and  in  ascertaining  how  close  the  points  of  compasses  might  be 
brought  to  each  other,  and  still  be  felt  as  two  bodies. 


X 

4 

1 

6 

4 

i 

6 

1 
3 

8 

5 

1  2 

10 

i 

13 

tV 

14 

H 

35 

1* 

37 

H 

37 

U 

37 

n 

37 

2 

50 

2 

50 

3* 

63 

H 

63 

H 

63 

2i 

63 

662  HANDBOOK    OF    PHYSIOLOGY. 

Table  of  variations  in  the  tactile  sensibility  of  the  different  parts,— jT/ie  med- 
surement  indicates  the  least  distance  at  which  the  two  blunted  points  of  a 
pair  of  compasses  could  be  separately  distinguished.     (E.  H.  Weber. ) 

Tip  of  tongue      .........         -}j  inch  1  mm. 

Palmar  surface  of  third  phalanx  of  forefinger      .         .  ^V    "  3     " 

Palmar  surface  of  second  phalanges  of  fingers 

Red  surface  of  under-lip        ...... 

Tip  of  nose  ......... 

Middle  of  dorsum  of  tongue  ..... 

Palm  of  hand      ......... 

Ce||tre  of  hard  palate      ....... 

Dorsal  surface  of  first  phalanges  of  fingers 

Back  of  hand  .         .         .         .         .         .         .         . 

Dorsum  of  foot  near  toes    ...... 

Gluteal  region 

Sacral  region       ........ 

Upper  and  lower  parts  of  forearm  .         .         . 

Back  of  neck  near  occiput  ...... 

Upper  dorsal  and  mid-lumbar  regions  .... 

Middle  part  of  forearm 

Middle  of  thigh 

Mid- cervical  region    ....... 

Mid- dorsal  region 

Moreover,  in  the  case  of  the  limbs,  it  was  found  that  before  they 
were  recognized  as  two,  the  points  of  the  compasses  had  to  be  further 
separated  when  the  line  joining  them  was  in  the  long  axis  of  the  limb, 
than  when  in  the  transverse  direction. 

According  to  Weber  the  mind  estimates  the  distance  between  two 
points  by  the  number  of  unexcited  nerve-endings  which  intervene  be- 
tween the  two  points  touched.  It  would  appear  that  a  certain  number 
of  intervening  unexcited  nerve-endings  are  necessary  before  two  points 
touched  can  be  recognized  as  separate,  and  the  greater  this  number  the 
more  clearly  are  the  points  of  contact  distinguished  as  separate.  By 
practice  the  delicacy  of  a  sense  of  touch  may  be  very  much  increased. 
A  familiar  illustration  occurs  in  the  case  of  the  blind,  who,  by  constant 
practice,  can  acquire  the  poAver  of  reading  raised  letters  the  forms  of 
which  are  almost  if  not  quite  undistinguishable  by  the  sense  of  touch  to 
an  ordinary  person. 

Localization. — The  power  of  correctly  localizing  sensations  of  touch 
is  gradually  derived  from  experience.  Thus  infants  when  in  pain  sim- 
jjly  cry,  but  make  no  effort  to  remove  the  cause  of  irritation,  as  an  older 
child  or  adult  would,  doubtless  on  account  of  their  imperfect  knowledge 
of  its  exact  situation. 

Illusions. — The  different  degrees  of  sensitiveness  possessed  by  differ- 
ent parts  may  give  rise  to  errors  of  judgment  in  estimating  the  distance 
between  two  points  where  the  skin  is  touched.  Thus,  if  blunted  points 
of  a  pair  of  compasses  (maintained  at  a  constant  distance  apart)  be 
slowly  drawn  over  the  skin  of  the  cheek  toward  the  lips,  it  is  almost  im- 
possible to  resist  the  conclusion  that  the  distance  between  the  points  is 


THE   SENSES.  r,!);] 

gradually  increasing.  •  WJicii  they  reiich  tliu  lips  they  seem  to  be  consid- 
erably further  apart  than  on  the  cheek.  Thus,  too,  our  estimate  of  the 
•size  of  a  cavity  in  a  tooth  is  usually  exaggerated  when  based  upon  sensa- 
tion derived  from  the  tongue  alorie.  Another  curious  illusion  may  here 
be  mentioned.  If  we  close  the  eyes,  and  place  a  small  marble  or  pea 
between  the  crossed  fore  and  middle  fingers,  we  seem  to  be  touching  two 
marbles.  This  illusion  is  due  to  an  error  of  judgment.  The  marble  is 
touched  by  two  surfaces  which,  uuder  ordinary  circumstances,  could 
only  be  touched  by  two  separate  marbles,  hence  the  mind,  taking  no 
cognizance  of  the  fact  that  the  lingers  are  crossed,  forms  the  conclusion 
that  two  sensations  are  due  to  two  marbles. 

Temperature. — The  whole  surface  of  the  body  is  more  or  less  sen- 
sitive to  differences  of  temperature.  The  sensation  of  heat  is  distinct 
from  that  of  touch :  and  it  would  seem  reasonable  to  suppose  that  there 
are  special  nerves  and  nerve-endings  for  temperature.  At  any  rate  the 
power  of  discriminating  temperature  may  remain  unimpaired  when  the 
sense  of  touch  is  temporarily  in  abeyance.  Thus  if  the  ulnar  nerve  be 
compressed  at  the  elbow  till  the  sense  of  touch  is  very  much  dulled  in 
the  fingers  which  it  supplies,  the  sense  of  temperature  remains  quite 
unaffected. 

The  sensations  of  heat  and  cold  are  often  exceedingly  fallacious,  and 
in  many  cases  are  no  guide  at  all  to  the  absolute  temperature  as  indi- 
cated by  a  thermometer.  All  that  we  can  with  safety  infer  from  our 
sensations  of  temperature,  is  that  a  given  object  is  warmer  or  cooler 
than  the  skin.  Thus  the  temperature  of  our  skin  is  the  standard;  and 
as  this  varies  from  hour  to  hour  according  to  the  activity  of  the  cutane- 
ous circulation,  our  estimate  of  the  absolute  temperature  of  any  body 
must  necessarily  vary  too.  If  we  put  the  left  hand  into  water  at  5°  C. 
(40°  F.)  and  the  right  into  Avater  at  45°  C.  (110°  F.),  and  then  immerse 
both  in  water  at  27°  C.  (80°  F.),  it  will  feel  warm  to  the  left  hand  but 
cool  to  the  right.  Again,  a  piece  of  metal  which  has  really  the  same 
temperature  as  a  given  piece  of  wood  will  feel  much  colder,  since  it  con- 
ducts away  the  heat  much  more  rapidly.  For  the  same  reason  air  in 
motion  feels  very  much  cooler  than  air  of  the  same  temperature  at  rest. 

In  some  cases  we  are  able  to  form  a  fairly  accurate  estimate  of  abso- 
lute temperature.  Thus,  by  plunging  the  elbow  into  a  bath,  a  practised 
bath-attendant  can  tell  the  temperature  sometimes  within  half  a  degree 
centigrade. 

The  temperatures  which  can  bo  readily  <.liscriminated  are  between 
10°-45°  C.  (o0°-115°  F.);  very  low  and  very  high  temperatures  alike 
produce  a  burning  sensation.  A  temperature  appears  higher  according 
to  the  extent  of  cutaneous  surface  exposed  to  it.  Thus,  water  of  a  tem- 
perature which  can  be  readily  borne  by  the  hand,  is  quite  intolerable  if 


664:  HANDBOOK    OF    PHYSIOLOGY. 

the  whole  body  be  immersed.  So,  too,  water  appears  much  hotter  to 
the  hand  than  to  a  single  finger. 

The  delicacy  of  the  sense  of  temperature  coincides  in  the  main  with 
that  of  touch,  and  appears  to  depend  largely  on  the  thickness  of  the 
skin ;  hence,  in  the  elbow,  where  the  skin  is  thin,  the  sense  of  tempera- 
ture is  delicate,  though  that  of  touch  is  not  remarkably  so.  Weber  has 
further  ascertained  the  following  facts:  two  compass  points  so  near  to- 
gether on  the  skin  that  they  produce  but  a  single  impression,  at  once 
give  rise  to  tico  sensations,  when  one  is  hotter  than  the  other.  More- 
over, of  two  bodies  of  equal  weight,  that  which  is  the  colder  feels  heavier 
than  the  other. 

As  every  sensation  is  attended  with  an  idea,  and  leaves  behind  it  an 
idea  in  the  mind  which  can  be  reproduced  at  will,  we  are  enabled  to  com- 
pare the  idea  of  a  past  sensation  with  another  sensation  really  present. 
Thus  we  can  compare  the  weight  of  one  body  with  another  which  we 
had  previously  felt,  of  which  the  idea  is  retained  in  our  mind.  Weber 
was  indeed  able  to  distinguish  in  this  manner  between  temj)eratures, 
experienced  one  after  the  other,  better  than  between  temperatures  to 
which  the  two  hands  were  simultaneously  subjected.  This  power  of 
comparing  present  with  past  sensations  diminishes,  however,  in  propor- 
tion to  the  time  which  has  elapsed  between  them.  After-sensations  left 
by  impressions  on  nerves  of  common  sensibility  or  touch  are  very  vivid 
and  durable.  As  long  as  the  condition  into  which  the  stimulus  has 
thrown  the  organ  endures,  the  sensation  also  remains,  though  the  excit- 
ing cause  should  have  long  ceased  to  act.  Both  j^ainful  and  pleasurable 
sensations  afford  many  examples  of  this  fact. 

Subjective  sensations,  or  sensations  dependent  on  internal  causes,  are 
in  no  sense  more  frequent  than  in  the  sense  of  touch.  All  the  sensations 
of  pleasure  and  ^Dain,  of  heat  and  cold,  of  lightness  and  Aveight,  of  fa- 
tigue, etc.,  may  be  produced  by  internal  causes.  Neuralgic  pains,  the 
sensation  of  rigor,  formication  or  the  creeping  of  ants,  and  the  states  of 
the  sexual  organs  occurring  during  sleep,  afford  striking  examples  of 
subjective  sensations.  The  mind  has  a  remarkable  power  of  exciting 
sensations  in  the  nerves  of  common  sensibility:  just  as  the  thought  of 
the  nauseous  excites  sometimes  the  sensation  of  nausea,  so  the  idea  of 
pain  gives  rise  to  the  actual  sensation  of  pain  in  a  jsart  predisposed  to 
it;  numerous  examples  of  this  influence  might  be  quoted. 

Pain. — As  regards  painful  sensations,  three  views  can  be  taken:  1, 
that  it  is  a  special  sensation  provided  Avith  a  special  conducting  apparatus 
in  each  part  of  the  body;  2,  that  it  is  produced  by  an  over-stimulation 
of  the  special  nerves  concerned  Avith  touch  or  temperature,  or  of  the 
other  nerves  of  special  sense;  or  3,  that  it  is  an  over-stimulation  of  the 
ner\'es  of  common  sensation,  Avhich  tell  us  of  the  condition  of  our  own 
bodies,  both   of    the  surface  and   also  of   the  internal  organs.     There 


T]IE   SEKSES.  (JCi'j 

seems  fo  he  niiiclj  h\  favor  of  all  of  these  views.  The  weight  of  evi- 
dence is,  however,  rather  against  there  being  any  special  pain  sense  witli 
a  special  end-organ  and  fibres.  It  is,  however,  certain  that  even  if  any 
variety  of  pain  be  a  special  sensation,  some  kind  of  jiain  may  be  pro- 
duced by  stimulation  of  the  bare  sensory  nerves  apart  from  any  special 
form  of  nerve  termination.  It  is  said  that  the  main  difference  between 
the  common  sensation  which  tells  us  of  the  condition  of  all  jiarts  of  the 
body  and  of  which  thirst  and  hunger  are  but  examples,  the  one  inform- 
ing us  of  the  condition  of  the  palate  and  the  other  of  the  state  of  our 
stomach,  and  the  special  sense  of  touch  and  temperature,  is  that  the 
latter  are  provided  with  special  apparatus.  By  means  of  this  apparatus 
we  are  able  to  localize  the  sensation  from  which  it  is  i:)ossible  to  form 
judgments.  Such  a  special  apparatus  is  evidently  not  absolutely  essen- 
tial for  the  sensation  of  jDain,  but  this  does  not  exclude  the  idea  that 
pain  may  result  from  over-stimulation  of  a  nerve  of  special  sense  or  of 
its  termination. 

The  Muscular  Sense. ^The  estimate  of  a  weight  is  usually  based 
on  tivo  sensations:   1,  of  pressure  on  the  skin,  and  2,  the  muscular  sense. 

The  estimate  of  weight  derived  from  a  combination  of  these  two 
sensations  (as  in  lifting  a  weight)  is  more  accurate  than  that  derived 
from  the  former  alone  (as  when  a  weight  is  laid  on  the  hand);  thus 
Weber  found  that  by  the  former  method  he  could  generally  distinguish 
19^  oz.  from  20  oz.,  but  not  19f  oz.  from  20,  while  by  the  latter  he  could 
at  most  only  distinguish  144-  oz.  from  15  oz. 

It  is  not  the  absolute,  but  the  relative,  amount  of  the  difference  of 
weight  which  we  have  thus  the  faculty  of  perceiving. 

It  is  not,  however,  certain,  that  our  idea  of  the  amount  of  muscular 
force  used  is  derived  solely  from  the  muscular  sense.  "We  have  the 
powder  of  estimating  very  accurately  beforehand,  and  of  regulating,  the 
amount  of  nervous  influence  necessary  for  the  production  of  a  certain 
degree  of  movement.  When  w^e  raise  a  vessel,  with  the  contents  of 
which  w'e  are  not  acquainted,  the  force  we  employ  is  determined  by  the 
idea  we  have  conceived  of  its  weight.  If  it  should  happen  to  contain 
some  very  heavy  substance,  as  quicksilver,  we  shall  probably  let  it  fall; 
the  amount  of  muscular  action,  or  of  nervous  energy,  which  we  had 
exerted  being  insufficient.  The  same  thing  occurs  sometimes  to  a  person 
descending  stairs  in  the  dark;  he  makes  the  movement  for  the  descent 
of  a  step  which  does  not  exist.  It  is  possible  that  in  the  same  wav  the 
idea  of  weight  and  pressure  in  raising  bodies,  or  in  resisting  forces,  mav 
in  part  arise  from  a  consciousness  of  the  amount  of  nervous  energy 
transmitted  from  the  brain  rather  than  from  a  sensation  in  the  muscles 
themselves.  The  mental  conviction  of  the  inability  longer  to  support  a 
weight  must  also  be  distinguished  from  the  actual  sensation  of  fatigue 
in  the  muscles. 


066  HANDBOOK   OP   PHYSIOLOGY. 

So,  with  regard  to  the  ideas  derived  from  sensations  of  touch  com- 
bined with  movements,  it  is  doubtful  how  far  the  consciousness  of  the 
extent  of  muscular  movement  is  obtained  from  sensations  in  the  muscles 
themselves.  The  sensation  of  movement  attending  the  motions  of  the 
hand  is  very  slight ;  and  persons  who  do  not  know  that  the  action  of 
l^articular  muscles  is  necessary  for  the  production  of  given  movements, 
do  not  suspect  that  the  movement  of  the  fingers,  for  example,  depends 
on  an  action  in  the  forearm.  The  mind  has,  nevertheless,  a  very  definite 
knowledge  of  the  changes  of  position  produced  by  movements;  and  it 
is  on  this  that  the  ideas  which  it  conceives  of  the  extension  and  form  of 
a  body  are  in  great  measure  founded. 

There  is  no  marked  development  of  common  sensibility  to  be  made 
out  in  muscles:  they  may  be  cut  without  the  production  of  pain.  On  the 
other  hand,  there  is  no  doubt  that  afferent  impulses  must  pass  upward 
from  muscles  and  tendons  acquainting  the  brain  with  their  condition. 
This,  then,  must  be  a  special  sense.  It  has  been  suggested  that  the  minute 
end-bulbs  of  Golgi  found  in  tendons,  and  that  the  Pacinian  corpuscles  in 
the  neighborhood  of  joints,  are  the  terminal  organs  of  this  special  sense. 

Judgment  of  the  Form,  and  Size  of  Bodies. — By  the  sense  of  touch  the 
mind  is  made  acquainted  with  the  size,  form,  and  other  external  char- 
acters of  bodies.  And  in  order  that  these  characters  may  be  easily 
ascertained,  the  sense  of  touch  is  especially  developed  in  those  parts 
which  can  be  readily  moved  over  the  surface  of  bodies.  Touch,  in  its 
more  limited  sense,  or  the  act  of  examining  a  body  by  the  touch,  consists 
merely  in  a  voluntary  employment  of  this  sense  combined  with  move- 
ment, and  stands  in  the  same  relation  to  the  sense  of  touch,  or  common 
sensibility,  generally,  as  the  act  of  seeking,  following,  or  examining 
odors,  does  to  the  sense  of  smell.  The  hand  is  the  best  adapted  for  it, 
by  reason  of  its  peculiarities  of  structure, — namely,  its  capability  of 
pronation  and  supination,  which  enables  it,  by  the  movement  of  rota- 
tion, to  examine  the  whole  circumference  of  the  body;  the  power  it 
possesses  of  opposing  the  thumb  to  the  rest  of  the  hand,  and  the  relative 
mobility  of  the  fingers;  and  lastly  from  the  abundance  of  the  sensory 
terminal  organs  which  it  possesses.  In  forming  a  conception  of  the 
figure  and  extent  of  a  surface,  the  mind  multiplies  the  size  of  the  hand 
or  fingers  used  in  the  inquiry  by  the  number  of  times  which  it  is  con- 
tained in  the  surface  traversed;  and  by  repeating  this  process  with 
regard  to  the  different  dimensions  of  a  solfd  body,  acquires  a  notion  of 
its  cubical  extent,  but,  of  course,  only  an  imperfect  notion,  as  other 
senses,  e.g..,  the  sight,  are  required  to  make  it  complete. 

It  is  impossible  in  this  consideration  to  say  how  much  of  our  knowl- 
edge of  the  thing  touched  depends  upon  pressure  and  how  much  upon 
the  muscular  sense. 


THK   SENSES.  C>C,7 


II.  Taste. 


Conditions  necessar//. — Tlic  conditions  for  the  perceptions  of  taste 
are: — 1,  tlie  jjresence  of  a  )ierve  ami  nerve-centre  with  special  endow- 
ments; 2,  the  excitation  of  the  nerve  by  the  sapid  matters,  which  for 
this  purpose  must  be  in  a  state  of  Hohitioii;  3,  a  temperature  of  about  37° 
to  40"  C.  (98°  to  100°  F.).  The  nerves  concerned  in  the  production  of 
the  sense  of  taste  have  been  already  considered  (p.  349  et  seq.)  The  mode 
of  action  of  the  substances  which  excite  taste  consists  in  the  production 
of  a  change  in  the  condition  of  the  gustatory  nerves,  and  the  conduction 
of  the  stimulus  thus  produced  to  the  nerve-centre;  and,  according  to 
the  difference  of  t'ue  susbtances,  an  infinite  variety  of  changes  of  condi- 
tion of  the  nerves,  and  consequently  of  stimulations  of  the  gustatory 
centre,  may  be  induced.  The  matters  to  be  tasted  must  either  be  in 
solution  or  be  soluble  in  the  moistu-re  covering  the  tongue;  hence  insolu- 
ble substances  are  usually  tasteless,  and  produce  merely  sensations  of 
touch.  i\Ioreover,  for  the  perfect  action  of  a  sapid,  as  of  an  odorous  sub- 
stance, it  is  necessary  that  the  sentient  surface  should  be  moist.  Hence, 
when  the  tongue  and  fauces  are  dry,  sapid  substances,  even  in  solution, 
are  with  ditficulty  tasted. 

The  nerves  of  taste,  like  the  nerves  of  other  special  senses,  may  have  their 
peculiar  properties  excited  by  various  other  kinds  of  irritation,  such  as  elec- 
tricity and  mechanical  impressions.  Thus,  a  small  current  of  air  directed 
upon  the  tongue  gives  rise  to  a  cool  saline  taste,  like  that  of  saltpetre ;  and  a 
distinct  sensation  of  taste  similar  to  that  caused  by  electricit}',  may  be  pro- 
duced by  a  smart  tap  applied  to  the  papillae  of  the  tongue.  Moreover,  the 
mechanical  irritation  of  the  fauces  and  palate  produces  the  sensation  of  nausea, 
which  is  probably  only  a  modification  of  taste. 

Seat. — The  principal  seat  (apparent  seat,  that  is,  to  our  senses)  of 
the  sense  of  taste  is  the  tongue.  But  the  result  of  experiments  as  well 
as  ordinary  experience  show  that  the  soft  palate  and  its  arches,  the  uvula, 
tonsils,  and  ])robaI)ly  the  up])er  ])art  of  the  ])harynx,  are  also  endowed 
with  taste.  These  parts,  together  M'ith  the  base  and  posterior  parts  of 
the  tongue,  are  supplied  with  branches  of  tlie  glosso-pharyngeal  nerve, 
and  evidence  has  been  already  adduced  that  the,  sense  of  taste  is  conferred 
upon  them  by  this  nerve.  In  most,  though  not  in  all  persons,  the  an- 
terior parts  of  the  tongue,  especially  the  edges  and  tip,  are  endowed 
with  the  sense  of  taste.  The  middle  of  the  dorsum  is  only  feebly  en- 
dowed with  this  sense,  probably  because  of  the  density  and  thickness  of 
the  epithelium  covering  the  filiform  papilla  of  this  part  of  the  tongue, 
which  will  prevent  the  sapid  substances  from  penetrating  to  their  sensi- 
tive parts. 

Other  Functions. — Beside  the  sense  of  taste,  the  tongue,  by  means 


668  HANDBOOK    OF   PHYSIOLOGY. 

also  of  its  papillse,  is  endued  (2)  especially  at  its  side  and  tip,  with  a  very 
delicate  and  accurate  sense  of  touch,  whicli  renders  it  sensible  of  the 
impressions  of  heat  and  cold,  pain  and  mechanical  pressure,  and  conse- 
quently of  the  form  of  surfaces.  The  tongue  may  lose  its  common  sen- 
sibility, and  still  retain  the  sense  of  taste,  and  vice  versa.  This  fact 
renders  it  probable  that,  although  the  senses  of  taste  and  of  touch  may 
be  exercised  by  the  same  papillae  supplied  by  the  same  nerves,  yet  the 
nervous  conductors  for  these  two  different  sensations  are  distinct,  just 
as  the  nerves  for  smell  and  common  sensibility  in  the  nostrils  are  dis- 
tinct; and  it  is  quite  conceivable  that  the  same  nervous  trunk  may  con- 
tain fibres  differing  essentially  in  their  specific  properties.  Facts  already 
detailed  seem  to  prove  that  the  lingual  branch  of  the  fifth  nerve  is  the 
conductor  of  sensations  of  taste  in  the  anterior  part  of  the  tongue;  and 
it  is  also  certain,  from  the  marked  manifestations  of  pain  to  which  its 
division  in  animals  gives  rise,  that  it  is  likewise  a  nerve  of  common  sen- 
sibility. The  glosso-pharyngeal  also  seems  to  contain  fibres  both  of 
common  sensation  and  of  the  special  sense  of  taste. 

The  functions  of  the  tongue  in  connection  with  (3)  speech,  (4)  mas- 
tication, (5)  deglutition,  (6)  suction,  have  been  referred  to  in  other 
chapters. 

Taste  a?id  Smell:  Perceptions. — The  concurrence  of  common  and  two 
kinds  of  special  sensibility,  *.e. ,  touch  and  taste  in  the  same  part,  makes 
it  sometimes  difficult  to  determine  whether  the  impression  produced  by 
a  substance  is  perceived  through  the  ordinary  sensitive  fibres,  or  through 
those  of  the  sense  of  taste.  In  many  cases,  indeed,  it  is  probable  that 
both  sets  of  nerve-fibres  are  concerned,  as  when  irritating  acrid  substances 
are  introduced  into  the  mouth. 

Much  of  the  perfection  of  the  sense  of  taste  is  often  due  to  the  sapid 
substances  being  also  odorous,  and  exciting  the  simultaneous  action  of 
the  sense  of  smell.  This  is  shown  by  the  imperfection  of  the  taste  of 
such  substances  when  their  action  on  the  olfactory  nerves  is  prevented 
by  closing  the  nostrils.  Many  fine  wines  lose  much  of  their  apparent 
excellence  if  the  nostrils  are  held  close  while  they  are  drunk. 

Varieties  of  Tastes. — Among  the  most  clearly  defined  tastes  are  the 
siueet  and  hitter  (which  are  more  or  less  ojoposed  to  each  other),  the  acid, 
alkaline.,  salt.,  and  metallic  tastes.  Acid  and  alkaline  taste  may  be  ex- 
cited by  electricity.  If  a  piece  of  zinc  be  placed  beneath  and  a  piece  of 
copper  above  the  tongue,  and  their  ends  brought  into  contact,  an  acid 
taste  (due  to  the  feeble  galvanic  current)  is  produced.  The  delicacy  of 
the  sense  of  taste  is  sufficient  to  discern  1  part  of  sulphuric  acid  in  1000 
of  water;  but  it  is  far  surpassed  in  acuteness  by  the  sense  of  smell.  Ex- 
periments have  shown  that  it  is  possible  to  entirely  do  away  with  the 
power  of  tasting  bitters  and  sweets  while  the  taste  for  acids  and  salts 


THE    SENSES.  Rfip 

remains.  This  is  done  hy  cliewiug  the  leaves  of  an  Indian  plant 
(Gymnema  sylvestre).  It  has  also  been  shown  that  the  power  of  tasting 
sweet  substances  disappears  before  that  of  tasting  bitter.  Other  experi- 
ments have  shown  that  the  apparatus  for  salt  and  for  acid  tastes  are 
distinct.  It  is  also  demonstrable  that  bitters  are  most  appreciated  at  the 
back  and  sweets  at  the  tip  of  the  tongue,  that  salts  are  also  most  potent  at 
the  tip,  and  acids  at  the  sides  of  the  tongue.  All  these  tastes  then,  are 
almost  certainly  provided  with  a  distinct  apparatus.  It  is  clear  there- 
fore that  the  taste  buds  cannot  be  the  only  terminal  organs  for  the  sense 
of  taste,  if  from  no  other  reason,  at  any  rate  from  their  exceedingly 
limited  distribution  in  the  human  tongue. 

Although  the  taste  aj)paratus  is  bilateral  the  sensation  cv  perception 
is  single,  and  in  this  respect  taste  resembles  vision. 

After-taste. — Very  distinct  sensations  of  taste  are  frequently  left  after 
the  substances  which  excited  them  have  ceased  to  act  on  the  nerve;  and 
such  sensations  often  endure  for  a  long  time,  and  modify  the  taste  of 
other  substances  ajDplied  to  the  tongue  afterward.  Thus,  the  taste  of 
sweet  substances  spoils  the  flavor  of  wine,  the  taste  of  cheese  improves  it. 
There  appears,  therefore,  to  exist  the  same  relation  between  tastes  as 
between  colors,  of  which  those  that  are  opposed  or  complementary  render 
each  other  more  vivid,  though  no  general  principles  governing  this  rela- 
tion have  been  discovered  in  the  case  of  tastes.  In  the  art  of  cooking, 
however,  attention  has  at  all  times  been  j)aid  to  the  consonance  or  har- 
mony of  flavors  in  their  combination  or  order  of  succession.  Just  as  in 
painting  and  music  the  fundamental  principles  of  harmony  have  been 
emplo}'ed  empirically  while  the  theoretical  laws  were  unknown. 

Frequent  and  continued  repetitions  of  the  same  taste  render  the  per- 
ception of  it  less  and  less  distinct,  in  the  same  aahv  that  a  color  becomes 
more  and  more  dull  and  indistinct  the  longer  tlu'  eye  is  fixed  upon  it. 
Thus,  after  frequently  tasting  first  one  and  then  the  other  of  two  kinds 
of  wine,  it  becomes  impossible  to  discriminate  between  them. 

The  simple  contact  of  a  sapid  substance  with  the  surface  of  the 
gustatory  organ  seldom  gives  rise  to  a  distinct  sensation  of  taste;  it  needs 
to  be  diii'used  over  the  surface,  and  brought  into  intimate  contact  with 
the  sensitive  parts  by  compression,  friction,  and  motion  between  the 
tongue  and  palate. 

Snhjedive  Sensations  of  Taste. — The  sense  of  taste  seems  capable  of 
being  excited  only  by  external  causes,  such  as  changes  in  the  conditions 
of  the  nerves  or  nerve-centres,  produced  by  congestion  or  other  causes, 
which  excite  subjective  sensations  in  the  other  organs  of  sense.  But 
little  is  known  of  the  subjective  sensations  of  taste;  for  it  is  difficult  to 
ilistinguish  the  phenomena  from  the  effects  of  external  causes,  such  as 
changes  in  the  nature  of  the  secretions  of  the  mouth. 


670 


HAXDBOOIi    OF    PHYSIOLOGY. 


III.  Smell. 

Conditions  necessary. — (1.)  The  first  conditions  essential  to  the  sense 
of  smell  are  a  special  nerve  and  nerve-tenninaiions  in  the  form  of  special 
cells,  the  changes  in  whose  condition  stimulate  a  special  nerve-centre, 
and  are  perceived  in  sensations  of  odor,  for  no  other  nervous  structure 
IS  capable  of  these  sensations,  even  though  acted  on  by  the  same  causes. 
The  same  substance  which  excites  the  sensation  of  smell  in  the  olfac- 
tory centre  may  cause  another  peculiar  sensation  through  the  nerves  of 
taste,  and  may  j)roduce  an  irritating  and  burning  sensation  on  the  nerves 
of  touch;  but  the  sensation  of  odor  is  yet  separate  and  distinct  from 
these,  though  it  maybe  simultaneously  perceived.  (2.)  The  material 
causes  of  odors  are,  usually,  in  the  case  of  animals  living  in  the  air, 


TutT^.T^^H 


Fig.  391.— Nerves  of  the  septum  uasi.  seen  from  the  riglit  side.  7^.— I,  the  olfactory  bulb; 
1,  the  olfactoi'y  nerves  passing  through  the  foramina  of  the  cribriform  plate,  and  descending  tO' 
be  distributed  on  the  septum ;  2,  the  internal  or  septal  twig  of  the  nasal  branch  of  the  ophthal- 
mic nerve;  3,  naso-palatine  nerves.     (From  Sappey,  after  Hirschfeld  and  Leveill6.) 

either  solids  suspended  in  a  state  of  extremely  fine  division  in  the  atmos- 
phere ;  or  gaseous  exhalations  often  of  so  subtle  a  nature  that  they  can 
be  detected  by  no  other  reagent  than  the  sense  of  smell  itself.  The 
matters  of  odor  must,  in  all  cases,  be  dissolved  in  the  mucus  of  the 
mucous  membrane  before  they  can  be  immediately  applied  to,  or  affect 
the  olfactory  nerves;  therefore  a  further  condition  necessary  for  the 
perception  of  odors  is,  that  the  mucous  membrane  of  the  nasal  cavity 
be  moist.  When  the  Schneiderian  membrane  is  dry,  the  sense  of  smell 
is  impaired  or  lost;  in  the  first  stage  of  catarrh,  when  the  secretion  of 
mucus  within  the  nostrils  is  lessened,  the  faculty  of  perceiving  odor  is 
either  lost,  or  rendered  very  imperfect.  (3.)  In  animals  living  in  the 
air,  it  is  also  requisite  that  the  odorous  matter  should  be  transmitted  in 
a  current  tiirough  the  nostrils.     This  is  effected  by  an  inspiratory  move- 


THE   SENSES. 


U7I 


ment,  the  montli  being  closed;  hence  we  have  voluDtary  influence  over 
the  sense  of  smell ;  for  by  interrupting  respiration  we  prevent  the  per- 
ception of  odors,  and  by  repeated  quick  inspiration,  assisted,  as  in  the 
act  of  sniffijii/,  by  the  action  of  the  nostrils,  wo  render  the  impression 
more  intense.  An  odorous  substance  in  a  lifpiid  form  injected  into  the 
nostrils  ap.pears  incapable  of  giving  rise  to  the  sensation  of  smell;  thus 
Weber  could  not  smell  the  slightest  odor  when  his  nostrils  were  com- 
pletely filled  with  water  containing  a  large  quantity  of  eau-de-Cologne. 

The  nose  is  not  entii'ely  an  organ  for  the  seat  of  smell.  In  fact  the 
nasal  cavities  are  divided  into  three  districts  called  respectively — (a)  Regio 
vestibularis,  which  is  the  entrance  to  the  cavity. 
It  is  lined  with  a  mucous  membrane  very  closely 
resembling  the  skin,  and  contains  hair  {vihris- 
aw)  with  sebaceous  glands,  (h)  Regio  reqnra- 
toi'ia,  which  includes  the  lower  meatus  of  the 
nose,  and  all  the  rest  of  the  nasal  passages  ex- 
cept (f);  it  is  covered  with  mucous  membrane 
covered  by  stratified  columnar  ciliated  epitheli- 
um. The  mucosa  is  thick  and  consists  of  fibrous 
connective  tissue;  it  contains  a  certain  number 
of  tubular  ujucous  and  serous  glands.  (c)  Re- 
gio olfactoria.  This  includes  the  anterior  two- 
thirds  of  the  superior  meatus,  the  middle  meatus, 
and  the  upper  half  of  the  septum  nasi.  It  is  of 
a  yellowish  color.  It  consists  of  a  thicker  muc- 
(His  membrane  than  in  (Z*),  '}uade  up  of  loose  are- 
olar connective  tissue  covered  by  epithelium  of 
a  special  variety,  resting  upon  a  basement  mem- 
brane. The  cells  of  the  epithelium  are  of  two 
principal  kinds:  (r/)  columnar  epithelial  cells 
whose  function  is  to  supiiort  (//)  the  bipolar 
olfactory  cells,      [n)  The  epithelial  cells  are  pris-        Fi^. 392. —Bipolar olfactory 

,  •       •  1  ,1  J.1      •  £  cells  from  tlie  nasal  fossae  of 

matic   m  sliape  ami    liave    upon    their    suriaces   th«  rat.  (fnU-term  fcetus).    .-i, 

£         L        •     L  1   •    1       ii  1-P       i  n       cl    i.\  Epitlielimn    of    the    olfactory 

facets  into  winch  the  oiiactory  cells  fit  them-  hhr-osu- e  epithelial  cells- //■ 
selves.  They  are  thus  analogous  to  the  cells  of  'i!^:^;;^^ ,.!^^^^^ 
Miiller  of  the  retina  (fig.  3!.2  0.  {0)  The  olfac-  [^^^'nbl^S^;!  ^uJ^T^ 
tory  cells  have  an  oblong  or  fusiform  shape,  which  J^^^f/')  ^'■'""  ""^  tngemmus. 
is  mainly  determined  by  the  large  nucleus.     The 

thin  protoplasmic  body  has  two  processes,  an  external  and  an  internal. 
The  external  is  large  and  passes  up  to  the  free  surface  to  end  in  a  small 
Ijunch  of  fibrils  that  are  not  vibratile.  The  internal  process  is  very 
fine,  often  varicose,  and  jjasses  through  the  mucous  membrane  to  be- 
cimie  continuous  with  the  fibres  of  the  olfactory  bulb. 

The   olfactory   bulb    must   be  studied   in   relation  with  the  nerve- 


672 


HANDBOOK    OF    PHYSIOLOGY. 


fibres  and  olfactory  cells  with  which  it  is  counected.  These  parts  to- 
gether form  a  sensory  end-organ  TvLich  resembles  in  many  respects  the 
retina.  The  discovery  of  its  true  structure  lias  thrown  a  flood  of  light 
on  the  architecture  of  the  nerve-centres  as  a  whole. 

The  olfactory  bulb  is  not  a  nerve,  but  a  modification  of  the  brain 
cortex.     A  transection  shows  it  to  be  made  up  of  four  layers: 

1st.   Peripheral  fibres. 

2d.   Olfactory  glomerules. 

3d.  Layer  of  mitral  cells. 


Ependymal  epithe- 
lium. 


'       Layer  of  central 
fibres. 


Layer  of  mitral 
cells. 


Layer  of  olfactory 
flbrillas. 


Fig.  393. — Principal  constituent  elements  of  the  olfactory  bulb  of  a  mammal.     (Tan  Gehuchten. ) 


4th.  Layer  of  granular  cells  and  deep  nerve-fibres. 

1st.  The  first  and  external  layer  is  composed  of  the  fino  nerve-fibrils 
of  the  olfactory  nerves.  They  pass  through  the  cribriform  plate  of  the 
ethmoid  and  continue  on,  ending  in  the  olfactory  cells. 

2d.  The  glomerular  layer  contains  numbers  of  small  round  bodies 
whose  structure  is  now  known  to  be  nervous.  They  are  made  up  of  the 
expansions  of  the  olfactory  fibres  on  the  one  hand  and  of  the  "mitral" 
cells  on  tlie  other.  These  are  mingled  in  a  close  network,  but  do  not 
anastomose,     It  was  by  the  study  of  these  bodies  in  part  that  the  fact  of 


THE   SENSES.  '>7;) 

the  non-continuity  of  the  neurons  uas  demonstrated  (fig.  393).  Tliid 
layer  also  contains  small  fusiform  cells  ■with  branching  dendrites  that 
extend  outward  to  the  glomeruli.  Each  has  an  axis-cylinder  process 
which  passes  inward  to  join  the  fibres  of  the  internal  olfactory  nerves. 

3d.  The  layer  of  mitral  cells  contains  large  cells,  some  of  them  trian- 
gular and  some  in  the  shape  of  a  mitre.  They  have  numerous  dendrites, 
one  of  which  passes  into  a  glomerule  and  then  breaks  up  in  a  fine  arbori- 
zation. An  axis-cylinder  process  (neuraxon)  passes  off  from  the  inner 
surface  and  is  continued  as  an  internal  olfactory  nerve-fibre. 

4th.  The  layer  of  granules  and  central  fibres.  This  contains  a 
large  number  of  very  small  nerve-cells,  which  are  peculiar  in  that  they 


Fig:.  394.— Nerves  of  the  outer  walls  of  the  nasal  fossae.  3-5.— 1,  network  of  the  branches  of 
the  olfactory  nerve,  descending?  upon  the  region  of  the  superior  and  middle  turbinated  bones: 
2,  external  twip  of  the  othuioidal  branch  of  the  nasal  nerves;  3,  spheno-palatine  ganglion:  4, 
ramification  of  the  anterior  jialatine  nerves;  5,  posterior,  and  6,  middle  divisions  of  the  palatine 
nerves;  7,  branch  to  the  region  of  the  infei-ior  turbinated  bone;  8,  branch  to  the  region  of  the 
supei'ior  and  middle  turbinated  bones:  9,  naso-palatine  branch  to  the  septum  cut  short.  (From 
Sappey,  after  Hirschfeld  and  Leveill6.) 


have  no  axis-cylinder.  Their  dendrites  extend  chiefly  into  the  layer 
of  mitral  cells.  They  resemble  the  spongioblasts  of  the  retina  and  prob- 
ably have  commissural  functions.  This  layer  has  also  some  small  star- 
shaped  cells  whose  dendrites  end  in  the  mitral  cell-layer.  Among  these 
cells  run  numerous  fibres,  chiefly  from  the  mitral  cells  and  the  fusiform 
cells  of  the  glomerular  layer. 

The  general  arrangement  is  shown  in  fig.  393. 

The  sense  of  smell  is  derived  exclusively  through  those  parts  of  the 
nasal  cavities  in  which  the  olfactory  nerves  are  distributed  ;  the  accessory 
cavities  or  sinuses  communicating  with  the  nostrils  seem  to  have  no  re- 
lation to  it.  Air  impregnated  with  the  vapor  of  camphor  was  injected 
43 


674  HANDBOOK    OF    PHYSIOLOGY. 

iuto  the  frontal  sinus  through  a  fistulous  opening  and  odorous  substances 
have  been  injected  into  the  antrum  of  Highmore;  but  in  neither  case 
Tvas  any  odor  perceived  by  the  patient.  The  purposes  of  these  sinuses 
appear  to  be  that  the  bones,  necessarily  large  for  the  action  of  the  mus- 
cles and  other  parts  connected  with  them,  may  be  as  light  as  possible, 
and  that  there  may  be  more  room  for  the  resonance  of  the  air  in  vocaliz- 
ing. The  former  purpose,  which  is  in  other  bones  obtained  by  tilling 
their  cavities  with  fat,  is  here  attained,  as  it  is  in  many  bones  of  birds, 
by  their  being  tilled  with  air. 

Other  Functions  of  tlie  JS^asal  Region. — All  jjarts  of  the  nasal  cavi- 
ties, Avhether  or  not  they  can  be  the  seats  of  the  sense  of  smell,  are  en- 
dowed with  common  sensibility  by  the  nasal  branches  of  the  first  and 
second  divisions  of  the  fifth  nerve.  Hence  the  sensations  of  cold,  heat, 
itching,  tickling,  and  jDain;  and  the  sensation  of  tension  or  pressure  in 
the  nostrils.  That  these  nerves  cannot  perform  the  function  of  the  ol- 
factory nerves  is  proved  by  cases  in  which  the  sense  of  smell  is  lost,  while 
the  mucous  membrane  of  the  nose  remains  susceptible  of  the  various 
modifications  of  common  sensation  and  of  touch.  But  it  is  often  difficult 
to  distinguish  the  sensation  of  smell  from  that  of  mere  feeling,  and  to 
ascertain  what  belongs  to  each  separately.  This  is  the  case  particulajly 
with  the  sensations  excited  in  the  nose  by  acrid  vapors,  as  of  ammonia, 
horse-radish,  mustard,  etc.,  which  resemble  much  the  sensations  of  the 
nerves  of  touch;  and  the  difficulty  is  the  greater  when  it  is  remembered 
that  these  acrid  vapors  have  nearly  the  same  action  upon  the  mucous 
membrane  of  the  eyelids.  It  was  because  the  common  sensibility  of  the 
nose  to  these  irritating  substances  remained  after  the  destruction  of  the 
olfactory  nerves  that  Magendie  was  led  to  the  erroneous  belief  that  the 
fifth  nerve  might  exercise  this  special  sense. 

Varieties  of  Odorous  Sensations. — Animals  do  not  all  equally  perceive 
the  same  odors;  the  odors  most  plainly  perceived  by  an  herbivorous  ani- 
mal and  by  a  carnivorous  animal  are  different.  The  Carnivora  have  the 
power  of  detecting  most  accurately  by  the  smell  the  special  peculiarities 
of  animal  matters  and  of  tracking  other  animals  by  the  scent;  but  have 
apparently  very  little  sensibility  to  the  odors  of  plants  and  flowers.  Her- 
bivorous animals  are  peculiarly  sensitive  to  the  latter,  and  have  a  nar- 
rower sensibility  to  animal  odors,  especially  to  such  as  proceed  from 
other  individuals  than  their  own  species.  Man  is  far  inferior  to  many 
animals  of  both  classes  (which  appear  to  have  a  special  epithelial 
arrangement  called  Jacohson's  organ,  for  the  purpose  of  ''scent"),  in 
respect  of  the  acuteness  of  smell;  but  his  sphere  of  susceistibility  to  various 
odors  is  more  uniform  and  extended.  The  cause  of  this  difference  lies 
probably  in  the  endowments  of  the  cerebral  parts  of  the  olfactory  appa- 
ratus.    The  delicacy  of  the  sense  of  smell  is  most  remarkable;  it  can  dis- 


THE    SENSES.  675 

ceru  the  presence  of  bodies  iu  quantities  so  minute  as  to  be  undiscover- 
able  even  by  spectrum  analysis;  yrnj-.ixlrir.-o-iro"  of  a  grain  of  musk  can  be  dis- 
tinctly smelt  (Valentin).  Opposed  to  the  sensation  of  an  agreeable  odor  is 
that  of  a  disagreeable  or  disgusting  odor,  which  corresponds  to  the  sensa- 
tions of  pain,  dazzling  and  disharmony  of  colors,  and  dissonance  in  the 
other  senses.  The  cause  of  this  diifereucc  in  the  effect  of  different  odors  is 
unknown;  but  this  much  is  certain,  that  odors  are  pleasant  or  offensive 
in  a  relative  sense  only,  for  many  animals  pass  their  existence  in  the 
miilst  of  odors  which  to  us  are  highly  disagreeable.  A  great  difference 
in  this  respect  is,  indeed,  observed  amongst  men:  many  odors,  generally 
thought  agreeable,  are  to  some  persons  intolerable;  and  different  per- 
sons describe  differently  the  sensations  that  they  severally  derive  from 
the  same  odorous  substances.  There  seems  also  to  be  in  some  jDcrsons 
an  insensibility  to  certain  odors,  comparable  with  that  of  the  eye  to  cer- 
tain colors;  and  among  different  persons,  as  great  a  difference  in  the 
acuteness  of  the  sense  of  smell  as  among  otbers  in  the  acuteness  of  sight. 
We  have  no  exact  proof  that  a  relation  of  harmony  and  disharmony  exists 
between  odors  as  between  colors  and  sounds;  though  it  is  probable  that 
such  is  the  case,  since  it  certainly  is  so  with  regard  to  the  sense  of  taste; 
and  since  such  a  relation  would  account  in  some  measure  for  the  differ- 
ent degrees  of  perceptive  power  in  different  persons;  for  as  some  have 
no  ear  for  music  (as  it  is  said),  so  others  have  no  clear  ajDpreciation  of 
the  relation  of  odors,  and  therefore  little  pleasure  in  them. 

Subjective  sensations. — The  sensations  of  the  olfactory  nerves,  inde- 
2:)endent  of  the  external  application  of  odorous  substances,  have  hitherto 
been  little  studied.  The  friction  of  the  electric  machine  produces  a 
smell  like  that  of  phosphorus.  Ritter,  too,  has  observed,  that  when  a 
galvanic  current  is  applied  to  the  organ  of  smell,  besides  the  impulse 
to  sneeze,  and  the  tickling  sensation  excited  in  the  filaments  of  the  fifth 
nerve,  a  smell  like  that  of  ammonia  was  excited  by  the  negative  pole,  and. 
an  acid  odor  by  the  positive  j^ole;  whichever  of  these  sensations  were  pro- 
duced, it  remained  constant  as  long  as  the  circle  was  closed,  and  changed 
to  the  other  at  the  moment  of  the  circle  being  opened.  Subjective  sen 
sations  occur  frequently  in  connection  with  the  sense  of  smell.  Fre- 
quently a  person  smells  something  which  is  not  present,  and  which  othev 
persons  cannot  smell;  this  is  very  frequent  with  nervous  people,  but  it  oc- 
casionally happens  to  every  one.  In  a  man  who  was  constantly  conscious 
of  a  bad  odor,  the  arachnoid  was  found  after  death  to  be  beset  with 
deposits  of  bone,  and  a  lesion  iu  the  middle  of  the  cerebral  hemispheres 
was  also  discovered.  Dubois  was  acquainted  with  a  man  who,  ever  after 
a  fall  from  his  horse,  wliich  occurred  several  years  before  his  death, 
believed  that  he  smelt  a  bail  odor. 


676 


HANDBOOK    OF    PHYSIOLOGY. 


IV.   Hearing. 

Anatomy  of  the  Ear. — For  descriptive  purposes,  the  Ear,  or  Organ 
of  Hearing,  is  divided  into  three  parts,  (1)  the  external,  (2)  the  middle, 
and  (3)  the  internal  ear.     The  two  iirst  are  only  accessory  to  the  third 


Fig.  395. — Diagrammatic  view  from  before  of  the  parts  composing  the  organ  of  hearing  of 
tKe  left  side.  The  temporal  bone  of  the  left  side,  with  the  accompanying  soft  parts,  has  been 
detached  from  the  head,  and  a  section  has  been  carried  through  it  ti-ansversely,  so  as  to  remove 
the  front  of  the  meatus  externus,  half  the  tympanic  membrane,  the  upper  and  anterior  wall  of 
the  tympanum  and  Eustachian  tube.  The  meatus  internus  has  also  been  opened,  and  the  bony 
labyrintli  exposed  by  the  removal  of  the  surrounding  parts  of  the  petrous  bone.  1,  the  pinna 
and  lobe;  2,  2',  meatus  externus;  2',  membrana  tympani;  3,  cavity  of  the  tympanum;  3',  its 
opening  backward  into  the  mastoid  cells;  between  3  and  3',  the  chain  of  small  bones;  4,  Eusta- 
chian tube;  .5,  meatus  internus,  containing  the  facial  (uppermost)  and  the  auditory  nerves;  6, 
placed  on  the  vestibule  of  the  labyrinth  above  the  fenestra  ovalis;  a,  apex  of  the  petrous  bone; 
6,  internal  carotid  artery;  c,  styloid  process;  d,  facial  nerve  issuing  from  the  stylo-mastoid 
foramen ;  e,  mastoid  process ;  /,  squamous  part  of  the  bone  covered  by  integument,  etc.    (Arnold.) 

or  internal  ear,  which  contains  the  essential  parts  of  an  organ  of  hear- 
ing. The  accomj)anying  figure  shoAvs  very  well  the  relation  of  these 
divisions,  one  to  the  other  (fig.  395). 

External  Ear. — The  external  ear  consists  of  the  pinna  or  auricle 
and  the  external  auditory  caoial  or  meatus. 

The  principal  parts  of  the  iiinna  (fig.  395)  are  two  prominent  rims 
inclosed  one  within  the  other  (Jielix  and  antihelix),  and  inclosing  a  cen- 
tral hollow  named  the  concha;  in  front  of  the  concha,  a  prominence 
directed  hackward,  the  tragus,  and. opposite  to  this  one  directed  for- 
V/ai'd,  the  anlitrugus.     From  the    concha,  the   auditory   canal,  with    a 


THE   SENSES. 


or 


slight  arch  directed  iqjward,  passes  inward  aud  a  little  forward  to  the 
membraBa  tympaui,  to  which  it  thus  serves  to  convoy  the  vibrating  aii-. 
Its  outer  part  consists  of  fibro-cartilage  continued  from  the  concha;  its 
inner  part  of  bone.  Both  are  lined  by  skin  continuous  with  that  of 
the  pinna,  and  extending  over  the  outer  jjart  of  the  membrana  tymimni. 

Toward  tlie  outer  part  of  the  canal  arc  fine  hairs  and  sebaceous 
glands,  wliile  deeper  in  the  canal  are  small  glands,  resembling  the  sweat- 
glands  in  structure,  "which  secrete  the  cerumen. 

Middle  Ear  or  Tympanum.— The  middle  ear,  or  tympanum  (3. 
fig.  395),  is  separated  by  the  membrana  tympani  from  the  external 
auditory  canal.  It  is  a  cavity  in  the  temporal  bone,  opening  through 
its  anterior  and   inner  wall  into  the  Eustachian   tube,   a  cylindriform 


Fig.  307. 


Fig.  398. 
1,  the  head;  2,  neck;   3,  short 


Fig.  396. — The  hammer-bone  or  maUeus,  seen  from  the  front 
process;  4,  long  process.     (Schwalbe.) 

Fig.  397.— The  incus,  or  anvil-bone.  1,  hody;  2,  ridged  articulation  for  the  malleus;  4,  pro- 
cessus brevis.  with  5.  rough  articular  siu^ace  for  ligament  of  incus;  6,  processus  magnus,  with 
articulating  surface  for  stapes ;  7,  nutrient  foramen.     (Schwalbe. ) 

Fig.  398.— The  stapes,  or  stirrup-bone.  1,  base;  2  and  3,  arch;  4,  head  of  bone,  which  articu- 
lates with  orbicular  process  of  the  incus;  5,  constricted  part  of  neck;  G,  one  of  the  crura 
(Schwalbe.) 

flattened  canal,  dilated  at  both  ends,  composed  partly  of  bone  and  partly 
of  elastic  cartilage,  and  lined  with  mucous  membrane,  which  forms  a 
communication  between  the  tympanum  and  the  pharynx.  It  opens  into 
the  cavity  of  the  pharynx  just  behind  the  posterior  aperture  of  the  nos- 
trils. The  cavity  of  the  tympanum  communicates  2:)osteriorly  with  air 
cavities,  the  was^oiV/ ce^fe  in  the  mastoid  process  of  the  temporal  bone; 
but  its  only  opening  to  the  external  air  is  through  the  Eustachian  tube 
(4,  fig.  395).  The  walls  of  the  tympanum  are  osseous,  except  where  aper- 
tures in  them  arc  closed  with  membrane,  as  at  the  fenestra  rotunda  and 
fenestra  ovalis,  and  at  the  outer  part  where  the  bone  is  replaced  by  the 
membrana  tympani.  The  cavity  of  the  tympanum  is  lined  with  mucous 
membrane,  the  epithelium  of  which  is  ciliated  and  continuous  with  that 
of  the  pharynx.  It  contains  a  chain  of  small  bones  [ossicida  auditus) 
which  extends  from  the  membrana  tympani  to  the  fenestra  ovalis. 


678  HAisTDBOOK    01?    PHYSIOLOGY. 

The  membrana  tympani  is  placed  in  a,  slanting  directiun  uL  the  bot- 
tom of  the  externa]  auditory  canal,  its  plane  being  at  an  angle  of  about 
■15°  with  the  lower  wall  of  the  canal.  It  is  formed  chiefly  of  a  tough 
and  tense  fibrous  membrane,  the  edges  of  which  are  set  in  a  bony  groove ; 


Fig.  399. —Interior  view  of  the  tympanum,  with  membrana  tympani  and  bones  in  natm-al 
position.  1,  Menibrana  tympani;  2,  Eustachian  tube;  3,  tensor  tympani  muscle;  4,  lig.  mallei 
super. ;  6,  corda-tympani  nerve;  a,  6,  and  c,  sinuses  about  ossicula.     (Schwalbe.) 

its  outer  surface  is  covered  with  a  continuation  of  the  cutaneous  lining 
of  the  auditory  canal,  its  inner  surface  with  part  of  the  ciliated  mucous 
membrane  of  the  tympanum. 

The  ossicles  are  three  in  number;  named  malleus,  incus,  and  stapes. 
The  malleus,  or  hammer-bone,  is  attached  by  a  long  slightly-curved  pro- 
cess, called  its  handle,  to  the  membrana  tympani;  the  line  of  attachment 
being  vertical,  including  the  whole  length  of  the  handle,  and  extending 
from  the  upper  border  to  the  centre  of  the  membrane.  The  head  of  the 
malleus  is  irregularly  rounded;  its  neck,  or  the  line  of  boundary  between 
it  and  the  handle,  supports  two  processes;  a  short  conical  one,  which 
receives  the  insertion  of  the  tensor  tympani,  and  a  slender  one,  processus 
gracilis,  which  extends  forward,  and  to  which  the  laxator  tympa7ii  mnsole 
is  attached.  The  incus,  or  anvil-bone,  shaped  like  a  bicuspid  molar  tooth, 
is  articulated  by  its  broader  part,  corresponding  with  the  surface  of  the 
crown  of  a  tooth,  to  the  malleus.  Of  its  two  fang-like  processes,  one, 
directed  backward,  has  a  free  end  lodged  in  a  depression  in  the  mastoid 
bone ;  the  other,  curved  downward  and  more  pointed,  articulates  by  means 
of  a  roundish  tubercle,  formerly  called  os  orhiculare,  with  the  stapes,  a 
little  bone  shaped  exactly  like  a  stirrup,  of  which  the  base  or  bar  fits  into 
the  fenestra  ovalis.  To  the  neck  of  the  stapes,  a  short  process,  correspond- 
ing with  the  loop  of  the  stirrup,  is  attached  the  stapedius  muscle. 

The  bones  of  the  ear  are  covered  with  mucous  membrane  reflected  over 
them  from  the  wall  of  the  tympanum;  and  are  movable  both  altogether 
and  one  upon  the  other.  The  malleus  moves  and  vibrates  with  every 
movement  and  vibration  of  the  membrana  tympani,  and  its  move- 
ments are  communicated  through  the  incus  to  the  stapes,  and  through 


THE   SEXSES. 


679 


it  to  the  nieinbrane  closing  tlio  i'cuestra,  ovalis.  The  malleus,  also, 
is  movable  in  its  articulation  with  the  incus;  and  the  membrana 
tympani  moving  with  it  is  altered  in  its  degree  of  tension  by  the  laxator 
and  tensor  tympani  muscles.  The  stapes  is  movable  on  tlie  process  of 
the  incus,  when  the  stapedius  muscle  acting,  draws  it  backAvard.  The 
axis  round  which  the  malleus  and  incus  rotate  is  the  line  joining  the  pro- 
cessus gracilis  of  the  malleus  and  the  posterior  (short)  process  of  the  incus. 

The  Internal  Ear. — The  proper  organ  of  hearing  is  formed  by  the 
distribution  of  the  auditory  nerve  within  the  internal  ear,  or  labyrinth, 
a  set  of  cavities  within  the  petrous  portion  of  the  temporal  bone.  The 
bone  which  forms  the  walls  of  these  cavities  is  denser  than  that  around 
it,  aiul  forms  the  osseous  labyrinth;  the  membrane  within  the  cavities 
forms  the  inemhranous  labyrinth.  The  membranous  labyrinth  contains  a 
fluid  called  endolymph ;  Avhile  outside  it,  between  it  and  the  osseous 
labyrinth,  is  a  fluid  caWed  perilymph.  This  fluid  is  not  pure  lymph; 
as  it  contains  mucin. 

The  osseous  labyrinth  consists  of  three  principal  parts,  namely 
the  vestibule,  the  cochlea,  and  the  semicircular  canals. 

The  vestibule  is  the  middle  cavity  of  the  labyrinth,  and  the  central 
organ  of  the  whole  auditory  apparatus.     It  presents,  in  its  inner  wall, 


Fig:.  4(X). 


Fig.  401. 


F'a:.  400. — Right  liony  labyrinth,  vipwcrl  from  the  outer  side.  The  specimen  here  represented 
Is  prepared  by  sui)araliiig  )iifcenieal  Ihc  looser  substance  of  the  petrous  bone  from  the  dense 
walls  which  imniediately  iiul(>st>  the  lal)yrinth.  1.  tlie  vestibule:  2,  fenestra  ovalis;  3.  suj^-rior 
semicircular  canal;  4,  horizontal  or  .external  canal;  .'">,  posterior  canal;  *,  ampullte  of  the  semi- 
circular canals;  U,  first  turn  of  the  cochlea;  7,  second  turn;  8,  apex;  9,  fenestra   rotunda.     The 

smaller  figure  in  outline  below  shows  the  natural  size.     ^^     (Sommering.) 

Fig.  401.— Vie  \  of  the  interior  of  the  left  labyrinth.  The  bony  wall  of  the  labvrinth  is  re- 
moved SI  periorly  and  externally.  1.  Fovea  heuiielliptica:  2.  fovea  hemispherica";  .S.  common 
opening  of  the  st")«rrior  and  posterior  semicircular  canals;  4,  opening  of  the  aqueduct  of  the 
vestibule;  5,  the  superior.  0.  the  posterior,  and  7.  the  external  semicircular  canals;  8.  spiral 
tube  of  the  cochlea  (scala  tympani);  S»,  opening  of  the  aqueduct  of  the  cochlea;  10.  placed  on 

the  lamina  spiralis  in  the  scala  vestibuli.    -"  -.     (Sommering.) 

several    openings   for    the   entrance    of   the    divisions   of  the    auditory 
nerve;    in   its   outer  wall,  the  fenestra   ovalis  (2,  fig.   -iOO),   an   open- 


680  HANDBOOK    OF    PHYSIOLOGY, 

ing  filled  by  the  base  of  the  stapes;  in  its  posterior  and  snperior 
walls,  five  openings  by  which  the  semicircular  canals  communicate  with 
it:  in  its  anterior  wall,  an  opening  leading  into  the  cochlea.  The  hinder 
part  of  the  inner  wall  of  the  vestibule  also  presents  an  opening,  the 
orifice  of  the  aqucednctus  vestibuli,  a  canal  leading  to  the  posterior  mar- 
gin of  the  petrous  bone,  with  uncertain  contents  and  unknown  purpose. 

Tha  semicircular  canals  (figs.  400,401)  are  three  arched  cylindriform 
bony  canals,  set  in  the  substance  of  the  petrous  bone.  They  all  open  at 
both  ends  into  the  vestibule  (two  of  them  first  coalescing).  The  ends  of 
each  are  dilated  just  before  opening  into  the  vestibule;  and  one  end 
being  more  dilated  than  the  other  is  called  an  amindla.  Two  of  the 
canals  form  nearly  vertical  arches;  of  these  the  superior  is  also  anterior; 
the  posterior  is  inferior;  the  third  canal  is  horizontal,  and  lower  and 
shorter  than  the  others. 

The  cochlea  (6,  7,  8,  figs.  400  and  401),  a  small  organ,  shaped  like  a 
common  snail-shell,  is  situated  in  front  of  the  vestibule,  its  base  resting 
on  the  bottom  of  the  internal  meatus,  where  some  apertures  transmit 
to  it  the  cochlear  filaments  of  the  auditory  nerve.  In  its  axis,  the 
cochlea  is  traversed  by  a  conical  column,  the  modiolus,  round  which  a 
spiral  canal  winds  with  about  two  turns  and  a  half  from  the  base  to  the 
apex.  At  the  apex  of  the  cochlea  the  canal  is  closed ;  at  the  base  it 
presents  three  openings,  of  which  one,  already  mentioned,  communicates 
with  the  vestibule ;  another  called  fenestra  rotunda,  is  separated  by  a 
membrane  from  the  cavity  of  the  tympanum ;  the  third  is  the  orifice  of 
the  aquceductus  cochlece,  a  canal  leading  to  the  jugular  fossa  of  the 
petrous  bone,  and  corresponding,  at  least  in  obscurity  of  purpose  and 
origin,  to  the  aquseductus  vestibuli.  The  spiral  canal  is  divided  into  two 
passages,  or  scal^e,  by  a  partition  of  bone  and  membrane,  the  lamina 
spiralis.  The  osseous  part  or  zone  of  this  lamina  is  connected  with  the 
modiolus. 

The  Membranous  Labyrinth.— The  membranous  labyrinth  corre- 
sponds generally  with  the  form  of  the  osseous  labyrinth,  so  far  as  regards 
the  vestibule  and  semicircular  canals,  but  is  separated  from  the  walls  of 
these  parts  by  perilymph,  except  where  the  nerves  enter  into  connection 
within  it.  The  labyrinth  is  a  closed  membrane  containing  endolyrapii, 
which  is  of  much  the  same  composition  as  perilymph,  but  contains  less 
solid  matter.  It  is  somewhat  viscid,  as  is  the  perilymph,  and  it  is 
secreted  by  the  epithelium  lining  its  cavity;  all  the  sonorous  vibrations 
impressing  the  auditory  nerves  in  these  parts  of  the  internal  ear,  are 
conducted  through  fluid  to  a  membrane  suspended  in  and  containing 
fluid.  In  the  cochlea,  the  membranous  labyrinth  completes  the  septum 
between  the  two  scalcB,  and  incloses  a  spiral  canal,  previously  mentioned. 
called   canalis  membranaceus  or  canalis  cochlece  (fig.  403).     The  fluid  in 


'I'll):   SKNSES.  f'.sl 

the  scalce  of  the  cochlea  is  eoiitiniiou.s  with  tlio  perilymph  in  the  vesti- 
bule and  semicircular  canals,  and  there  is  no  fluid  external  to  its  linin^^ 
membrane.  The  vestibular  portion  of  the  membranous  labyrinth  cam- 
prises  two,  probably  communicating  cavities,  of  which  the  larger  and 
upper  is  named  the  utricidus;  the  lower,  the  mcculut<.  They  are 
lodged  in  depressions  in  tlie  bony  labyrinth,  termed  resi)ectively/oiTc/ 
hemielliptica  and  fovea  hemispherica.  Into  the  former  o^Dcn  the  orifices  of 
the  membranous  semicircular  canals;  into  the  latter  the  atnaJis  cocldcie. 
The  membranous  labyrinth  of  all  these  parts  is  laminated,  transparent, 
very  vascular,  and  covered  on  the  inner  surface  with  nucleated  cells,  of 
which  those  that  line  the  ampullse  are  prolonged  into  stiff  hair-like  pro- 
cesses; the  same  appearance,  but  to  a  much  less  degree,  being  visible  in 
ihe  utricule  and  saccule.  In  the  cavities  of  the  utriculus  and  sacculus 
dire  small  masses  of  calcareous  particles,  otoconia  or  otoliths;    and  the 


Fie:.  402.— View  of  the  osseous  cochlea  divided  throiifrh  the  middle.  1,  central  canal  of  the 
iiiodioliis;  ~',  lamina  spii-alis  ossea;  3,  scala  tympani;  4,  scala  vestibuli;  5,  porous  substance  of 
Lhe  modiolus  near  one  of  the  sections  of  the  canalis  spiralis  modioli.     X  5.     (Arnold.) 

same,  although  in  more  minute  quantities,  are  to  be  found  in  the  interior 
of  some  other  parts  of  the  membranous  labyrinth. 

Auditory  Nerve. — All  the  organs  now  described  are  provided  for  the 
appropriate  exiDosure  of  the  filaments  of  the  auditory  nerve  to  sonorous 
vibrations.  It  is  characterized  as  a  nerve  of  special  sense  by  its  softness 
(whence  it  derived  its  name  of  porfi/i  inollis  of  the  seventh  pair),  and  by 
the  fineness  of  its  component  fibres.  It  enters  the  bony  canal  (the  meatus 
auditorius  internus),  with  the  facial  nerve  and  the  nervus  intermedins, 
and,  traversing  the  bone,  enters  the  labyrinth  at  the  angle  between  the 
base  of  the  cochlea  and  the  vestibule,  in  two  divisions;  one  for  the  ves- 
tibule and  semicircular  canals,  and  the  other  for  the  cochlea. 

There  are  two  branches  for  the  vestibule,  one,  superior,  distributed 
to  the  utricule  and  to  the  superior  and  horizontal  semicircular  canals, 
and  the  other,  inferior,  ending  in  the  saccule  and  posterior  semicircular 
canal.  Where  the  nerve  comes  in  connection  with  the  utricule  and 
saccule,  the  structure  of  the  membrane  is  modified  somewhat  and  the 
places  are  called  macula}  acusticm.  The  epithelium  in  this  region  is,  as 
ve  shall  see  directly,  considerably  specialized,  and  where  the  nerve  is  in 
connection  with  the  ampulla)  of  the  semicircular  canals,  too,  the  struet- 
nre  is  altered,  becoming  elevated  into  a  horse-shoe  ridge,  which  projects' 


682  SA>rDBOOK    OP    PHYSIOLOGY. 

into  the  interior  of  the  cavity,  forming  the  crista  acustica.  Here,  too, 
the  epithelium  is  of  a  special  kind.  The  nerve  fibres  spread  out  and 
radiate  on  the  inner  surface  of  the  membranous  labyrinth:  their  exact 
termination  is  uncertain.  The  distribution  of  the  other  division  of  the 
auditory  nerve,  the  cochlear,  will  be  more  clearly  understood  after  the 
description  of  the  cochlea  itself. 

Structure. — The  structure  of  the  membranous  labyrinth  consists  of 
three  coats,  externally  a  layer  of  areolar  tissue,  next  a  hyaloid  membrane, 
elevated  into  minute  papillae,  and  internally  a  layer  of  flattened  epi- 
thelium. At  the  position  where  the  branches  of  the  vestibular  branch 
of  the  auditory  nerve  join  it,  viz.,  at  the  saccule,  utricule,  and  ampullfe 
of  the  semicircular  canals,  there  is  a  marked  difference  in  the  structure, 
the  external  and  middle  layers  are  thicker  and  the  epithelium  becomes 
columnar.  The  epithelium  in  which  the  fibres  of  the  vestibular  nerve 
are  said  to  terminate  are  of  two  kinds,  called  cylinder  or  hair  cells.,  and 
rod  cells.  The  hair  cells  occupy  only  one-half  of  the  thickness  of  the 
membrane;  from  their  inner  end  hair-like  processes  project  into  the 
cavity  of  the  labyrinth.  Their  outer  end  is  rounded  and  contains  a 
large  round  nucleus.  To  these  cells  the  primitive  fibrillae  of  the  axis 
cylinders  pass  up,  some  of  them  being  distinctly  varicose.  The  exact 
relation  of  the  nerve  fibrillse  to  the  hair-cells  is  unknown;  by  some  th(^y 
are  believed  actually  to  enter  .the  cells,  by  others  they  are  stated  to  form 
a  kind  of  nest  of  fibrillse  into  which  the  cells  fit.  The  rod-cells  are  of 
somewhat  varying  form.  They  are  elongated  cells  extending  from  the 
surface  to  the  basement  membrane,  broad  at  the  upper  or  surface  end, 
and  containing  oval  nuclei  toward  their  attached  end,  but  not  exactly  at 
the  same  level  in  all  cases.  These  nuclei,  therefore,  form  a  distinct 
broad  nuclear  layer  on  a  vertical  section  of  the  membrane,  as  the  celly 
are  numerous,  much  more  so,  indeed,  than  the  other  variety  of  cell. 
The  lower  or  attached  part  of  the  cell  may  be  branched. 

The  membranous  part  of  the  cochlea,  with  a  muscular  zone,  forming 
its  outer  margin,  is  attached  to  the  outer  wall  of  the  canal.  Oommen(!- 
ing  at  the  base  of  the  cochlea,  belween  its  vestibular  and  tympanic  open- 
ings, it  forms  a  partition  between  these  apertures;  the  two  scalse  are, 
therefore,  in  correspondence  with  this  arrangement,  named  scala  vesti- 
huli  and  scala  tympani  (fig.  403).  At  the  apex  of  the  cochlea,  the 
lamina  spiralis  ends  in  a  small  haimdus,  the  inner  and  concave  part  of 
which,  being  detached  from  the  summit  of  the  modiolus,  leaves  a  small 
aperture  named  helicotrema,  by  which  the  two  scalfe,  separated  in  all  the 
rest  of  their  length,  communicate. 

Besides  the  scala  vestibuli  and  scala  tympani,  there  is  a  third  space 
between  them,  called  scala  media  or  ccmcd  memhranaceus  (CC,  fig.  403). 
In  section  it  is  triangular,  its  external  wall  being  formed  by  the  wall  of 


THE   SENSES.  GS3 

the  cochlea,  its  upper  wall  (separating  it  from  the  scala  vestibuli)  by 
the  membrane  of  Keissner,  and  its  lower  wall  (separating  it  from  the 
scala  tympani)  by  the  basilar  membrane,  these  two  meeting  at  the  outer 
edge  of  the  bony  lamina  spiralis.  Following  the  turus  of  the  cochlea  to 
its  apex,  the  scala  media  there  terminates  blindly;  while  toward  the  base 
of  the  cochlea  it  is  also  closed  with  the  exception  of  a  very  narrow  pas- 
sage (canalis  reuniens)  uniting  it  with  the  sacculus.  The  scala  media 
(like  the  rest  of  the  membranous  labyrinth)  contains  endolympli. 

Organ  of  Corti. — Upon  the  basilar  membrane  are  arranged  cells  of 
various  shapes.     About  midway  between  the  outer  edge  of  the  lamina 


Fig.  403. — Section  throufch  one  of  the  coils  of  the  eoclilea  (diafrrammatic).  ST,  scala  tym- 
pani; SV,  scala  vestibuli;  CC.  canalis  cochleae  or  canalis  membranaceus:  i?,  membrane  of 
Keissner;  Iso,  lamina  spiralis  ossea;  Us,  limbus  lamina?  spiralis;  s.s.  sulcus  spiralis;  nc.  cochlear 
nerve;  gs,  ganglion  spirale;  t.  membrana  tectoria  (below  the  meuibrana  tectoria  is  the  lamina 
recticularis) ;  b,  membrana  basilaris;  Co,  rods  of  Corti;  Up,  ligamentum  spirale.     (Quain.) 

spiralis  and  the  outer  wall  of  the  cochlea  are  situated  the  rods  of  Corti. 
Viewed  sideways,  they  are  seen  to  consist  of  an  external  and  internal 
pillar,  each  rising  from  an  expanded  foot  or  hase  on  the  basilar  mem- 
brane (o,  n,  fig.  404:).  They  slant  inward  toward  each  other,  and  each 
ends  in  a  swelling  termed  the  head ;  the  head  of  the  inner  pillar  overly- 
ing that  of  the  outer  (fig.  404).  Each  pair  of  jiillars  forms,  as  it  were, 
;i  pointed  roof  arching  over  a  space,  and  by  a  succession  of  tliem  a  little 
tunnel  is  formed. 

It  has  been  estimated  that  there  are  about  3000  of  these  pairs  of  pil- 
lars, in  proceeding  from  the  base  of  the  cochlea  toward  its  ai)ex.  Thoy 
are  found  progressively  to  increase  in  length,  and  become  more  oblique; 
in  other  words  the  tunnel  becomes  wider,  but  diminishes  in  height  as  we 
approach  the  apex  of  the  cochlea.  Leaning,  as  it  were,  against  these 
external  and  internal  pillars  are  certain  other  cells,  of  which  the  external 
ones,  hair  cells,  terminate  in  small  hair-like  processes.  Most  of  the 
above  details  are  shown  in  the  accompanying  figure  (fig.  404).  This 
complicated  structure  rests,  as  we  have  seen,  upon  the  basilar  membrane; 
it  is  roofed  in  by  a  remarkable  fenestrated  membrane  or  lamina  reticu- 


684 


HANDBOOK    OF    PHYSIOLOGY. 


laris  into  the  fenestra  of  which  the  tops  of  the  various  rods  and  cells 
are  received.  When  viewed  from  above,  the  organ  of  Corti  shows  a 
remarkable  resemblance  to  the  key-board  of  a  piano.     In  close  relation 


Fig.  404.  — Vertical  section  of  the  organ  of  Corti  from  the  dog.  1  to  2,  Homogeneous  layer 
of  the  so-called  membrana  basilaris;  u,  vestibular  layer;  v,  tympanal  layer,  with  nuclei  and 
protoplasm;  a,  prolongation  of  tympanal  periosteum  of  lamina  spiralis  ossca:  c,  thickened 
commencement  of  the  membrana  basilaris  near  the  point  of  perforation  of  the  nerves  h;  d, 
blood-vessel  (vas  spirale) ;  <>,  blood-vessel;  /,  nerves;  g.  the  epithelium  of  the  sulcus  spiralis 
internus;  i,  internal  or  tufted  cell,  with  basil  process  fc,  surrounded  with  nuclei  and  protoplasm 
(of  the  granular  layer),  into  which  the  nerve-fibres  radiate;  I,  hairs  of  the  internal  hair-cell;  n, 
base  or  foot  of  inner  pillar  of  organ  of  Corti;  wi,  head  of  the  same  uniting  with  the  correspond- 
ing part  of  an  external  pillar,  whose  under  half  is  missing,  while  the  next  pillar  beyond,  o,  pre- 
sents both  middle  portion  and  base;  r  s  d,  three  external  hair-cells;  t,  bases  of  two  neighboriujj 
hair  or  tufted  cells ;  x,  so-called  supporting  cell  of  Hensen ;  ro,  nerve-fibre  terminating  in  the  first 
of  the  external  hair-cells;  I  I  to  I,  lamina  reticularis.     X  800.     (Waldeyer.) 

with  the  rods  of  Corti  and  the  cells  inside  and  outside  them,  and  proba. 
bly  projecting  by  free  ends  into  the  little  tunnel  containing  fluid  (roofed 
in  by  them),  are  filaments  of  the  auditory  nerve.  These  are  derived 
from  the  cochlear  division  already  mentioned.  This  passes  up  the  axia 
of  the  cochlea,  and  in  its  course  gives  off  fibres  to  the  lamina  spiralis. 
These  fibres  are  thick  at  their  origin,  but  thin  out  peripherally,  and 
containing  bipolar  ganglion  cells  form  the  ganglion  spirale.  Beyond 
the  ganglion  at  the  edge  of  the  lamina  the  fibres  pass  up  and  become 
connected  witii  the  orsran  of  Corti. 


The  Physiology  of  Heaeing. 

All  the  acoustic  contrivances  of  the  organ  of  hearing  are  means  for 
conducting  sound.  Since  all  matter  is  capable  of  propagating  sonorous 
vibrations,  the  simplest  conditions  must  be  sufficient  for  mere  hearing; 
for  all  substances  surrounding  the  auditory  nerve  would  stimulate  it. 
The  whole  development  of  the  organ  of  hearing,  therefore,  can  have  for  its 
object  merely  the  rendering  more  perfect  the  propagation  of  the  sono- 
rous vibrations,  and  their  multiplication  by  resonance;  and,  in  fact,  the 
whole  of  the  acoustic  apparatus  may  be  shown  to  have  reference  to  these 
principles. 

The  external  auditory  passages  influence  the  propagation  of  sound 


THE   SENSES.  (iSo 

to  the  tympanum  in  three  ways: — 1,  by  causing  the  sonorous  undulations, 
entering  directly  from  the  atmosphere,  to  be  transmitted  by  the  air  in 
the  passage  immediately  to  the  membrana  tympani,  and  thus  preveutiiig 
them  from  being  dispersed ;  2,  by  the  Avails  of  the  passage  conducting 
the  sonorous  undulations  imparted  to  the  external  ear  itself,  by  the 
shortest  path  to  the  attachment  of  the  membrana  tympani,  and  so  to  this 
membrane;  3,  by  the  resonance  of  the  column  of  air  contained  Avithin  the 
passage;  4,  the  external  ear,  es2Decially  Avheu  the  tragus  is  provided  with 
hairs,  is  also,  doubtless,  of  service  in  protecting  the  meatus  and  mem- 
brana tympani  against  dust,  insects,  and  the  like. 

liegarding  the  cartilage  of  the  external  ear,  therefore,  as  a  conductor 
of  sonorous  vibrations,  all  its  inequalities,  elevations,  and  depressions, 
become  of  evident  importance ;  for  those  elevations  and  depressions  upon 
which  the  undulations  fall  joerpendicularly,  will  bo  affected  by  them  in 
the  most  intense  degree;  and,  in  consequence  of  the  various  form  and 
position  of  these  inequalities,  sonorous  undulations,  in  whatever  direc- 
tion they  may  come,  must  fall  perpendicularly  upon  the  tangent  of  some 
one  of  them.  This  affords  an  ex2:)lanation  of  the  extraordinary  form 
given  to  this  part. 

In  animals  living  in  the  atmosphere,  the  sonorous  vibrations  are  con- 
veyed to  the  auditory  nerve  by  three  different  media  in  succession; 
namely,  the  air,  the  solid  parts  of  the  body  of  the  animal  and  of  the 
auditory  apparatus,  and  the  fluid  of  the  labyrinth.  Sonorous  vibrations 
are  imparted  too  imperfectly  from  air  to  solid  bodies,  for  the  propaga- 
tion of  sound  to  the  internal  ear  to  be  adequately  effected  by  that  means 
alone;  yet  already  an  instance  of  its  being  thus  propagated  has  been 
mentioned.  In  passing  from  air  directly  into  water,  sonorous  vibra- 
tions suffer  also  a  considerable  diminution  of  their  strength;  but  if  a 
tense  mombrane  exists  between  the  air  and  the  water,  the  sonorous  a  i- 
bi'ations  are  communicated  from  tlie  former  to  the  latter  medium  witli 
very  great  intensity.  This  fact,  of  A\diich  Midler  gives  experimental 
proof,  furnishes  at  once  an  explanation  of  the  use  of  the  fenestra  rotunda, 
a.nd  of  the  meml)rane  closing  it.  They  arc  the  means  of  communicat- 
ing, in  full  intensity,  the  vibrations  of  the  air  in  the  tympanum  to 
tlie  fluid  of  the  labyrinth.  This  peculiar  projDerty  of  membranes  is  the 
result,  not  of  their  tenuity  alone,  but  of  the  elasticity  and  capability  of 
displacement  of  their  particles;  and  it  is  not  impaired  Avhen,  like  the 
membrane  of  the  fenestra  rotunda,  they  are  iiot  impregnated  Avith 
moisture. 

Sonorous  vibrations  are  also  communicated  Avithout  any  jicrceptible 
loss  of  intensity  from  the  air  to  the  Avater,  when  to  the  membrane  form- 
ing the  medium  <'\'  (■oininunication,  there  is  attached  a  short,  solid  body, 
Avliich  occu])ie.s  the  greater  part  of  its  surface,  and  is  alone  in  contact 


686  HAXDBOOK    OF    PHYSIOLOGY. 

with  the  water.  This  fact  elucidates  the  action  of  the  fenestra  ovalis, 
and  of  the  plate  of  the  stapes  which  occupies  it,  and,  with  the  preceding 
fact,  shows  that  both  fenestras — that  closed  by  membrane  only,  and  that 
with  which  the  movable  stapes  is  connected — transmit  very  freely  the 
sonorous  vibrations  from  the  air  to  the  fluid  of  the  labyrinth. 

A  small,  solid  body,  fixed  in  an  opening  by  means  of  a  border  of 
membrane,  so  as  to  be  movable,  communicates  sonorous  vibrations  from 
air  on  the  one  side,  to  water,  or  the  fluid  of  the  labyrinth,  on  the  other 
side,  much  better  than  solid  media  not  so  constructed.  But  the  propa- 
gation of  sound  to  the  fluid  is  rendered  much  more  perfect  if  the  solid 
conductor  thus  occupying  the  ojjening,  or  fenestra  ovalis,  is  by  its  other 
end  fixed  to  the  middle  of  a  tense  membrane,  which  has  atmospheric  air 
on  both  sides.  A  tense  membrane  is  a  much  better  conductor  of  the 
vibrations  of  air  than  any  other  solid  body  bounded  by  definite  surfaces: 
and  the  vibrations  are  also  communicated  very  readily  by  tense  mem- 
branes to  solid  bodies  in  contact  with  them.  Thus,  then,  the  membrana 
tympani  serves  for  the  transmission  of  sound  from  the  air  to  the  chain 
of  ossicles.  Stretched  tightly  in  its  osseous  ring,  it  vibrates  with  the 
air  in  the  auditory  passage,  as  any  thin  tense  membrane  Avill,  Avhen  the 
air  near  it  is  thrown  into  vibrations  by  the  sounding  of  a  tuning-fork 
or  a  musical  string.  And,  from  such  a  tense  vibrating  membrane,  the 
vibrations  are  communicated  with  great  intensity  to  solid  bodies  which 
touch  it  at  any  point.  If,  for  example,  one  end  of  a  flat  piece  of  wood 
be  applied  to  the  membrane  of  a  drum,  while  the  other  end  is  held  in 
the  hand,  vibrations  are  felt  distinctly  when  the  vibrating  tuning-fork 
is  held  over  the  membrane  without  touching  it;  but  the  wood  alone, 
isolated  from  the  membrane,  will  only  very  feebly  propagate  the  vibra- 
tions of  the  air  to  the  hand. 

In  comparing  the  membrana  tymjDani  to  the  membrane  of  a  drum, 
however,  it  is  necessary  to  point  out  certain  important  difl'erences. 

When  a  drum  is  struck,  a  certain  definite  tone  is  elicited  (funda- 
mental tone) ;  similarly  a  drum  is  thrown  into  vibration  when  certain 
tones  are  sounded  in  its  neighborhood,  while  it  is  quite  unaffected  by 
others.  In  other  words  it  can  only  take  up  and  vibrate  in  response  to 
those  tones  whose  vibrations  nearly  correspond  in  number  with  those  of 
its  own  fundamental  tone.  The  tympanic  membrane  can  take  up  an 
immense  range  of  tones  produced  by  vibrations  ranging  from  30  to  4000 
or  5000  per  second.  This  would  be  clearly  impossible  if  it  were  an 
evenly  stretched  membrane. 

The  fact  is,  that  the  membrana  tympani  is  by  no  means  evenly 
stretched,  and  this  is  due  partly  to  its  slightly  funnel-like  form,  and 
partly  to  its  being  connected  with  the  chain  of  auditory  ossicles.  Fur- 
ther,  if  the  menibrane  were  quite  free  in  its  centre,  it  would  go  on 


THE    SENSES. 


G87 


vibrating  as  a  drum  does  some  time  after  it  is  struck,  and  each  sound 
would  be  prolonged,  leading  to  considerable  confusion,  This  evil  is 
obviated  by  the  ear-bones,  which  check  the  continuance  of  the  vibrations 
like  the  "  dampers"  in  a  pianoforte. 

The  ossicles  of  the  ear  are  the  better  conductors  of  the  sonorous  vi- 
brations communicated  to  them,  on  account  of  being  isolated  by  an 
atmosphere  of  air,  and  not  continuous  with  the  bones  of  the  cranium; 
for  every  solid  body  thus  isolated  by  a  different  medium,  propagates 
vibrations  with  more  intensity  through  its  own  substance  than  it  com- 
municates them  to  the  surrounding  medium,  which  thus  prevents  a 
depression  of  the  sound;  just  as  tlie  vibrations  of  the  air  in  the  tubes 
used  for  comlucting  the  voice  from  one  apartment  to  another  are  pre- 
vented from  being  dispersed  by  the  solid  walls  of  the  tube.  The  vibra- 
tions of  the  membrana  tympani  are  transmitted,  therefore,  by  the  chain 
of  ossicula  to  the  fenestra  ovalis  and  fluid  of  the  labyrinth,  their  disper- 
sion in  the  tympanum  being  prevented  by  the  difficulty  of  the  transition 
of  vibratiens  from  solid  to  gaseous  bodies. 

The  necessity  of  the  presence  of  air  on  the  inner  side  of  the  mem- 
brana tympani,  in  order  to  enable  it  and  the  ossicula  auditus  to  fulfil  the 
objects  just  described,  is  obvjous.  "Without  this  provision,  neither 
would  the  vibrations  of  the  membrane  be  free,  nor  the  chain  of  bones 
isolated,  so  as  to  propagate  the  sonorous  undulations  with  concentration 
of  their  intensity.  But  while  the  oscillations  of  the 
membrana  tympani  are  readily  communicated  to  the  air 
in  the  cavity  of  the  tympanum,  those  of  the  solid  ossi- 
cula will  not  be  conducted  away  by  the  air,  but  will  be 
propagated  to  the  labyrinth  without  being  dispersed  in 
the  tympanum. 

The  2)ropagatit)ii  of  sound  through  the  ossicula  tym- 
pani to  the  labyrinth,  must  be  affected  either  by  oscil- 
lations of  the  bones,  or  by  a  kind  of  molecular  vibration 
of  tlieir  particles,  or,  most  probably,  by  both  these  kinds 
of  motion. 

It  has  been  shown  that  the  existence  of  the  mem- 
brane over  the  fenestra  rotunda  will  permit  approxima- 
tion and  renu)val  of  the  stapes  to  and  from  the  laby- 
rinth. When  by  the  stapes  the  membrane  of  the 
fenestra  ovalis  is  pressed  toward  the  labyrinth,  the 
membrane  of  the  fenestra  rotunda  may,  by  the  pressure  communicated 
through  the  fluid  of  the  labyrinth,  be  pressed  toward  the  cavity  of  the 
tympanum. 

The  long  process  of  the  nuilleus  receives  the  undulations  of  the  mem- 
brana tympani  (fig.  405,  a,  a)  and  of  the  air  in  a  direction  indicated  by 


Fig.  -lOS.  —Dia- 
gram to  illustrate 
the  action  of  the  os- 
sicles of  the  middli' 
ear  in  the  conduc- 
tion of  sound  to  the 
internal  ear. 


688  HANDBOOK    OF    PHYSIOLOGY. 

the  arrows,  nearly  perpendicular  to  itself.  From  the  long  process  of 
the  malleus  thqy  are  propagated  to  its  head  (b) :  thence  into  the  incus  (c), 
the  long  process  of  which  is  parallel  with  the  long  process  of  the  malleus. 
From  the  long  process  of  the  incus  the  undulations  are  communicated 
to  the  stapes  (d),  which  is  united  to  the  incus  at  right  angles.  The 
several  changes  in  the  direction  of  the  chain  of  bones  hare,  however,  no 
influence  in  changing  the  character  of  the  undulations,  which  remain  the 
same  as  in  the  meatus  externus.  From  the  long  process  of  the  malleus, 
the  undulations  are  communicated  by  the  stapes  to  the  fenestra  ovalis 
in  a  perpendicular  direction. 

Increasing  tension  of  the  membrana  tympani  diminishes  the  facility 
of  transmission  of  sonorous  undulations  from  the  air  to  it. 

The  dry  membrana  tympani,  on  the  approach  of  a  body  emits  a  loud 
sound,  rejects  particles  of  sand  strewn  upon  it  more  strongly  when  lax 
than  when  very  tense;  and  it  has  been  inferred,  therefore,  that  hearing 
is  rendered  less  acute  by  increasing  the  tension  of  the  membrana  tym- 
pani. 

The  pharyngeal  orifice  of  the  Eustachian  tube  is  usually  shut;  dur- 
ing swallowing,  however,  it  is  opened ;  this  may  be  shown  as  follows : — • 
If  the  nose  and  mouth  be  closed  and  the  cheeks  blown  out,  a  sense  of 
pressure  is  produced  in  both  ears  the  moment  we  swallow;  this  is  due, 
doubtless,  to  the  bulging  out  of  the  tympanic  membrane  by  the  com- 
pressed air,  which  at  that  moment  enters  the  Eustachian  tube. 

Similarly  the  tympanic  membrane  may  be  pressed  in  by  rarefying 
the  air  in  the  tympanum.  This  can  be  readily  accomplished  by  closing 
the  mouth  and  nose,  and  making  an  inspiratory  efPort  and  at  the  same 
time  swallowing.  In  both  cases  the  sense  of  hearing  is  temporarily 
dulled;  proving  that  equality  of  pressure  on  both  sides  of  the  tympanic 
membrane  is  necessary  for  its  full  efficiency. 

The  principal  office  of  the  Eustachian  tube  has  relation  to  the  pre- 
vention of  these  effects  of  increased  tension  of  the  membrana  tympani. 
Its  existence  and  openness  will  provide  for  the  maintenance  of  the  equi- 
librium between  the  air  within  the  tympanum  and  the  external  air,  so 
as  to  prevent  the  inordinate  tension  of  the  membrana  tympani  which 
would  be  produced  by  too  great  or  too  little  pressure  on  eithei"  side. 
AVhile  discharging  this  office,  however,  it  will  serve  to  render  sounds 
clearer,  as  the  apertures  in  violins  do;  to  supply  the  tympanum  with 
air;  and  to  bean  outlet  for  mucus.  If  the  tube  were pei^nicmently  open, 
the  sound  of  one's  own  voice  would  jirobably  be  greatly  intensified,  a 
condition  which  would  of  course  interfere  with  the  perception  of  other 
sounds.  At  any  rate,  it  is  certain  that  sonorous  vibrations  can  be  prop- 
agated up  tlie  tnl)e  to  the  tympanum  l)y  means  of  a  catheter  inserted 
into  the  pharyngeal  orifice  of  the  Eustachian  tube. 


THE  SENSES,  689 

The  influence  of  the  tensor  tympani  muscle  in  modifying  hearing 
may  also  be  probably  explained  in  connection  with  the  regulation  of  the 
tension  of  the  membrana  tympani.  If,  through  reflex  nervous  action, 
it  can  be  excited  to  contraction  by  a  very  loud  sound,  then  it  is  mani- 
fest that  a  very  intense  sound  would,  through  the  action  of  this  muscle, 
induce  a  deafening  or  muffling  of  the  ears.  In  favor  of  this  supposition 
we  have  the  fact  that  a  loud  sound  excites,  by  reflection,  nervous  action, 
winking  of  the  eyelids,  and,  in  persons  of  irritable  nervous  system,  a 
sudden  contraction  of  many  muscles. 

The  exact  influence  of  the  stapedius  muscle  in  hearing  is  unknown. 
It  acts  upon  the  stapes  in  such  a  manner  as  to  make  it  rest  obliquely  in 
the  fenestra  ovalis,  depressing  that  side  of  it  on  which  it  acts,  and  ele- 
vating the  other  side  to  the  same  extent.  It  prevents  too  great  a  move- 
ment of  the  bone. 

The  fluid  of  the  labyrinth  is  the  most  general  and  constant  of  the 
acoustic  provisions  of  the  labyrinth.  In  all  forms  of  organs  of  hearing, 
the  sonorous  vibrations  affect  the  auditory  nerve  through  the  medium 
of  liquid — the  most  convenient  medium,  on  many  accounts,  for  such  a 
purpose. 

The  otoliths  in  the  labyrinth  would  reinforce  the  sonorous  vibrations 
by  their  resonance,  even  if  they  did  not  actually  touch  the  membranes 
upon  which  the  nerves  are  expanded ;  but,  inasmuch  as  these  bodies  lie 
in  contact  with  the  membranous  parts  of  the  labyrinth,  and  the  vestibu- 
lar nerve-fibres  are  imbedded  in  them,  they  communicate  to  these  mem- 
branes and  the  nerves,  vibratory  impulses  of  greater  intensity  than  the 
fluid  of  the  labyrinth  can  impart.  This  appears  to  be  their  office.  So- 
norous undulations  in  water  are  not  perceived  by  the  hand  itself  immersed 
in  the  water,  but  are  felt  distinctly  through  the  medium  of  a  rod  held 
in  the  hand.  The  fine  hair-like  prolongations  from  the  epithelial  cells 
of  the  ampullas  have,  probably,  the  same  function. 

The  function  of  the  semicircular  canals  in  the  co-ordination  of 
movements  necessary  to  the  maintenance  of  the  equilibrium  of  the  body 
has  already  been  indicated. 

The  cochlea  seems  to  be  constructed  for  the  spreading  out  of  the 
nerve-fibres  over  a  wide  extent  of  surface,  upon  a  solid  lamina  which 
communicates  with  the  solid  walls  of  the  labyrinth  and  cranium,  at  the 
same  time  that  it  is  in  contact  with  the  fluid  of  the  labyrinth,  and 
which,  besides  exposing  the  nerve-fibres  to  the  influence  of  sonorous 
undulations,  by  two  media,  is  itself  insulated  by  fluid  on  either  side. 

The  connection  of  the  lamina  spiralis  with  the  solid  walls  of  the 
labyrinth,  adapts  the  cochlea  for  the  perception  of  the  sonorous  undula- 
tions propagated  by  the  solid  parts  of  the  head  and  the  walls  of  the  laby- 
rinth. The  membranous  labyrinth  of  the  vestibule  and  semicircular 
44 


6 DO  HANDBOOK    OF    PHYSIOLOGY. 

canals  is  suspended  free  in  the  perilymph,  and  is  destined  more  particu- 
larly for  the  perception  of  sounds  through  the  medium  of  that  fluid, 
whether  the  sonorous  undulations  be  imparted  to  the  fluid  through  the 
fenestrse,  or  by  the  intervention  of  the  cranial  bones,  as  when  sounding 
bodies  are  brought  into  communication  with  the  head  or  teeth.  The 
spiral  lamina  on  which  the  nervous  fibres  are  expanded  in  the  cochlea, 
is,  on  the  contrary,  continuous  with  the  solid  walls  of  the  labyrinth,  and 
receives  directly  from  them  the  impulses  which  they  transmit.  This  is 
an  important  advantage;  for  the  impulses  imparted  by  solid  bodies, 
have,  cceteris  imribus^  a  greater  absolute  intensity  than  those  communi- 
cated by  water.  And,  even  when  a  sound  is  excited  in  the  water,  the 
sonorous  undulations  are  more  intense  in  the  water  near  the  surface  of 
the  vessel  containing  it,  than  in  other  parts  of  the  water  equally  distant 
from  the  point  of  origin  of  the  sound;  thus  we  may  conclude  that, 
cceteris  paribus,  the  sonorous  undulations  of  solid  bodies  act  with  greater 
intensity  than  those  of  water.  Hence,  we  perceive  at  once  an  important 
use  of  the  cochlea. 

This  is  not,  however,  the  sole  office  of  the  cochlea;  the  spiral  lamina, 
as  well  as  the  membranous  labyrinth,  receives  sonorous  impulses  through 
the  medium  of  the  fluid  of  the  labyrinth  from  the  cavity  of  the  vestibule, 
and  from  the  fenestra  rotunda.  The  lamina  spiralis  is,  indeed,  much 
better  calculated  to  render  the  action  of  these  undulations  upon  the 
auditory  nerve  efficient,  than  the  membranous  labyrinth  is ;  for  as  a  solid 
body  insulated  by  a  different  medium,  it  is  capable  of  resonance. 

The  rods  of  Corti  are  probably  arranged  so  that  each  is  set  to  vibrate 
in  unison  with  a  particular  tone,  and  thus  strike  a  particular  note,  the 
sensation  of  which  is  carried  to  the  brain  by  those  filaments  of  the  audi- 
tory nerve  with  which  the  little  vibrating  rod  is  connected.  The  dis- 
tinctive function,  therefore,  of  these  minute  bodies  is,  probably,  to 
render  sensible  to  the  brain  the  various  musical  notes  and  tones,  one  of 
them  answering  to  one  tone,  and  one  to  another;  while  perhaps  the 
other  parts  of  the  organ  of  hearing  discriminate  between  the  intensities 
of  different  sounds,  rather  than  their  qualities. 

"  In  the  cochlea  we  have  to  do  with  a  series  of  apparatus  adapted  for 
performing  sympathetic  vibrations  witli  wonderful  exactness.  We  have 
here  before  us  a  musical  instrument  which  is  designed,  not  to  create 
musical  sounds,  but  to  render  them  perceptible,  and  which  is  similar  in 
construction  to  artificial  musical  instruments,  but  which  far  surpasses 
them  in  the  delicacy  as  well  as  the  simplicity  of  its  execution.  For, 
while  in  a  piano  every  string  must  have  a  separate  hammer  by  means  of 
which  it  is  sounded  the  ear  possesses  a  single  hammer  of  an  ingenious 
form  in  its  ear  bones,  which  can  make  every  string  of  the  organ  of  Corti 
sound  separately. "     (Bernstein.) 


THE    SENSES.  691 

Since  about  3000  rods  of  Corti  are  present  in  the  liuman  ear,  this 
would  give  about  400  to  eacli  of  the  seven  octaves  whicli  are  within  the 
compass  of  tlie  ear.  Thus  about  32  wouhl  go  to  each  semi-tone.  Weber 
asserts  that  accomplished  musicians  can  appreciate  differences  in  pitch 
as  small  as  g^^^^  ^^  ^  tone.  Thus  on  the  tlieory  above  advanced,  the 
delicacy  of  discrimination  would,  in  this  case,  appear  to  have  reached 
its  limits. 

Sounds. 

Any  elastic  body,  e.y.,  air,  a  membrane,  or  a  string  performing  a 
certain  number  of  regular  vibrations  in  the  second,  gives  rise  to  what 
is  termed  a  musical  sound  or  tone.  We  must,  however,  distinguish  be- 
tween a  musical  sound  and  a  mere  noise;  the  latter  being  due  to  irregular 
vibrations. 

Musical  sounds  are  distinguished  from  each  other  by  three  qualities. 
1.  Strength  or  intensity,  which  is  due  to  the  amplitude  or  length  of  the 
vibrations.  2.  Pitch,  which  depends  upon  the  number  of  vibrations  in 
a  second.  3.  Quality,  Color,  or  Timbre.  It  is  by  this  property  that 
we  distinguish  the  same  note  sounded  on  two  instruments,  e.g.,  a  piano 
and  a  flute.  It  has  been  proved  by  Helmholtz  to  depend  on  the  number 
of  secondary  tones,  termed  harmonic.'<,  which  are  present  with  the  pre- 
dominating or  fundamental  tone. 

It  would  appear  that  two  impulses,  which  are  equivalent  to  four  single 
or  half  vibrations,  are  sufficient  to  produce  a  definite  note,  audible  as 
such  through  the  auditory  nerve. 

The  maximum  and  minimum  of  the  intervals  of  successive  impulses 
still  appreciable  through  the  auditory  nerve  as  determinate  sounds,  have 
been  determined  by  Savart.  If  their  intensity  is  sufficiently  great, 
sounds  are  still  audible  which  result  from  the  succession  of  4.8,000  half 
vibrations,  or  24,000  impulses  in  a  second;  and  this,  probably,  is  not 
the  extreme  limit  in  acuteness  of  sounds  perceptible  by  the  ear.  For 
the  opposite  extreme,  he  has  succeeded  in  rendering  sounds  audible 
Avhicli  were  produced  by  only  fourteen  or  eighteen  half  vibrations,  or 
seven  or  eight  impulses  in  a  second ;  and  sounds  still  deeper  might  prob- 
ably be  heard,  if  the  individual  impulses  could  be  sufficiently  prolonged. 

Direction. — The  power  of  iierceiving  the  direction  of  sounds  is  not 
a  faculty  of  the  sense  of  hearing  itself,  but  is  an  act  of  the  mind  judging 
on  experience  previously  acquired.  From  the  modifications  which  the 
sensation  of  sound  undergoes  according  to  the  direction  in  which  the 
sound  reaches  us,  the  mind  infers  the  position  of  the  sounding  body. 
The  only  true  guide  for  this  inference  is  the  more  intense  action  of  the 
sound  upon  one  than  upon  the  other  ear.  But  even  here  there  is  room 
for  much  deception,  by  the  influence  of  reflexion  or  resonance,  and  by 


692  HANDBOOK    OF    PHYSIOLOGY. 

the  propagation  of  sound  from  a  distance,  without  loss  of  intensity, 
through  curved  conducting  tubes  filled  with  air.  By  means  of  such  tubes, 
or  of  solid  conductors,  which  convey  the  sonorous  vibrations  from  their 
source  to  a  distant  resonant  body,  sounds  may  be  made  to  appear  to  orig- 
inate in  a  new  situation.  The  direction  of  sound  may  also  be  judged 
of  by  means  of  one  ear  only;  the  position  of  the  ear  and  head  being 
varied,  so  that  the  sonorous  undulations  at  one  moment  fall  upon  the 
ear  in  a  perpendicular  direction,  at  another  moment  obliquely.  But 
when  neither  of  these  circumstances  can  guide  us  in  distinguishing  the 
direction  of  sound,  as  when  it  falls  equally  upon  both  ears,  its  source 
being,  for  example,  either  directly  in  front  or  behind  us,  it  becomes 
impossible  to  determine  whence  the  sound  comes. 

Distance. — The  distance  of  the  source  of  sounds  is  not  recognized  by 
ihe  sense  itself,  but  is  inferred  from  their  intensity.  The  sense  itself  is 
always  seated  but  in  one  place,  namely,  in  our  ear ;  but  it  is  interpreted 
:as  coming  from  an  exterior  soniferous  body.  When  the  intensity  of  the 
voice  is  modified  in  imitation  of  the  effect  of  distance,  it  excites  the 
idea  of  its  originating  at  a  distance.  Ventriloquists  take  advantage  of 
the  difficulty  with  which  the  direction  of  sound  is  recognized,  and  also 
the  influence  of  the  imagination  over  our  judgment,  when  they  direct 
their  voice  in  a  certain  direction,  and  at  the  same  time  pretend,  them- 
selves, to  hear  the  sounds  as  coming  from  thence. 

Intensity. — By  removing  one  or  several  teeth  from  the  toothed  wheel 
the  fact  has  been  demonstrated  that  in  the  case  of  the  auditory  nerve, 
as  in  that  of  the  optic  nerve,  the  sensation  continues  longer  than  the  im- 
pression which  causes  it ;  for  a  removal  of  a  tooth  from  the  wheel  pro- 
duced no  interruption  of  the  sound.  The  gradual  cessation  of  the  sen- 
sation of  sound  renders  it  difficult,  however,  to  determine  its  exact 
duration  beyond  that  of  the  impression  of  the  sonorous  impulses. 

So  we  see  that  the  effect  of  the  action  of  sonorous  undulations  upon 
the  nerve  of  hearing,  endures  somewhat  longer  than  the  period  during 
which  the  undulations  are  passing  through  the  ear.  If,  however,  the 
impressions  of  the  same  sound  be  very  long  continued,  or  constantly 
repeated  for  a  long  time,  then  the  sensation  produced  may  continue  for 
a  very  long  time,  more  than  twelve  or  twenty-four  hours  even,  after  the 
original  cause  of  the  sound  has  ceased. 

Binaural  Sensations. — Corresponding  to  the  double  vision  of  the 
same  object  with  the  two  eyes,  is  the  double  hearing  with  the  two  ears; 
and  analogous  to  the  double  vision  with  one  eye,  dependent  on  unequal 
refraction,  is  the  double  hearing  of  a  single  sound  with  one  ear,  owing 
to  the  sound  coming  to  the  ear  through  media  of  unequal  conducting 
power.  The  first  kind  of  double  hearing  is  very  rare;  instances  of  it, 
however,  have  been  recorded.     The  second  kind  which  depends  on  the 


THE   SENSES.  693 

Imequal  conducting  power  of  two  media  through  which  the  same  sound 
is  transmitted  to  the  ear,  may  easily  be  experienced.  If  a  small  bell  be 
sounded  in  water,  while  the  ears  are  closed  by  plugs,  and  a  solid  con- 
ductor be  interposed  between  the  water  and  the  ear,  two  sounds  will  be 
heard  differiug  in  intensity  and  tone;  one  being  conveyed  to  the  ear 
through  the  medium  of  the  atmosphere,  the  other  through  the  conduct- 
ing-rod. 

Siibjcctive  Sensations. — Subjective  sounds  are  the  result  of  a  state  of 
irritation  or  excitement  of  the  auditory  nerve  produced  by  other  causes 
than  sonorous  impulses.  A  state  of  excitement  of  this  nerve,  however 
induced,  gives  rise  to  the  sensation  of  sound.  Hence  the  ringing  and 
buzzing  in  the  ears  heard  by  persons  of  irritable  and  exhausted  nervous 
system,  and  by  jDatients  with  cerebral  disease,  or  disease  of  the  auditory 
nerve  itself;  hence  also  the  noise  in  the  ears  heard  for  some  time  after  a 
long  journey  in  a  rattling,  noisy  vehicle.  Ritter  found  that  electric 
currents  also  excite  sounds  in  the  ears.  From  the  above  truly  subjective 
sound  we  must  distinguish  those  dependent,  not  on  a  state  of  the  audi- 
tory nerve  itself  merely,  but  on  sonorous  vibrations  excited  in  the  audi- 
tory apparatus.  Such  are  the  buzzing  sounds  attendant  on  vascular 
congestion  of  the  head  and  ear,  or  on  aneurismal  dilatation  of  the  ves- 
sels. Frequently  even  the  simple  pulsatory  circulation  of  the  blood  in 
the  ear  is  heard.  To  the  sounds  of  this  class  belong  also  the  buzz  or 
hum,  heard  during  the  contraction  of  the  palatine  muscles  in  the  act  of 
yawning,  during  the  forcing  of  air  into  the  tympanum  so  as  to  make 
tense  the  membrana  tympani,  and  in  the  act  of  blowing  the  nose,  as  well 
as  during  the  forcible  depression  of  the  lower  jaw. 

Irritation  or  excitement  of  the  auditory  nerve  is  capable  of  giving 
rise  to  movements  in  the  body,  and  to  sensations  in  other  organs  of 
sense.  In  both  cases  it  is  probable  that  the  laws  of  retiex  action,  through 
the  medium  of  the  brain,  come  into  play.  An  intense  and  sudden  noise 
excites,  in  every  person,  closure  of  the  eyelids,  and,  in  nervous  indi- 
viduals, a  start  of  the  whole  body  or  an  unpleasant  sensation,  like  that 
produced  by  an  electric  shock,  throughout  the  body,  and  sometimes  a 
particular  feeling  in  the  external  ear.  Various  sounds  cause  in  uiany 
people  a  disagreeable  feeling  in  the  teeth,  or  a  sensation  of  cold  tickling 
through  the  body,  and,  in  some  people,  intense  sounds  are  said  to  make 
the  saliva  collect. 

V.   Sight. 

Ana f GUI  1/  of  f fie  Optical  Apparatus. — The  eyelids  consist  of  two  mov- 
able folds  of  skin,  each  of  which  is  kept  in  shape  by  a  thin  plate  of 
yellow  elastic  tissue.  Along  their  free  edges  are  inserted  a  number  of 
curved  hairs   (eyelashes),   which,    when  the  lids  are  half  closed,   serve 


694  HAXDBOOK    OF    PHYSIOLOGY. 

to  protect  the  eye  from  dust  and  other  foreign  bodies:  their  tactile  sen- 
sibility is  also  very  delicate. 

On  the  inner  surface  of  the  elastic  tissue  are  disposed  a  number  of 
small  racemose  glands  (Meibomian),  whose  ducts  open  near  the  free  edge 
•of  the  lid. 

The  orbital  surface  of  each  lid  is  lined  by  a  delicate,  highly  sensitive 
mucous  membrane  [conjunctiva),  which  is  continuous  with  the  skin  at 
the  free  edge  of  each  lid,  and  after  lining  the  inner  surface  of  the  eyelid 
is  reflected  on  to  the  eyeball,  being  somewhat  loosely  adherent  to  the 
sclerotic  coat.  The  epithelial  layer  is  continued  over  the  cornea  at  its 
anterior  epithelium.  At  the  inner  edge  of  the  e3'e  the  conjunctiva 
becomes  continuous  with  the  mucous  lining  of  the  lachrymal  sac  and 
duct,  which  again  is  continuous  with  the  mucous  membrane  of  the 
inferior  meatus  of  the  nose. 

The  lachrymal  gland,  comjiosed  of  several  lobules  made  up  of  acini 
resembling  the  serous  salivary  glands,  is  lodged  in  the  upjjer  and  outer 
angle  of  the  orbit.  Its  secretion,  Avhich  issues  from  several  ducts  on 
the  inner  surface  of  the  upjier  lid,  under  ordinary  circumstances  just 
suffices  to  keep  the  conjunctiva  moist.  It  passes  out  through  two  small 
openings  (puncta  lachrymalia)  near  the  inner  angle  of  the  eye,  one  in 
each  lid,  into  the  lachrymal  sac,  and  thence  along  the  nasal  duct  into 
the  inferior  meatus  of  the  nose.  The  excessive  secretions  poured  out 
under  the  influence  of  any  irritating  vapor  or  painful  emotion  overflows 
the  lower  lid  in  the  form  of  tears. 

The  eyelids  are  closed  by  the  contraction  of  a  sphincter  muscle 
{orbicula7'is),  supplied  by  the  facial  nerve;  the  upper  lid  is  raised  by  the 
levator  j^alpehrcB  superioris,  which  is  supplied  by  the  third  nerve. 

The  Eyeball. 

The  eyeball  or  the  organ  of  vision  (fig.  406)  consists  of  a  variety  of 
structures  Avhich  may  be  thus  enumerated : — 

The  sclerotic,  or  outermost  coat,  envelops  about  five-sixths  of  the 
eyeball:  continuous  with  it,  in  front,  and  occupying  the  remaining 
sixth,  is  the  cornea.  Immediately  within  the  sclerotic  is  the  clioroid 
coat,  and  within  the  choroid  is  the  retina.  The  interior  of  the  eyeball 
is  well-nigh  filled  by  the  aqueous  and  vitreous  Imniors  and  the  crystalline 
lens;  but,  also,  there  is  suspended  in  the  interior  a  contractile  and  per- 
forated curtain, — the  iris,  for  regulating  the  admission  of  light,  and 
behind  at  the  junction  of  the  sclerotic  and  cornea  is  the  ciliary  muscle, 
the  function  of  which  is  to  adapt  the  eye  for  seeing  objects  at  various 
distances. 

Structure  of  the  Sclerotic  Coat. — The  sclerotic  coat  is  composed  of 


THE    SEN'SES. 


G'J5 


white  fibrous  tissue,  with  some  elastic  fibres  near  the  inner  surface, 
arranged  in  variously  disposed  and  interlacing  layers.  Many  of  the 
bundles  of  fibres  cross  the  others  almost  at  right  angles.     It  is  strong, 


Ciliary  muscle 

Ciliarj  process  — ] 

Canal  of  Petit  — '. 

Cornea  — 

Anterior  chanaber  — 


Liens  — 1 
Iris  — 
Ciliary  process  — ] 
Ciliary  muscle 


Fig.  400.  — Seciton  of  the  anterior  four-fifths  of  the  eyeball. 

tough,  and  opaque,  and  not  very  elastic.  It  is  separated  from  the 
choroid  by  a  considerable  lymphatic  space  {■periclioroidal),  and  this  is  in 
connection  with  smaller  spaces  lined  with  endothelium  in  the  sclerotic 
coat  itself.  There  is  .a  lymphatic  space  also  outside  the  sclerotic  sepa- 
rating it  from  a  loose  investment  of  connective  tissue  called  the  capsule 
of  Tenon.  The  innermost  layer  is  made  up  of  loose  connective  tissue 
and  pigment-cells,  and  is  called  the  lamina  fusca. 

Structure  of  the  Cornea. — The  cornea  is  a  transparent  membrane 
which  forms  a  segment  of  a  smaller  sphere  than  the  rest  of  the  eyeball. 


Fig.  407.— Vertical  section  of  rabbit's  cornea,  a.  Anterior  epithelium,  showing  the  different 
shapes  of  the  cells  at  various  depths  from  the  free  surface:  6.  portion  of  the  substance  of 
cornea.     (Klein.) 

and  is  let  in,  as  it  were,  into  the  sclerotic  with  which  it  is  continuous 
all  round.     It  is  covered  by  laminated  epithelium  («,  fig.  407),  consist- 


696 


HANDBOOK    OF    PHYSIOLOGY. 


ing  of  seven  or  eight  layers  of  cells,  of  which  the  superficial  ones  are 
flattened  and  scaly,  and  the  deeper  ones  more  or  less  columnar.  Imme- 
diately beneath  this  is  the  anterior  elastic  lamina  of  Bowman,  which 


Fig.  408.  — Horizontal  preparation  of  cornea  of  frog ;  showing  the  network  of  branched  cornea- 
corpuscles.     The  ground  substance  is  completely  colorless.     X  400.  (Klein.) 

differs,  only  in  being  more  condensed  tissue,  from  the  general  structure 
of  the  cornea  or  cornea  proper. 

This  latter  tissue,  as  well  as  its  epithelium  is,  in  the  adult,  com- 
pletely destitute  of  blood-vessels ;  it  consists  of  an  intercellular  ground- 
substance  of  rather  obscurely  fibrillated  flattened  bundles  of  connective 
tissue,  arranged  parallel  to  the  free  surface,  and  forming  the  boundaries 
of  branched  anastomosing  spaces  in  which  the  cornea-corpuscles  lie. 
These  branched  cornea-corpuscles  have  been  seen  to  creep  by  amoeboid 


Fig,  409.— Surface  view  of  part  of  lamella  of  kitten's  cornea,  prepared  first  with  caustic 
potash  and  then  with  nitrate  of  silver.  (By  this  method  the  branched  cornea-corpuscles  with 
their  granular  protoplasm  and  large  oval  nuclei  are  brought  out.)  X  450.  (Klein  and  Noble 
Smith.) 

movement  from  one  branched  space  into  another.  At  its  posterior  sur- 
face the  cornea  is  limited  by  the  posterior  elastic  lamina,  or  membrane 
of  Descemet,  similar  in  structure  to  the  anterior  elastic  lamina,  the  inner 
layer  of  which  consists  of  a  single  stratum  of  epithelial  cells  (fig.  410,  d). 
Nerves. — The  nerves  of  the  cornea  are  both  large  and  numerous:  they 


THE    SENSES. 


69? 


are  derived  from  the  ciliary  nerves.  They  traverse  the  substance  of  the 
cornea,  in  which  some  of  them  near  the  anterior  surface  break  up  into  axis 
cylinders,  and  their  primitive  fibrillae.  The  latter  form  a  plexus  imme- 
diately beneath  the  epithelium,  from  which  delicate  fibrils  pass  up 
between  the  cells  anastomosing  with  horizontal  branches,  and  forming  a 
deep  intra-epithelial  plexus,  from  which  still  finer  fibres  ascend,  till  near 
the  surface  they  form  a  superficial  intra-epithelial  net-work.  Most  of 
the  primitive  fibrilhv  have  a  beaded  or  varicose  appearance.     The  cornea 


■j^.a.j^-r+r-'-^"^^ 


Fig.  410. 


Fig.  411. 


Fig.  410. —Vertical  section  of  raljbit's  (•drnea,  stained  with  gold  chloride,  e.  Laminated 
anterior  epithelium.  Immediately  beneath  tliis  is  the  anterior  elastic  lamina  of  Bowman,  n. 
Nerves  forming  a  delicate  sub-epithelial  plexus,  and  sending  up  fine  twigs  between  the  epithelial 
cells  to  end  in  a  second  plexus  on  the  free  surface:  d,  Descemet's  membrane,  consisting  of  a 
fine  elastic  layer,  and  a  single  layer  of  ejiithelial  cells;  the  substance  of  the  cornea,  /,  is  seen 
to  be  fibri Hated,  and  contains  many  layers  of  branched  corpuscles,  ajrranged  parallel  to  tlie  free 
surface,  and  here  seen  edgewise.     (Schofleld.) 

Fig.  411. — Section  through  the  choroid  coat  of  the  human  eye.  1,  elastic  membrane,  struc- 
tureless or  linely  (iln-illated :  •.?.  ehorio-canillaris  or  timica  Ruyschiana;  3,  Pi'oper  substance  of 
the  choroid  witli  large  vessels  cut  through;  4,  supraclioroidea ;  5,  sclerotic.       (Scliwalbe. ) 


has  no  blood-vessels  penetrating  its  structure,  nor  yet  lymphatic  vessels 
proper.  It  is  nourished  by  the  circulation  of  lymph  in  the  spaces  in 
which  the  cornea  corpuscles  lie.  These  communicate  freely  and  form  a 
lymph-canalicular  system. 

Structure  of  the  Choroid  Coat  {tuuica  rascuhsa). — This  coat  is 
attached  to  the  inner  layer  of  the  sclerotic  in  front  at  the  corneo-scleral 
junction  and  behind  at  the  entrance  of  the  optic  nerve,  elsewhere  it  i? 


(]98  HANDBOOK    OF    PHYSIOLOGY. 

connected  to  it  only  by  loose  connective  tissue.  Its  external  coat  is 
formed  chiefly  of  elastic  fibres  and  large  pigment  corpuscles  loosely 
arranged  and  containing  lymphatic  spaces  lined  with  endothelium.  This 
is  the  supraclioroidea.  More  internally  is  a  layer  of  arteries  and  veins 
arranged  in  a  system  of  venous  whorls,  together  with  elastic  fibres  and 


i 


Fig.  412. — Section  through  the  eye  carried  through  the  ciliary  processes.  1,  Cornea;  2,  mem- 
brane of  Descemet ;  3,  sclerotic;  3',  corneo-scleral  junction;  4,  canal  of  Schlemm;  5,  vein;  6, 
nucleated  network  on  inner  wall  of  canal  of  Schlemm;  7,  lig.  pectinatum  iridis,  abc;  8,  iris 
stroma;  9,  pigment  of  iris;  10,  ciliary  processes;  11,  ciliary  muscle;  12,  choroid  tissue;  13, 
meridional  and  14,  radiating  fibres  of  ciliary  muscle ;  15,  ring  muscle  of  Miiller ;  16,  circular  or 
angular  bundles  of  ciliary  muscle.     (Schwalbe.) 

pigment  cells.  The  lymphatics,  too,  are  well  developed  around  the 
blood-vessels,  and  there  are  besides  distinct  lymph  spaces  lined  with  en- 
dothelium. Internally  to  this  is  a  layer  of  fine  capillaries,  very  dense  and 
derived  from  the  arteries  of  the  outer  coat  and  ending  in  veins  in  that 
coat.  It  contains  corpuscles  without  pigment,  and  lymph  spaces  which 
surround  the  blood-vessels  {memhrana  chorio-capillaris).  It  is  separated 
from  the  retina  by  a  fine  elastic  membrane  {membrane  of  Bri(ch),  which 
is  either  structureless  or  finely  fibrillated. 

The  choroid  coat  ends  in  front  in  what  are  called  the  ciliary  i^t'ocesses 
{fig.  412).  These  consist  of  from  70  to  80  meridionally  arranged 
radiating  plaits,  which  consist  of  blood-vessels,  fibrous  connective  tissue, 
and  pigment  corpuscles.  They  are  lined  by  a  continuation  of  the  mem- 
brane of  Bruch.  The  ciliary  processes  terminate  abruptly  at  the  margin 
of  the  lens.  The  ciliary  muscle  (13,  14  and  15,  fig.  412),  which  may  be 
considered  to  form  part  of  the  processes,  is  situated  between  the 
sclerotic  (at  the  corneo-scleral  junction)  and  the  folds  of  the  ciliary 
processes.  It  is  a  ring  of  muscle,  3  mm.  broad  and  8  mm.  thick,  made 
up  of  fibres  running  in  two  or  three  directions,  {a)  Meridional  fibres 
near  the  sclerotic  and  passing  to  the  choroid;  {b)  radial  fibres,  passing 
toward  the  centre;  and  (c)  circular  fibres,  more  internal,  and  constitut- 
ing the  so-called  ciliary  sphincter. 

The  Iris. — The  iris  is  a  continuation  of  the  choroid  inward  beyond 


THE   SENSES. 


699 


the  ciliary  processes.  It  is  a  fibro-mnscular  membrane  perforated  by  a 
central  aperture,  the  pupil.  It  is  made  up  chiefly  of  blood-vessels  and 
connective  tissue  with  pigment  and  unstriated  muscle. 

Posteriorly  are  two  layers  of  pigment  cells  (uvea),  in  which  are  repre- 
sented the  two  layers  of  cells  of  which  the  optic  vesicle  is  originally 
formed,  and  behind  which  are  the  retina  proper  and  its  pigment  layer. 
In  the  iris  representatives  of  both  layers  are  deeply  pigmented.  The 
structure  of  the  iris  proper  is  made  of  connective  tissue  in  front  with 
corpuscles  which  may  or  may  not  be  pigmented,  and  behind  of  similar 
tissue  supporting  blood-vessels  inclosed  in  connective  tissue.  The  pig- 
ment cells  are  usually  well  developed  here,  as  are  also  many  nerve-fibres 
radiating  toward  the  pupil.  Surrounding  the  pupil  is  a  layer  of  circu- 
lar unstrijied  muscle,  the  sphincle)'  pup  nice .  In  some  animals  there  are 
also  muscle-fibres  which  radiate  from  the  sphincter  in  the  substance  of 
the  iris  forming  the  dilator  pvpilla'.  The  iris  is  covered  anteriorly  by 
a  layer  of  endotlielium  continued  upon  it  from  the  posterior  surface  of 
the  cornea;  posteriorly  there  is  a  very  fine  layer  which  is  a  continuation 
of  the  membrana  limitans  interna  of  the  retina. 

T/ic  Lens. — -The  lens  is  situated  behind  the  iris,  being  inclosed  in  a 
distinct  capsule,  the  i50sterior  surface  of  which  is  less  thick  than  the 
anterior.  It  is  suj^ported  in  place  by  the  suspensory  ligament,  fused 
to  the  anterior  surface  of  the  capsule.  The  suspensory  ligament  is 
derived  from  the  hyaloid  membrane,  which  incloses  the  vitreous  humor. 

Structure. — The  lens  is  made  up  of  a  series  of  concentric  laminse 
(fig.  414),  whieli  wlien  it  luis  been  hardened,  can  be  peeled  off  like  the 


Fig.  413. 


Fig.  414. 


Fig  413  — Ciliarv  processes,  as  seen  from  V)ehind.  1,  posterior  surface  of  the  iris,  with  the 
sphincW  muscle  of  "the  pupil :  ~'.  anterior  part  of  the  choroid  coat :  3,  one  of  the  ciliary  processes, 
of  which  about  seventy  are  represented.     ^.  .  ,.  /■»      i       i 

Fig  414  — Laminat<?d  structure  of  the  crystalline  lens.  The  laminae  are  split  up  after  hara- 
ening  in  alcohol.  1,  the  denser  central  part  or  nucleus;  i,  the  successive  external  layers.  X  4. 
(Arnold.) 

leaves  of  an  onion.     Tlu-  laminae  consist  of  long  ribbon-shaped  fibres, 
which  in  the  course  of  development  have  originated  from  cells. 


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HANDBOOK    OF    PHYSIOLOGY. 


The  lens  itself  is  made  up  of  trauspareut  longitudinal  fibres,  hexag- 
onal and  prismatic,  thickened  posteriorly.  Those  fibres  at  the  cortex 
have  nuclei  and  are  smooth,  those  near  the  centre  are  without  nuclei 
and  have  serrated  edges.  The  fibres  are  united  together  by  a  scanty 
amount  of  cement  substance. 

The  arrangement  is  such  that  no  fibres  run  the  whole  half  of  the 
lens,  from  front  to  back,  since,  if  a  fibre  starts  near  the  anterior  pole, 
its  other  end  is  far  from  the  posterior  pole  (fig.  415.) 

The  epithelium  of  the  lens  consists  of  a  layer  of  cubical  cells  anteriorly, 
which  merges  at  the  equator  into  the  lens  fibres.  The  development  of 
the  lens  explains  this  transition.  The  lens  at  first  consists  of  a  closed 
sac  composed  of  a  single  layer  of  epithelium.  The  cells  of  the  posterior 
part  soon  elongate  forward  and  obliterate  the  cavity,  the  anterior  cells  do 


Fig.  415.— Meridional  section  through  the  lens  of  a  rabbit.     1,  Lens  capsule-  2,  epithelifKii  of 
lens;  3,  transition  of  the  epithelium  into  the  fibres;  4,  lens  fibres.     (Bubuchin.) 


not  grow,  but  at  the  edge  they  become  continuous  with  the  posterior 
cells,  which  are  gradually  developed  into  fibres.  The  lens  contains 
globulin  or  crystallin,  but  no  native-albumin;  it  also  contains  choles- 
terin.  The  capsule  is  a  homogeneous  transparent  elastic  membrane. 
The  hardest  portion  of  the  lens  is  that  which  is  most  internal.  It  forms 
the  so-called  nucleus  of  the  lens  (fig.  414,  1). 

Corneoscleral  junction. — At  this  junction  the  relation  of  parts  (fig. 
412)  is  so  important  as  to  need  a  short  description.  In  the  neighbor- 
hood, the  iris  and  ciliary  processes  join  with  the  cornea.  The  proper 
substance  of  the  cornea  and  the  posterior  elastic  lamina  become  continuous 
with  the  iris,  at  the  angle  of  tlie  iris,  and  the  iris  sends  forward  processes 
toward  the  posterior  elastic  lamina,  forming  the  ligamenfum  pectinatum 
iridis,  and  these  join  with  fibres  of  the  elastic  lamina.  The  endothelial 
covering  of  the  posterior  surface  of  the  cornea  is,  as  we  have  seen,  con- 
tinuous over  the  front  of  the  iris.  At  the  iridic  angle,  the  compact 
inner  substance  of  the  cornea  is  looser,  and  between  the  bundles  are 
lymph  spaces  filled  with  fluid,  called  the  spaces  of  Fontana.  They  are 
little  developed  in  the  human  cornea.  Where  the  cornea  and  sclerotic 
join,  there  is  an  intermediate  part  which  resembles  both,  but  which  is 
still  not  transparent,  as  the  internal  part  remains  scleral  in  structure. 

The  spaces  which  are  present  in  the  broken  up  bundles  of  corneal 
tissue  at  the  angle  of  the  iris,  are  continuous  with  the  larger  lymphatic 


THE    SENSES. 


7ul 


.space  of  the  anterior  chamber.  Above  the  angle  at  the  corneo-scleral 
junction  is  a  canal,  which  is  called  the  canal  of  Schlemm.  It  is  a  lym- 
phatic channel,  but  appears  to  be  in  communication  with  blood-vessels, 
as  it  may  be  under  certain  circumstances  filled  with  blood. 

Structure  of  the  Retina. — The  retina  (tig.  410)  is  a  delicate  membrane, 
concave  with  the  concavity  directed  forward  and  apparently  ending  in 
front,  near  the  outer  part  of  the  ciliary  processes,  in  a  finely  notched 
edge, — the  ora  serrata,  but  really  represented  to  the  very  margin  of  the 
pupil.  Semitransparent  when  fresh,  it  soon  becomes  clouded  and  opaque, 
with  a  pinkish  tint  from  the  blood  in  its  minute  vessels.  It  results  from 
the  sudden  spreading  out  or  expansion  of  the  optic  nerve,  of  whose  ter- 


<s>: 


»   S^, 


a9 


Fig.  416.— A  section  of  tlie  retina,  choroid,  and  part  of  the  sclerotic,  moderately  magnified. 
</,  Membrana  liinitans  interna;  6,  uerve-fibre  hiyer  traversed  liy  MUlIer's  sustentacular  fibres; 
f,  i^anglioii-cell  hiyer;  rf,  molecular  layer;  e,  internal  nuclear  layer;  /,  internuclear  layer;  g.  ex- 
ternal luiclear  layer;  li,  membrana  limitans  externa,  running  along  the  lower  part  of  /,  the  layer 
uf  rods  and  cones;  k.  pigment-cell  layer;  lin,  internal  and  external  vascular  portions  of  the  chor- 
oid, the  first  containing  capillaries,  the  second  larger  blood-vessels,  cut  in  transverse  section;  n, 
sclerotic.    (W.  Pye.) 


minal  fibres,  apparently  deprived  of  their  external  white  substance,  to- 
gether with  nerve  cells,  it  is  essentially  composed. 

Exactly  in  the  centre  of  the  retina  is  a  round  yellowish  elevated  spot, 
about  ^  of  an  inch  (1  mm.)  in  diameter,  having  a  minute  depression  in 
the  centre,  called  after  its  discoverer  the  macula  lutea,  or  yellow  spot  of 
Scemmeriiig.  The  minute  depression  in  its  centre  is  called  the  fovea 
centralis.     About  ^  of  an  inch  (2.5  mm.)  to  the  inner  side  of  the  yel- 


702  HANDBOOK    OF    PHYSIOLOGY. 

low  spot,  is  the  poiut  at  which  the  optic  nerve  enters  the  eyeball,  and 
begins  to  spread  out  its  fibres  into  the  retina. 

The  optic  nerve  passes  forward  from  the  -ventral  surface  of  the  cere- 
brum toward  the  orbit  inclosed  in  prolongations  of  the  membranes,  the 
dura  mater,  arachnoid  and  pia  mater,  which  cover  the  brain.  The  ex- 
ternal sheath  at  the  entrance  of  the  nerve  into  the  eyeball  becomes  con- 
tinuous with  the  sclerotic,  which  at  this  part  is  perforated  by  holes  to 
allow  of  passage  of  the  optic  nerve-fibres  and  tlie  pia  mater  with  the 
choroid,  tlie  perforated  'pavt  being  the  lamina  cribrosa.  The  pia  mater 
here  becomes  incomplete,  and  the  subarachnoid  and  the  superarachnoid 
spaces  become  continuous.  The  pia  mater  sends  in  processes  into  the 
nerve  to  support  the  fibres.  The  fibres  of  the  nerve  themselves  are  ex- 
ceedingly fine,  and  are  surrounded  by  the  myelin  sheath,  but  do  not 
possess  the  ordinary  external  nerve-sheath.  As  they  pass  into  the  retina 
they  lose  their  myelin  sheaths  and  proceed  as  axis-cylinders.  ^Neuroglia 
supports  the  nerve-fibres  in  the  optic  nerve-trunk.  In  the  centre  of  the 
nerve  is  a  small  artery,  the  arteria  centralis  retince.  The  number  of 
fibres  in  the  optic  nerve  is  said  to  be  upward  of  500,000.  The  axis- 
cylinders  jiass  on  to  the  retina,  turning  over  the  edges  of  the  porus 
opticus^  to  be  distributed  on  the  inner  surface  of  the  retina,  as  far  as  the 
ora  serrata,  as  a  layer  of  optic  nerve-fibres,  and  separated  from  the 
hyaloid  membrane  which  contains  the  vitreous  humor  to  be  presently 
described,  by  a  very  thin  layer,  the  membrana  limitans  interna. 

The  retina  consists  of  certain  nervous  elements  arranged  in  several 
layers  and  supported  by  a  very  delicate  connective  tissue. 

The  researches  of  Cajal  upon  the  structure  of  the  retina  of  verte- 
brates has  shown  that  this  membrane  is  a  much  simpler  structure  than 
has  heretofore  been  described.  Cajal's  observations  being  confirmed  by 
other  observers  and  accepted  by  neuro-anatomists,  it  will  be  safe  to  give 
the  descriptions  here,  as  representing  our  present  knowledge  of  the 
structure  of  this  membrane. 

The  retina  is  a  nervous  tissue  formed  essentially  of  three  layers  of 
nerve-cells.  From  without  inward  they  are:  the  layer  of  visual  cells,  the 
layer  of  bipolar  cells,  and  the  layer  of  ganglionic  cells.  This  subdivision 
is  shown  in  the  diagram  (fig.  417).  These  difl'erent  layers  may  be  sub- 
divided so  as  to  give  the  following  layers  from  without  inward: 

1.  The  layer  of  rods  and  cones,  j  p^,.,,^;     .  ^1,^  j        .  ^f  visual  cells. 

2.  The  external  granular  layer.  \  ^  •' 

3.  The  external  molecular  layer,  j  Fanning  the  layer  of  bipolar  cells. 

4.  Internal  granular  layer.  )  &  j  i 

5.  Internal  molecular  layer.  }  Forming  the  layer  of 

6.  Ganglionic  layer,  with  the  fibres  of  the  optic  nerve,  f     ganglion  cells. 

The  layer  of  visual  cells  is  subdivided,  as  seen  in  the  figure,  into  that 
of  the  rods  and  cones  externally  and  that  of  the  external  granular  inter- 


THE    SENSES. 


703 


nally.  This  is,  however,  practically  a  layer  made  up  simply  of  bipolar 
iierve-cells  with  prolongations  more  or  less  long  which  run  to  the  ex- 
ternal surface  of  the  retina  and  there  form  a  series  of  bodies  known  as 
the  rods  and  cones. 

1.  The  rods  iDtd  conea  9.\-(i  really  a  kind  of  secretion  from  the  pro- 
toplasm of  the  bipolar  cell  beneath,  and  are  not  distinct  nerve-cells. 
They  consist  of  bodies  more  or  less  alike,  which  extend  up  through  the 
external  limiting  membrane  from  the  cells  beneath. 


Fig.  417.— Transverse  sectioa  of  a  mammalian  retina.  A,  Layer  of  rods  and  cones;  B,  bodies 
of  visual  cells  (external  granular);  C,  external  molecular  layer;  E,  layer  of  bipolar  cells  (internal 
granular);  i^,  internal  molecular  layer;  G,  layer  of  ganglionic  cells:  jy,  layer  of  optic-nerve  fibres; 
a,  rod;  6,  cone;  c,  body  of  the  cone  cell;  rt,  body  of  the  rod  cell;  c,  bipolar  rod  cells;  /,  bipolar  coue 
cells;  gji,  i,j,  k\  ganghonic  cells  ramifying  in  the  various  strata  of  the  internal  nidlecular  zone: 
r,  inferior  arborization  of  the  bipolar  rod  cells,  connecting  with  the  ganglionic  cells;  i-j,  inferior  ar- 
borization of  the  bipolar  cone  cells;  t,  epithelial  or  Jliiller  cells;  .c,  point  of  contact  between  Hie 
rods  and  their  bipolar  cells;  «,  point  of  contact  between  the  cones  and  their  bipolar  cells;  .s,  centri- 
fugal nerve-tibre.     (Cajal.) 


The  Rods. — Each  rod  (tig.  417,  a)  is  made  up  of  two  parts,  very  differ- 
ent in  structure,  called  the  outer  and  inner  limbs.  The  outer  limb  of  the 
rods  is  about  oO/x  -^-^  inch  long  and  'iii  broad,  is  transparent,  and  doubly 
refractive.  It  is  said  to  be  made  up  of  fine  superimposed  discs.  It  re- 
sembles in  some  ways  the  myelin  sheath  of  a  mcdullated  nerve.  Ic 
swells  up  on  exposure  to  light,  and  is  part  of  tlio  layer  in  which  the 
pigment  called  visndl  pvrple  is  found.  The  inner  limb  is  about  as 
long  but  slightly  broader  than  the  outer,  is  longitudinally  striated  at 
its  outer  and  granular  at  its  inner  part.  Each  rod  is  connected  by 
a  fine  hair-like  process  to  a  nerve-cell  in  the  external  granular  layer  be- 
low (figs.  417,  d;  417a,  3). 

The  Cones. — Each  cone  (fig.  417,  c),  like  the  rods,  is  made  up  of  two 
limbs,  outer  and  inner.  The  outer  limb  is  tapering  and  not  cylindrical 
like  the  corresponding  part  of  the  rod,  and  about  one-third  only  of  its 


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HANDBOOK    OF    PHYSIOLOGY. 


length,  but  it  resembles  this  in  structure.  There  is,  however,  no  visual 
purple  found  in  the  cone.  The  inner  limb  of  the  cone  is  broader  in  the 
centre;  each  cone  is  in  connection  by  its  internal  end  with  a  cone  fibre, 
which  has  much  the  same  structure  as  the  rod  fibre,  but  is  much  stouter. 
This  connects  with  a  nerve-cell  of  the  layer  below  (fig.  417a,  4). 

In  the  rod  and  cone  layer  of  birds,  the  cones  usually  predominate 


Fig.  417a.— Schematic  diagram  of  the  elementary  structure  of  the  retina,  sz,  Rods  and  cones; 
te,  membranalimitans  externa;  gi\  external  granules;  e,  external  molecular  layer);  bz,  internal 
granular  layer;  t,  internal  molecular  layer;  mz,  multipolar  cell  layer  (ganglion  optici);  nf,  nerve- 
fibre  layer;  li,  membrana  limitans  interna. 

1,  Rod;  2,  rod  granule;  .3,  cone;  4,  cone  granule;  1-1',  rod  visual  cell;  8-3',  cone  visual  cell ;  5, 
central  termination  of  the  visual  cells  and  peripheral  terminal  arborization  of  the  bipolar  ceUs; 
6,  6,  two  bipolar  cells  for  rods;  6,  one  bipolar  cell  for  cone;  7,  7,  7,  7,  7,  7,  the  central  processes  of 
bipolar  cells  with  the  terminal  arborizations  situated  in  the  various  layers  of  the  internal  molecular 
layer;  7',  central  process  of  a  bipolar  cell  for  cone;  8,  multipolar  cells  with  their  peripheral  den- 
drites and  central  neuraxons;  9,  9,  9,  nerve-fibres  and  terminal  arborizations  of  remote  cells. 

largely  in  number,  whereas  in  man  the  rods  are  by  far  the  more  numer- 
ous, except  in  the  fovea  centralis,  where  cones  only  are  present,  as  is  the 
case  at  the  anterior  part  of  the  retina  near  the  ora  serrata.  The  num- 
ber of  cones  has  been  estimated  at  3,000,000.  In  nocturnal  birds,  how- 
ever, such  as  the  owl,  only  rods  are  present,  and  the  same  appears  to  be 
the  case  in  many  nocturnal  and  burrowing  mammalia,  e.g.^  bat,  hedge- 
hog, mouse,  and  mole.     The  rods  are  absent  in  reptiles. 

External  Limiting  Membrane. — A  delicate  membrane  lies  beneath 


THE   SENSES. 


705 


the  rods  and  cones  and  separates  them  from  the  layer  beneath.  This 
is  called  tlie  external  limit iiKj  mcmhnuii;  {^v^.  417a,  /r). 

2.  External  Grroiuhtr  Layer. — The  cells  of  the  external  granular 
layer  are  the  bipolar  or  visual  cells  which  contain  the  protoplasm  not  yet 
transformed  into  rods  and  cones  in  the  layer  above.  The  cells  whose 
bodies  are  continued  upward  as  cones  are  different  in  shape  from  those 
which  are  connected  with  the  rods.  The  cells  of  the  cones  are  situ- 
ated close  to  the  external  limiting  membrane.  They  have  a  large  ovoid 
nucleus.  From  the  inner  side  of  the  cell-body  a  process  descends 
tovvard  the  external  molecular  layer  where  it  ends  in  a  slight  dilatation 
(see  fig.  417).  On  its  outer  side  a  process  of  the  body  ascends  through 
into  tlie  external  limiting  membrane  and  swells  into  a  cone  (fig.  417,  r). 

The  bipolar  cells  giving   birth   to  the  rods  lie  at  deeper  levels  in  the 


Fig.  418.— The  posterior  half  of  the  retina  of  the  left  eye.  viewed  from  before;  s.  the  cut 
edge  of  the  sclerotic  coat :  ch.  the  choroid;  r,  the  retina;  "in  the  interior  at  the  middle  the 
macula  lutea  with  the  depression  of  the  fovea  centralis  is  represented  by  a  slight  oval  shade: 
toward  the  left  side  the  light  spot  indicates  the  colliculus  or  eminence  at  the  entrance  of  the 
optic  uei-ve,  from  the  centre  of  which  the  arteria  centralis  is  seen  spreading  its  branches  into 
tne  retina,  leaving  the  part  occupied  by  the  macula  comparatively  free.     (After  Henle.) 

granular  layer.  They  contain  an  ovoid  nucleus  of  a  smaller  volume  than 
those  of  the  cone  cells.  The  protoplasm  of  the  cell-body  gives  olf  two 
fibres,  one  ascending,  and  the  other  descending.  The  ascending  fibre 
runs  up  through  tlie  limiting  niembraue  and  is  continued  as  a  rod.  The 
descending  fibre  goes  into  the  molecular  layer  and  ends  here  in  a  small 
nodule.  According  to  Cajal,  these  cells  of  the  visual  layer  have  no  di- 
rect anatomical  continiiity  with  the  cells  of  the  bipolar  layer  below, 
though  Dogiol  and  others  have  denied  this. 

3.  T/ie  externahnolecidar  layer  ox  external  plexiform  layer  (fig.  417,  C) 
is  composed  of  numerous  protoplasmic  processes  (dendrites)  which  come 
from  the  cells  of  the  internal  granular  layer  below  and  from  the  visual 
cells  above.  Some  subdivisions  of  this  layer  are  made,  there  being  an 
outer  part  in  which  the  rod  ceils  meet  the  branching  fibres  of  the  bi- 
45 


706 


HANDBOOK   OF   PHYSIOLOGY. 


polar  layer,   and  a  slightly  deeper  layer  in  wliich   the  cone  cells  come 
in  contact  with  the  dendrites  of  the  bipolar  cells. 

4.  The  internal  granular  layer  (fig.  417,  E)  is  an  inner  subdivision  of  a 
layer  of  bipolar  cells,  and  is  the  most  complicated  of  any  of  the  layers  of  the 
retina.  It  is  made  up,  however,  mainly  of  bipolar  cells,  which  are  fusi- 
form in  shape,  vertical  in  arrangement,  and  have  two  processes,  one  as- 
cending and  the  other  descending.  The  descending  fibre  is  always  single 
and  ends  at  different  levels  in  the  internal  molecular  or  plexiform  layer, 
where  it  forms  flattened  and  brush-like  expansions.  The  ascending 
process  is  often  multiple,  and  it  ends  in  a  large  number  of  different 
branches,  which  arrange  themselves  in  something  like  a  horizontal  layer 
in  the  lower  jiart  of  the  external  molecular  layer. 


Fig.  418a. — Perpendicular  section  of  tlie  retina  of  a  mammal.  A,  External  grrainsor  bodies  of 
rods;  i?,  bodies  of  cones;  a,  horizontal  external  or  small  cell;  f),  horizontal  internal  or  large  cell; 
c,  horizontal  internal  cell  with  descending^  protoplasmic  appendages;  e,  flattened  arborization  of  one 
of  the  large  cells;  /.  p,  7i,  j,  Z,  spongioblasts  ramifying  in  the  varioiisstrata  of  the  internal  molecular 
zone;  m,  n,  diffuse  spongioblasts;  o,  ganglionic  cell;  1,  external  molecular  zone;  2,  internal  mole- 
cular zone.     (Cajal.) 


Besides  these  vertical  bipolar  cells  there  are  flattened  star-shaped 
cells  lying  just  beneath  the  external  molecular  layer,  sending  out  branches 
parallel  to  the  periphery  and  ending  in  numerous  ramifying  expansions 
which  come  in  contact  with  the  different  descending  branches  of  the 
cone  cells.  Their  general  arrangement  is  horizontal.  These  little  cells 
appear  to  have  as  their  function  the  connecting  of  the  visual  cells  with 
each  other  (fig.  418a,  e,  h).  There  are  other  horizontal  cells,  larger  than 
these,  but  having  practically  the  same  shape  and  arrangement,  and  lying 
somewhat  more  deeply  in  the  layer;  these  connect  the  processes  of  the  rod 
cells  with  each  other  and  have  thus  an  associative  function.  There  is,  in 
addition,  in  this  layer,  a  series  of  larger  cells,  called  by  Cajal  fijjongioUasts, 
which  lie  deep  in  the  internal  granular  layer,  and  whose  branches  take 
a  horizontal  direction  and  appear  to  have  the  function  of  associating  the 
cells  of  the  ganglionic  layer  below  (see  fig.  418a). 

5.    I'he  internal  molecular   layer   is  composed  of  a  plexus  of  fibres 


THE   SENSES.  707 

formed  by  the  processes  of  the  bijxjlar  cells  from   above  and  of  the  gan- 
glionic colls  below,  and  of  libres  from  the  spongioblasts. 

6.  The  most  internal  of  the  nervous  layers  is  a  layer  of  ganglionic 
cells,  consisting  of  large  multipolar  nerve-cells,  with  large  round  nuclei. 
In  some  parts  of  the  retina,  especially  near  the  macula  lutca,  this  layer 
is  very  thick  and  consists  of  several  distinct  strata  of  nerve-cells.  These 
cells  lie  in  the  spaces  of  the  connective-tissue  framework.  They  are  ar- 
ranged with  their  single  neuraxon  or  axis-cylinder  processes  directed  in- 
ward. These  pass  into  and  are  continuous  with  the  layer  of  optic  fibres. 
Externally  the  cells  send  u})  numerous  branching  processes  or  dendrites 
which  interlace  with  the  iibres  of  the  bipolar  cells  and  the  horizontal 
processes  of  the  spongioblasts. 

All  the  elements  of  the  retina  are  sustained  and  isolated  by  huge 
cells  lying  vertically  which  are  known  as  the  fibres  of  JliiUer,  or  epi- 
thelial retinal  cells.  Like  the  corresponding  cells  of  the  olfactory 
mucous  membrane,  tliese  Iibres  have  upon  their  sides  an  infinite  number 
of  facets  which  serve  as  receptacles  to  the  nerve-corpuscles  and  fibres 
of  the  retina.  The  nucleus  of  the  fibre  of  Miiller  is  found  at  the 
level  of  the  internal  granular  layer,  and  the  two  extremities  of  the  proto- 
plasm or  cell-body  are  condensed  in  two  homogeneous  layers,  known  as 
the  external  and  internalliinitimj  laijer.  The  external  limiting  ]a3'er  is 
placed,  as  already  described,  just  between  the  layer  of  rods  and  cones 
and  that  of  the  visual  cells.  The  other  is  situated  upon  the  internal 
surface  of  the  retina.  The  fibres  of  jVliiller  are  completely  independent 
of  each  other,  having  between  themselves  and  the  nerve  elements  only 
the  relation  of  contact.  It  is  believed  that  their  function  is  that  of 
supporting  the  nerve-tissues  and  also  isolating  them. 

It  will  be  seen  now  that  the  retina  is  composed  essentially  of  three 
layers  of  vertical  cells,  whose  processes  have  a  vertical  direction,  and 
which  are  connected  with  each  other  by  contact  of  these  processes;  that 
there  are  also  two  other  sets  of  cells  which  form  horizontal  layers  of 
nerve-processes,  these  being  in  the  inner  and  outer  parts  of  the  internal 
granular  layer.  Tliero  arc,  therefore,  J-triftly  speaking,  five  layers  of 
nerve-cells,  three  vertical  and  two  horizontal.  Two  other  layers  are 
made  up  by  the  modification  of  the  protoiihism  of  the  fibres  of  ]\Iiiller 
and  are  purely  mechanical  in  function.  They  are  the  external  and  in- 
ternal limiting  layers. 

rigment-cenidyer^  which  was  formerly  considered  part  of  the  choroid, 
consists  of  cells  whic^h  cover  and  entiii'ly  surround  the  outer  limbs  of  the 
rods  and  cones. 

The  further  subdivisions  of  the  retina  arc  more  for  purposes  of  fine 
anatomy  than  of  functional  iuiportance. 

Differoires  in  Slnictiirr  of  Pijf'erent  Parts. — Toward  the  centre  of  the 
macula  luteaall  the  layers  of  the  retina  become  greatly  thiuned  out  and 


708  HANDBOOK   OF   fMYSlOLOGT. 

almost  disappear,  except  the  rod  and  cone  layer,  whicli  considerably  in- 
creases in  thickness  but  at  the  fovea  centralis  comes  to  consist  almost 
entirely  of  long  slender  cones  and  cone-fibres,  which  curve  toward  the 
periphery.  They  are  supported  by  neuroglia,  which  is  also  found  inter- 
nally as  a  thin  layer,  the  rods  being  absent.  There  are  capillaries  here, 
but  none  of  the  larger  branches  of  the  retinal  arteries. 

Toward  the  edge  of  the  macula  hitea,  not  only  are  all  the  layers 
present,  but  the  ganglionic  layer  consists  of  many  strata  of  cells  (7  or  8), 
and  with  this  increase  there  is  also  an  increase  in  the  thickness  of  the 
inner  granular  layer.  The  cells  are  generally  bipolar.  Toward  the 
ceutre  the  layers  diminish  in  this  order:  optic  nerve-fibres,  ganglionic 
layer,  inner  molecular  layer,  and  inner  granular  layer.  Tl^e  rods  grow 
scanty  and  then  are  absent. 

At  the  ora  serrata  the  layers  are  not  perfect  and  disappear  in  this 
order:  nerve-fibres  and  ganglion  cells,  then  the  rods,  leaving  only  the 
inner  limbs  of  the  cones,  these  cease,  then  the  inner  molecular  layer. 
The  Miillerian  fibres  persist. 

At  the  pars-ciliaris  retinse,  the  retina  is  represented  by  a  layer  of 
columnar  cells,  derived  from  the  fusion  of  the  nuclear  layers.  The  cells 
are  covered  by  the  membrana  limitans  interna,  and  externally  are  in 
contact  with  the  pigment  layers  of  the  retina,  which  is  continued  over 
the  ciliary  processes. 

The  chamhei's  of  the  eye. — The  a/i^fen'o?"  chamber  is  the  space  behind 
the  cornea  and  in  front  of  the  lens.  It  is  filled  with  aqueous  humor, 
which  is  essentially  a  diluted  lymph  with  a  small  amount  of  proteid  in 
it,  viz.,  of  fibrinogen,  serum-globulin,  and  septum-albumin.  It  is  seldom 
spontaneously  coagulable.  It  contains  salts,  chiefly  sodium  chloride, 
sometimes  a  substance  which  reduces  cop]Der  sulphate,  but  is  not  sugar, 
and  a  trace  of  urea  and  sarcolactic  acid.  There  are  no  formed  elements 
in  the  fluid.  It  is  stated  that  the  aqueous  humor  is  secreted  by  glands 
in  the  ciliary  region,  but  the  cavity  is  itself  obviously  a  lymph  sac. 

The  posterior  chamber,  or  that  behind  the  lens,  contains  the  vitreons 
humor,  which  is  a  semifluid  substance  contained  in  the  meshes  of  an 
indistinct  connective  tissue.  It  is  inclosed  in  a  distinct  membrane 
called  mernhrana  hyaloidea,  from  the  anterior  surface  of  this  membi-ane 
at  the  ora  serrata  fibres  pass  off  to  the  back  of  the  lens  capsule,  forming 
an  incomplete  canal,  called  the  Canal  of  Petit,  the  membrane  itself  being 
the  Zonule  of  Zinn.  The  hyaloid  membrane  separates  the  vitreous  from 
the  retina. 

Blood-vessels  of  the  Eyeball. — The  eye  is  very  richly  supplied 
with  blood-vessels.  In  addition  to  the  conjunctival  vessels  which  are 
derived  from  the  palpebral  and  lachrymal  arteries,  there  are  at  least  two 


THE   SENSES.  709 

other  distinctsetsof  vessels  supplying  the  tunics  of  the  eyeball.  (1)  The 
vessels  of  the  sclerotic,  choroid,  and  iris,  and  (2)  the  vessels  of  the  retina. 
(1. )  These  are  the  short  and  long  posterior  ciliary  arteries  which  pierce 
the  sclerotic  in  the  posterior  half  of  the  eyeball,  and  the  anterior  ciliary 
which  enter  near  the  insertions  of  the  recti.  These  vessels  anastomose 
and  form  a  very  rich  choroidal  plexus;  they  also  supply  the  iris  and 


Fig.  419.— Section  through  the  macula  Intea  and   I'.. v. -a  c-.-nnalis  ..i  human  retina,     o,  fovea;    6, 
descent  of  the  macula  toward  fovea.    The  numbers  indicate  the  layers  of  the  retina.     (Kuhnt.) 

ciliary  processes,  forming  a  very  highly  vascular  circle  round  the  outer 
margin  of  the  iris  and  adjoining  portion  of  the  sclerotic. 

The  distinctness  of  these  vessels  from  those  of  the  conjunctiva  is 
well  seen  in  the  difference  between  the  bright  red  of  blood-shot  eyes 
(conjunctival  congestion),  and  the  pink  zone  surrounding  the  cornea 
which  indicates  deep  seated  ciliary  congestion. 

(2.)  The  retinal  vessels  (fig.  418)  are  derived  from  the  arteria  cen- 
tralis retina:,  which  enters  the  eyeball  along  the  centre  of  the  optic 
nerve.  They'  ramify  all  over  the  retina,  chiefly  in  its  inner  layers. 
They  can  be  seen  by  direct  ophthalmoscopic  examination. 

The  Optical  Apparatus. 

The  optical  apparatus  may  be  supposed,  for  the  sake  of  description, 
to  consist  of  several  parts.  Firstly,  of  a  system  of  transparent  refract- 
ing surfaces  and  media  by  means  of  which  images  of  external  objects  are 
brought  to  a  focus  upon  the  back  of  the  eye;  and  secondly,  of  a  sensitive 
screen,  the  retina,  which  is  a  specialized  termination  of  the  optic  nerve, 
capable  of  being  stimulated  by  luminous  objects,  and  of  sending  through 
the  optic  nerve,  such  an  impression  as  to  produce  in  the  brain  visual 
sensations.  To  these  main  parts  may  be  added,  thirdly,  an  apparatus 
for  focussing  objects  at  different  distances  from  the  eye,  called  accommo- 
dation. Even  this  does  not  complete  the  description  of  the  whole  organ 
of  vision,  since  both  eyes  are  usually  employed  in  vision,  and  fourthly, 
an  arrangement  exists  by  means  of  which  the  eyes  may  be  turned  in 
the  same  direction  by  a  system  of  muscles,  so  that  binocular  vision  is 
possible. 


710  HANDBOOK    OF    PHYSIOLOGY. 

The  arrangement  of  the  optic  nerve-fibres,  and  of  the  continuation 
of  these  backward  in  the  optic  chiasma,  and  thence  to  special  districts  of 
the  brain,  have  abeady  been  discussed. 

The  eye  may  be  compared  to  a  photographic  camera^  and  the  trans- 
parent media  corresponds  to  the  johotographic  lens.  In  such  a  camera 
images  of  external  objects  are  thrown  upon  a  ground-glass  screen  at  the 
back  of  a  box,  the  interior  of  which  is  painted  black.  In  the  eye,  the 
camera  proper  is  represented  by  the  eyeball  with  its  choroidal  pigment, 
the  screen  by  the  retina,  and  the  lens  by  the  refracting  media.  In  the 
case  of  the  camera,  the  screen  is  enabled  to  receive  clear  images  of  objects 
at  different  distances,  by  an  apparatus  for  focussing.  The  corresjsonding 
contrivance  in  the  eye  is  the  accommodation. 

The  iris,  which  is  capable  of  allowing  more  or  less  light  to  pass  into 
the  eye,  corresponds  with  the  different  sized  diaphragms  used  in  the 
protographic  apparatus. 

Refractive  media  and  surfaces. — At  first  sight  it  would  seem  as  if  the 
refracting  apparatus  of  the  eye  were  very  complicated,  seeing  that  it 
consists  of  so  many  parts.  These  parts  are :  the  anterior  surface  of  the 
cornea  itself,  the  posterior  surface  of  the  cornea,  the  aqueous  humor, 
the  anterior  surface  of  the  lens,  the  substance  of  the  lens  itself  (which  is 
also  unequally  refractive),  the  posterior  surface  of  the  lens,  and  the  vit- 
reous humor.  Thus  there  are  four  surfaces,  and  at  least  including  the 
air,  five  media.  For  all  practical  purposes,  however,  these  may  be  re- 
solved into  a  somewhat  simpler  form,  and  the  cornea  may  be  considered 
as  one  surface,  the  anterior,  and  one  medium;  the  aqueous  and  vitreous 
humors  as  one  medium ;  the  lens,  as  two  surfaces  and  one  medium.  It 
will  be  as  well  to  consider  the  laws  which  govern  the  refraction  of  light 
under  such  circumstances. 

In  its  simplest  form,  we  may  consider  the  refraction  through  a  simple 
transparent  spherical  surface,  separating  two  media  of  different  density. 

The  rays  of  light  which  fall  upon  the  surface  exactly  perpendicularly 
do  not  suffer  refraction,  but  pass  through,  cutting  the  optic  axis  (0  A, 
fig.  420),  a  line  which  passes  exactly  through  the  centre  of  the  surface, 
at  a  certain  point,  the  nodal  point  (fig.  420,  N"),  or  centre  of  curvature. 
Any  rays  which  do  not  so  strike  the  curved  surface  are  refracted  toward 
the  optical  axis.  Eays  which  impinge  upon  the  spherical  surface  paral- 
lel to  the  optical  axis,  will  meet  at  a  point  behind,  upon  the  said  axis 
which  is  called  the  chief  posterior  focus  (fig.  420,  F,) ;  and  again  there 
is  a  point  in  the  optical  axis  in  front  of  the  surface,  rays  of  light  from 
which  so  strike  the  surface  that  they  are  refracted  in  a  line  parallel  with 
the  axis  df"\  such  a  point  (fig.  420,  FJ  is  called  the  chief  anterior 
focus.  The  optic  axis  cuts  the  surface  at  what  is  called  the  principal 
point. 


THE   SEXSES,  711 


It  is  quite  obvious  that  the  eye,  even  in  the  simplified  form  above 
indicated,  is  a  much  more  comi^licated  optical  apparatus  than  the  one 
described  in  the  figure.     It  is,  however,  possible  to  reduce  the  refractive 


Fig.  420.— Diagram  of  a  simple  optical  system  (after  M.  Foster).  The  curved  surface,  6,  d, 
is  supposed  to  separate  a  less  refractive  medium  toward  the  left  from  a  more  refractive  medium 
toward  the  right. 

surfaces  and  media  to  a  simpler  form  when  the  refractive  indices  of  the 
different  media  and  the  curvature  of  each  surface  are  known.  All  of 
these  data  have  been  very  carefully  collected.     They  are  as  follows; — 

Index  of  refraction  of  aqueous  and   vitreous  =  1.3365 

lens        ....=:  1.4371 

Radius  of  curvature  of  cornea  .         .         .  =  7. 829  mm. 

"  "  anterior  surface  of  lens  =  10  " 

"  "  posterior  "  =  6  " 

Distance  from  anterior  surface  of  cornea  and 

anterior  surface  of  lens        .         .         .         .  =  3.6        " 
Distance  from  posterior  surface  of  cornea  and 

posterior  surface  of  lens        .         .         .         .  =  7. 2        " 

With  these  data,  it  has  been  found  comparatively  easy  to  reduce  by 
calculation  the  different  surfaces  of  different  curvatures,  into  one  mean 
curved  surface  of  known  curvature,  and  the  differently  refracting  media 
into  one  mean  medium  the  refractive  power  of  which  is  known. 

The  simplest  so-called  schematic  eye  formed  upon  this  principle, 
suggested  by  Listing  as  the  reduced  eye,  has  the  following  dimensions: — 

From  anterior  surface  of  cornea  to  the  princi- 
pal point  ....... 

From  the  nodal  point  to  the  posterior  surface 
of  lens      ........ 

Posterior  chief  focus  lies  behind  cornea  . 

Anterior  chief  focus  in  front  of  cornea    . 

Radius  of  curvature  of  ideal  surface 

In  tliis  reduced  or  simplified  eye  the  principal  posterior  focus,  about 
23  mm.  behind  tlie  spherical  surface,  would  correspond  to  the  position 
of  the  retina  behind  anterior  surface  of  cornea.  The  refracting  surface 
would  be  situated  about  midway  between  the  posterior  surface  of  the 
cornea  and  the  anterior  surface  of  the  lens. 

The  optical  axis  of  the  eye  is  a  line  drawn  through  the  centres  of 


2.3448 

mm. 

.4764 

ii 

22.8237 

i( 

12.8326 

u 

5. 1248 

" 

712 


HANDBOOK    OF   PHYSIOLOGY. 


curvature  of  the  cornea  and  lens,  prolonged  backward  to  touch  the  retina 
between  the  porus  opticus  and  fovea  centralis,  and  this  differs  from  the 
visual  axis  which  passes  through  the  nodal  point  of  the  reduced  eye  to 


Fig.  421.— Diagram  of  the  optical  angle. 

the  fovea  centralis ;  this  forms  an  angle  of  5°  with  the  optical  axis. 
By  some  the  optical  axis  and  the  visual  axis  are  considered  to  be  iden- 
tical. The  visual  or  optical  angle  is  included  between  the  lines  drawn 
from  the  borders  of  any  object  to  the  nodal  point;  if  the  lines  be  pro- 


Fig.  421  A.— Diagram  of  the  method  of  the  formation  of  an  inverted  image  exactly  focussed 
upon  the  retina.     The  dotted  line  is  the  ideal  surface  of  curvature. 

longed  backward  they  include  an  equal  angle.  It  has  been  shown  by 
Helmholtz  that  the  smallest  angular  distance  between  two  points  which 
can  be  appreciated  =  50  seconds,  the  size  of  the  retinal  image  being 
3.6o/x;  this  jDractically  corresponds  to  the  diameter  of  the  cones  at  the 


Fig.  422.— Diagram  of  the  course  of  a  ray  of  light,  to  show  how  a  blurred  or  indistinct  image 
is  formed  if  the  object  be  not  exactly  focussed  upon  retina.  The  surface  C  C  should  be  sup- 
posed to  represent  the  ideal  curvature.  The  nodal  point  should  be  nearer  the  posterior  surface 
of  lens  as  in  flg.  421  a. 

fovea  centralis  which  =  3/j,  the  distance  between  the  centres  of   two  ad- 
jacent cones  being  =  4//. 

The  image  of  an  object,  then,  is  thus  formed  upon  the  retina.     An 


THE   SENSES.  713 

object  may  be  considered  as  a  series  of  points,  from  each  of  which  a 
pencil  of  light  diverges  to  the  eye,  and  this  pencil  has  for  its  centre  or 
axis,  a  ray  which  impinging  uijou  the  refractive  surface  perpendicularly 
to  the  surface  is  not  refracted,  but  passes  through  the  nodal  point,  and 
is  prolonged  backward  to  the  retina,  whereas  the  diverging  rays  are  also 
made  to  converge  to  a  principal  posterior  focus  behind  the  lens,  or  the 
chief  axis  of  the  pencil  of  light  proceeding  from  the  point  in  question, 
and  this  focus,  if  the  image  is  to  be  clear,  should  fall  on  the  retina. 

Thus  from  each  point  of  an  object  a  corresponding  image  is  formed 
on  the  retina,  so  that  an  image  of  the  distal  object  is  produced.  It  is 
an  inverted  image.  Whether  the  image  is  blurred  or  not  depends  upon 
the  refractive  power  of  the  media,  and  upon  the  distance  of  the  anterior 
surface  of  the  cornea  from  the  retina.  If  the  refractive  media  are  too 
powerful,  or  the  eye  too  long,  the  image  is  formed  in  front  of  the  retina 
(fig.  422) ;  if  the  reverse,  the  image  is  formed  behind  the  retina,  and  in 
both  cases  an  indistinct  and  blurred  image  is  the  result. 

Accommodation. 

The  distinctness  of  the  image  formed  upon  the  retina,  is  mainly  de- 
pendent on  the  rays  emitted  by  each  luminous  point  of  the  object  being 
brought  to  a  perfect  focus  upon  the  retina.  If  this  focus  occur  at  a 
point  either  in  front  of,  or  behind  the  retina,  indistinctness  of  vision 
ensues,  in  the  way  we  have  already  described,  with  the  production  of  a 
halo.  The  focal  distance,  i.e.,  the  distance  from  a  lens  of  the  point  at 
which  the  luminous  rays  are  collected,  besides  being  regulated  by  the 
degree  of  convexity  and  density  of  the  lens,  varies  with  the  distance  of 
the  object  from  the  lens,  being  greater  as  this  is  shorter,  and  vice  versd. 
Hence,  since  objects  placed  at  various  distances  from  the  e3'e  can  within 
a  certain  range,  different  in  different  persons,  be  seen  with  almost  equal 
distinctness,  there  mast  be  some  provision  by  which  the  eye  is  enabled  to 
adapt  itself,  so  that  whatever  length  the  focal  distance  may  be,  the  focal 
point  may  always  fall  exactly  upon  the  retina. 

This  power  of  accommodation,  or  the  adaptation  of  the  eye  to  vision 
at  different  distances,  has  received  the  most  varied  explanations.  It  is 
obvious  that  the  effect  might  be  produced  in  either  of  two  ways,  viz. ,  {a) 
by  altering  the  convexity,  and  thus  the  refracting  power,  either  of  the 
cornea  or  of  the  lens;  or  {b)  by  changing  the  position  either  of  the 
retina  or  of  the  lens,  so  that  whether  the  object  be  near  or  distant,  the 
focal  points  to  which  the  rays  are  converged  by  the  lens  may  always  fall 
exactly  on  the  retina.  The  amount  of  either  of  these  changes,  which 
would  be  required  in  even  the  widest  range  of  yision,  Tronld  be  extremely 
small.     For,  from  the  refractive  powers  of  the  media,  of.  tfeie  eye,  tihe,  diS- 


714  HANDBOOK   OF   PHYSIOLOGY. 

fereuce  between  the  focal  distances  of  the  images  of  an  object  at  a  distance, 
and  of  one  at  the  c'istance  of  four  inches,  is  only  about  0.143  of  an  inch 
(3.5  mm.).  On  this  calculation  the  change  in  the  distance  of  the  retina 
from  the  lens  required  for  vision  at  all  distances,  supposing  the  cornea 
and  lens  to  remain  the  same,  would  not  be  more  than  about  one  line. 

The  adaptation  of  the  eye  for  objects  at  different  distances  is  pri- 
marily due  to  a  varying  shape  of  the  lens,  its  front  surface  becoming 
more  or  less  convex,  according  as  the  distance  of  the  object  looked  at  is 
near  or  far.  The  nearer  the  object,  the  more  convex,  up  to  a  certain 
limit,  the  front  surface  of  the  lens,  and  vice  versa;  the  back  surface  tak- 
ing little  or  no  share  in  the  production  of  the  effect  required.  And  this 
surface,  which  during  rest  is  more  convex  than  the  anterior,  becomes 
the  less  convex  of  the  two  during  accommodation.  The  following  simple 
experiment  illustrates  this  point:  If  a  lighted  candle  be  held  a  little  to 
one  side  of  a  person's  eye,  an  observer  looking  at  the  eye  from  the  other 
side  sees  three  distinct  images  of  the  flame  (fig.  423).  The  first  and 
brightest  is  (1)  a  small  erect  image  formed  by  the  anterior  convex  surface 
of  the  cornea;  the  second  (2)  is  also  erect,  but  larger  and  less  distinct  than 
the  preceding,  and  is  formed  at  the  anterior  convex  surface  of  the  lens; 
the  third  (3)  is  smaller,  inverted,  and  indistinct;  it  is  formed  at  the 
posterior  surface  of  the  lens,  which  is  concave  forward,  and  therefore, 
like  all  concave  mirrors,  gives  an  inverted  image.  If  now  the  eye  under 
observation  be  made  to  look  at  a  near  object,  the  second  image  becomes 
smaller,  clearer,  and  approaches  the  first.  If  the  eye  be  now  adjusted 
for  a  far  point,  the  second  image  enlarges  again,  becomes  less  distinct, 
and  recedes  from  the  first.     In  both  cases  alike  the  first  and  third  images 


Fig.  423.— Diagram  showing  three  reflections  of  a  candle.  1,  From  the  anterior  surface  of 
cornea ;  2,  from  the  anterior  sml^ace  of  lens ;  3,  from  the  posterior  surface  of  lens.  For  further 
explanation,  see  text.  The  experiment  is  best  performed  by  employing  an  instrument  invented 
by  Helmholtz,  termed  a  Phakoscope. 

remain  unaltered  in  size,  distinctness,  and  relative  position.  This 
proves  that  during  accommodation  for  near  objects  the  curvature  of  the 
cornea,  and  of  the  posterior  of  the  lens,  remains  unaltered,  while  the 
anterior  surface  of  the  lens  becomes  more  convex  and  approaches  the 
cornea. 


THE  SENSES. 


715 


The  experiment  (fig.  423  a)  is  more  striking  when  two  candles  are 
used,  and  the  images  of  the  two  candles  from  the  front  surface  of  the 
lens  during  accommodation  not  only  approach  those  from  the  cornea, 


B 

Fig.  423  A.  Fig.  •134. 

Fig.  423  A.— Diagram  of  Sanson's  images.  A,  when  the  eyes  are  not,  and  B,  when  they  are 
focussed  for  near  objects.  The  flg.  to  the  right  in  A  and  B  is  the  inverted  image  from  the  pos- 
terior surface  of  the  lens. 

Fig.  4^4,— Phalvoscope  of  Helmholtz.  At  B  B'  are  two  prisms,  by  which  the  light  of  a  candle 
is  concentrated  on  the  eye  of  the  person  experimented  with  at  C.  A  is  the  aperture  for  the 
eye  of  the  observer.  The  observer  notices  three  doul)le  images,  as  in  fig.  42-3,  reflected  from  the 
eye  under  examination  when  the  eye  is  fixed  upon  a  distant  object ;  the  position  of  the  images 
having  been  noticed,  the  eye  is  then  made  to  focus  a  near  object,  such  as  a  reed  pushed  up  by 
C;  the  images  from  the  anterior  surface  of  the  lens  will  be  observed  to  move  toward  each  other, 
in  consequence  of  the  lens  becoming  more  convex. 

but  also  approach  one  another,  and  become  somewhat  smaller.     {San- 
son''s  images.) 

Mechanism  of  accommodation. — The  lens  having  no  inherent  power 
of  contraction,  its  changes  of  outlines  must  be  produced  by  some  power 
from  without;  this  power  is  supplied  by  the  ciliary  muscle.  It  is  some- 
times termed  the  tensor  clioroidecB.  Its  action  is  to  draw  forward  the 
choroid,  and  by  so  doing  to  slacken  the  tension  of  the  suspensory  liga- 
ment of  the  lens  which  arises  from  it.  The  anterior  surface  of  the  lens 
is  kept  flattened  by  the  action  of  this  ligament.  The  ciliary  muscle 
during  accommodation  by  diminishing  its  tension,  diminishes  to  a  pro- 
portional degree  the  flattening  of  which  it  is  the  cause.  On  diminution 
or  cessation  of  the  action  of  the  ciliary  muscle,  the  lens  returns  to  its 
former  shape,  by  virtue  of  the  elasticity  of  the  suspensory  ligament 
(tig.  425).  From  this  it  wll  appCaf  that  the  eye  is  usually  focussed 
for  distant  objects.  In  viewing  near  objects  the  pupil  contracts,  the 
opposite  effect  taking  place  on  withdrawal  of  the  attention  from  near 
objects,  and  fixing  it  on  those  distant. 


716  HANDBOOK    OF   PHYSIOLOGY.  , 

Range  of  Distinct  Vision.  Near-point. — In  every  eye  there  is  a  limit 
to  the  power  of  accommodation.  If  a  book  be  brought  nearer  and 
nearer  to  the  eye,  the  type  at  last  becomes  indistinct,  and  cannot  be 
brought  into  focus  by  any  effort  of  accommodation,  however  strong. 
This,  which  is  termed  the  near-point,  can  be  determined  by  the  follow- 


Fig.  425.— Diagram  representing  by  dotted  lines  the  alteration  in  the  shape  of  the  lens  on  ac- 
commodation for  near  objects.     (E.  Landolt.) 

ing  experiment  (Scheiner).  Two  small  holes  are  pricked  in  a  card  with 
a  pin  not  more  than  a  twelfth  of  an  inch  (2  mm. )  apart,  at  any  rate 
their  distance  from  each  other  must  not  exceed  the  diameter  of  the  pu- 
pil. The  card  is  held  close  in  front  of  the  eye,  and  a  small  needle 
viewed  through  the  pin-holes.  At  a  moderate  distance  it  can  be  clearly 
focussed,  but  when  brought  nearer,  beyond  a  certain  point,  the  image 
appears  double  or  at  any  rate  blurred.  This  point  where  the  needle 
ceases  to  appear  single  is  the  near-point.  Its  distance  from  the  eye  can 
of  course  be  readily  measured.  It  is  usually  about  5  or  6  inches  (13 
cm.).     In  the  accompanying  figure  (fig.  426)  the  lens  ^  represents  the 


Fig.  426.— Diagram  of  experiment  to  ascertain  the  minimum  distance  of  distinct  vision. 

eye;  efthe  two  pin-holes  in  the  card,  7in  the  retina;  a  represents  the  po- 
sition of  the  needle.  When  the  needle  is  at  a  moderate  distance,  the 
two  pencils  of  light  coming  from  e  and  /,  are  focussed  at  a  single  point  on 
the  retina  nn.  If  the  needle  be  brought  nearer  than  the  near-point,  the 
strongest  effort  of  accommodation  is  not  suflQcient  to  focus  the  two  pen- 


THE   SENSES.  'J'17 

oils,  they  meet  at  a  point  behind  the  retina.  The  effect  is  the  same 
as  if  the  retina  were  shifted  forward  to  mm.  Two  images  h.g.  are 
formed,  one  from  each  hole.  It  is  interesting  to  note  that  wlieu  two 
images  are  produced,  the  lower  one  ^  really  appears  in  the  position  q, 
while  the  upj^er  one  aj)pears  in  the  ])osition  p.  This  may  be  readily 
verified  by  covering  the  holes  in  succession. 

During  accommodation  two  other  changes  take  ^Xhcq  in  the  eyes, 
(1)  Tlte  eyes  converge  by  the  action  of  the  extra-ocular  muscles  chiefly 
by  the  internal  and  inferior  recti,  or  internal  and  superior  recti.  The 
superior  oblique  and  the  inferior  oblique  may  also  be  used  to  turn  the 
eye  upward  or  downward. 

Movements  of  the  Eye. — The  eyeball  possesses  movement  around  three  axes 
indicated  in  fig.  427,  viz.,  an  autero- posterior,  a  vertical,  oud  a  trans%'erse, 
passing  tln-ough  a  centre  of  rotation  a  little  behind  the  centre  of  the  optic  axis. 
The  movements  are  accomplished  by  pairs  of  muscles. 

Direction  of  Movement.  By  what  muscles  accomplished. 

Inward          .....          .  Internal  rectus. 

Outward  .......  External  rectus. 

Upward j  Superior  rectus. 

^  {  Interior  oblique. 

■n^,„„„,„^,i  \  Inferior  rectus. 

JJownward        .         .         .         .         •     •      -  o  ■        \  ^■ 

(  Superior  oblique. 

Inward  and  upward    ....      -I  Internal  and  superior  rectus. 
^  {  Interior  oblique. 

Inward  and  downward  .         .         ,     .      i  Internal  and  inferior  rectus. 

\  Superior  oblique. 
Outward  and  upward  .        .         .      \  External  and  superior  rectus. 

^  {  Inferior  oblique. 

Outward  and  downward  .         .     .      3  External  and  inferior  rectus. 

I  Superior  oblique. 

(2)  The  second  change  which  takes  place  in  the  eyes  is,  that  the 
pupils  contract.  The  contraction  of  all  of  the  muscles  which  have  to  do 
with  accommodation,  viz.,  of  the  ciliary  muscle,  of  the  recti  muscles, 
and  of  the  sphincter  pupillre  is  under  the  control  of  the  third  nerve. 
But  the  superior  oblique  may  also  be  employed,  in  which  case  the  fourth 
nerve  is  also  concerned. 

Contractio7i  of  the  pupil  may  also  occur  under  the  following  circum- 
stances: (1)  On  exposure  of  the  eye  to  a  bright  light;  (2)  on  the  local 
application  of  eserine  (active  principle  of  Calabar  bean) ;  (3)  on  the 
administration  internally  of  opium,  aconite,  and  in  the  early  stages  of 
chloroform  and  alcohol  poisoning;  (4)  on  division  of  the  cervical 
sympathetic  or  stimulation  of  the  third  nerve,  and  dilatation  of  the  pupil 
occurs  (1)  in  a  dim  light;  (2)  when  the  eye  is  focussed  for  distant  ob- 
jects; (3)  on  the  local  application  of  atropine  and  its  allied  alkaloids; 
(4)  on  the  internal  administration  of  atropine  and  its  allies;  (5)  in 
the  later  stages  of  poisoning  by  chloroform,  opium,  and  other  drugs; 
(6)  on  paralysis  of  the  third  nerve ;  (7)  on  stimulation  of  the  cervical 


?18  HAKDBOOK  01?  fSYSlOLOGT. 

sympathetic,  or  of  its  centre  in  the  floor  of  the  front  of  the  aqueduct  of 
Sylvius.  The  contraction  of  the  pupil  appears  to  he  under  the  control 
of  a  centre  in  the  hulb  or  in  the  corpora  quadrigemina,  and  this  is 
reflexly  stimulated  by  a  bright  light,  and  the  dilatation  when  the  reflex 
centre  is  not  in  action  is  due  to  the  more  powerful  sympathetic  action ; 
but  in  addition,  it  appears  that  both  contraction  and  dilatation  may  be 


Fig.  427.— Diagram  of  the  axes  of  rotation  to  the  eye.    The  thin  lines  indicate  axes  of  rotation, 
tlie  thick  the  position  of  muscular  attachment. 

produced  by  a  local  mechanism,  upon  which  certain  drugs  can  act,  Avhich 
is  independent  of  and  probably  often  antagonistic  to  the  action  of  the 
central  apparatus  of  the  third  and  sympathetic  nerve.  The  action  of  the 
fifth  nerve  upon  the  pupil  is  not  well  understood,  but  its  apparent  effect 
in  producing  dilatation  is  due  to  the  mixture  of  sympathetic  fibres 
with  its  nasal  branch.  The  sympathetic  influence  upon  the  radiating 
fibres  is  believed  to  be  conveyed  not  by  the  long  ciliary  branches  of  that 
nerve,  but  by  the  short  ciliary  branches  from  the  ophthalmic  ganglion. 
The  close  sympathy  subsisting  between  the  two  eyes  is  nowhere  better 
shown  than  by  the  condition  of  the  pupil.  If  one  eye  be  shaded  by  the 
hand  its  pupil  will  of  course  dilate;  but  the  jjupil  of  the  other  eye  will 
also  dilate,  though  it  is  unshaded. 

Defects  in  the  Optical  Apparatus. 

Defects  in  the  Refracting  Media. — ^Under  this  head  we  may  con- 
sider the  defects  known  as  (1)  Myopia,  (2)  Hypermetropia,  (3)  Astig- 
matism, (4)  Spherical  Aberration,  (5)  Chromatic  Aberration. 


THE   SENSES. 


719 


The  norma,]  (emmetropic)  eye  is  so  adjusted  that  parallel  rays  are 
brought  exactly  to  a  focus  on  the  retina  without  any  effort  of  accommo- 
dation (1,  fig.  428).  Hence  all  objects  except  near  ones  (practically  all 
objects  more  than  twenty  feet  off)  are  seen  without  any  effort  of  accom- 
modation; in  other  words,  the  far-point  of  the  normal  eye  is  at  an  infinite 
distance.  In  viewing  near  objects  we  are  conscious  of  the  effort  (the  con- 
traction of  the  ciliary  muscle)  by  which  the  anterior  surface  of  the  lens  is 
rendered  more  convex,  and  rays  which  would  otherwise  be  focussed  lehind 
the  retina  are  converged  upon  the  retina  (see  dotted  lines  2,  fig.  428). 


FiR.  428. —Diagram  showinp:— 1,  normal  foinmetropic")  eye  bringinR  paraUel  rays  exactly  to 
a  focus  on  the  retina:  2.  normal  eve  adapted  to  a  near  point;  without  accommodation  the  rays 
would  be  focussed  behind  tlu'  retina,  but  bv  increasing  the  curvature  of  the  anterior  surface  of 
the  lens  (shown  by  a  dotted  line)  the  rays  are  focussed  on  the  retina  (as  indicated  by  the  meet- 
ing of  the  two  do'tted  lines);  ;i,  hupermctropic  eve,  in  this  case  the  axis  of  the  eye  is  shorter, 
and  the  lens  flatter,  than  normal';  parallel  ravs  are  focussed  behind  the  retina;  4,  myopic  eye; 
in  this  case  the  axis  of  the  eye  is  abnormally  long,  and  the  lens  too  convex;  parallel  rays  are 
focussed  in  front  of  the  retina. 

1.  il/?/o;;m  (short-sight)  (4,  fig.  428).— This  defect  is  due  to  an  abnor- 
mal elongation  of  the  eyeball.  Tlie  eye  is  usually  larger  than  normal 
and  is  always  longer  than  normal;  the  lens  is  also  probably  too  convex. 
The  retina  is  too  far  from  the  lens  and  consequently  parallel  rays  are 


?'20  HANDBOOK   OF   PSYSlOLOGY. 

focussed  in  front  of  the  retina,  and,  crossing,  form  little  circles  on  the 
retina;  thns  the  images  of  distant  objects  are  blurred  and  indistinct. 
The  eye  is,  as  it  were,  permaiiently  adjusted  for  a  near-point.  Rays 
from  a  point  near  the  eye  are  exactly  focussed  in  the  retina.  But  those 
which  issue  from  any  object  beyond  a  certain  distance  {far-point)  cannot 
be  distinctly  focussed.  This  defect  is  corrected  hj  concave  glasses  which 
cause  the  rays  entering  the  eye  to  diverge ;  hence  they  do  not  come  to  a 
focus  so  soon.  Such  glasses  of  course  are  only  needed  to  give  a  clear 
vision  of  distant  objects.  For  near  objects,  except  in  extreme  cases,  they 
are  not  required. 

Hypermetropia  (long-sight)  (3,  fig.  428). — This  is  the  reverse  defect. 
The  eye  is  too  short  and  the  lens  too  flat.  Parallel  rays  are  focussed 
behind  the  retina:  an  effort  of  accommodation  is  required  to  focus  even 
parallel  rays  on  the  retina;  and  when  they  are  divergent,  as  in  viewing 
a  near  object,  the  accommodation  is  insufficient  to  focus  them.  Thus 
in  well-marked  cases  distant  objects  require  an  effort  of  accommodation 
and  near  ones  a  very  powerful  effort.  Thus  the  ciliary  muscle  is  con- 
stantly acting.  This  defect  is  obviated  by  the  use  of  convex  glasses, 
which  renders  the  pencils  of  light  more  convergent.  Such  glasses  are  of 
course  especially  needed  for  near  objects,  as  in  reading,  etc.  They  rest 
the  eye  by  relieving  the  ciliary  muscle  from  excessive  work. 

3.  Astigmatism. — This  defect,  which  was  first  discovered  by  Airy,  is 
due  to  a  greater  curvature  of  the  eye  in  one  meridian  than  in  others. 
The  eye  may  be  even  myopic  in  one  plane  and  hypermetropic  in  others. 
Thus  vertical  and  horizontal  lines  crossing  each  other  cannot  both  be 
focussed  at  once ;  one  set  stands  out  clearly  and  the  others  are  blurred 
and  indistinct.  This  defect,  which  is  present  in  a  slight  degree  in  all 
eyes,  is  generally  seated  in  the  cornea,  but  occasionally  in  the  lens  as 
well;  it  may  be  corrected  by  the  use  of  cylindrical  glasses  {i.e.,  curved 
only  in  one  direction). 

4.  Spherical  Aberration. — The  rays  of  a  cone  of  light  from  an  object 
situated  at  the  side  of  the  field  of  vision  do  not  meet  all  in  the  same 
point,  owing  to  their  unequal  refraction ;  for  the  refraction  of  the  rays 
which  pass  through  the  circumference  of  a  lens  is  greater  than  that  of 
those  traversing  its  central  portion.  This  defect  is  known  as  spherical 
aberration,  and  in  the  camera,  telescope,  microscope,  and  other  optical 
instruments,  it  is  remedied  by  the  interposition  of  a  screen  with  a  circu- 
lar aperture  in  the  path  of  the  rays  of  light,  cutting  off  all  the  marginal 
rays  and  only  allowing  the  passage  of  those  near  the  centre.  Such  cor- 
rection is  effected  in  the  eye  by  the  iris,  which  forms  an  annular 
diaphragm  to  cover  the  circumference  of  the  lens,  and  to  prevent  the 
rays  from  passing  through  any  part  of  the  lens  but  its  centre  which  cor- 
responds to  the  pupil.     The  posterior  surface  of  the  iris  is  coated  with 


THE   SENSES.  721 

pigment,  to  prevent  the  passage  of  rays  of  light  through  its  substance. 
The  image  of  an  object  will  be  most  defined  and  distinct  when  the 
pupil  is  narrow,  the  object  at  the  proper  distance  for  vision,  and  the 
light  abundant ;  so  that,  while  a  suflBcient  number  of  rays  are  admitted, 
the  narrowness  of  the  pupil  may  prevent  the  production  of  indistinctness 
of  the  image  by  spherical  aberration.  But  even  the  image  formed  by 
the  rays  passing  through  the  circumference  of  the  lens,  when  the  pupil 
is  much  dilated,  as  in  the  dark,  or  in  a  feeble  light,  may,  under  certain 
circumstances,  be  well  defined. 

Distinctness  of  vision  is  further  secured  by  the  pigment  of  the  outer 
surface  of  the  retina,  the  posterior  surface  of  the  iris  and  the  ciliary 
processes,  which  absorbs  any  rays  of  light  that  may  be  reflected  within 
the  eye,  and  prevents  their  being  thrown  again  upon  the  retina  so  as  to 
interfere  with  the  images  there  formed.  The  pigment  of  the  retina  is 
especially  important  in  this  respect;  for  with  the  exception  of  its  outer 
layer  the  retina  is  very  transparent,  and  if  the  surface  behind  it  were  not 
of  a  dark  color,  but  capable  of  reflecting  the  light,  the  luminous  rays 
which  had  already  acted  on  the  retina  would  be  reflected  again  through 
it,  and  would  fall  upon  other  parts  of  the  same  membrane,  producing 
both  dazzling  from  excessive  light,  and  indistinctness  of  the  images. 

5.  Chromaiic  Aherration. — In  the  passage  of  light  through  an  ordi- 
nary convex  lens,  decomposition  of  each  ray  into  its  elementary  colored 
part,  commonly  ensues,  and  a  colored  margin  appears  around  the  image, 
owing  to  the  unequal  refraction  which  the  elementary  colors  undergo. 
In  optical  instruments  this,  which  is  termed  chromatic  aberration^  is  con- 
nected by  the  use  of  two  or  more  lenses,  differing  in  shape  and  density, 
the  second  of  which  continues  or  increases  the  refraction  of  the  rays 
produced  by  the  first,  but  by  recombining  the  individual  parts  of  each 
ray  into  its  original  white  light,  corrects  any  chromatic  aberration  which 
may  have  resulted  froin  ^le  first.  It  is  probable  that  the  unequal  refrac- 
tive power  of  the  transparent  media  in  front  of  the  retina  may  be  the 
means  by  which  the  eye  is  enabled  to  guard  against  the  effect  of  chromatic 
aberration.  The  human  eye  is  achromatic,  however,  only  so  long  as 
the  image  is  received  at  its  focal  distance  upon  the  retina,  or  so  long  as 
the  eye  adapts  itself  to  the  different  distances  of  sight.  If  either  of 
these  conditions  be  interfered  with,  a  more  or  less  distinct  appearance 
of  colors  is  produced. 

An  ordinary  ray  of  white  light  in  passing  through  a  prism,  is  refract- 
ed, i.e.,  bent  out  of  its  course,  but  the  different  colored  rays  which  go 
to  make  up  white  light  are  refracted  in  different  degrees,  and  therefore 
appear  as  colored  bands  fading  off  into  each  other:  thus  a  colored  band 
known  as  the  "spectrum"  is  produced,  the  colors  of  which  are  arranged 
as  follows — red,  orange,  yellow,  green,  blue,  indigo,  violet;  of  these 
46 


722  HANDBOOK    OF    PHYSIOLOGY. 

the  red  ray  is  the  least,  and  the  violet  the  most  refracted.  Hence,  as 
Helmholtz  has  shown,  a  small  white  object  cannot  be  accurately  focussed 
on  the  retina,  for  if  we  focus  for  the  red  rays,  the  violet  are  out  of  focus, 
and  vice  versa :  such  objects,  if  not  exactly  focussed,  are  often  seen  sur- 
rounded by  a  pale  yellowish  or  bluish  fringe. 

For  similar  reasons  a  red  surface  looks  nearer  than  a  blue  one  at  an 
equal  distance,  because,  the  red  rays  being  less  refrangible,  a  stronger 
effort  of  accommodation  is  necessary  to  focus  them,  and  the  eye  is  adjusted 
as  if  for  a  nearer  object,  and  therefore  the  red  surface  appears  nearer. 

From  the  insufficient  adjustment  of  the  image  of  a  small  white  ob- 
ject, it  appears  surrounded  by  a  sort  of  halo  or  fringe.  This  phenom- 
enon is  termed  Irradiation.  It  is  from  this  reason  that  a  white  square 
on  a  black  ground  appears  larger  than  a  black  square  of  the  same  size  on 
a  white  ground. 

As  an  optical  instrument,  the  eye  is  superior  to  the  camera  in  the 
following,  among  many  other  particulars,  which  may  be  enumerated  in 
detail.  1.  The  correctness  of  images  even  in  a  large  field  of  view.  2. 
The  simplicity  and  efficiency  of  the  means  by  which  chromatic  aberra- 
tion is  avoided.  3.  The  perfect  efficiency  of  its  adaptation  to  different 
distances.  In  the  photographic  camera,  it  is  well  known  that  only  a  com- 
paratively small  object  can  be  accurately  focussed.  In  the  photograph 
of  a  large  object  near  at  hand,  the  upper  and  lower  limits  are  always 
more  or  less  hazy,  and  vertical  lines  appear  curved.  This  is  due  to  the 
fact  that  the  image  produced  by  a  convex  lens  is  really  slightly  curved  and 
can  only  be  received  without  distortion  on  a  slightly  curved  concave 
screen,  hence  the  distortion  on  a  flat  surface  of  ground  glass.  It  is 
different  with  the  eye,  since  it  possesses  a  concave  background,  upon 
which  the  field  of  vision  is  depicted,  and  with  which  the  curved  form  of 
the  image  coincides  exactly.  Thus,  the  defect  of  the  camera  obscura 
is  entirely  avoided;  for  the  eye  is  able  to  embrace  a  large  field  of  vision, 
the  margins  of  which  are  depicted  distinctly  and  without  distortion.  If 
the  retina  had  a  plane  surface  like  the  ground  glass  plate  in  a  camera, 
it  must  necessarily  be  much  larger  than  is  really  the  case  if  we  were  to 
see  as  much;  moreover,  the  central  portion  of  the  field  of  vision  alone 
would  give  a  good  clear  picture  (Bernstein). 

Defective  Acco7nmodation — PresTjyopia. — This  condition  is  due  to  the 
gradual  loss  of  the  power  of  accommodation  which  is  part  of  the  general 
decay  of  old  age.  In  consequence  the  patient  would  be  obliged  in  read- 
ing to  hold  his  book  further  and  further  away  in  order  to  focus  the 
letters,  till  at  last  the  letters  are  held  too  far  for  distinct  vision.  The 
defect  is  remedied  by  weak  convex  glasses,  which  are  very  commonly 
worn  by  old  people.  It  is  due  chiefly  to  the  gradual  increase  in  density 
of  the  lens,  which  is  unable  to  swell  out  and  become  convex  when  near 


THE    SENSES.  723 

objects  are  looked  at,  and  also  to  a  weakening  of  the  ciliary  muscle,  and 
a  general  loss  of  elasticity  in  the  parts  concerned  in  the  mechanism. 

Visual  Sensations. 

Excitation  of  the  Retina. — Light  is  the  normal  agent  in  the  ex* 
citation  of  the  retina.  Tlie  onl}'  layer  of  the  retina  capable  of  reacting 
to  the  stimulus  is  the  rods  and  cones.  The  proofs  of  this  statement 
may  be  summed  up  thus: — 

(1.)  The  point  of  entrance  of  the  optic  nerve  into  the  retina,  where 
the  rods  and  cones  arc  absent,  is  insensitive  to  light  and  is  called  the 
hlind  spot.  The  phenomenon  itself  is  very  readily  demonstrated.  If 
we  diret^t  one  eye,  the  other  being  closed,  upon  a  point  at  such  a  dis- 
tance to  the  side  of  any  object,  that  the  image  of  the  latter  must  fall 
upon  the  rotiiia  at  the  point  of  entrance  of  the  optic  nerve,  this  image 
is  lost  eitlier  instantaneously,  or  very  soon.  If,  for  example,  we  close  the 
left  eye,  and  direct  the  axis  of  the  right  eye  steadily  toward  the  circular 


spot  here  represented,  while  the  page  is  held  at  a  distance  of  about  six 
inches  from  tlic  eye,  both  dot  and  cross  are  visible.  On  gradually  in- 
creasing the  distance  between  the  eye  and  the  object,  by  removing  the 
book  farther  and  farther  from  the  face,  and  still  keeping  the  right  eye 
steadily  on  the  dot,  it  will  be  found  that  suddenly  the  cross  disappears 
from  view,  wliile  on  removing  the  book  still  farther,  it  suddenly  comes 
in  sight  again.  The  cause  of  this  i^henomenon  is  simply  that  the  por- 
tion of  retina  which  is  occupied  by  the  entrance  of  the  optic  nerve,  is 
quite  blind;  and  therefore  that  when  it  alone  occupies  the  field  of  vision, 
ol)jects  cease  to  be  visible.  (2.)  In  the  fovea  centralis  and  macula 
lutea  Avhich  contain  rods  and  cones  but  no  optic  nerve-fibres,  light  pro- 
duces tlie  greatest  effect.  In  the  latter,  cones  occur  in  large  numbers, 
and  in  the  former  cones  without  rods  are  fouiul,  whereas  in  the  rest  of  the 
retina  which  is  not  so  sensitive  to  light,  there  are  fewer  cones  than  rods. 
We  may  conclude,  therefore,  that  cones  are  even  more  important  to 
vision  thnn  rods.  (3.)  If  a  small  lighted  candle  be  moved  to  and  fro 
at  tlie  side  of  and  close  to  one  eye  in  a  dark  room  while  the  eyes 
look  steadily  forward  into  the  darkness,  a  remarkable  braiu'hing 
figure  {P N rkitije' s  fit/nrt's)  is  seen  floating  before  the  eye,  consisting  of 
dark  lines  on  n  reddish  ground.  As  the  candle  moves,  the  figure  moves 
in  the  opposite  direction,  and  from  its  whole a]ipearance  there  can  be  no 
doubt  that  it  is  a  reversed  ])icture  of  the  retinal  vessels  projected  before 
the  eye.  The  two  large  branching  arteries  passing  up  and  down  from 
the  optic  disc  are  clearly  visible  together  with  their  minutest  branches. 


724  HANDBOOK    OF   PHYSIOLOGY. 

A  little  to  one  side  of  the  disc,  in  a  part  free  from  vessels,  is  seen  the 
yellow  spot  in  the  form  of  a  slight  depression.  This  remarkable  appear- 
ance is  due  to  shadows  of  the  retinal  vessels  cast  by  the  candle.  The 
branches  of  these  vessels  are  chiefly  distributed  in  the  nerve-fibre  and 
ganglionic  layers;  and  since  the  light  of  the  candle  falls  on  the  retinal 
vessels  from  in  front,  the  shadow  is  cast  behind  them,  and  hence  those 
elements  of  the  retina  which  perceive  the  shadows  must  also  lie  behind 
the  vessels.  Here,  then,  we  have  a  clear  proof  that  the  light-perceiving 
elements  of  the  retina  are  not  the  fibres  of  the  optic  nerve  forming  the 
innermost  layer  of  the  retina,  but  the  external  layers  of  the  retina,  rods 
and  cones,  which  indeed  appear  to  be  the  special  terminations  of  the 
optic  nerve-fibres. 

Duration  of  Visual  Sensations. — The  duration  of  the  sensation  pro- 
duced by  a  luminous  impression  on  the  retina  is  always  greater  than  that 
of  the  impression  which  produces  it.  However  brief  the  luminous  imj^res- 
sion,  the  effect  on  the  retina  always  lasts  for  about  one-eighth  of  a  second. 
Thus,  supposing  an  object  in  motion,  say  a  horse,  to  be  revealed  on  a 
dark  night  by  a  flash  of  lightning.  The  object  would  be  seen  apparently 
for  an  eighth  of  a  second,  but  it  would  not  appear  in  motion;  because, 
although  the  image  remained  on  the  retina  for  this  time,  it  was  really 
revealed  for  such  an  extremely  short  period  (a  flash  of  lightning  being 
almost  instantaneous)  that  no  appreciable  movement  on  the  part  of 
the  object  could  have  taken  place  in  the  period  during  which  it  was 
revealed  to  the  retina  of  the  observer.  And  the  same  fact  is  proved  in  a 
reverse  way.  The  spokes  of  a  rapidly  revolving  wheel  are  not  seen  as 
distinct  objects,  because  at  every  point  of  the  field  of  vision  over  which 
the  revolving  spokes  pass,  a  given  impression  has  not  faded  before  another 
comes  to  replace  it.  Thus  every  part  of  the  interior  of  the  wheel 
appears  occupied. 

The  duration  of  the  after-sensation,  produced  by  an  object,  is  greater 
in  a  direct  ratio  with  the  duration  of  the  impression  which  caused  it. 
Hence  the  image  of  a  bright  object,  as  of  the  panes  of  a  window  through 
which  the  light  is  shining,  may  be  perceived  in  the  retina  for  a  con- 
siderable period,  if  we  have  previously  kei)t  our  eyes  fixed  for  some  time 
on  it.  But  the  image  in  this  case  is  negative.  If,  however,  after 
shutting  the  eyes  for  some  time,  we  open  them  and  look  at  an  object  for 
an  instant,  and  again  close  them,  the  after-image  \s  positive. 

Intensity  of  Visual  Sensations. — It  is  quite  evident  that  the  more 
luminous  a  body  the  more  intense  is  the  sensation  it  produces.  But  the 
intensity  of  the  sensation  is  not  directly  proportional  to  the  intensity 
of  the  luminosity  of  the  object.  It  is  necessary  for  light  to  have  a  cer- 
tain intensity  before  it  can  excite  the  retina,  but  it  is  impossible  to  fix  an 
arbitrary  limit  to  the  power  of  excitability.     As  in  other  sensations,  so 


THE   SENSES.  725 

also  in  visual  sensations,  a  stimulus  may  be  too  feeble  to  produce  a  sen- 
sation. If  it  be  increased  in  amount  sufficiently  it  begins  to  produce  an 
effect  which  is  increased  on  the  increase  of  the  stimulation;  tliis  in- 
crease in  the  effect  is  not  direclly  proportional  to  the  increase  in  the 
excitation,  but,  according  to  Fcclmcr's  laiv,  "  as  the  logarithm  of  the 
stimulus,"  i.e.,  in  each  sensation,  there  is  a  constant  ratio  between  the 
increase  in  the  stimulus  and  the  increase  in  the  sensation,  this  constant 
ratio  for  each  sensation  expresses  the  least  perceptible  increase  in  the 
sensation  or  minimal  increment  of  excitation. 

This  law,  which  is  true  only  within  certain  limits,  may  be  best 
understood  by  an  example.  When  the  retina  has  been  stimulated  by  the 
liglit  of  one  candle,  the  light  of  two  candles  will  produce  a  difEerence  in 
sensation  which  can  be  distinctly  felt.  If,  however,  the  first  stimulus 
had  been  that  of  an  electric  light,  the  addition  of  the  light  of  a  candle 
would  make  no  difference  in  the  sensation.  So,  generally,  for  an  addi- 
tional stimulus  to  be  felt,  it  may  be  joroportionately  small  if  the  original 
stimulus  have  been  small,  and  must  be  greater  if  the  original  stimulus 
have  been  great.  The  stimulus  increases  as  the  ordinary  numbers,  while 
the  sensation  increases  as  the  logarithm. 

Part  of  the  light  which  enters  the  eye  is  absorbed  and  produces  some 
change  in  the  retina,  of  which  we  shall  treat  further  on;  the  rest  is 
reflected. 

Every  one  is  perfectly  familiar  with  the  fact,  that  it  is  quite  imjDos- 
sible  to  see  the  fundus  or  back  of  another  person's  eye  by  simply  looking 
into  it.  The  interior  of  the  eye  forms  a  perfectly  black  background  to 
the  pupil.  The  same  remark  applies  to  an  ordinary  photographic 
camera,  and  may  be  illustrated  by  the  difficulty  we  experience  in  seeing 
into  a  room  from  the  street  through  the  window,  unless  the  room  be 
lighted  within.  In  the  case  of  the  eye  this  fact  is  partly  due  to  the 
feebleness  of  the  light  reflected  from  the  retina,  most  of  it  being  absorbed 
by  the  retinal  pigment,  as  mentioned  above;  but  far  more  to  the  fact  that 
every  such  ray  is  reflected  straight  to  the  source  of  light  {e.g.,  candle),  and 
cannot,  therefore,  be  seen  by  the  unaided  eye  without  intercepting  the 
incident  light  from  the  candle,  as  well  as  the  reflected  rays  from  the 
retina.     This  difficulty  is  surmounted  by  the  use  of  the  ophthahnoscope. 

The  ophthalmoscope,  broufi;ht  iuto  use  by  Helmholtz,  consists  in  its  simplest 
form  of  a,  a  sliglitly  concave  mirror  of  metal  or  silvered  glass  perforated  in 
the  centre,  and  fixed  into  a  liandle ;  and  b,  a  biconvex  lens  of  about  2\-8  inches 
focal  length.  Two  methods  of  examining  the  eye  witli  this  instrument  are  in 
common  use — the  direct  and  the  indirect:  both  methods  of  investigation  should 
be  employed.  A  normal  eye  should  be  examined ;  a  drop  of  a  solution  of  atro- 
pia  (two  grains  to  the  ounce)  or  of  homatropia  hydrobromate,  should  be  in- 
stilled about  twenty  minutes  before  the  examination  is  commenced  ;  the  ciliary 
muscle  is  thereby  paralyzed,  the  power  of  accommodation  is  abolished,  and  the 


726 


HANDBOOK   OF    PHYSIOLOGY. 


pupil  is  dilated.  This  will  materially  facilitate  the  examination ;  but  it  is 
quite  possible  to  observe  all  the  details  to  be  presently  described  without  the  use 
of  this  drug.  The  room  being  now  darkened,  the  observer  seats  liimself  in  front 
of  the  pei'son  whose  eye  he  is  about  to  examine,  placing  himself  upon  a  some- 
what higher  level.  A  brilliant  and  steady  light  is  placed  close  to  the  left  ear 
of  the  patient.  The  atropia  having  been  put  into  the  right  eye  only  of  the  pa- 
tient, this  eye  is  examined.  Taking  the  mirror  in  his  right  hand,j,and  looking 
through  the  central  hole,  the  operator  directs  a  beam  of  light  into  the  eye  of 


Fig.  429. — Diagram  to  illustrate  the  action  of  the  Ophthalmoscope,  when  a  plane  concave 
glass  is  used.  c.  observer's  eye.  The  light  reflected  from  any  point,  d,  on  retina  of  a,  would 
naturally  be  focussed  at  e;  if  the  lens  b  is  used  it  would  be  focussed  at  j,  in  other  words,  at 
back  of  c.  The  image  would  be  enlarged,  as  though  of  g,  and  would  be  inverted.  (After  Mc- 
Gregor Robertson.) 

the  patient.  A  red  glare,  known  as  the  reflex,  is  seen  ;  it  is  due  to  the  illumi- 
nation of  the  retina.  The  patient  is  then  told  to  look  at  the  little  finger  of  the 
observer's  right  hand  as  he  holds  the  mirror ;  to  effect  this  the  eye  is  rotated 
somewhat  inward,  and  at  the  same  time  the  reflex  changes  fi-om  red  to  a 
lighter  color,  owing  to  the  reflection  from  the  o^jtic  disc.  The  observer  now 
approximates  the  mirror,  and  with  it  his  eye  to  the  eye  of  the  patient,  taking 
care  to  keep  the  light  fixed  upon  the  pupil,  so  as  not  to  lose  the  reflex.  At  a 
certain  point,  which  varies  with  diff'erent  eyes,  but  is  usually  when  there  is  an 
interval  of  about  two  or  three  inches  between  the  observed  and  the  observing 
eye,  the  vessels  of  the  retina  will  become  visible  as  lines  running  in  diff'erent 
directions.  Distinguish  the  smaller  and  brighter  red  arteries  from  the  larger 
and  darker  colored  veins.  Examine  carefully  the  fundus  of  the  eye,  i.e.,  the 
red  surface — until  the  optic  disc  is  seen ;  trace  its  circular  outline,  and  observe 


Fig.  430.— Diagram  to  illustrate  action  of  ophthalmoscope  when  a  bi-convex  glass  is  used. 
The  fig.  d  on  retina  of  a  is  under  ordinary  conditions  focussed  at  /  and  inverted.  If  the  lens  b 
be  placed  between  eyes,  the  image  h  is  seen  by  the  eye  c  as  an  enlarged  image.  (After  McGregor 
Robertson.) 

the  small  central  white  spot,  the  porus  opticus,  physiological  pit:  near  the 
centre  is  the  central  artery  of  the  retina  breaking  up  upon  the  disc  into  branches ; 
veins  also  are  present,  and  correspond  roughly  to  the  course  of  the  arteries. 
Trace  the  vessels  over  the  disc  on  to  the  retina.  The  optic  disc  is  bounded  by 
two  delicate  rings,  the  more  external  being  the  choroidal,  while  the  more  in- 
ternal is   the  sclerotic  opening.     Somewhat  to  the  outer  side,  and  only  visible 


THE   SENSES. 


727 


after  some  practice,  is  the  yelloiv  spot,  with  the  smaller  lighter-colored  fovea 
centralis  in  its  centre.     This  constitutes  the  direct  method  of  examination  (fig. 
429)  ;  by  it  the  various  details  of  the  fundus  are  seen 
as  they  really  exist,  and   it   is  this  method   which 
should  be  adopted  for  ordinary  use. 

If  the  observer  is  ameti-opic,  i.e.,  is  myopic  or 
hypermeti'opic,  he  will  be  unable  to  employ  the 
direct  method  of  examination  until  he  has  remedied 
his  defective  vision  by  the  use  of  proper  glasses. 

In  the  indirect  method  (fig.  430)  the  patient  is 
placed  as  before,  and  the  operator  holds  the  mirror 
in  his  right  hand  at  a  distance  of  twelve  to  eighteen 
inches  from  the  patient's  right  eye.  At  the  same 
time  he  rests  his  left  little  finger  lightly  upon  the 
right  temple,  and  holding  the  lens  between  his 
thumb  and  forefinger,  two  or  three  inches  in  front 
of  the  patient's  eye,  dii'ects  the  light  through  the 
lens  into  the  eye.  The  red  reflex,  and  subsequently 
the  white  one,  having  been  gained,  the  operator 
slowly  moves  his  mirror,  and  with  it  his  eye,  toward 
or  away  from  the  face  of  the  patient,  until  the  out- 
line of  one  of  the  retinal  vessels  becomes  visible, 
when  very  slight  movements  on  the  part  of  the 
operator  will  suflice  to  bring  into  view  the  details 
of  the  fundus  above  described,  but  the  image  will 
be  much  smaller  and  inverted.  The  lens  should  be 
kept  fixed  at  a  distance  of  two  or  three  inches,  the 
mirror  being  alone  moved  until  tlie  disc  becomes 
visible  :  should  the  image  of  the  mirror,  however, 
obscure  the  disc,  the  lens  may  be  slightly  tilted. 


Fig.  4;il.— The  ophthalmo- 
scope. The  small  upper  mir- 
ror is  for  direct,  the  larger 
for  indirect  illumination. 


Visual  Purple. — Tlie  method  by  Avhicli  a  ray  of  light  is  able  to 
stiniuhite  the  endiugs  of  the  optic  nerve  in  the  retina  in  such  a  manner 
that  a  visual  sensation  is  jierceived  by  the  cerebrum  is  not  yet  under- 
stood. It  is  su2i]>osed  that  the  change  effected  by  the  agency  of  the 
light  which  falls  upon  the  retina  is  in  fact  a  chemical  alteration  in  the 
protoplasm,  and  that  this  change  stimulates  the  optic  nerve-endings. 
The  discovery  of  a  certain  temporary  reddish-purple  pigmentation  of  the 
outer  limbs  of  the  retinal  rods  in  certain  animals  (ef^.,  frogs)  which  had 
been  killed  in  the  dark,  forming  the  so-called  rJtodop.sin  or  visual  purple, 
appeared  likely  to  offer  some  explanation  of  the  matter,  especially  as  it 
was  also  found  that  the  pigmentation  disappeared  when  the  retina  was 
exposed  to  light,  and  reappeared  when  the  light  was  removed,  and  also 
that  it  underwent  distinct  changes  of  color  when  other  than  Avhite 
light  was  used.  It  was  also  found  that  if  the  operation  were  performed 
quickly  enough,  the  image  of  an  object  {optogram)  might  be  fixed  in  the 
pigment  on  the  retina  by  soaking  the  retina  of  an  animal,  which  has 
been  killed  in  the  dark,  in  alum  solution. 


728  HANDBOOK    OF    PHYSIOLOGY. 

The  visual  purple  cannot  however  be  absolutely  essential  to  the  due 
production  of  visual  sensations,  as  it  is  absent  from  the  retinal  cones, 
and  from  the  macula  lutea  and  fovea  centralis  of  the  human  retina,  and 
does  not  appear  to  exist  at  all  in  the  retinee  of  some  animals,  e.g.,  bat, 
dove,  and  hen,  which  are,  nevertheless,  possessed  of  good  vision. 

However  the  fact  remains  that  light  falling  upon  the  retina  {a) 
bleacltes  the  visual  jnirple,  and  this  must  be  considered  as  one  of  its  effects. 
It  bas  been  found  that  certain  pigments,  also  sensitive  to  light,  are  con- 
tained in  the  inner  segments  of  the  cones.  These  colored  bodies  are  said 
to  be  oil  globules  of  various  colors,  red,  green,  and  yellow,  called  chromo- 
pluines.,  and  are  found  only  in  the  retinas  of  animals  not  mammals.  The 
rhodopsin  at  any  rate  appears  to  be  derived  in  some  way  from  the  retinal 
pigment,  since  the  color  is  not  renewed  after  bleaching  if  the  retina  be 
detached  from  its  pigment  layer,  {h)  Tbe  second  change  produced  by 
the  action  of  the  light  u]3on  the  retina  is  the  movement  of  the  pigment 
cells.  On  the  stimulation  of  light  the  granules  of  pigment  in  the  cells 
which  overlie  the  outer  part  of  the  rod  and  cone  layer  of  the  retina 
become  diffused  in  the  parts  of  the  cells  between  the  rods  and  cones,  the 
melanin  or /M6"Ci7^  granules,  as  they  are  called,  passing  down  into  the  pro- 
cesses of  tbe  cells,  (c)  A  movement  of  the  cones  and  possibly  of  the  rods 
is  also  said  to  occur,  as  has  been  already  incidentally  mentioned;  on  tbe 
stimulus  of  light  the  outer  parts  of  the  cones,  which  in  an  eye  protected 
from  light  extend  to  the  pigment  layer,  are  retracted.  It  is  even 
thought  that  the  contraction  is  under  the  control  of  the  nervous  system; 
and  finally,  according  to  the  careful  researches  of  Dewar  and  McKen- 
drick,  and  of  Holmgren,  it  aj^pears  that  the  stimulus  of  light  is  able  to 
produce  {d)  a  variation  of  the  natural  electrical  currents  of  the  retina. 
The  current  is  at  first  increased  and  then  diminished.  McKendrick 
believes  that  this  is  the  electrical  expression  of  those  chemical  changes 
in  the  retina  of  which  we  have  already  spoken. 

Visual  Pekceptions  and   Judgments. 

Reversion  of  the  Image. — It  will  be  as  well  to  repeat  here  that 
the  direction  given  to  the  rays  by  their  refraction  is  regulated  by  that 
of  the  central  ray,  or  axis  of  the  cone,  toward  which  the  rays  are  bent. 
The  image  of  any  point  of  an  object  is,  therefore,  as  a  rule  (the  exceptions 
to  which  need  not  here  be  stated),  always  formed  in  a  line  identical  with 
the  axis  of  the  cone  of  light,  as  in  the  line  of  b  ^,  or  a  a  (fig.  432),  so  that 
the  spot  where  the  image  of  any  point  will  be  formed  upon  the  retina 
may  be  determined  by  prolonging  the  central  ray  of  the  cone  of  light, 
or  that  ray  which  traverses  the  centre  of  the  pupil.  Thus  a  a  is  the 
axis  or  central  ray  of  the  cone  of  light  issuing  from  a;  b  b  the  central 


THE    SENSES.  729 

ray  of  the  cone  of  light  issuing  from  b;  the  image  of  a  is  formed  at  a, 
the  image  of  jj  at  /j,  in  the  inverted  position:  therefore  what  in  the  ob- 
ject was  above  is  in  the  image  below,  and  vice  versa, — the  right-hand 
part  of  the  object  is  in  the  image  to  the  left,  the  left-hand  to  the  right. 
If  an  upening  be  made  in  an  03-0  at  its  superior  surface,  so  that  the 
retina  can  be  seen  tlii'inigh  tlie  vitreous  liuinor,  this  image  of  any  bright 
object,  such  as  the  windows  of  the  room,  maybe  perceived  inverted  upon 
the  retina.  Or  still  better,  if  the  eye  of  any  albino  animal,  such  as  a 
white  rabbit,  in  which  the  coats,  from  the  absence  of  pigment,  are  trans- 
parent, is  dissected  clean,  and  held  with  the  cornea  toward  the  window, 
a  very  distinct  image  of  the  window  completely  inverted  is  seen  depicted 
on  the  posterior  translucent  wall  of  the  eye.      Volkmann  has  also  shown 


Fig    432.— Diagram  of  the  formation  of  the  image  on  the  retina. 

that  a  similar  experiment  may  be  successfully  performed  in  a  living  per- 
son possessed  of  large  prominent  eyes,  and  an  unusually  transjiarent 
sclerotic. 

An  image  formed  at  any  point  on  the  retina  is  referred  to  a  point 
outside  the  eye,  lying  on  a  straight  line  drawn  from  the  point  on  the 
retina  outward  through  the  centre  of  the  pupil.  Thus  an  image  on  the 
left  side  of  the  retina  is  referred  by  the  mind  to  an  object  on  the  right 
side  of  the  eye,  and  vice  versa.  Thus  all  images  on  the  retina  are  men- 
tally, as  it  were,  projected  in  front  of  the  eye,  and  the  objects  are  seen 
erect  though  the  image  on  the  retina  is  inverted.  Much  needless  con- 
fusion and  ditticulty  have  been  raised  on  this  subject  for  want  of  re- 
membering that  when  Ave  are  said  to  see  an  object,  the  mini  is  merely 
conscious  of  the  picture  on  the  retina,  and  when  it  refers  it  to  the  ex- 
ternal object,  or  "  projects"  it  outside  the  eye,  it  necessarily  reverses  it 
and  sees  the  object  as  erect,  though  the  retinal  image  is  inverted. 
This  is  further  corroborated  by  the  sense  of  touch.  Thus  an  object 
whose  picture  falls  on  the  left  half  of  the  retina  is  reached  by  the  right 
hand,  and  hence  is  said  to  lie  to  the  right.  Or,  again,  an  object  whose 
image  is  formed  on  the  upper  part  of  the  retina  is  readily  touched  by 
the  feet,  and  is  therefore  said  to  be  in  the  lower  jiart  of  the  field,  and 
so  on. 

Hence  it  is  also,  that  no  discordance  arises  between  the  sensations  of 
inverted  vision  and   those  of  touch,  which  perceives  everything  in  its 


730  HAifDBOOK    OF    PHYSIOLOGY. 

erect  position;  for  the  images  of  all  objects,  even  of  our  own  limbs,  on 
the  retina,  are  equally  inverted,  and  therefore  maintain  the  same  rela- 
tive position. 

Even  the  image  of  our  hand,  while  used  in  touch,  is  seen  inverted. 
The  position  in  which  we  see  objects,  we  call,  therefore,  the  erect  posi- 
tion. A  mere  lateral  inversion  of  our  body  in  a  mirror,  where  the  right 
hand  occupies  the  left  of  the  image,  is  indeed  scarcely  remarked :  and 
there  is  but  little  discordance  between  the  sensations  acquired  by  touch 
in  regulating  our  movements  by  the  image  in  the  mirror,  and  those  of 
sight,  as,  for  example,  in  tying  a  knot  in  the  cravat.  There  is  some 
want  of  harmony  here,  on  account  of  the  inversion  being  only  lateral, 
and  not  complete  in  all  directions. 

The  perception  of  the  erect  position  of  objects  appears,  therefore,  to 
be  the  result  of  an  act  of  the  mind.  And  this  leads  us  to  a  consideration 
of  the  several  other  properties  of  the  retina,  and  of  the  co-opei'ation  of 
the  mind  in  the  several  other  parts  of  the  act  of  vision.  To  these  belong 
not  merely  the  act  of  sensation  itself  and  the  perception  of  the  changes 
produced  in  the  retina,  as  light  and  colors,  but  also  the  conversion  of  the 
mere  images  depicted  in  the  retina  into  ideas  of  an  extended  field  of 
vision,  of  proximity  and  distance,  of  the  form  and  size  of  objects,  of  the 
reciprocal  influence  of  different  parts  of  the  retina  upon  each  other,  the 
simultaneous  action  of  the  two  eyes,  and  some  other  phenomena. 

Field  of  Vision. — The  actual  size  of  the  field  of  vision  depends  on 
the  extent  of  the  retina,  for  only  so  many  images  can  be  seen  at  any  one 
time  as  can  occupy  the  retina  to  the  same  time;  and  thus  considered, 
the  retina,  the  conditions  of  which  are  perceived  by  the  brain,  is  itself 
the  field  of  vision.  But  to  the  mind  of  the  individual  the  size  of  the 
field  of  vision  has  no  determinate  limits;  sometimes  it  appears  very 
small,  at  another  time  very  large;  for  the  mind  has  the  power  of  pro- 
jecting images  on  the  retina  toward  the  exterior.  Hence  the  mental 
field  of  vision  is  very  small  when  the  sphere  of  the  action  of  the  mind  is 
limited  to  impediments  near  the  eye:  on  the  contrary,  it  is  very  exten- 
sive when  the  projection  of  the  images  on  the  retina  toward  the  exterior, 
by  the  influence  of  the  mind,  is  not  impeded.  It  is  very  small  when 
we  look  into  a  hollow  body  of  small  capacity  held  before  the  eyes;  large 
when  we  look  out  upon  the  landscape  through  a  small  opening;  more  ex- 
tensive when  we  look  at  the  landscape  through  a  window ;  and  most  so 
when  our  view  is  not  confined  by  any  near  object.  In  all  these  cases  the 
idea  which  we  receive  of  the  size  of  the  field  of  vision  is  very  different, 
although  its  absolute  size  is  in  all  the  same,  being  dependent  on  the  ex- 
tent of  the  retina.  Hence  it  follows,  that  the  mind  is  constantly  co- 
operating in  the  acts  of  vision,  so  that  at  last  it  becomes  difficult  to  say 
what  belongs  to  mere  sensation,  and  what  to  the  influence  of  the  mind. 


THE   SENSES.  731 

By  a  mental  operation  of  this  kind,  we  obtain  a  correct  idea  of  the  size 
of  individual  objects,  as  well  as  of  the  extent  of  the  field  of  vision. 
To  illustrate  this,  it  will  be  well  to  refer  to  fig.  433. 

The  angle  a:,  included  between  the  decussating  central  raj^s  of  two 
cones  of  light  issuing  from  dilferent  points  of  an  object,  is  called  the 


/I, 
T 

y 

'  h 

Fig.  43:3. 

optical  angle — angulus  opticus  sen  visorius.  This  angle  becomes  larger, 
the  greater  the  distance  between  the  points  a  and  b;  and  since  the  angles 
X  and  y  are  equal,  the  distance  between  the  points  a  and  h  in  the  image 
on  the  retina  increases  as  the  angle  becomes  larger.  Objects  at  dilferent 
distances  from  the  eye,  but  having  the  same  optical  angle  x — for  exam- 
ple, the  objects,  c,  d,  and  e, — must  also  throw  images  of  equal  size  \\])on 
the  retina;  and,  if  they  occupy  the  same  angle  of  the  field  of  vision, 
their  image  must  occupy  the  same  spot  in  the  retina. 

Nevertheless,  these  images  appear  to  the  mind  to  be  of  very  unequal 
size  when  the  ideas  of  distance  and  proximity  come  into  play;  for,  from 
the  image  a  b,  the  mind  forms  the  conception  of  a  visual  space  extend- 
ing to  e,  d,  or  c,  and  of  an  object  of  the  size  which  that  represented  by 
the  image  on  tlie  retina  appears  to  have  when  viewed  close  to  the  e3'e,  or 
under  the  most  usual  circumstances. 

Estimation  of  Size. — Our  estimate  of  the  size  of  various  objects  is 
based  partly  on  the  visual  augle  under  which  they  are  seen,  but  much 
more  on  the  estimate  we  form  of  their  distance.  Thus  a  lofty  mountain 
many  miles  off  may  be  seen  under  the  same  visual  augle  as  a  small  hill 
near  at  hand,  but  we  infer  that  the  former  is  mucli  the  larger  object 
because  we  know  it  is  much  further  off"  than  the  hill.  Our  estimate  of 
distance  is  often  erroneous,  and  cousequeutly  the  estimate  of  size  also. 
Thus  persons  seen  walking  on  the  top  of  a  small  hill  againts  a  clear 
twilight  sky  ajipear  unusually  large,  because  we  over-estimate  their  dis- 
tance, and  for  similar  reasons  most  objects  in  a  fog  appear  immensely 
magnified.  The  same  mental  process  gives  rise  to  the  idea  of  depth  in 
the  field  of  vision;  this  idea  being  fixed  in  our  mind  principally  by  the 
circumstance  that,  as  we  ourselves  move  forward,  different  images  in 
succession  become  depicted  on  our  retina,  so  that  we  seem  to  pass 
between  these  images,  which  to  the  uiiiul  is  the  same  thing  as  passing 
between  the  objects  themselves. 


732  HANDBOOK    OF   PHYSIOLOGY. 

The  action  of  the  sense  of  vision  in  relation  to  external  objects  is, 
therefore,  quite  different  from  that  of  the  sense  of  touch.  The  objects 
of  the  latter  sense  are  immediatel}'  present  to  it;  and  our  own  body,  with 
which  they  come  in  contact,  is  the  measure  of  their  size.  The  part  of 
a  table  touched  by  the  hand  appears  as  large  as  the  part  of  the  hand 
receiving  an  impression  from  it,  for  a  part  of  our  body  in  which  a  sensa- 
tion is  excited,  is  here  the  measure  by  which  we  judge  of  the  magnitude 
of  the  object.  In  the  sense  of  vision,  on  the  contrary,  the  images  of  ob- 
jects are  mere  fractions  of  the  objects  themselves  realized  upon  the 
retina,  the  extent  of  which  remains  constantly  the  same.  But  the  imagina- 
tion, which  analyzes  the  sensations  of  vision,  invests  the  images  of  ob- 
jects, together  with  the  whole  field  of  vision  in  the  retina,  with  very 
varying  dimensions;  the  relative  size  of  the  image  in  proportion  to  the 
whole  field  of  vision,  or  of  the  afPected  parts  of  the  retina  to  the  whole 
retina,  alone  remaining  unaltered. 

Estimation  of  Direction. — The  direction  in  which  an  object  is 
seen,  depends  on  the  part  of  the  retina  which  receives  the  image,  and  on 
the  distance  of  this  part  from,  and  its  relation  to,  the  central  point  of 
the  retina.  Thus,  objects  of  which  the  images  fall  upon  the  same  parts 
of  the  retina  lie  in  the  same  visual  direction;  and  when,  by  the  action 
of  the  mind,  the  images  or  affections  of  the  retina  are  projected  into  the 
exterior  world,  the  relation  of  the  images  to  each  other  remains  the 
same. 

Estimation  of  Form. — The  estimation  of  the  form  of  bodies  by 
sight  is  the  result  partly  of  the  mere  sensation,  and  partly  of  the  associ- 
ation of  ideas.  Since  the  form  of  the  images  perceived  by  the  retina 
depends  wholly  on  the  outline  of  the  part  of  the  retina  affected,  the  sen- 
sation alone  is  adequate  to  the  distinction  of  only  superficial  forms  of 
each  other,  as  of  a  square  from  a  circle.  But  the  idea  of  a  solid 
body  as  a  sphere,  or  a  body  of  three  or  more  dimensions,  e.g.,  a  cube, 
can  only  be  attained  by  the  action  of  the  mind  constructing  it  from  the 
different  superficial  images  seen  in  different  positions  of  the  eye  with 
regard  to  the  object,  and,  as  shown  by  AVheatstone  and  illustrated  in  the 
stereoscope.,  from  two  different  perspective  projections  of  the  body  being 
present  simultaneously  to  the  mind  by  the  two  eyes.  Hence,  when,  in 
adult  age,  sight  is  suddenly  restored  to  persons  blind  from  infancy,  all 
objects  in  the  field  of  vision  appear  at  first  as  if  painted  flat  on  one 
surface;  and  no  idea  of  solidity  is  formed  until  after  long  exercise  of 
the  sense  of  vision  combined  with  that  of  touch. 

The  clearness  with  which  an  object  is  perceived  irrespective  of  accom- 
modation, would  appear  to  depend  largely  on  the  number  of  rods  and 
cones  which  its  retinal  image  covers.  Hence  the  nearer  an  object  is  to 
the  eye   (within  moderate  limits)   the  more  clearly  are  all  its  details 


THE   SENSES.  733 

seen.  Moreover,  if  we  want  carefully  to  examine  any  object,  we  always 
direct  the  eyes  straight  to  it,  so  that  its  image  shall  fall  on  the  yellow 
spot  where  an  image  of  a  given  area  will  cover  a  larger  number  of  cones 
than  anywhere  else  in  the  retina.  It  has  been  found  tliat  the  images  of 
two  points  must  be  at  least  3/i  apart  on  the  yellow  spot  in  order  to  be 
distinguished  separately;  if  the  images  are  nearer  together,  the  points 
appear  as  one.  The  diameter  of  each  cone  in  this  part  of  the  retina  is 
about  3//. 

Estimation  of  Movement. — We  judge  of  the  motion  of  an  object, 
partly  from  the  motion  of  its  image  over  the  surface  of  the  retina,  and 
partly  from  the  motion  of  our  eyes  following  it.  If  the  image  upon  the 
retina  moves  while  our  eyes  and  our  body  are  at  rest,  we  conclude  that 
the  object  is  changing  its  relative  position  witli  regard  to  ourselves.  In 
such  a  case  the  movement  of  the  object  may  be  apparent  only,  as  when 
we  are  standing  upon  a  body  which  is  in  motion,  such  as  a  shijD.  If,  on 
the  other  hand,  the  image  does  not  move  with  regard  to  the  retina,  but 
remains  fixed  upon  the  same  spot  of  that  membrane,  while  our  eyes  fol- 
low the  moving  body,  we  judge  of  the  motion  of  the  object  by  the  sensa- 
tion of  the  muscles  in  action  to  move  the  eye.  If  the  image  moves  over 
the  surface  of  the  retina  while  the  muscles  of  the  eye  are  acting  at  the 
same  time  in  a  manner  corresponding  to  this  motion,  as  in  reading,  we 
infer  that  the  object  is  stationary,  and  we  know  that  we  are  merely 
altering  the  relations  of  our  eyes  to  the  object.  Sometimes  the  object 
appears  to  move  when  both  object  and  eye  are  fixed,  as  in  vertigo. 

The  mind  can,  by  the  faculty  of  attention,  concentrate  its  activity 
more  or  less  exclusively  upon  the  sense  of  sight,  hearing,  and  touch  alter- 
nately. When  exclusively  occupied  with  the  action  of  one  sense,  it  is 
scarcely  conscious  of  the  sensations  of  the  others.  The  mind,  when  deeply 
immersed  in  contemplations  of  another  nature,  is  indifferent  to  the  ac- 
tions of  the  sense  of  sight,  as  of  every  other  sense.  We  often,  when 
deep  in  thought,  have  our  eyes  open  and  fixed,  but  see  nothing,  because 
of  the  stimulus  of  ordinary  light  being  unable  to  excite  the  brain  to 
perception,  when  otherwise  engaged.  The  attention  which  is  tlius 
necessary  for  vision,  is  necessary  also  to  analyze  what  the  field  of  vision 
presents.  The  mind  does  not  perceive  all  the  objects  presented  by  the 
field  of  vision  at  the  same  time  with  equal  acuteness,  but  directs  itself 
iirst  to  one  and  then  to  another.  The  sensation  becomes  more  intense, 
according  as  the  particular  object  is  at  the  time  the  principal  object  of 
luiMital  contemplation.  Any  compound  mathematical  figure  produces  a 
dilTerent  impression  according  as  the  attention  is  directed  exclusively  to 
one  or  the  other  \v,\xt  of  it.  Thus  in  fig.  433  a,  we  may  in  succession 
have  a  vivid  jierception  of  the  whole,  or  of  distinct  parts  oidy ;  of  the 
six  triangles  near  the  outer  circle,  of  the  hexagon  in  the  middle,  of  the 


734  HA]S"DBOOK   OF   PHYSIOLOGY. 

three  large  triangles.  The  more  numerous  and  varied  the  parts  of  which 
a  figure  is  composed  the  more  scope  does  it  afford  for  the  play  of  the 
attention.     Hence  it  is  that  architectural  ornaments  have  an  enlivening 


Fig.  433  A. 

effect  on  the  sense  of  vision,  since  they  afford   constantly  fresh   subject 
for  the  action  of  the  mind. 

Color  Sensations. — If  a  ray  of  sunlight  be  allowed  to  pr.ss  tlirough 
a  prism,  it  is  decomposed  by  its  passage  into  rays  of  diiferent  colors, 
which  are  called  the  colors  of  the  spectrum;  they  are  red,  orange,  yellow, 
green,  blue,  indigo,  and  violet.  The  red  rays  are  the  least  turned  out  of 
their  course  by  the  prism,  and  the  violet  the  most,  while  the  other  colors 
occupy  in  order  places  between  these  two  extremes.  The  differences  in 
the  color  of  the  rays  depend  upon  the  number  of  vibrations  producing 
each,  the  red  rays  being  the  least  rapid  and  the  violet  the  most.  In 
addition  to  the  colored  rays  of  the  spectrum,  there  are  others  which  are 
invisible,  but  which  have  definite  properties,  those  to  the  left  of  the  red, 
and  less  refrangible,  being  the  calorific  rays  which  act  uj^on  the  ther- 
mometer, and  those  to  the  right  of  the  violet,  which  are  called  the  actinic 
or  chemical  rays,  which  have  a  powerful  chemical  action.  The  rays 
which  can  be  perceived  by  the  brain,  i.e.,  the  colored  rays,  must  stimu- 
late the  retina  in  some  special  manner  in  order  that  colored  vision  may 
result,  and  two  chief  explanations  of  the  method  of  stimulation  have 
been  suggested. 

(1.)  The  one,  originated  by  Young  and  elaborated  by  Helmholtz,  holds 
that  there  are  three  primary  colors,  viz.,  red,  green,  and  violet,  and  that 
in  the  retina  are  contained  rods  or  cones  which  answer  to  each  of  these 
primary  colors,  whereas  the  innumerable  intermediate  shades  of  color  are 
produced  by  stimulation  of  the  three  primary  color  terminals  in  different 
degrees,  the  sensation  of  white  being  produced  at  the  same  time  when 
the  three  elements  are  equally  excited.  Thus  if  the  retina  be  stimalated 
by  rays  of  certain  wave  length,  at  the  red  end  of  the  spectrum,  the 
terminals  of  the  other  colors,  green  and  violet,  are  hardly  stimulated  at 
all,  but  the  red  terminals  are  strongly  stimulated,  the  resulting  sensation 
being  red.  The  orange  rays  excite  the  red  terminals  considerably,  the 
green  rather  more,  and  the  violet  slightly,  the  resulting  sensation  being 
that  of  orange,  and  so  on  (fig.  434). 

(2.)  The  second  theory  of  color  (Bering's)  supposes  that  there  are  sis 


THE  SESrsES. 


nt 


primary  color  sensations,  of  three  pair  of  antagonistic  or  complemeutal 
colors,  black  and  white,  red  and  green,  and  yellow  and  blue,  and  that 
these  are  produced  by  the  changes  either  of  disintegration  or  of  assimu- 
lation  taking  place  in  certain  substances,  somewhat  it  may  be  supposed  of 
the  nature  of  the  visual  purple,  which  (the  theory  supposes  to)  exist  in 
the  retina.  Each  of  the  substances  corresponding  to  a  pair  of  colors, 
being  capable  of  undergoing  two  changes,  one  of  construction  and  the 
other  of  disintegration,  with  the  result  of  producing  one  or  other  color. 
For  instance,  in  the  white-black  substance,  when  disintegration  is  in 
excess  of  construction  or  assimihition,  the  sensation  is  white,  and  when 
assimilation  is  in  excess  of  disintegration  the  reverse  is  the  case;  and 
similarly  with  tlic  red-green  substance,  and  with  the  yellow-blue  sub- 
stance.    When  the  repair  and  disintegration  are  equal  with  the  first 


reiL 


omnqej 


J" 


'Mow 


Fip.  4.34. —Diagram  of  the  three  primary  color  sensations.  (Toungr-Helmholtz  theory  )  1.  is 
the  red;  2.  green,  and  3,  violet.  ])rimary  color  sensations.  The  lettering  indicates  the  colors  of 
the  spectrum.  The  diagram  indicates"  by  the  height  of  the  curve  to  what  extent  the  several 
primary  sensations  of  color  are  excited  by  vibrations  of  different  wave  lengths. 

Fig.  4:i5. — Diagram  of  the  various  simple  and  compound  colors  of  light,  and  those  which  are 
complemeutal  of  each  other,  i.e.,  which,  when  mixed,  produce  a  neutral  gray  tint.  The  three 
simple  colors,  red,  yellow,  and  blue,  are  placed  at  the  angles  of  an  equilateral  triangle,  which 
are  connected  together  by  means  of  a  circle:  the  mixed  colors,  green,  orange,  and  violet,  are 
placed  intermediate  between  the  corresjjonding  simple  or  homogeneous  colors;  and  the  com- 
plemental  coloi-s,  of  which  tin-  pigments,  when  mixed,  would  constitute  a  gray,  and  of  which  the 
prismatic  spectra  woidd  togctlicr  produce  a  wliite  light,  will  be  found  to  be  placed  in  each  cast- 
opposite  to  each  other,  but  cimnccted  by  a  line  imssing  through  the  centre  of  the  circle.  The  fig- 
ure is  also  useful  in  showing  the  further  shades  of  color  which  are  complementary  of  each 
other.  If  the  circle  be  sui)pt)sed  to  contain  every  transition  of  color  between  the  six  marked 
down,  those  which,  when  united,  yield  a  white  or  gray  color,  will  always  be  found  directly  op- 
posite to  each  other;  thus,  for  example,  the  intermediate  tint  between  "orange  and  red  is  "com- 
pleraental  of  the  middle  tint  between  green  and  blue. 

substance,  the  visual  sensation  is  gray;  but  in  the  other  pairs  when  this 
is  the  case,  no  sensation  occurs.  The  rays  of  the  spectrum  to  the  left 
produce  changes  in  the  red-green  substance  only,  with  a  resulting  sensa- 
tion of  red,  while  the  (orange)  rays  further  to  the  right  affect  both  the 
red-green  and  the  yellow-blue  substances;  blue  rays  cause  constructive 
changes  in  the  yellow-blue  substances  but  none  in  the  red-green  and  so 
on.  These  changes  produced  in  the  vi.sunl  substances  in  the  retina  are 
perceived  by  the  brain  as  sensations  of  color. 

The  spectra  left  by  the  images  of  white  or  luminous  objects  are 
ordinarily  white  or  luminous ;  those  loft  by  dark  objects  are  dark.  Some- 
times, however,  the  relation  of  the  light  and  dark  parts  in  the  image 


736  HAI^DBOOK   OF   PHYSIOLOGY. 

niav,  under  certain  circumstances,  be  reversed  in  the  spectrum;  what 
wus  bright  may  be  dark,  and  wliat  was  dark  may  appear  light.  This 
occurs  whenever  the  eye,  wliich  is  tlie  seat  of  the  spectrum  of  a  luminous 
object,  is  not  closed,  but  iixed  upon  another  bright  or  white  surface,  as 
a  white  wall,  or  a  sheet  of  white  paper.  Hence  the  spectrum  of  the  sun, 
which,  while  light  is  excluded  from  the  eye,  is  luminous,  appears  black 
or  gray  when  the  eye  is  directed  upon  a  white  surface.  The  explanation 
of  this  is,  that  the  part  of  the  retina  which  has  received  the  luminous 
image  remains  for  a  certain  period  afterward  in  an  exhausted  or  less 
sensitive  state,  while  that  which  has  received  a  dark  image  is  in  an 
unexhausted,  and  therefore  much  more  excitable  condition. 

The  ocular  spectra  which  remain  after  the  impression  of  colored  ob- 
jects upon  the  retina  are  always  colored ;  and  their  color  is  not  that  of 
the  object,  or  of  the  image  produced  directly  by  the  object,  but  the  oppo- 
site, or  complemental  color.  The  spectrum  of  a  red  object  is,  therefore, 
green;  that  of  a  green  object,  red;  that  of  violet,  yellow;  that  of  yellow, 
violet,  and  so  on.  The  reason  of  this  is  obvious.  The  part  of  the 
retina  which  receives,  say,  a  red  image,  is  wearied  by  that  particular 
color,  but  remains  sensitive  to  the  other  rays  which  with  red  make  up 
white  light;  and,  therefore,  these  by  themselves  reflected  from  a  white 
object  produce  a  green  hue.  If,  on  the  other  hand,  the  first  object 
looked  at  be  green,  the  retina  being  tired  of  green  rays,  receives  a  red 
image  when  the  eye  is  turned  to  a  white  object.  And  so  with  the  other 
colors;  the  retina  while  fatigued  by  yellow  rays  will  suppose  an  object  to 
be  violet,  and  vice  versa;  the  size  and  shape  of  the  spectrum  correspond- 
ing with  the  size  and  shape  of  the  original  object  looked  at.  The  colors 
which  thus  reciprocally  excite  each  other  in  the  retina  are  those  placed 
at  opposite  points  of  the  circle  in  fig.  435.  The  peripheral  parts  of  the 
retina  do  not  react  to  rays  of  red.  The  area  of  the  retina  which  is 
capable  of  receiving  impressions  of  color,  and  therefore  the  field  of 
vision,  is  slightly  difPerent  for  each  color. 

Color  Blindness  or  Daltonism. — Daltonism  or  color-blindness  is  a  by 
no  means  uncommon  visual  defect.  One  of  the  commonest  forms  is  the 
inability  to  distinguish  between  red  and  green.  The  simplest  explana- 
tion of  such  a  condition  is,  that  the  elements  of  the  retina  which  receive 
the  impression  of  red,  etc.,  are  absent,  or  very  imperfectly  developed,  or, 
according  to  the  other  theory,  that  the  red-green  substance  is  absent 
from  the  retina.  Other  varieties  of  color  blindness  in  which  the  other 
color-perceiving  elements  are  absent  have  been  shown  to  exist  occasionally. 

The  Eeciprogal  Action  of  Different  Parts   of  the   Retina. 

Although  each  elementary  part  of  the  retina  represents  a  distinct 
portion  of  the  field  of  vision,  yet  the  different  elementary  parts,  or  sensi- 


THE   SENSES.  737 

tive  points  of  that  membrane,  have  a  certain  influence  on  each  other; 
the  particular  condition  of  one  influencing  the  other,  so  that  the  image 
perceived  by  one  part  is  modified  by  the  image  depicted  in  the  other. 
The  phenomena  which  result  from  this  relation  between  the  different 
parts  of  the  retina,  may  be  arranged  in  two  classes:  the  one  including 
those  where  the  condition  existing  in  the  greater  extent  of  the  retina  is 
imparted  to  the  remainder  of  that  membrane;  the  other,  consisting  of 
those  in  which  the  condition  of  the  larger  portion  of  the  retina  excites, 
in  the  less  extensive  portion,  the  opposite  condition. 

1.  When  two  opposite  impressions  occur  in  contiguous  parts  of  an 
image  on  the  retina,  the  one  impression  is,  under  certain  circumstances, 
modified  by  the  other.  If  the  impressions  occujjy  each  one-half  of  the 
image,  this  does  not  take  place;  for  in  that  case,  their  actions  are  equally 
balanced.  But  if  one  of  the  impressions  occupies  only  a  small  part  of 
the  retina,  and  the  other  the  greater  j^art  of  its  surface,  the  latter  may, 
if  long  continued,  extend  its  influence  over  the  whole  retina,  so  that 
the  opposite  less  extensive  impression  is  no  longer  perceived,  and  its 
place  becomes  occupied  l^y  the  same  sensation  as  the  rest  of  the  field  of 
vision.  Thus,  if  we  fix  the  eye  for  some  time  upon  a  strip  of  colored 
paper  lying  upon  a  white  surface,  the  image  of  the  colored  object,  espe- 
cially when  it  falls  on  the  lateral  parts  of  the  retina  will  gradually  dis- 
appear, and  the  white  surface  be  seen  in  its  place. 

2.  In  the  second  class  of  phenomena,  the  affection  of  one  part  of  the 
retina  influences  that  of  another  part,  not  in  such  a  manner  as  to  ob- 
literate it,  but  so  as  to  cause  it  to  become  the  contrast  or  opposite  of 
itself.  Thus  a  gray  sjjot  ujDon  a  white  ground  appears  darker  than  the 
same  tint  of  gray  would  do  if  it  alone  occupied  the  whole  field  of  vision, 
and  a  shadow  is  always  rendered  deeper  when  the  light  which  gives  rise  to 
it  becomes  more  intense,  owing  to  the  greater  contrast. 

The  former  phenomena  ensue  gradually,  and  only  after  the  images 
have  been  long  fixed  on  the  retina;  the  latter  are  instantaneous  in  their 
production,  and  are  joermauent. 

In  the  same  way,  also,  colors  may  be  produced  by  contrast.  Thus,  a 
very  small  dull  gray  strip  of  pajter,  lying  upon  an  extensive  surface  of 
any  bright  color,  does  not  appear  gray,  but  has  a  faint  tint  of  tlie  color 
which  is  the  complement  of  that  of  the  surrounding  surface.  A  strip 
of  gray  paper  upon  a  green  field,  for  example,  often  apjiears  to  have 
a  tint  of  red,  and  Avhen  lying  upon  a  red  surface,  a  greenish  tint;  it  has 
an  orange-colored  tiut  upon  a  bright  blue  surface,  and  a  bluish  tint 
upon  an  orange-colored  surface;  a  yellowish  color  upon  a  bright  violet, 
and  a  violet  tint  upon  a  bright  yellow  surface.  The  color  excited  thus,  as 
a  contrast  to  the  exciting  color,  being  wholly  independent  of  any  rays  of 
the  corresponding  color  acting  from  without  upon  the  retina,  must  arise  as 
47 


738  HANDBOOK    OF    PHYSIOLOGY. 

an  opposite  or  antagonistic  condition  of  that  membrane ;  and  the  opposite 
conditions  of  which  the  retina  thus  becomes  the  subject  would  seem  to 
balance  each  other  by  their  reciprocal  reaction.  A  necessary  condition 
for  the  production  of  the  contrasted  colors  is,  that  the  part  of  the  retina 
in  which  the  new  color  is  to  be  excited,  shall  be  in  a  state  of  comparative 
repose ;  hence  the  small  object  itself  must  be  gray.  A  second  condition 
is,  that  the  color  of  the  surrounding  surface  shall  be  very  bright,  that  is, 
shall  contain  much  white  light. 

Binocular  Vision. 

Although  the  sense  of  sight  is  exercised  by  the  two  eyes,  yet  the  im- 
pression of  an  object  conveyed  to  the  mind  is  single.  Various  theories 
have  been  advanced  to  account  for  this  phenomenon. 

By  Gall  it  was  supposed  that  we  do  not  really  employ  both  eyes  si- 
multaneously in  vision,  but  always  see  with  only  one  at  a  time.  This 
especial  employment  of  one  eye  in  vision  certainly  occurs  in  persons 
whose  eyes  are  of  very  unequal  focal  distance,  but  in  the  majority  of 
individuals  both  eyes  are  simultaneously  in  action,  in  the  perception  of 
the  same  object;  this  is  shown  by  the  double  images  seen  under  certain 
conditions.  If  two  fingers  be  held  up  before  the  eyes,  one  in  front  of 
the  other,  and  vision  be  directed  to  the  more  distant,  so  that  it  is  seen 
singly,  the  nearer  will  appear  double;  while,  if  the  nearer  one  be 
regarded,  the  most  distant  will  be  seen  double ;  and  one  of  the  double 
images  in  each  case  will  be  found  to  belong  to  one  eye,  the  other  to  the 
other  eye. 

Diplopia. — Single  vision  results  only  when  certain  parts  of  the  two 
retinae  are  affected  simultaneously;  if  different  parts  of  the  retinae  re- 
ceive the  image  of  the  object,  it  is  seen  double.  This  may  be  readily 
illustrated  as  follows : — the  eyes  are  fixed  upon  some  near  object,  and  one 
of  them  is  pressed  by  the  thumb  so  as  to  be  turned  slightly  in  or  out ;  two 
images  of  the  object  (Diplopia)  are  at  once  perceived,  just  as  is  frequently 
the  case  in  persons  who  squint.  This  diplopia  is  due  to  the  fact  that  the 
images  of  the  object  do  not  fall  on  corresponding  points  in  the  two 
retinse. 

The  parts  of  the  retinae  in  the  two  eyes  which  thus  correspond  to 
each  other  in  the  property  of  referring  the  images  which  affect  them 
simultaneously  to  the  same  spo.  in  the  field  of  vision,  are,  in  man,  just 
those  parts  which  would  correspond  to  each  other,  if  one  retina  were 
placed  exactly  in  front  of,  and  over  the  other  (as  in  fig.  436).  Thus, 
as  we  have  noticed  in  speaking  of  the  distribution  of  the  optic  nerve- 
fibres,  the  temporal  portion  of  one  eye  corresponds  to,  or,  to  use  a  better 
term,  is  identical  with  the  nasal  portion  of  the  other  eye;  or  a  of  the 


THE    SENSES.  739 

eye  a  (fig.  430),  with  a  of  the  eye  b.  The  upper  part  of  one  retina  is 
also  identical  with  the  upjier  part  of  the  other;  and  the  lower  parts  of 
the  two  eyes  are  identical  with  each  other.  The  distribution  of  the  optic 
nerve-fibres  correspond  with  their  distribution.  The  identical  points  on 
the  upper  and  lower  parts  of  the  retinae  may  also  be  shown  by  the  fol- 
lowing simple  experiment. 

Pressure  upon  any  part  of  the  ball  of  the  eye,  so  as  to  afEect  the  retina, 
produces  a  luminous  circle,  seen  at  the  opposite  side  of  the  field  of  vision 
to  that  on  which  the  pressure  is  made.  If,  now,  in  a  dark  room,  we 
press  with  the  finger  at  the  upper  part  of  one  eye,  and  at  the  lower  part 
of  the  other,  two  luminous  circles  are  seen,  one  above  the  other;  so, 
also,  two  figures  are  seen  when  pressure  is  made  simultaneously  on  the 
two  outer  or  the  two  inner  sides  of  both  eyes.  It  is  certain,  therefore, 
that  neither  the  upper  part  of  one  retina  and  the  lower  part  of  the  other 
are  identical,  nor  the  outer  lateral  parts  of  the  two  retina?,  nor  their 
inner  lateral  portions.     But  if  pressure  be  made  with  the  fingers    upon 


Fig.  436.— Diagram  to  sliow  tlie  corresponding  parts  of  both  retina. 

both  eyes  simultaneously  at  their  lower  part,  one  luminous  ring  is  seen 
at  the  middle  of  the  upper  part  of  the  field  of  vision;  if  the  pressure  be 
applied  to  the  upjjer  part  of  both  eyes  a  single  luminous  circle  is  seen  in 
the  middle  of  the  field  of  \dsion  beloAV.  So,  also,  if  we  press  upon  the 
outer  side  a  of  the  eye  a,  and  upon  the  inner  side  a'  of  the  eye  B,  a 
single  spectrum  is  produced,  and  is  apparent  at  the  extreme  right  of  the 
field  of  vision ;  if  upon  the  point  h  of  one  eye,  and  the  point  h'  of  the 
other,  a  single  spectrum  is  seen  to  the  extreme  left. 

The  spheres  of  the  two  retina?  may,  therefore,  be  regarded  as  lying 
one  over  the  other,  as  in  c,  fig.  436 ;  so  that  the  left  portion  of  one  eye  lies 
over  the  identical  left  i^ortiou  of  the  other  eye,  the  right  portion  of  one 
eye  over  the  identical  right  portion  of  the  other  eye;  and  with  the 
upper  and  lower  portions  of  the  two  eyes,  a  lies  over  a',  1)  over  J',  and  c 
over  c' .  The  points  of  the  one  retina  interuiediate  between  a  and  c  are 
again  identical  with  the  corresponding  points  of  the  other  retina  between 
«'  and  d ;  those  between  J  and  c  of  the  one  retina,  with  those  between  V 
and  d  of  the  other.  If  the  axes  of  the  eyes,  a  and  B  (fig.  437),  be  so 
directed  that  they  meet  at  «,  an  object  at  a  will  be  seen  singly,  for  the 


740 


HANDBOOK    OF    PHYSIOLOGY. 


point  a  of  the  one  retina,  and  a'  of  the  other  are  identical.  So,  also,  if 
the  object  /?  be  so  situated  that  its  image  falls  in  both  eyes  at  the  same 
distance  from  the  central  point  of  the  retina, — namely,  at  h  in  the  one 
eye,  and  at  1)'  in  the  other, — /?  will  be  seen  single,  for  it  affects  identical 
parts  of  the  two  retinae.     The  same  will  apply  to  the  object  y. 

In  quadrupeds,  the  relation  betw^een  the  identical  and  non-identical 
parts  of  the  retina  cannot  be  the  same  as  in  man ;  for  the  axes  of  their 
eyes  generally  diverge,  and  can  never  be  made  to  meet  in  one  point  of 
an  object.  When  such  an  animal  regards  an  object  situated  directly  in 
front  of  it,  the  image  of  the  object  must  fall,  in  both  eyes,  on  the  outer 
portion  of  the  retinge.  Thus  the  image  of  the  object  a  (fig.  438)  will  fall 
at  a'  in  one,  and  at  a"  in  the  other:  and  these  points  a'  and  a"  must  be 
identical.     So,  also,  for  distinct  and  single  vision  of  objects,  h  or   c,  the 


Fig.  437. 


Fig.  438. 


Fig.  437. —Diagram  to  show  the  simultaneous  action  of  the  eyes   in  viewing  objects  in  dif- 
ferent directions. 

Fig.  438.  —Diagram  to  show  the  corresponding  parts  of  the  retina  in  the  horse. 

points  b'  and  h"  or  c'  c\  in  the  two  retinae,  on  which  the  images  of  these 
objects  fall,  must  be  identical.  All  points  of  the  retina  in  each  eye 
which  receive  rays  of  light  from  lateral  objects  only,  can  have  no  corre- 
sponding identical  points  in  the  retina  of  the  other  eye;  for  otherwise 
two  objects,  one  situated  to  the  right  and  the  other  to  the  left,  would 
appear  to  lie  in  the  same  spot  of  the  field  of  vision.  It  is  probable, 
therefore,  that  there  are  in  the  eyes  of  animals,  parts  of  the  retinge 
which  are  identical,  and  parts  which  are  not  identical,  ?".e.,  parts  in  one 
which  have  no  corresponding  parts  in  the  other  eye.  And  the  relation 
of  the  two  retinae  to  each  other  in  the  field  of  vision  may  be  represented 
as  in  fig.  439. 

The  cause  of  the  impressions  on  the  identical  points  of  the  two  retinae 
giving  rise  to  but  one  sensation,  and  the  perception  of  a  single  image, 


THE    SENSES. 


741 


must  either  lie  in  the  structural  organization  of  the  deeper  or  cere- 
bral portion  of  the  visual  apparatus,  or  be  the  result  of  a  mental  opera- 
tion ;  for  in  no  other  case  is  it  the  property  of  the  corresponding  nerves 
of  the  two  sides  of  the  body  to  refer  their  sensations  as  one  to  one  sjDot. 


Many  attempts  have  been  made  to  explain  this  remarkable  relation 
between  the  eyes,  by  referring  it  to  anatomical  relation  between  the 
optic  nerves.  The  circumstance  of  the  inner  portion  of  the  fibres  of  the 
two  optic  nerves  decussating  at  the  commissure,  and  passing  to  the  eye 
of  the  opposite  side,  while  the  outer  portion  of  the  fibres  continue  their 
course  to  the  eye  of  the  same  side,  so  that  the  left  side  of  both  retinae  is 
formed  from  one  root  of  the  nerves,  and  the  right  side  of  both  retinae 
from  the  outer  root,  naturally  led  to  an  attempt  to  explain  the  phenomenon 
by  this  distribution  of  the  fibres  of  the  nerves.  And  this  explanation  is 
favored  by  cases  in  which  the  entire  of  one  side  of  the  retina,  as  far  as 
the  central  point  in  both  eyes,  sometimes  becomes  insensible.  But 
Miiller  has  endeavored  to  show  the  inadeqnateness  of  this  theory  to  ex- 
plain the  phenomenon,  unless  it  be  supposed  that  each  fibre  in  each  cere- 
bral portion  of  the  optic  nerves  divides  in  the  optic  commissure  into  two 


Fig.  440.— Diagrams  to  illustrate  three  theories  to  explain  the  action  of  sjininetrical  part=  cf 

the  retina. 

branches  for  tlie  identical  points  of  the  two  retina?,  as  is  shown  in  a, 
fig.  4-40.     But  there  is  no  foundation  for  such  supposition. 

By  another  theory  it  is  assumed  that  each  optic  nerve  contains  exactly 
the  same  number  of  fibres  as  the  other,  and  that  the  corresponding  fibres 
of  the  two  nerves  are  united  in  the  sensorium  (as  in  fig.  440,  b).  But 
in  this  theory  no  account  is  taken  of  the  partial  decussation  of  the  fibres 
of  the  nerves  in  the  optic  commissure. 


742 


HAN"DBOOK    or    PHYSIOLOGY. 


According  to  a  third  theory,  the  fibres  a  and  «',  fig.  440,  c,  coming 
from  identical  points  of  the  two  retinae,  are  in  the  optic  commissure 
brought  into  one  optic  nerve,  and  in  the  brain  either  are  united  by  a 
loop,  or  spring  from  the  same  point.  The  same  disposition  prevails  in 
the  case  of  the  identical  fibres  h  and  V .  According  to  this  theory,  the 
left  half  of  each  retina  would  be  represented  in  the  left  hemisphere  of 
the  brain,  and  the  right  half  of  each  retina  in  the  right  hemisphere. 

Another  explanation  is  founded  on  the  fact,  that  at  the  anterior  23art 
of  the  commissure  of  the  optic  nerve,  certain  fibres  pass  across  from  the 
distal  portion  of  one  nerve  to  the  corresponding  portion  of  the  other 
nerves,  as  if  they  were  commissural  fibres  forming  a  connection  between 
the  retinse  of  the  two  eyes.  It  is  supposed,  indeed,  that  these  fibres  may 
connect  the  corresponding  parts  of  the  two  retina?,  and  may  thus  explain 
their  unity  of  action ;  in  the  same  way  that  corresponding  parts  of  the 
cerebral  hemispheres  are  believed  to  be  connected  together  by  the  com- 
missural fibres  of  the  corpus  callosum,  and  so  enabled  to  exercise  unity  of 
function. 

Judgment  of  Solidity. — On  the  whole,  it  is  probable,  that  the  power 
of  forming  a  single  idea  of  an  object  from  a  double  impression  conveyed 


F      t 


Hi, 


Fig.  441.— Diagrams  to  iUustrate  how  a  judgment  of  a  figure  of  three  dimensions  is  obtained. 

by  it  to  the  eyes  is  the  result  of  a  mental  act.  This  view  is  supported 
by  the  same  facts  as  those  employed  by  Wheatstone  to  show  that  this 
power  is  subservient  to  the  purpose  of  obtaining  a  right  jserception  of 
bodies  raised  in  relief.  When  an  object  is  placed  so  near  the  eyes  that 
to  view  it  the  optic  axes  must  converge,  a  different  perspective  projec- 
tion of  it  is  seen  by  each  eye,  these  perspectives  being  more  dissimilar  as 
the  convergence  of  the  optic  axes  becomes  greater.  Thus,  if  any  figure 
of  three  dimensions,  an  outline  cube,  for  example,  be  held  at  a  moderate 
distance  before  the  eyes,  and  viewed  with  each  eye  successively  while  the 
head  is  kept  perfectly  steady,  a  (fig.  441)  will  be  the  picture  presented 
to  the  right  eye,  and  b  that  seen  by  the  left  eye.  Wheatstone  has  shown 
that  on  this  circumstance  depends  in  a  great  measure  our  conviction 
of  the  solidity  of  an  object,  or  of  its  projection  in  relief.  If  different 
perspective  drawings  of  a  solid  body,  one  representing  the  image  seen  by 
the  right  eye,  the  other  that  seen  by  the  left  (for  example,  the  drawing 


THE    SENSES.  743 

of  a  cube,  a,  b,  fig.  441)  be  presented  to  corresponding  jiarts  of  the  two 
retinae,  as  may  be  readily  done  by  means  of  the  stereoscope,  the  mind 
will  perceive  not  merely  a  single  representation  of  the  object,  but  a  body 
projecting  in  relief,  the  exact  counterpart  of  that  from  which  the  draw- 
ings were  made. 

By  transjjosing  two  stereoscopic  pictures  a  reverse  effect  is  produced ; 
the  elevated  parts  appear  to  be  depressed,  and  vice  versa.  An  instru- 
ment contrived  with  this  purpose  is  termed  a  2}seudoscope.  Viewed  with 
this  instrument  a  bust  appears  as  a  hollow  mask,  and  as  may  readily  be 
imagined  the  effect  is  most  bewildering. 

There  can  be  no  doubt  in  order  that  the  image  of  an  object  should  fall 
upon  corresponding  points  in  the  two  retinte,  it  is  essential  that  the  move- 
ments of  the  eyes  should  be  accurately  co-ordinated,  and  the  method  of 
this  co-ordination  is  not  so  easily  understood  when  examined  carefully. 
Thus,  suppose  the  eyes  be  directed  downward  and  to  the  left.  On  the  left 
side,  the  inferior  rectus,  the  external  rectus,  and  the  superior  oblique 
would  contract,  and,  on  the  right  side  the  inferior  rectus,  internal  rectus, 
and  superior  oblique.  In  other  words,  a  different  set  of  muscles  on 
either  side,  and  supplied  to  a  certain  extent  by  different  nerves.  There 
must  be  some  co-ordinating  centre  for  these  binocular  movements.  It  is 
thought  that  this  centre  is  localized  in  the  anterior  corjDus  quadrigemi- 
num,  since  stimulation  of  it  causes  conjugal  lateral  movement  of  the  visual 
axes  to  the  opposite  side,  and  stimulation  at  another  spot  produces  move- 
ments downward  and  inward.  The  posterior  longitudinal  bundle  of  fibres 
described  as  found  in  the  pons  and  crus,  appears  to  be  concerned  in  some 
way  with  the  simultaneous  movement  of  the  ej'es;  it  appears  to  unite  the 
nuclei  of  the  three  nerves  to  the  ocular  muscles,  the  sixth,  fourth,  and 
third.  In  it  are  said  to  be  contained  fibres  from  the  sixth  nerve  of  the 
opposite  side  which  go  to  the  nucleus  of  the  third  nerve  of  the  same  side; 
and  this  would  serve  to  connect  the  nerve  supply  of  the  internal  rectus 
of  one  side,  and  the  external  rectus  of  the  other  side.  It  appears,  how- 
ever, that  there  is  no  evidence  to  assume  that  the  fibres  of  the  sixth 
nerve  decussate,  but  those  of  the  fourth  nerve  do  entirely,  and  those  of 
the  third,  partially. 


CHAPTER  XTIII. 

THE    REPRODUCTIVE     ORGANS. 

Befoee  describing  the  method  of  Eeproduction,  or  the  way  which  the 
species  is  propagated,  it  will  be  advisable  to  describe 

The  Genital  Organs  of  the  Female. 

The  female  organs  of  generation  (fig.  442)  consist  of  two  ovaries,  the 
function  of  which  is  the  formation  of  ova;  of  a  Fallopian  tube,  or 
oviduct,  connected  with  each  ovary,  for  the  purpose  of  conducting  the 
ovum  from  the  ovary  to  the  uterus  in  the  cavity  of  which,   if  impreg- 


Fig.  442.  —Diagrammatic  view  of  the  uterus  and  its  appendages,  as  seen  from  behind.  The 
uterus  and  upper  part  of  the  vagina  have  been  laid  open  by  removing  the  posterior  wall;  the 
Fallopian  tube,  round  ligament,  and  ovarian  ligament  have  been  cut  short,  and  the  broad  liga- 
ment removed  on  the  left  side;  m,  the  upper  part  of  the  uterus;  c,  the  cervix  opposite  the  os  in- 
ternum; the  triangular  shape  of  the  uterine  cavity  is  shown,  and  the  dilatation  of  the  cervical 
cavity  with  the  rugae  termed  arbor  vitfe;  i\  upper  part  of  the  vagina ;  od.  Fallopian  tube  or 
oviduct;  the  narrow  communication  of  its  cavity  with  that  of  the  cornu  of  the  uterus  on  each 
side  is  seen;  ^,  round  ligament;  ?o,  ligament  of  the  ovary;  o,  ovary;  i,  wide  outer  part  of  the 
right  Fallopian  tube;  fi,  its  fimbriated  extremity;  jao,  parovarium;  7i,  one  of  the  hydatids  fre- 
quently found  connected  with  the  broad  ligament.     J^.     (Allen  Thomson.) 

nated,  it  is  retained  until  the  embryo  is  fully  developed,  and  fitted  to 
maintain  its  existence  independently  of  internal  connection  with  the 
parent ;  and,  lastly,  of  a  canal,  or  vagina,  with  its  appendages,  for  the 
reception  of  a  male  organ  in  the  act  of  copulation,  and  for  the  subsequent 
discharge  of  the  foetus. 

The  Ovaries. — The  ovaries  are  two  oval  compressed  bodies,  situated 
in  the  cavity  of  the  pelvis,  one  on  each  side,  and  are  adherent  to  the 
posterior  surface  of  the  broad  ligament  by  their  anterior  border.     This 

744 


THE    KEPRODUCTIVE    ORGANS. 


745 


border  of  the  ovary  is  called  the  hilum,  and  it  is  at  this  point  that  the 
blood-vessels  and  nerves  enter  it.  Each  ovary  measures  about  an  inch 
and  a  half  in  length  (3,75  cm.),  three  quarters  of  an  inch  in  width 
(1.8G  cm,),  and  nearly  half  an  inch  (1.25  cm.)  in  thickness,  and  is 
attached  to  the  uterus  by  a  narrow  fibrous  cord  (the  ligament  of  the 
ovary),  and,  more  slightly,  to  the  Fallopian  tubes,  by  one  of  the  fimbriae 
into  which  the  walls  of  the  extremity  of  the  tube  expand. 

Structure. — A  laj'er  of  condensed  connective  tissue,  called  the  tunica 
albuginea,  surrounds  the  ovary,  and  this  is  covered  on  the  outside  by  epi- 
thelium (germ-epithelium),  the  cells  of  which  although  continuous  with, 


Fig.  443.— View  of  a  section  of  the  ovary  of  the  cat.  1.  outer  covering  and  free  border  of 
the  ovary;  1',  attached  border;  2.  the  ovarian  stroma,  presenting  a  fibrous  and  vascular  struct- 
ure; 3,  granular  substance  lying  external  to  the  fibrous  stroma;  4.  blood-vessels;  5,  ovigerms  in 
their  earliest  stages  occupying  a  part  of  the  granular  layer  near  the  surface;  G.  ovigerms  which 
liave  begun  to  enlarge  and  to  pa.ss  more  deeply  into  the  ovary;  7,  ovigerms  round  which  the 
■Graafian  follicle  and  tunica  granulosa  are  now  formed,  and  which  have  passed  somewhat  deeper 
into  the  ovary  and  are  surrounded  by  the  fibrous  stroma:  8.  more  advanced  Graafian  follicle 
with  the  O'iTiiu  imbedded  in  the  laj-er  of  cells  constituting  the  proligerous  disc;  9.  the  most  ad- 
vanced follicle  containing  the  ovum,  etc.  ;  9',  a  follicle  from  which  the  ovum  has  accidentally 
■escaped;  10,  corpus  luteum.     x  C.     (SchrGn.) 


and  originally  derived  from,  the  squamous  epithelium  of  the  peritoneum, 
are  short  columnar  (A,  fig.  444). 

The  internal  structure  of  the  organ  consists  of  a  peculiar  soft  fibrous 
tissue — a  kind  of  undeveloped  connective  tissue,  wath  long  nuclei 
closely  resembling  unstriped  muscle  (C,  fig. 444) — or  stroma,  abundantly 
supplied  with  blood-vessels,  and  having  embedded  in  it, in  various  stages 
of  development,  numerous  minute  follicles  or  vesicles,  the  Graafian 
follicles,  or  sacculi,  containing  the  ova  (fig.  444). 

If  the  ovary  be  examined  at  any  period  between  early  infancy  and 
advanced  age,  but  especially  during  that  period  of  life  in  which  the 
power  of  conception  exists,  it  will  be  found  to  contain  a  number  of 
these  vesicles.  Immediately  after  the  tunica  albuginea  (fig.  444)  they 
are  small  and  numerous,  either  arranged  as  a  continuous  layer,  as  in  the 
cat  or  rabbit,  or  in  groups,  as  in  the  human  ovary.     These  small  follicles 


746 


HANDBOOK    OF    PHYSIOLOGY. 


embedded  in  the  soft  stroma  of  fine  connective  tissue  and  unstriped 
muscle  form  here  the  cortical  layer;  they  are  sometimes  called  ovisacs. 

Each  of  the  small  follicles  of  this  layer  has  an  external  membranous 
envelope,  or  memhrana  propria.     This  envelope  or  tunic  is  lined  with  a 


Fig.  444. — Section  of  the  ovary  of  a  cat.  A,  germinal  epithelium;  B,  immature  Graafian 
follicle;  C,  stroma  of  ovary;  D,  vitelline  membrane  containing  the  ovum;  E,  Graafian  follicle 
showing  lining  cells;  F,  follicle  from  which  the  ovum  has  fallen  out.     (V.  D.  Harris.) 

layer  of  nucleated  cells,  forming  a  kind  of  ej)ithelium  or  internal  tunic, 
and  named  the  membrana  granulosa.  The  cavity  of  the  follicle  is  filled 
up  by  a  nucleated  mass  of  protoplasm  inclosed  in  a  very  delicate  mem- 
brane, which  is  the  Ovum.  The  large  spherical  nucleus  contains  one 
or  more  nucleoli.  The  nucleus  is  known  as  the  germinal  vesicle,  and 
the  nucleolus  as  the  germinal  spot. 

The  central  portion  of  the  stroma  of  the  ovary  extends  from  the  cor- 
tical layer  to  the  hilum  of  the  organ,  at  which  enter  the  numerous 
arteries,  fibrous  tissue,  and  unstriped  muscle,  forming  a  highly  vascular 
zona  vasculosa.  Within  this  central  zone  are  contained  the  fully-devel- 
oped Graafian  follicles,  varying  in  size  however,  but  considerably  larger 
than  those  of  the  cortical  layer.  In  these  follicles  the  cavity  is  not 
nearly  filled  by  the  ovum,  which  is  attached  at  one  side  to  the  zona 
granulosa  by  a  collection  of  small  cells,  the  discus  proligerus,  the 
remainder  of  the  cavity  being  filled  with  fluid,  the  liquor  follicidi.  The 
envelope  of  the  ovum,  or  zona pellucida,  is  much  thicker.  The  zona 
granulosa  is  formed  of  several  layers  of  cells,  instead  of  one  only.  Its 
membrana  jaropria  is  much  thicker,  so  as  to  form  a  distinct  fibrous  in- 
vestment; the  memhr ana  fibrosa  and  the  blood-vessels  surrounding  it  are 
numerous,  and  may  be  said  to  form  a  membrana  vasculosa  about  it. 

The  human  ovum  measures  about  yts  ^^  ^^^  m6h  (about  .2  mm.)  in 
diameter.     Its  external  investment,  or  the  zona  pellucida,  or  vitelline 


THE    REPRODUCTIVE    ORGAXS.  747 

membrane,  is  a  transparent  membrane,  about  ytjtu  o^'  ^^^  i"cli  (lO/v.)  in 
thickness,  which  under  the  microscopic  appears  as  a  briglit  ring  (tig. 
445),  bounded  externally  and  internally  by  a  dark  outline.  Within  this 
transparent  investment  or  zona  pellucida,  and  usually  in  close  contact 
with  it,  lies  the  yolk  or  vitellns,  which  is  composed  of  granules  and  glob- 
ules of  various  sizes,  imbedded  in  a  more  or  less  fluid  substance.  The 
smaller  gra'aules,  which  are  the  more  numerous,  resemble  in  their  appear- 
ance, as  well  as  their  constant  motion,  pigment-granules.  The  larger 
granules  or  globules,  which  have  the  aspect  of  fat-globules,  are  in 
greatest  number  at  the  periphery  of  the  yolk.  The  number  of  the  gran- 
ules is  greatest  in  the  ova  of  carnivorous  animals.  In  the  human  ovum 
their  quantity  is  comparatively  small. 

In  the  substance  of  the  yolk  is  imbedded  the  germinal  vesicle,  or  ves- 
icula  germinativa,  -^^  of  an  inch  (.05  mm.)  (fig.  445).  The  vesicle  is  of 
greatest  relative  size  in  the  smallest  ova,  and  is  in  them  surrounded 
closely  by  the  yolk,  nearly  in  the  centre  of  Avhich  it  lies.  During  the 
development  of  the  ovum,  the  germinal  vesicle  increases  in  size  much  less 
rapidly  than  the  yolk,  and  comes  to  be  placed  near  to  its  surface.  It 
consists  of  a  fine,  transparent,  structureless  membrane,  containing  a  clear, 
watery  fluid,  in  which  are  sometimes  a  few  granules;  and  at  that  part  of 
the  periphery  of  the  germinal  vesicle  which  is  nearest  to  the  perijihery  of 
the  yolk  is  situated  the  germinal  spot,  or  macula  germinativa,  of  a  finely 


Nucleus  or  germinal  vesicle. 
^ Nucleolus  or  germinal  spot. 

Space  left  by  retraction  of 
"      yolk. 


.Yolk  or  vitellus. 


c .Vitelline  membrane. 

Fig.  44,5.  — Semidiagi-ammatic  represention  of  a  human  ovum,  showing  the  parts  of  an  auiuial 

cell.    (Cadiat.) 

granulated  appearance  and  of  a  yellowish  color,  strongly  refracting  the 
rays  of  light. 

Such  are  the  parts  of  which  the  Graafian  follicle  and  its  contents, 
including  the  ovum,  are  composed.  "With  regard  to  the  mode  and  order 
of  development  of  these  parts  there  is  considerable  uncertainty. 

The  Graafian  follicles  are  formed  in  tlie  following  manner: — The  em- 
bryonic ovary  is  covered  with  short  columnar  cells,  or  the  so-called  germ- 
inal epithelium.  The  cells  of  this  layer  undergo  proliferation,  so  as  to 
form  several  strata,  and  grow  into  the  ovarian  stroma  as  longer  or  shorter 


748 


HAISTDBOOK    OF    PHYSIOLOGY. 


columns  or  tubes.  By  degrees  these  tubes  become  cut  off  from  the  surface 
epithelium,  and  form  cell  nests,  small,  if  near  the  surface,  larger  if  in 
the  depth  of  the  stroma.  The  nests  increase  in  size  from  multiplication 
of  their  cells,  and  may  even  give  off  new  nests  laterally  by  constriction  of 
them  in  various  directions.  Certain  of  the  cells  of  the  germinal 
epithelium  enlarge,  and  form  ova ;  and  the  formation  of  ova  also  takes 
place  in  the  nests  within  the  stroma.  The  ova  of  a  nest  may  multiply 
by  division.  The  small  cells  of  a  nest  surround  the  ova,  and  form  their 
membrana  granulosa,  and  the  stroma  growing  up  separates  the  surrounded 
ova  into  so  many  Graafian  follicles.  The  other  layers,  namely,  the  mem- 
brana fibrosa  and  the  membrana  vasculosa,  are  derived  from  the  stroma. 

The  smallest  follicles  are  formed  at  the  surface,  and  make  up  the  cor- 
tical layer.  It  is  said  by  some  that  the  superficial  follicles  as  they  ripen 
become  more  deeply  placed  in  the  ovarian  stroma;  and,  again,  that  as 
they  increase  in  size,  they  make  their  way  toward  the  surface  (fig.  443) . 

When  mature,  they  form  little  prominences  on  the  exterior  of  the 
ovary,  covered  only  by  a  thin  layer  of  condensed  fibrous  tissue  and  epithe- 
lium.    Only  a  few  follicles  ever  reach  maturity. 

From  the  earliest  infancy,  and  through  the  whole  fruitful  period  of 
life,  there  appears  to  be  a  constant  formation,  development,  and  matura- 


-"^^Rr^^ 


Fig.  446. —Germinal  epithelium  of  the  sarface  of  the  ovary  of  five  days'  chick, 
blasts ;  6,  larger  ovoblasts.     (Cadiat. ) 


a,  small  ovo- 


tion  of  Graafian  vesicles,  with  their  contained  ova.  Until  the  period  of 
puberty,  however,  the  process  is  comparatively  inactive ;  for,  previous  to 
this  period,  the  ovaries  are  small  and  pale,  the  Graafian  vesicles  in  them 
are  very  minute,  and  probably  never  attain  full  development,  but  soon 
shrivel  and  disappear,  instead  of  bursting,  as  matured  follicles  do; 
the  contained  ova  are  also  incapable  of  being  impregnated.  But,  coin- 
cident with  the  other  changes  which  occur  in  the  body  at  the  time  of 
puberty,  the  ovaries  enlarge,  and  become  very  vascular,  the  formation 
of  Graafian  vesicles  is  more  abundant,  the  size  and  degree  of  development 
attained  by  them  are  greater,  and  the  ova  are  capable  of  being  fecun- 
dated. 

The  Fallopian  Tubes  {Oviducts). — The  Fallopian  tubes  are  about 
four  inches  in  length  (10  cm.),  and  extend  between  the  ovaries  and  the 


THE    REPRODUCTIVE    ORGANS.  749 

upper  angles  of  the  uterus.  At  the  point  of  attachment  to  the  uterus, 
each  tube  is  very  narrow ;  but  in  its  course  to  the  ovary  it  increases  to 
about  an  eighth  of  an  incli  (3  mm.)  in  thickness;  at  its  distal  extremity, 
which  is  free  and  floating,  it  bears  a  number  of  fimhrice,  one  of  which, 
longer  than  the  rest,  is  attached  to  the  ovary.  The  canal  by  which  each 
tube  is  traversed  is  narrow,  especially  at  its  point  of  entrance  into  tbe 
uterus,  at  which  it  will  scarcely  admit  a  bristle;  its  other  extremity  is 
wider,  and  opens  into  the  cavity  of  the  abdomen,  surrounded  by  the  zone 
of  fimbrice.  Externally,  the  Fallojoiau  tube  is  invested  Avith  peritoneum ; 
intei'nally,  its  canal  is  lined  with  mucous  membrane,  which  is  apt  to  be 
thrown  into  numerous  longitudinal  folds,  covered  with  ciliated  epithe- 
lium: between  the  peritoneal  and  mucous  coats  the  walls  are  composed, 
like  those  of  the  uterus,  of  fibrous  tissue  and  uustriped  muscular  fibres, 
chiefly  circular  in  arrangement. 

The  Uterus. — The  uterus  {u.  e,  fig.  442)  is  a  somewhat  pyriform 
shaped  organ,  and  in  the  unimpreguated  state  is  about  three  inches  (7.5 
cm.)  in  lengtli,  two  (5  cm.)  in  breadth  at  its  upjier  part  or  fioidus,  but  at 
its  lower  pointed  part,  nech  or  cervix,  only  about  half  an  inch  (1.25  cm.). 
The  part  between  the  fundus  and  neck  is  termed  the  bodi/  of  the 
uterus:  it  is  about  an  inch  (2.5  cm.)  in  thickness. 

Structure. — The  uterus  is  constructed  of  three  principal  layers,  or 
coats — serous,  fibrous  and  muscular,  and  mucous,  {a)  The  serous  coat, 
Avhich  has  the  same  general  structure  as  the  peritoneum,  covers  the 
organ  before  and  behind,  but  is  absent  from  the  front  surface  of  the 
neck,  ih)  The  middle  coat  is  composed  of  unstriped  muscle,  arranged 
in  the  human  uterus  in  three  layers  from  without  inward,  longitudinal, 
circular,  oblique  and  circular.  They  become  enormously  developed  dur- 
ing joregnancy.  The  arteries  and  veins  are  found  in  large  numbers  in 
the  outer  jiart  of  their  coat,  so  as  to  form  almost  a  special  vascular  coat. 
{c)  The  mucous  membrane  of  the  uterus  is  lined  by  columnar  ciliated 
epithelium,  which  extends  also  to  the  interior  of  the  tubular  glands,  of 
which  the  mucous  membrane  is  largely  made  up. 

In  the  cervix  uteri  the  mucous  membrane  is  arranged  in  permanent 
longitudinal  folds,  |>r//y»/ej!7/?'cf/te.  The  glands  of  this  part  are  of  the 
tubulo-racemose  type,  branching  repeatedly  and  extending  deeply  into 
the  substance  of  the  cervix.  They  are  lined  by  columnar  epithelium, 
and  open  on  the  ridges  and  furrows  of  the  mucous  membrane.  Tliey 
secrete  a  thick  glairy  mucus,  resembling  unboiled  white  of  ogg. 

The  mucous  membrane  of  the  cavity  of  the  body  of  the  uterus 
forms  a  thin  membrane  about  -^V  inch  (1  mm.)  thick,  and  is  covered  on  its 
surface  by  columnar  ciliated  epithelium.  Imbedded  in  its  substance  are 
numerous  simple  tubular  glands  set  somewhat  obliquely  and  lined  with 
columnar  ciliated  epithelium.       These  glands  often  bifurcate  at  their 


750  HANDBOOK    OF    PHYSIOLOGY. 

lower  ends.  The  glands  are  imbedded  in  a  delicate  connective  tissue, 
consisting  of  round  and  spindle-shaped  cells. 

The  cavity  of  the  uterus  corresponds  in  form  to  that  of  the  organ 
itself :  it  is  very  small  in  the  unimpregnated  state,  the  sides  of  its  mucous 
surface  being  almost  in  contact.  Into  its  upper  part,  at  each  side,  opens 
the  canal  of  the  corresponding  Fallopian  tube :  below,  it  communicates 
with  the  vagina  by  a  fissure-like  opening  in  its  neck,  the  os  uteri,  the 
margins  of  which  are  distinguished  into  two  lips,  an  anterior  and  pos- 
terior. 

The  Vagina  is  a  membranous  canal,  five  or  six  inches  (12.5  to  15 
cm.)  long,  extending  obliquely  downward  and  forward  from  the  neck 
of  the  uterus,  which  it  embraces,  to  the  external  organs  of  generation. 
It  is  lined  with  mucous  membrane,  covered  with  stratified  squamous 
epithelium,  which  in  the  ordinary  contracted  state  of  the  canal  is  thrown 
into  transverse  folds.  External  to  the  mucous  membrane  the  walls  of 
the  vagina  are  constructed  of  unstriped  muscle  and  fibrous  tissue, 
within  which  in  the  submucosa,  especially  around  the  lower  part  of  the 
tube,  is  a  layer  of  erectile  tissue.  This  exists  also  in  the  mucosa.  The 
lower  extremity  of  the  vagina  is  embraced  by  an  orbicular  muscle,  the 
sjjhincter  vagince;  its  external  orifice,  in  the  virgin,  is  partially  closed  by 
a  fold  or  ring  of  mucous  membrane,  termed  the  hymen.  The  external 
organs  of  generation  consist  of  the  clitoris,  a  small  elongated  body, 
situated  above  and  in  the  middle  line,  and  constructed  of  two  erectile 
masses  or  corpora  cavernosa.  They  are  not  perforated  by  the  urethra; 
of  two  folds  of  mucous  membrane,  termed  labia  interna,  or  nymj)lice;  and, 
in  front  of  these, of  two  other  folds,  the  labia  externa,  ov  pudenda,  formed 
of  the  external  integument,  and  lined  internally  by  mucous  membrane. 
Between  the  nymphse  and  beneath  the  clitoris  is  an  angular  space,  termed 
the  vestibule,  at  the  centre  of  whose  base  is  the  orifice  of  the  meatus 
nrinarius.  Numerous  mucous  follicles  are  scattered  beneath  the  mucous 
membrane  composing  these  parts  of  the  external  organs  of  generation; 
and  at  the  side  of  the  lower  part  of  the  vagina  are  two  larger  lobulated 
glands,  vulvo-vagiual  or  Duverney's  glands,  which  are  analogous  to  Cow- 
per's  glands  in  the  male.  The  ducts  of  these  glands  are  about  ^  inch 
(12.5  mm.)  long  and  open  immediately  external  to  the  hymen  at  the 
mid-point  of  the  lateral  wall  of  the  vaginal  orifice.  The  vulvo-vaginal 
glands  secrete  a  thick  brownish  mucus. 

The  Genital  Organs  of  the   Male. 

The  male  organs  of  generation  comprise  the  two  Testes,  in  which 
the  semen  is  formed ;  each  with  a  duct,  the  Vas  Deferens,  and  accessory 
Vesicula  Seminalis;  the  Penis,  an  erectile  organ,   through  which  the 


THE    REPRODUCTIVE    ORGANS. 


751 


semen  as  well  as  the  urine  is  discharged.  The  Prostate  gland,  the 
exact  function  of  which  is  not  understood,  is  generally  included  in  the 
same  class. 

The  Testes. — The  secreting  structure  of  the  testicle  and  its  duct 
are  disposed  of  in  two  contiguous,  parts  (1)  the  body  of  the  testicle  proper, 
inclosed  within  a  thick  and  tough  white  fibrous  membrane,  the  tunica 
albugifiea,  on  the  outer  surface  of  which  is  the  serous  covering  formed  by 
the  tunica  vaginalis,  and  (2)   the  epiclidymis  and  vas  deferens. 

The  Vas  deferens,  or  duct  of  the  testicle,  which  is  about  two  feet 
(60  cm.)  in  length,  is  constructed  externally  of  connective  tissue,  and 
internally  is  lined  by  a  mucous  membrane,  covered  with  columnar  epithe- 
lium ;  while  between  these  two  coats  is  a  middle  coat,  very  firm  and  tough, 
made  up  of  unstriped  muscle,  chiefly  arranged  longitudinally,  but  also 
containing  some  circular  fibres.  When  followed  back  to  its  origin,  the 
vas  deferens  is  found  to  pass  to  the  lower  part  of  the  epididymis,  with 


Fig.  447 


Fig.  44S. 


Fig.  447.— Plan  of  a  vertical  section  of  t'le  testicle,  showing  the  arrangement  of  the  ducts. 
The  true  lengtli  and  diameter  of  the  ducts  have  been  disregarded,  a  a,  tubuli  seminiferi  coiled 
up  in  the  separate  lobes;  6,  tubuli  recti  or  vasa  recta;  c.  rete  testis;  f/,  va.sa  efferentia  ending 
in  the  C(ini  vasculosi;  /,  e,  .7,  convoluted  canal  of  the  epididymis;  /i,  vas  deferens;  /,  section  of 
the  back  part  of  the  tunica  albuginea;  i,  /,  fibrous  processes  running  between  the  lobes;  .•!,  me- 
diastinum. 

Fig,  448.— Section  of  the  epididymis  of  a  dog.— The  tube  is  cut  in  several  places,  both  trans- 
versely and  obliquely;  it  is  seen  to  be  lined  by  a  ciliated  epitheiium,  the  nuclei  of  wliich  are 
well  shown,     c,  connective  tissue.     (Schofield.) 


which  it  is  directly  continuous  (fig. 447),  and  assumes  there  a  much  smaller 
diameter  witli  an  exceedingly  tortuous  course. 

The  Epididymis,  which  is  lined,  except  at  its  lowest  part,  by  co- 


752  HA^-DBOOK    OF    PHYSIOLOGY. 

lumnar  ciliated  epithelium  (fig.  447),  is  commonly  described  as  con- 
sisting (fig.  447)  of  Q, globus  minor  (g),  the  ioclg  (e),  and  the  globus  major 
(l.)  When  unravelled  it  is  found  to  be  constructed  of  a  single  tube,  meas- 
uring about  twenty  feet  in  length. 

At  the  globus  major  this  duct  divides  into  ten  or  twelve  small 
branches,  the  convolutions  of  which  form  coniform  masses,  named  Coni 
vasculosi;  and  the  ducts  continued  from  these,  the  Vasa  efferentia,  after 
anastomosing,  one  with  another  in  what  is  called  the  Rete  testis,  lead 
finally  as  the  Tuhuli  recti  ox  Vasa  recta  to  the  seminal  tubules  {tuhuli 
seminifei'i) ,  which  form  the  proper  substance  of  the  testicle.  The 
epithelium  lining  the  coni  vasculosi  and  vasa  elferentia  is  columnar  and 
ciliated ;  that  of  the  rete  testis  is  squamous. 

The  seminal  tubules  are  arranged  in  lobules,  separated  from  one 
another  by  incomplete  fibrous  septa  or  cords,  which  pass  from  the  front 
of  the  tunica  albuginea  internally  to  a  firm  incomplete  vertical  septum 
of  thick  extending  fibrous  tissue  at  the  posterior  border,  from  the  upper 
to  near  the  lower  part,  called  the  corpus  Highmori,  or  mediastinum 
testis.  Through  this  very  firm  fibrous  tissue  pass  the  seminal  tubes  from 
the  vasa  recta.  The  tunica  albuginea  is  covered  by  a  very  fine  plexus  of 
blood-vessels  internally,  derived  from  the  spermatic  vessels.  The  fibrous 
cords  which  may  contain  unstriped  muscle  are  also  covered  with  a  similar 
capillary  plexus. 

Tuhuli  Seminiferi. — The  seminal  tubes,  which  compose  the  paren- 
chyma of  the  testicle,  are  loosely  arranged  in  lobules  between  the  connec- 
tive tissue  septa. 

They  are  relatively  large,  very  wavy,  and  much  convoluted;  and 
they  possess  a  few  lateral  branches,  by  which  they  become  connected 


Fig.  449. — From  a  section  of  the  testis  of  dog,  showing  portions  of  seminal  tubes.  A,  semi- 
nal epithelial  cells,  and  numerous  small  cells  loosely  arranged ;  B,  the  small  cells  or  sperm- 
atoblasts converted  into  spermatozoa;  groups  of  these  in  a  further  stage  of  development. 
CKlein.) 

into  a  network.  They  form  terminal  loops,  and  in  the  peripheral  por- 
tion of  the  testis  the  tubules  are  possessed  of  minute  lateral  csecal 
branchlets. 

Each  seminal  tubule  in  the  adult  testis  is  limited  by  a  membrana 


THE    KEPKODUCTIVE    ORGANS. 


:5:3 


propria,  which  appears  as  a  hyaline  elastic  menibraue,  but  which  is 
really  made  up  of  several  incomplete  layers  of  flattened  cells,  contain- 
ing oval  flattened  nuclei  at  regular  intervals.  Inside  this  membrana 
propria  are  several  layers  of  epithelial  cells,  the  seminal  cells  (fig.  449). 
These  consist  of  two  or  more  layers,  the  outermost  being  situated  next 
the  membrana  propria.     These  cells  are  of  two  kinds,  those  that  are  in 


Fig  450.— Section  of  a  tubule  of  the  testicle  of  a  rat.  to  show  the  formation  of  the  sperm- 
atozoa; a  spermatozoa;  h,  seminal  cells;  c,  spermatoblasts,  to  ■which  the  spermatozoa  are  still 
adherent;  rf,  membrana  propria;  e.  fibro-plastic  elements  of  the  connective  tissue.     (Cadiat.') 

a  resting  state,  which  generally  form  a  complete  layer,  and  those  that 
are  in  a  state  of  division,  of  which  there  may  be  two  layers.  The  latter 
are  called  mother  cells,  and  the  smaller  cells  resulting  from  their  division 
are  called  daughter  cells  or  spermatoblasts.  From  these  the  sperma- 
tozoa are  formed,  their  head  corresponding  with  the  nuclei  of  the 
daughter  cells;  and  during  their  development  they  lie  in  groups  (figs. 
449,450),  and  are  supported  by  irregular  masses  of  so-called  nutritive 
cells;  but  when  fully  formed,  they  become  detached,  and  fill  the  lumen 
of  the  seminiferous  tubule  (fig.  450).  This  detachment  is  effected  by 
the  liquefaction  of  the  nutritive  cells  in  which  the  groups  of  spermatozoa 
are  imbedded. 

In  the  fine  connective  tissue  which  supports  the  tubules  of  the  testis, 
are  to  be  found  flattened  and  nucleated  epithelial  cells,  probably  the 
remains  of  the  Wolffian  body.  The  lymphatics  of  the  testes  are  numer- 
ous, and  may  be  injected  by  inserting  the  needle  of  an  injecting  syringe 
into  the  tunica  albuginea,  and  pressing  in  the  injection  with  slight 
effort. 

The  VesiculcE  Seminales. — The  vesiculs  seminales  have  the  appear- 
ance of  outgrowths  from  the  vasa  deferentia.      Each  vas  deferens,  just 
i8 


754 


HAIs^DBOOK    OF    PHYSIOLOGY. 


before  it  enters  the  prostate  gland,  through  part  of  which  it  passes  to 
terminate  in  the  urethra,  gives  off  a  side  branch,  which  bends  back 
from  it  at  an  acute  angle :  and  this  branch  dilating,  variously  branching, 
and  pursuing  in  both  itself  and  its  branches  a  tortuous  course,  forms 
the  vesicula  seminalis. 

Structure. — Each  vesicula  may  be  unravelled  into  a  single  branching 
tube  sacculated,  convoluted,  and  folded  up. 

The  structure  resembles  closely  that  of  the  vasa  deferentia.  The 
mucous  membrane,  like  that  of  the  gall-bladder,  is  minutely  wrinkled 
and  set  with  folds  and  ridges  arranged  so  as  to  give  it  a  finely  reticu- 
lated appearance. 

The  Penis. — The  penis  is  composed  of  three  long  more  or  less 
cylindrical   masses,    inclosed    in    remarkably  firm  fibrous    sheaths,   of 


-.^r:?:^^ 


Fig.  451.  —Dissection  of  the  base  of  the  bladder  and  prostate  gland,  showing  the  vesiculae 
seminales  and  vasa  deferentia.  o,  lower  surface  of  the  bladder  at  the  place  of  reflection  of  the 
peritoneum ;  6,  the  part  above  covered  by  the  peritoneum ;  i,  left  vas  deferens,  ending  in  e,  the 
ejaculatory  duct;  the  vas  deferens  has  been  divided  near  t,  and  all  except  the  vesical  por- 
tion has  been  taken  away;  s,  left  vesicula  seminalis  .ioining  the  same  duct;  s,  s,  the  right  vas 
deferens  and  right  vesicula  seminalis,  which  has  been  unravelled;  »,  under  side  of  the  prostate 
gland;  m,  part  of  the  urethra;  -u,  u.  the  ureters  (cut  short),  tne  right  one  turned  aside. 
CHaller.) 


which  two,  the  corpora  cavernosa,  are  alike,  and  are  firmly  joined 
together,  and  receive  below  and  between  them  the  third  part,  or  corpus 
spongiosum.  The  urethra  passes  through  the  corpus  spongiosum.  The 
penis  is  attached  to  the  symphysis  pubis  by  its  root.  The  enlarged  ex- 
tremity or  glans  penis  is  continuous  with  the  corpus  spongiosum.  The 
integument  covering  the  penis  forms  a  loose  fold  from  the  junction  of 
the  glans  with  the  body,  called  the  prepuce  or  foreskin. 


THE    REPRODUCTIVE    ORGANS.  755 

Structure.  —  (a.)  The  urethra  is  lined  by  stratified  pavement  epithe- 
lium in  the  prostatic  portion;  in  front  of  the  bulb  the  epithelium 
becomes  columnar,  while  at  the  fossa  navicularis  it  is  again  lined 
with  stratified  pavement  epithelium.  The  mucous  membrane  consists 
chiefly  of  fibrous  connective-tissue,  intermixed  with  which  are  many  elastic 
fibres.     It  is  surrounded  by  unstriped  muscular  tissue.     In  the  inter- 


Ns%=r-. 


Fig.  452. — Erectile  tissue  of  the  human  i)enis.    o,  fibrous    trabeculae  with  their  ordinan 
capillaries;  6,  section  of  the  venous  sinuses;  c,  muscular  tissue.     (Cadiat.) 


mediate  portion  many  large  veins  run  amongst  the  bundles  of  muscular 
tissue.     Many  mucous  glands,  glands  of  Littre,  are  present. 

ip.)  The  corpora  cavernosa,  a  true  erectile  structure,  are  surrounded 
by  a  dense  fibrous  and  elastic  sheath,  and  from  the  inner  surface  of  this, 
and  from  the  septum  which  separates  the  two  corpora  cavernosa,  pass 
numerous  bundles  of  fibrous,  elastic,  and  plain  muscular  fibres,  called 
traheculm,  and  these  by  their  anastomosis  form  a  series  of  irregular 
spaces.  These  si)aces  are  lined  with  endothelium,  and  are  filled  with 
venous  blood.  The  inter-trabecular  spaces  or  sinuses  of  one  corpus 
cavernosum  anastomose  with  those  of  the  other,  especially  in  front  where 
the  dividing  septum  is  incomplete. 

{c.)  The  corpus  spongiosum  urethrae  consists  of  an  inner  portion  or 
plexus  of  longitudinal  veins,  and  of  an  outer  or  really  cavernous  portion 
identical  in  structure  with  that  which  has  just  been  described.  The 
lymphatics  of  the  penis  are  very  numerous,  both  superficially  and  also 
around  the  urethra.     They  join  the  inguinal  glands. 

The  nerves,  derived  from  the  pudic  nerves  and  hypogastric  plexus, 
are  distributed  to  the  skin  and  mucous  membrane  and  to  the  corpora 
cavernosa  and  spongiosum  respectively.  The  nerves  are  provided  with 
end  bulbs  and  Pacinian  corpuscles  in  the  glans  penis,  and  form  also  a 
dense  subepithelial  plexus. 

Cowper^s  glands    are  two  small  glands,  the  ducts  of  which  open    into 


T56 


HANDBOOK    OF    PHYSIOLOGY. 


the  second  part  of  the  urethra.  They  are  small  round  bodies,  of  the 
size  of  a  pea,  yellow  in  color,  resembling  the  sublingual  gland;  in 
structure  they  are  compound  tubular  mucous  glands. 

The  Prostate  Gland. — The  prostate  is  situated  (fig.  451)  at  the 
neck  of  the  urinary  bladder,  and  incloses  the  commencement  of  the 
urethra.  It  is  somewhat  chestnut- shaped.  It  measures  an  inch  and  a 
half  in  breadth,  and  an  inch  and  a  quarter  long,  and  half  an  inch  in 
thickness. 

Structure. — The  prostate  is  made  up  of  small  compound  tubular 
glands  imbedded  in  an  abundance  of  muscular  fibres  and  connective  tissue. 

The  glandular  substance,  which  is  nearly  absent  from  the  front  part 
of  the  organ,  consists  of  numerous  small  saccules,  opening  into  elongated 
ducts,  which  unite  into  a  smaller  number  of  excretory  ducts.      The  acini 


463.— Section  of  a  small  portion  of  the  prostate,     a,  gland  duct  cut  across  obliquely ;  6, 
gland  structure ;  c,  prostatic  calculus.     (Cadiat. ) 


of  the  upper  part  of  the  prostate  are  small  and  hemispherical;  while 
in  the  middle  and  lower  parts  the  tubes  are  longer  and  more  convoluted. 
The  acini  are  of  two  kinds,  namely,  those  {a)  lined  with  a  single  layer  of 
thin  and  long  columnar  cells,  each  with  an  oval  nucleus  in  outer  part  of 
wall ;  and  those  {h)  acini  resembling  the  foregoing,  but  with  a  second 
layer  of  small  cortical,  polyhedral,  or  fusiform  cells  between  the  mem- 
brana  propria  and  the  columnar  cells.  The  ducts,  twelve  to  twenty  in 
number,  open  into  the  urethra.  They  are  lined  by  a  layer  of  columnar 
cells,  beneath  which  is  a  layer  of  small  polyhedral  cells. 

The  tunica  adventitia  consists  of  dense  fibrous  tissue  of  two  layers, 
between  which  is  situated  a  plexus  of  veins.  Large  vessels  pass  into  the 
interior  of  the  organ,  to  form  a  broad,  meshed,  capillary  system.  Nerves 
with  numerous  large  ganglion-cells  surround  the  cortex.  Pacinian 
bodies  are  sometimes  found  in  the  substance  of  the  organ. 


THE    REPRODUCTIVE    ORGANS.  7nT 

The  muscular  tissue  of  the  prostate  not  only  forms  the  chief  part  of 
the  stroma  of  the  gland,  but  also  forms  a  continuous  layer  inside  the 
fibrous  sheath,  as  well  as  a  layer  surrounding  the  urethra,  which  is  con- 
tinous  with  the  sphincter  vesicae. 

Physiology  of  the  Sexual  Organs. 

Of  the  Female. — lu  the  jjrocess  of  development  in  the  ovary  of 
individual  Graafian  vesicles,  it  has  been  already  observed,  that  as  each 
increases  in  size,  it  gradually  approaches  the  surface  of  the  ovary,  and 
when  fully  ripe  or  mature,  forms  a  little  projection  on  the  exterior. 
Coincident  with  the  increase  in  size,  caused  by  the  augmentation  of  its 
liquid  contents,  the  external  envelope  of  the  distended  vesicle  becomes 
very  thin  and  eventually  bursts.  By  these  means,  the  ovum  and  fluid 
contents  of  the  vesicle  are  liberated,  and  escape  on  the  exterior  of  the 
ovary,  Avhence  they  pass  into  the  Fallopian  tube  or  oviduct,  the  fimbri- 
ated processes  of  the  extremity  of  which  are  supposed  coincidentally  to 
grasp  the  ovary,  while  the  aperture  of  the  tube  is  applied  to  the  part 
corresponding  to  the  matured  and  bursting  vesicle. 

In  animals  whose  special  capability  of  being  impregnated  occurs  at 
regular  periods,  as  in  the  human  subject,  and  most  mammalia,  the 
Graafian  vesicles  and  their  contained  ova  appear  to  arrive  at  maturity, 
and  the  latter  to  be  discharged  at  such  periods  only.  But  in  other 
animals,  e.g.,  the  common  fowl,  the  formation,  maturation,  and  dis- 
charge of  ova  appear  to  take  place  almost  constantly. 

It  has  long  been  known,  that  in  the  so-called  oviparous  animals,  the 
separation  of  ova  from  the  ovary  may  take  place  independently  of  im- 
pregnation by  the  male,  or  even  of  sexual  union.  And  it  is  now 
established  that  a  like  maturation  and  discharge  of  ova,  independently 
of  coition,  occurs  in  mammalia,  the  periods  at  which  the  matured  ova 
are  separated  fi'om  the  ovaries  and  received  into  the  Fallopian  tubes 
being  indicated  in  the  lower  mammalia  by  the  phenomena  of  heat  or 
rut:  in  the  human  female,  although  not  always  with  exact  coincidence, 
by  the  phenomena  of  menstruatmi.  If  the  union  of  the  sexes  take 
place-,  the  ovum  may  be  fecundated,  and  if  no  union  occur  it  perishes. 

That  this  maturation  and  discharge  occur  periodically,  and  only 
during  the  phenomena  of  heat  in  the  lower  mammalia,  is  made  probable 
by  the  facts  that,  in  all  instances  in  which  Graafian  vesicles  have  been 
found  presenting  the  appearance  of  recent  rupture,  the  animals  were  at 
the  time,  or  had  recently  been,  in  heat;  that  on  the  other  hand,  there  is  no 
authentic  and  detailed  account  of  Graafian  vesicles  being  found  ruptured 
in  the  intervals  of  the  period  of  heat;  and  that  female  animals  do  not 
admit  the  males,  and  never  become  impregnated,  except  at  those  periods. 


758  HAN"DBOOK    OF   PHYSIOLOGY. 

Relation  of  Menstruation  to  the  Discharge  of  Ova. — The  human  female 
is  subject  to  the  same  law  as  the  females  of  other  mammiferous  animals; 
her  ova  are  matured  and  discharged  from  the  ovary  independent  of  sexual 
unio7i.  This  maturation  and  discharge  occur,  moreover,  periodically  at 
or  about  the  epochs  of  menstruation. 

The  evidence  of  the  periodical  discharge  of  ova  at  the  menstrual 
periods  is  that  in  most  cases  in  which  signs  of  menstruation  have  been 
found  in  the  uterus,  follicles  in  a  state  of  maturity  or  of  rupture  have 
been  seen  in  the  ovary;  and  although  conception  is  not  confined  to  the 
periods  of  menstruation,  yet  it  is  more  likely  to  occur  about  a  menstrual 
epoch  than  at  other  times. 

The  exact  relation  between  the  discharge  of  ova  and  menstruation  is 
not  very  clear.  It  was  formerly  believed  that  the  monthly  flux  was  the 
result  of  a  congestion  of  the  uterus  arising  from  the  enlargement  and 
rupture  of  a  Graafian  follicle ;  but  though  a  Graafian  follicle  is,  as  a 
rule,  ruptured  at  each  menstrual  epoch,  yet  several  instances  are  recorded 
in  which  menstruation  has  occurred  where  no  Graafian  follicle  can  have 
been  ruptured,  and  on  the  other  hand  cases  are  known  where  ova  have 
been  discharged  in  amenorrhseic  women.  It  must  therefore  be  admitted 
that  menstruation  is  not  dependent  on  the  maturation  and  discharge  of 
ova. 

It  was,  moreover,  formerly  understood  that  ova  were  discharged 
toward  the  close  or  soon  after  the  cessation  of  a  menstrual  flow.  Obser- 
vations made  after  death,  and  facts  obtained  by  clinical  investigation, 
however,  do  not  support  this  view.  Eupture  of  a  Graafian  follicle  does 
not  happen  on  the  same  day  of  the  monthly  period  in  all  women.  It 
may  occur  toward  the  close  or  soon  after  the  cessation  of  a  flow;  but  only 
in  a  small  minority  of  the  subjects  examined  after  death  was  this  the 
case.  On  the  other  hand,  in  almost  all  such  subjects  of  which  there  is 
record,  rupture  of  the  follicle  appears  to  have  taken  place  before  the 
commencement  of  the  catamenial  flow.  Moreover,  the  custom  of  the 
Jews — a  prolific  race,  to  whom  by  the  Levitical  law  sexual  intercourse 
during  the  week  following  menstruation  was  forbidden — militates 
strongly  in  favor  of  the  view  that  conception  usually  occurs  before  and 
not  soon  after  a  menstrual  epoch,  and  necessarily,  therefore,  for  the  view 
that  ova  are  usually  discharged  before  the  catamenial  flow.  This,  to- 
gether with  the  anatomical  condition  of  the  uterus  just  before  the 
catamenia,  seems  to  indicate  that  the  ovum  fertilized  is  that  which  is 
discharged  in  connection  with  the  first  absent,  and  not  that  with  the 
last  present  menstruation. 

Though  menstruation  does  not  appear  to  depend  upon  the  discharge 
of  ova,  yet  the  presence  of  the  ovaries  seems  necessary  for  the  perform- 
ance of  the  function;  for  women  do  not  menstruate  when  both  ovaries 


THE    REPRODUCTIVE    ORGANS. 


759 


have  been  removed  by  operation.  Some  instances  have  been  recently 
recorded,  indeed,  of  a  sanguineous  discharge  occurring  periodically  from 
the  vagina  after  both  ovaries  have  been  previously  removed  for  disease ; 
and  it  has  been  inferred  from  this  that  menstruation  is  a  function  inde- 
pendent of  the  ovary :  but  this  evidence  is  not  conclusive,  inasmuch  as 
it  is  possible  that  portions  of  ovarian  tissue  were  left  after  the  operation. 
Source  and  Characters  of  Menstrval  Discharge. — The  menstrual  dis- 
charge is  a  thin  sanguineous  fluid,  having  a  peculiar  odor.  It  is  of  a 
dark  color,   and    consists  of   blood,   eijithelium,   and   mucus  from    the 


Fig.  454. 


Fig.  455. 


Fig.  456. 


Fig.  454.— Diagram  of  uterus  just  before  menstruation;  the  sliaded  portion  represents  the 
thickened  mucous  membrane. 

Fig.  455.— Diagram  of  uterus  when  menstruation  has  just  ceased,  showing  the  cavity  of  the 
uterus  deprived  of  mucous  membrane. 

Fig.  456. — Diagram  of  uterus  a  week  after  the  menstrual  flux  has  ceased:  the  shaded  portion 
represents  renewed  raucous  membrane.    (J.  Williams.) 


uterus  and  vagina.  The  menstrual  flow  is  preceded  by  a  general  engorg- 
ment  of  all  the  pelvic  organs  with  blood.  The  cervix  and  vagina  become 
darker  in  color  and  softer  in  texture,  and  the  quantity  of  mucus  secreted 
by  the  glands  of  the  cervix  and  body  is  increased.  The  uterine  mucous 
membrane  is  swollen  and  the  glands  are  elongated  and  tortuous.  The 
discharge  of  blood,  the  source  of  which  is  the  mucous  membrane  of  the 
body  of  the  uterus,  is  probably  associated  with  uterine  contractions. 
There  is  great  difference  of  opinion  as  to  whether  or  not  any  of  the 
uterine  mucous  membrane  is  normally  shed  during  the  process  of  men- 
struation. John  Williams  believes  that  the  whole  of  the  mucous  mem- 
brane of  the  body  of   the  uterus  is  throwu  otf  at  each  monthly  period, 


7fiO  HANDBOOK    OF    PHYSIOLOGY. 

forming  a  true  decidua  menstrualis  (fig.  454),  while  Moricke  and  others 
believe  that  the  mucons  membrane  remains  intact.  Leopold  believes 
that  red  blood  corpuscles  escape  from  the  congested  capillaries  and  un- 
dermine the  superficial  epithelium,  and  that  in  this  way  the  superficial 
layer  of  the  mucous  membrane  is  eroded  and  subsequently  regenerated. 
It  is  probable  that  menstruation  is  not  a  sign  of  the  capability  of  being 
impregnated,  as  much  as  of  disappointed  impregnation. 

Menstrual  Life. — The  occurrence  of  a  menstrual  discharge  is  one  of 
the  most  prominent  indications  of  the  commencement  of  puberty  in  the 
female  sex;  though  its  absence  even  for  several  years  is  not  necessarily 
attended  with  arrest  of  the  other  characters  of  this  period  of  life,  or 
with  inaptness  for  sexual  union,  or  incapability  of  impregnation.  The 
average  time  of  its  first  appearance  in  females  of  this  country  and  others 
of  about  the  same  latitude,  is  from  fourteen  to  fifteen ;  but  it  is  much 
influenced  by  the  kind  of  life  to  which  girls  are  subjected,  being  accel- 
erated by  habits  of  luxury  and  indolence,  and  retarded  by  contrary 
conditions.  Its  appearance  may  be  slightly  earlier  in  persons  dwelling 
in  warm  climes  than  in  those  inhabiting  colder  latitudes.  Much  of  the 
influence  attributed  to  climate  appears  due  to  the  custom  prevalent  in 
many  hot  countries,  as  in  Hindostan,  of  giving  girls  in  marriage  at  a 
very  early  age,  and  inducing  sexual  excitement  previous  to  the  proper 
menstrual  time.  The  menstrual  functions  continue  through  the  whole 
fruitful  period  of  a  woman's  life  and  usually  cease  between  the  forty- 
fifth  and  fiftieth  years. 

The  several  menstrual  periods  usually  occur  at  intervals  of  a  lunar 
month,  the  duration  of  each  being  from  three  to  six  days.  In  some 
women  the  intervals  are  so  short  as  three  weeks  or  even  less ;  while  in 
others  they  are  longer  than  a  month.  The  periodical  return  is  usually 
attended  by  pain  in  the  loins,  a  sense  of  fatigue  in  the  lower  limbs,  and 
other  symptoms,  which  are  different  in  different  individuals.  Menstru- 
ation does  not  usually  occur  in  pregnant  women,  or  in  those  who  are 
suckling;  but  instances  of  its  occurrence  in  both  these  conditions  are  by 
no  means  rare. 

Corpus  Luteum. — Immediately  before,  as  well  as  subsequent  to,  the 
rupture  of  a  Graafian  follicle,  and  the  escape  of  its  ovum,  certain  changes 
ensue  in  the  interior  of  the  vesicle,  which  result  in  the  production  of  a 
yellowish  mass,  termed  a  Corpus  luteum. 

When  fully  formed  the  corpus  luteum  of  mammiferous  animals  is  a 
roundish  solid  body,  of  a  yellowish  or  orange  color,  and  composed  of  a 
number  of  lobules,  Avhich  surround,  sometimes  a  small  cavity,  but  more 
frequently  a  small  stelliform  mass  of  white  substance,  from  which  deli- 
cate processes  pass  as  septa  between  the  several  lobules.  Very  often,  in 
the  cow  and   sheep,  there  is  no  white  substance  in  the  centre;  and  the 


THE    HKPKODUCTIVE    OHGANS. 


761 


lobules  projecting  from  the  opposite  walls  of  the  Graafian  follicle  appear 
in  a  section  to  be  separated  by  the  thinnest  possible  lamina  of  semi- 
transparent  tissue. 

"When  a  follicle  is  about  to  burst  and  expel  the  ovum,  it  becomes 
highly  vascular  and  opaque;  and,  immediately  before  the  rupture  takes 
place,  its  walls  appear  thickened  on  the  interior  by  a  reddish  glutinous 
or  fleshy-looking  substance.  Immediately  after  the  rupture,  the  inner 
layer  of  the  wall  of  the  vesicle  appears  pulpy  and  flocculent.  It  is 
thrown  into  Avrinkles  by  the  contraction  of  the  outer  layer,  and,  soon, 
red  fleshy  mammillary  processes  grow  from  it,  and  gradually  enlarge  till 
they  nearly  fill  the  vesicle,  and  even  protrude  from  the  orifice  in  the 
external  covering  of  the  ovary.  Subsequently  this  orifice  closes,  but  the 
fleshy  growth  within  still  increases  during  the  earlier  period  of  preg- 
nancy, the  color  of  the  substance  gradually  changing  from  red  to  yellow, 
and  its  consistence  becoming  firmer. 

The  human  corpus  luteum  (fig.  457)  differs  from  that  of  the  domestic 
quadruped  in  being  of  a  firmer  texture,  and  having  more  frequently  a 


Fig.  457. — Corpora  lutea  of  different  periods.  B,  corpus  luteum  of  about  the  sixth  week 
after  impregnation,  showing  its  plicated  form  at  that  period.  1,  substance  of  the  ovary;  2,  sub- 
stance or  the  corpus  luteum;  3,  a  grayish  coagulum  in  its  cavity.  (Paterson.)  A,  corpus  li»- 
teum  two  days  after  delivery ;  D,  m  the  twelfth  week  after  deliverj-.     Qlontgomery. ) 

persistent  cavity  at  its  centre,  and  in  the  stelliform  cicatrix,  which  re- 
mains in  the  cases  where  the  cavity  is  obliterated,  being  proportionately 
of  much  larger  bulk.  The  quantity  of  yellow  substance  formed  is  also 
much  less:  and  although  the  deposit  increases  after  the  vesicle  has 
burst,  yet  it  does  not  usually  form  mammillary  growths  projecting  into 
the  cavity  of  the  vesicle,  and  never  protrudes  from  the  orifice,  as  is  the 
case  in  other  Mammalia.  It  maintains  the  character  of  a  uniform,  or 
nearly  uniform,  layer,  which  is  thrown  into  wrinkles,  in  consequence  of 
the  contraction  of  the  external  tunic  of  the  A-esicle.  After  the  orifice  of 
the  vesicle  has  closed,  the  growth  of  the  yellow  substance  continues  dur- 
ing the  first  half  of  pregnancy,  till  the  cavity  is  reduced  to  a  compara- 
tively small  size,  or  is  obliterated;  in  the  latter  case,  merely  a  white 
stelliform  cicatrix  remains  in  the  centre  of  the  corpus  luteum. 

An  effusion  of  blood  generally  takes  place  into  the  cavity  of  the  fol- 


762 


HANDBOOK    OF    PHTSIOLOGT. 


licle  at  the  time  of  its  rupture,  especially  in  the  human  subject,  but  it 
has  no  share  in  forming  the  yellow  body ;  it  gradually  loses  its  coloring 
matter.  The  serum  of  the  blood  sometimes  remains  included  within  a 
cavity  in  the  centre  of  the  coagulum,  and  then  the  decolorized  fibrin 
forms  a  membraniform  sac,  lining  the  corpus  luteum.  At  other  times 
the  serum  is  removed,  and  the  fibrin  constitutes  a  solid  stelliform  mass. 

The  yellow  substance  of  which  the  corpus  luteum  consists,  both  in 
the  human  subject  and  in  the  domestic  animals,  is  a  growth  from  the 
inner  surface  of  the  ruptured  follicle,  the  result  of  an  increased  devel- 
opment of  the  membrana  granulosa. 

The  first  changes  of  the  internal  coat  of  the  Graafian  vesicle  in  the 
process  of  formation  of  a  corpus  luteum  seem  to  occur  in  every  case  in 
which  an  ovum  escapes;  as  well  in  the  human  subject  as  in  the  domestic 
quadrupeds.  If  the  ovum  is  impregnated,  the  growth  of  the  yellow  sub- 
stance continues  daring  nearly  the  whole  period  of  gestation  and  forms 
the  large  corpus  luteum  commonly  described  as  a  characteristic  mark  of 
impregnation.  If  the  ovum  is  not  impregnated,  the  growth  of  yellow 
substance  on  the  internal  surface  of  the  vesicle  proceeds,  in  the  human 
ovary,  no  further  than  the  formation  of  a  thin  layer,  which  shortly  dis- 
appears; but  in  the  domestic  animals  it  continues  for  some  time  after 
the  ovum  has  perished,  and  forms  a  corpus  luteum  of  considerable  size. 
The  fact  that  a  structure,  in  its  essential  characters  similar  to,  though 
smaller  than,  a  corpus  luteum  observed  during  pregnancy,  is  formed  in 
the  human  subject,  independent  of  impregnation  or  of  sexual  union, 
coupled  with  the  varieties  in  size  of  corpora  lutea  formed  during  preg- 
nancy, necessarily  renders  unsafe  all  evidence  of  previous  impregnation 
founded  on  the  existence  of  a  corpus  luteum  in  the  ovary. 

The    following    table  by  Dalton,  expresses  well  the  differences  between  the 
corpus  luteum  of  the  pregnant  and  unimpregnated  condition  respectively : — 

Corpus  Luteum  of  Menstru-        Corpus  Luteum  of  Pregnancy. 

ation. 
Three-quarters  of  an  inch  in  diameter  ;  central  clot  reddish  ;  con 
voluted  wall  pale. 

Larger  ;  convoluted  wall  bright    yel- 
low ;  clot  still  reddish. 


At  the  end  of 

three  weeks 

One  month  . 


Two  months 


Six  m,onths 


Nirce  months 


wall 
still 


Smaller ;  convoluted 
bright  yellow  ;  clot 
reddish. 

Reduced  to  the  condition 
of  an  insignificant  cica- 
trix. 

Absent. 


Absent. 


Seven-eighths  of  an  inch  in  dia- 
meter ;  convoluted  wall  bright 
yellow ;  clot  perfectly  decolor- 
ized. 

Still  as  large  as  at  end  of  second 
month  ;  clot  fibrinous  ;  convoluted 
wall  paler. 

One-half  an  inch  in  diameter ;  cen- 
tral clot  converted  into  a  radi- 
ating cicatrix  ;  the  external  wall 
tolerably  thick  and  convoluted, 
hut  without  any  bright  yellow 
color. 


THE    EEPRODUCTIVE    ORGANS. 


763 


Of  the  Male. — In  order  that  the  ovum  should  be  fecundated,  it  is 
necessary  that  it  should  meet  with  the  seminal  fluid  of  the  male.  This 
is  accomplished  by  the  junction  of  the  sexes  in  the  act  of  coition, 
whereby  the  seminal  fluid  is  discharged  into  the  neighborhood  of,  if  not 
within,  the  cervix  uteri.  Before  considering  the  changes  which  are 
produced  in  the  ovum  by  impregnation,  it  will  be  as  well  to  describe  the 
nature  of  the  seminal  fluid.  This  consists  essentially  of  the  semen  se- 
creted, by  the  testes,  and  to  this  are  added  a  material  secreted  by  the 
vesiculae  seminales,  as  well  as  the  secretion  of  the  prostate  gland,  and  of 
Cowper's  glands.  Portions  of  -these  several  fluids  are  discharged,  to- 
gether with   the  proper  secretion  of  the  testicles. 

The  semen  is  a  viscid,  whitish,  albuminous  fluid  of  a  peculiar  odor. 
It  contains  epithelium,  granules  or  colorless  particles,  and  large  num- 
bers of  sperinatozoa,   which  are  the  characteristic  and  essential  elements. 


^v 


Fig.  458. 


Fig.  459. 


Fig.  458. —Spermatic  filaments  from  the  human  vas  deferens.     1,  magnified  300  diameters;  2, 
maffQifled  800  diameters;  o,  from  the  side;  6,  from  above.     (From  Kfilliker.) 
Fig.  459. —Spermatozoa.     1,  Of  salamander;  2,  human.     (H.  Gibbes. ) 


The  spermatozoa  are  minute  bodies  each  consisting  of  a  flattened  oval 
head  and  attached  to  it  a  long  slender  tapering  mobile  flagellum  or  tail. 
In  some  forms  of  spermatozoa  there  is  a  small  middle  piece  interposed 
between  the  head  and  the  tail.  The  head  is  about  u-ginrtli  "^c^i  (about 
4:fJL)  long  and  i-g-J-jj-g-th  inch  (about  2.5ai)  broad.  The  tail  is  about  ■gVinr^'^ 
to  4Q^j)Qth  inch  (5m-6m)  long.  The  spermatozoa  possess  the  power  of 
active  movement,  and  it  is  by  this  sinuous,  cilia-like  movement  that 
they  are  propelled  in  the  female  and  so  helped  in  their  progress  to  meet 
the  ovum.     The  lashing  cilium-like  movement  of  a  spermatozoon  may 


7t)4  HANDBOOK    OP    PHYSIOLOGY. 

go  on  for  hoars  or  days  in  the  alkaline  fluids  of  the  body.  It  is  stopped 
by  any  of  the  agencies  which  stop  ciliary  movement,  e.g.,  acids,  or 
strong  alkalies,  alcohol,  chloroform,  cold  to  0°  C,  and  heat  above  50°  C. 

On  examining  the  spermatozoon  of  Triton  cristatus,  one  of  the  am- 
phibia which  possess  the  largest  spermatozoa  of  all  vertebrate  animals, 
H.  Gibbes  found  that  the  organism  consisted  of  {a)  a  long  pointed  head, 
at  the  base  of  which  is  (J),  an  elliptical  structure  joining  the  head  to 
(c;),  a  long  filiform  body;  (fZ),  a  fine  filament,  much  longer  than  the 
body,  is  connected  with  this  latter  by  (e),  a  homogeneous  membrane. 

The  head,  as  it  appears  in  the  fresh,  specimen,  has  a  different  refrac- 
tive power  from  that  of  the  rest  of  the  organism,  and  with  a  high  power 
appears  to  be  a  light  green  color ;  there  is  also  a  central  line  running  up 
it,  from  which  it  appears  to  be  hollow. 

The  elliptical  structure  at  the  base  of  the  head  connects  it  with  the 
long  threadlike  body,  and  the  filament  springs  from  it. 

While  the  spermatozoon  is  living,  this  filament  is  in  constant  mo- 
tion; at  first  this  is  so  quick  that  it  is  difficult  to  see  it,  but  as  its  vital- 
ity becomes  impaired  the  motion  gets  slower,  and  it  is  then  easily  per- 
ceived to  be  a  continuous  waving  from  side  to  side. 

The  spermatozoa  of  all  mammalia  examined,  consisting  of  man,  hull, 
dog,  horse,  cat,  pig,  mouse,  rat,  guinea-pig,  had  instead  of  the  long-pointed 
head  of  the  amphibian,  a  blunt  thick  process  of  different  shapes  in  the 
different  animals ;  and  from  the  root  or  neck  of  this  proceeded  the  long 
filament  just  as  in  the  amphibia,  only  so  delicate  as  to  be  invisible  except 
with  very  high  powers. 

In  man  the  head  (fig.  459)  is  club-shaped,  and  from  its  base  springs 
the  very  delicate  filament,  which  is  three  or  four  times  as  long  as  the 
body ;  and  the  membrane  which  attaches  it  to  the  body  is  much  broader, 
and  allows  it  to  lie  at  a  greater  distance  from  the  body  than  in  the  sper- 
matozoa of  any  other  Mammal  examined. 

From  his  investigation,  Gibbes  concluded : — 1st,  that  the  head  of  the 
spermatozoon  is  inclosed  in  a  sheath,  which  is  a  continuation  of  the 
membrane  which  surrounds  the  filament,  and  connects  it  to  the  body, 
acting  in  fact  the  part  of  a  mesentery.  2ndly.  That  the  substance  of  the 
head  is  quite  distinct  in  its  composition  from  the  elliptical  structure, 
the  filament  and  the  long  body,  and  that  it  is  readily  acted  on  by  alkalies ; 
these  reagents  have  no  effect,  however,  on  the  other  part,  exempting 
the  membraneous  sheath.  3rdly.  That  this  elliptical  structure  has  its 
analogue  in  the  mammalian  spermatozoon;  in  the  one  case  the  head  is 
drawn  out  as  a  long  pointed  process,  in  the  other  it  is  of  a  globular 
form,  and  surrounds  the  elliptical  structure.  4thly.  That  the  motive 
power  lies,  in  a  great  measure,  in  the  filament  and  the  membrane  at- 
taching it  to  the  body. 


THE    REPRODUCTIYE    ORGANS.  765 

The  spermatozoa  are  derived  from  the  breaking  up  of  the  seminal 
cells  or  daughter  cells.     They  must  be  looked  upon  as  modified  cells. 

The  occurrence  of  spermatozoa  in  the  impregnating  fluid  of  nearly 
all  classes  of  animals,  proves  that  they  are  essential  to  the  process  of 
impregnation,  and  their  actual  contact  with  the  ovum  is  necessary  for 
its  development. 

The  seminal  fluid  is,  probably,  after  the  period  of  puberty  secreted 
constantly,  though,  except  under  excitement,  very  slowly,  in  the  tubules 
of  the  testicles.  From  these  it  passes  along  the  vasa  deferentia  into  the 
vesiculse  seminales,  whence,  if  not  expelled  in  emission,  it  may  be  dis- 
charged, as  slowly  as  it  enters  them,  either  with  the  urine,  which  may 
remove  minute  quantities,  mingled  with  the  mucus  of  the  bladder  and 
the  secretion  of  the  prostate,  or  from  the  urethra  in  the  act  of  defaeca- 
tion. 

To  the  vesiculte  seminales  a  double  function  maybe  assigned;  for 
they  both  secrete  some  fluid  to  be  added  to  that  of  the  testicles,  and 
serve  as  reservoirs  for  the  seminal  fluid.  The  former  is  their  most  con- 
stant and  probably  most  important  office;  for  in  the  horse,  bear,  guinea- 
pig,  and  several  other  animals,  in  whom  the  vesiculae  seminales  are  large 
and  of  apparently  active  functions,  they  do  not  communicate  with  the 
vasa  deferentia,  but  pour  their  secretions,  separately,  though  it  may  be 
simultaneously,  into  the  urethra. 

There  is  a  complete  want  of  information  respecting  the  nature  and 
purposes  of  the  secretions  of  the  prostate  and  Cowper's  glands.  That 
they  contribute  to  the  right  composition  of  the  impregnating  fluid,  is 
shown  both  by  the  position  of  the  glands  and  by  their  enlarging  with 
the  testicles  at  the  approach  of  an  animal's  breeding  time.  But  that 
they  contribute  only  a  subordinate  part  is  shown  by  the  fact,  that,  when 
the  testicles  are  lost,  though  these  other  organs  be  perfect,  all  procrea- 
tive  power  ceases. 

The  fluid  part  of  the  semen  or  liquor  seminis  has  not  been  satisfac- 
torily analyzed :  but  Henle  says  it  contains  fibrin,  because  shortly  after 
being  discharged,  flocculi  form  in  it  by  spontaneous  coagulation,  and 
leave  the  rest  of  it  thinner  and  more  liquid,  so  that  the  filaments  move 
in  it  more  actively.  The  chief  constituents  of  the  semen  are  said  to  be  a 
variety  of  nuclein,  which  does  not  contain  sulphur;  certsim proteids,  one 
of  which  contains  four  per  cent,  of  sulphur;  lecithin;  cliolesterin;  faty 
and  extractives. 


CHAPTER  XIX. 

DEVELOPMENT. 

Changes  which  occur  in  the  Ovum. 

Of  the  changes  which  take  place  in  the  ovum,  some  occur  before 
and  are  as  it  were  preparatory  to  impregnation,  and  others  ensue  after 
impregnation.  It  will  be  as  well  to  consider  the  respective  changes 
separately. 

Changes  jjrior  to  Impregnation. — These  changes  especially  concern 
the  germinal  vesicle,  and  have  been  observed  chiefly  in  the  ova  of  low 
types.  The  ovum  when  ripe  and  detached  from  the  ovary  consists,  it 
will  be  remembered,  of  a  granular  yolk  inclosed  within  the  protoplasmic 
zona  pellucida,  and  containing  the  germinal  vesicle  and  germinal  spot  situ- 
ated eccentrically.  The  yolk  granules  are  of  different  sizes,  from  the 
minutest  molecules  up  to  a  diameter  of  toVo^^^  ^^  yJQ-g-th  of  an  inch 
(about  25,a).  The  germinal  vesicle  consists  of  reticulated  protoplasm 
inclosed  in  a  distinct  membrane,  and  containing  one  or  more  nucleoli 
or  germinal  spots.  The  primary  change  observed  in  the  ovum  consists 
in  the  travelling  of  the  germinal  vesicle  to  the  surface,  and  the  disap- 
pearance of  its  inclosing  membrane,  with  a  consequent  indentation  and 
indistinctness  of  its  outline.  Its  protoplasm  becomes  to  a  considerable 
extent  confounded  with  the  yolk  substance,  and  its  germinal  spot  disap- 
pears. The  next  step  in  the  process  is  the  appearance  in  the  yolk  of 
two  stars  in  a  clear  space  near  the  poles  of  the  vesicle  elongated  to  a 
certain  extent,  and  from  this  results  a  nuclear  spindle,  with  the  stars  at 
either  end  lying  near  the  surface  of  the  yolk.  This  spindle  next  becomes 
vertical,  the  nucleus  divides  into  two  parts,  and  that  nearer  the  surface 
protrudes  from  the  ovum  enveloped  in  a  protoplasmic  mass,  which  by 
constriction  forms  the  first  polar  cell.  A  second  polar  cell  arises  in  the 
same  way.  The  remaining  daughter  nucleus  again  divides — one-half  of 
it  is  extruded  from  the  ovum,  forming  a  second  polar  cell;  the  other 
half  remains  behind  and  is  called  the  female  j)ro-nucleus.  This  is 
clearly  derived  from  the  original  germinal  vesicle.  It  must  be  remem- 
bered that  these  changes  have  been  so  far  observed  only  in  a  certain 
number  of  instances.  It  is  very  possible,  not  to  say  probable,  that  such 
changes  are  universal  in  the  animal  kingdom  (Balfour). 

Balfour's  view  as  to  the  formation  of  the  polar  bodies  may  be  given 

766 


DEVELOPMENT.  7^7 

in  his  own  words: — "  My  view  amounts  to  the  following,  viz.,  that  after 
the  formation  of  the  polar-cells,  the  remainder  of  the  germinal  vesicle 
within  the  ovum  (the  female  pro-nucleus)  is  incapable  of  further  devel- 
opment without  the  addition  of  the  nuclear  part  of  the  male  element 
(spermatozoon),  and  that  if  polar-cells  were  not  formed,  parthenogenesis 
might  normally  occur." 

Changes  following  Impregnation. — The  process  of  impregnation 
of  the  ovum  has  been  observed  most  accurately  in  the  lower  types.  In 
mammalia,  although  spermatozoa  pass  in  numbers  through  the  yolk 
envelope,  yet  their  further  progress  is  only  inferred  from  observations  on 
the  lower  animals.  The  process  in  asteinas  gJacialis,  according  to  Bal- 
four, is  as  follows: — Tlie  head  of  a  single  spertnatozoon  joins  with  an 
elevation  of  the  yolk  substance,  the  tail  remaining  motionless,  and  then 
disappearing.  The  head  enveloped  in  the  protoplasm  then  sinks  into  the 
yolk  and  becomes  a  nucleus,  from  which  the  yolk  substance  is  arranged 
in  radiating  lines.  This  is  the  male  pro-mideus.  At  first,  at  some  dis- 
tance from  the  female  jDro-nucleus,  it  after  a  while  approaches  nearer, 
and  the  female  pro-nucleus,  which  was  before  inactive,  becomes  active. 
The  nuclei  at  last  meet  and  unite.  The  result  of  their  union  is  i\\e  first 
sepiientalioii  sphere,  or  hlasto-spliere.  It  is  a  nucleated  protoplasmic  cell. 
The  changes  which  have  resulted  in  the  formation  of  the  blasto-sphere 
or  primitive  segmentation  germ  are  followed  by  the  process  known  as 
segmentation  of  the  yolk. 

This  jarocess  and  the  earlier  stages  in  development  are  so  fundamen- 
tally similar  in  all  vertebrate  animals,  from  fishes  up  to  man,  that  the 
gaps  existing  in  our  knowledge  of  the  process  in  the  higher  mammalia, 
such  as  man,  may  be,  in  part,  at  any  rate,  filled  up  by  the  more  accu- 
rate knowledge  which  we  possess  of  the  development  of  the  ovum  in 
such  animals  as  the  trout,  frog,  and  fowl. 

One  important  distinction  between  the  ova  of  various  vertebrata  should  be 
remembered.  In  the  hen's  egg,  besides  the  shell  and  the  wliite  or  albumen,  two 
other  structures  are  to  be  distinguished — the  germ,  often  called  the  cicatricula 
or  "tread."  and  the  yolk,  inclosed  in  its  vitelline  membrane. 

The  germ  is  (as  was  mentioned  in  the  description  already  given)  essentially 
a  cell,  consisting  of  protoplasm  inclosing  a  nucleus  and  nucleolus.  It  alone 
participates  in  the  process  of  segmentation,  the  great  mass  of  the  yolk  (food- 
yolk)  remaining  quite  unaffected  by  it.  Since  only  the  germ,  which  forms  but 
a  small  portion  of  the  yolk,  undergoes  segmentation,  the  ovum  is  called  mero- 
blastic. 

In  the  mammalia,  on  the  other  hand,  there  is  no  large  unsegmented  mass 
corresponding  to  the  food-yolk  of  birds  ;  the  entire  ovum  undergoes  segmenta- 
tion, and  is  hence  termed  holoblastie. 

The  eggs  of  fishes,  reptiles,  and  birds,  are  meroblastic,  wliile  tliose  of  am- 
phibia and  mammalia  are  holoblastic. 

Of  the  changes  which  the  mammalian  ovum  undergoes  previous  to 


768 


HAITDBOOK    OF    PHYSIOLOGY. 


the  formation  of  the  embryo,  those  which  occur  while  it  is  still  in  the 
ovary  are  independent  of  impregnation :  others  take  place  after  it  has 
reached  the  Fallopian  tube.     The  knowledge  we  possess  of  these  changes 

is  derived  almost  exclusively  from  obser- 
vations on  the  ova  of  the  bitch  and  rabbit: 
but  it  may  be  inferred  that  analogous 
changes  ensue  in  the  human  ovum. 

As  the  ovum  approaches  the  middle  of 
the  Fallopian  tube,  it  begins  to  receive  a 
new  investment,  consisting  of  a  layer  of 
transparent  albuminous  or  glutinous  sub- 
stance, which  forms  upon  the  exterior  of 
the  zona  pellucida.  It  is  at  first  exceed- 
ingly fine,  and  owing  to  this,  and  to  its 
transparency,  is  not  easily  recognized, 
but  at  the  lower  part  of  the  Fallopian 
tube  it  acquires  considerable  thickness. 

Segmentation. — ^The  first  visible  result 
of  fertilization  is  a  slight  amoeboid  move- 
ment in  the  protoplasm  of  the  ovum: 
this  has  been  observed  in  some  fish,  in  the 
frog,  and  in  some  mammals.  Immediately 
succeeding  to  this  the  process  of  segmen- 
tation commences,  and  is  completed  dur- 
ing the  passage  of  the  ovum  through  the 
Fallopian  tube.  In  mammals,  in  which 
the  process  is  an  example  of  complete  seg- 
mentation, the  yolk  becomes  constricted 
in  the  middle,  and  is  surrounded  by  a 
furrow  which,  gradually  deepening,  at 
length  cuts  it  in  half,  while  the  same  pro- 
cess begins  almost  immediately  in  each 
half  of  the  yolk,  and  cuts  it  also  in  two. 
The  same  process  is  repeated  in  each  of 
the  quarters,  and  so  on,  until  at  last  by 
continual  cleavings,  the  whole  yolk  is 
changed  into  a  mulberry-like  mass  of 
small  and  more  or  less  rounded  bodies, 
sometimes  called  vitelline  spheres^  the 
whole  still  inclosed  by  the  zona  pellucida  (fig.  460).  Each  of  these  lit- 
tle spherules  contains  a  transparent  vesicle,  like  an  oil-globule,  which  is 
seen  with  difiQculty,  on  account  of  its  being  enveloped  by  the  yolk-gran- 
ules which  adhere  closely  to  its  surface. 


Fig.  460. — Diagrams  of  the  vari- 
ous stages  of  cleavage  of  the  yolk, 
(Dalton.) 


DEVELOPMENT.  7C,J) 

The  cause  of  this  singular  subdivision  of  the  yolk  is  quite  obscure: 
though  the  inimediate  agent  in  its  production  seems  to  be  the  central 
vesicle  contained  in  each  division  of  the  yolk.  Originally  there  was  i^rob- 
ably  but  one  vesicle,  situated  in  the  centre  of  the  entire  granular  mass 
of  the  yolk,  and  probably  derived  in  the  manner  already  described  from 
the  germinal  vesicle.  This  divides  and  subdivides :  each  successive  divi- 
sion and  subdivision  of  the  vesicle  being  accompanied  by  a  corresponding 
division  of  the  yolk. 

About  the  time  at  which  the  mammalian  ovum  reaches  the  uterus, 
the  process  of  division  and  subdivision  of  the  yolk  ajDpears  to  have 
ceased,  its  substance  having  been  resolved  into  its  ultimate  and  smallest 
divisions,  while  its  surface  jn-esents  a  uniform  finely-granular  aspect, 
instead  of  its  late  mulberry-like  appearance.  The  ovum,  indeed,  ap- 
pears at  first  sight  to  have  lost  all  trace  of  the  cleavage  process,  and, 
with  the  exception  of  being  jjaler  and  more  translucent,  almost  exactly 
resembles  the  ovarian  ovum,  its  yolk  consisting  apparently  of  a  confused 
mass  of  finely  granular  substance.  But  on  a  more  careful  examination, 
it  is  found  that  these  granules  are  aggregated  into  numerous  minute 
spheroidal  masses,  each  of  which  contains  a  clear  vesicle  or  nucleus  in 
its  centre,  and  is,  in  fact,  an  embryonal  cell  The  zona  jDellucida,  and 
the  layers  of  albuminious  matter  surrounding  it,  have  at  this  time  the 
same  character  as  when  at  the  lower  part  of  the  Fallopian  tube. 

The  passage  of  the  ovum,  from  the  ovary  to  the  uterus,  occupies 
probably  eight  or  ten  days  in  the  human  female. 

When  the  peripheral  cells,  which  are  formed  first,  are  fully  devel- 
oped, they  arrange  themselves  at  the  surface  of  the  yolk  into  a  kind  of 
membrane,  and  at  the  same  time  assume  a  polyhedral  shape  from  mutual 
pressure,  so  as  to  resemble  pavement  epithelium.  The  deeper  cells  of  the 
interior  pass  gradually  to  the  surface  and  accumulate  there,  thus  in- 
creasing the  thickness  of  the  membrane  already  formed  by  the  more 
superficial  layer  of  cells,  while  the  central  part  of  the  yolk  remains  filled 
only  with  a  clear  fluid.  By  this  means  the  yolk  is  shortly  converted 
into  a  kind  of  secondary  vesicle,  the  walls  of  which  are  composed  exter- 
nally of  the  original  vitelline  membrane,  and  within  by  the  newly  formed 
cellular  layer,  the  blastoderm  or  germinal  membrane,  as  it  is  called. 

Segmentation  in  the  Chick. — The  embryo  chick  affords  an  illustra- 
tion of  what  is  known  as  incomplete  or  partial  segmentation,  or  mero- 
blastic  segmentation.  In  the  youngest  ova  the  germinal  vesicle  is  situ- 
ated subcentrally,  but  as  development  proceeds  it  passes  to  the  periphery, 
and  the  protoplasm  surrounding  it  remaining  free  from  yolk  granules, 
the  germinal  disc  is  formed.  This  germinal  disc  is  not  marked  out  by 
any  sharp  line  from  the  remaining  protoplasm,  but  passes  insensibly 
into  it.  The  first  change  consists  in  the  appearance  of  a  furrow  run- 
49 


770  HAi^DBOOK    OF   PHYSIOLOGY. 

ning  across  the  disc  dividing  it  into  two;  it  does  not  extend  across 
the  whole  breadth.  A  second  furrow,  at  right  angles,  cutting  the  first 
a  little  eccentrically,  next  appears,  and  the  disc  is  thus  cut  into  four 
quadrants.  The  furrows  do  not  extend  through  the  whole  thickness  of 
the  disc,  and  the  segments  are  not  separated  out  on  the  lower  aspect. 
The  quadrants  are  next  bisected  by  radiating  furrows,  and  the  disc  is 
thus  divided  into  eight  parts.  The  central  portion  of  each  segment  is 
now  cut  off  from  the  peripheral  furrow,  so  that  a  number  of  smaller 
central  and  larger  peripheral  portions  result.  As  the  primary  division 
was  eccentric  and  the  succeeding  followed  the  same  plan,  there  results 
a  bilateral  symmetry ;  but  the  relation  of  the  axis  of  symmetry  and  the 
long  axis  of  the  embryo  is  not  known.  Eapid  division  of  the  segments 
by  furrows  in  various  directions  now  ensues,  and  the  small  central  por- 
tions are  more  rapidly  broken  up  than  the  larger,  and  therefore  become 
more  numerous.  During  this  superficial  segmentation  a  similar  process 
goes  on  throughout  the  whole  mass,  and  division  goes  on  not  only  by 
vertical  but  also  by  horizontal  furrows.  The  result  of  this  process  of 
segmentation  is  that  the  original  germinal  disc  is  cut  into  a  large  num- 
ber of  small  rounded  protoplasmic  cells,  small  in  the  centre,  larger  to 
the  periphery,  and  that  the  superficial  cells  are  smaller  than  those  be- 
low :  the  two  original  layers  of  the  blastoderm  are  thus  early  represented. 
The  process  of  segmentation  proceeds  at  the  periphery  of  the  ger- 
minal disc,  and  at  the  same  time  further  division  of  the  cells  at  the 


Fig.  461. — Vertical  section  of  area  pellucida  and  area  opaca  (left  extremity  of  figure)  of 
blastoderm  of  a  fresh-laid  egg  (unincubated).  S,  superficial  layer  corresponding  to  epiblast ; 
D,  deeper  layer,  corresponding  to  hypoblast,  and  probably  in  part  to  mesoblastj  M,  large 
"formative  cells,"  filled  with  yolk  granules,  and  lying  on  the  floor  of  the  segmentation  cavity; 
A,  the  white  yolk  immediately  underlying  the  segmentation  cavity.     (Strieker.) 

centre  proceeds.  The  nucleus  of  the  original  cell  divides  coincidently 
with  the  protoplasm,  and  so  it  comes  that  the  protoplasmic  masses  are 
nucleated;  and  besides  this,  nuclei  derived  from  the  original  nucleus 
are  found  in  the  ovum  below  the  area  of  segmentation,  and  from  these 
by  the  protoplasm  which  surrounds  them  being  constricted  o£E  with 
them,  supplementary  segmentation  masses  come  to  be  formed.  The 
blastoderm  is  thus  formed  as  the  result  of  segmentation,  and  between  it 
and  the  subjacent  white  yolk  is  a  cavity  containing  fiuid.  The  segmen- 
tation having  been  completed  toward  the  centre,  although  it  still  pro- 
ceeds at  the  periphery,  the  superficial  layer  of  the  blastoderm  becomes 


DEVELOPMENT.  771 

a  layer  of  columnar  nucleated  cells,  and  the  lower  layer  consists  of  larger 
masses  indistinctly  nucleated,  still  granular  and  rounded,  irregularly 
disposed.  In  the  segmentation  cavity  are  the  supplementary  segmenta- 
tion masses  or  formative  cells. 

When  the  egg  is  incubated,  rapid  changes  take  place  in  the  blasto- 
derm, resulting  in  the  formation  first  of  all  of  two,  then  of  the  three 
layers,  which  have  been  already  mentioned  in  the  first  chapter.  The 
superficial,  or  epiblast,  tloes  not  at  first  enter  into  these  changes,  but 


Fig.  462.— Impregnated  egg,  with  eonimeucement  of  formation  of  embryo;  showing  the  area 
germinativa  or  emoryonic  spot,  the  area  peUucida,  and  tlie  primitive  groove  or  trace. 
(Dalton.) 

continues  to  be  a  layer  of  nucleated  columnar  cells.  But  in  the  lower 
layer  of  larger  rounded  cells  certain  of  the  cells  become  flattened  hori- 
zontally, their  granules  disappear,  and  the  luielei  become  distinct.  A 
membrane  of  flattened  nucleated  cells  is  then  formed,  first  of  all  toward 
the  centre  of  the  area,  afterward  2ieripherally  also:  this  is  the  hypoblast. 
Between  the  two  layers  some  cells,  not  belonging  to  either  layer,  remain. 
These  cells  are  almost  entirely  at  the  liack  })art  of  the  area.  Tlie  for- 
mation of  tlie  intermediate  layer  of  mesoblast  is  more  complicated, 
and  will  now  be  described. 

At  this  period  it  is  necessary  to  return  to  the  surface  view  of  the 
blastoderm.  Before  incubation  it  is  seen  to  consist  of  a  more  or  less 
circular  transparent  area,  the  area  pellucida,  surrounded  by  an  opaque 
rim,  which  is  called  the  area  opaca.  'IMie  area  opaca  rests  upon  the 
Avhite  yolk:  beneatli  the  area  pclluci(hi  is  a  cavity  containing  fluid.  In 
the  centre  of  the  area  pcUucida  is  a  white  shining  spot,  or  nucleus  of 
Pander^  shining  through.  This  is  the  upper  dilated  extremity  of  the 
flask-shajjcd  accunuilation  of  white  yolk  upon  which  the  blastoderm 
rests. 

The  yellow  yolk  consists  of  spheres  ^o//  to  100//  in  diameter,  filled  with 
highly  refractive  granules  of  an  albuminous  nature,  and  the  white  yelk 
being  distinguished  from  the  yellow  not  only  by  its  lighter  color,  but 
also  because  its  vesicles  are  smaller  than  those  of  the  yellow.     Each  con- 


772 


HANDBOOK    OF    PHYSIOLOGY. 


tains  a  highly  refractive  body.  Some  large  spheres  contain  a  number  of 
spherules.  Some  of  these  are  vacuolated.  The  white  yolk  not  only  en- 
velopes the  yellow  yolk  in  a  thin  layer,  and  merges  with  the  central 
flask-shaped  mass,  already  mentioned,  but  also  is  found  in  the  yellow 
yolk,  forming  with  it  alternate  layers. 

Except  that  the  central  shining  opacity  of  the  pellucid  area  has  dis- 
appeared, that  the  size  of  the  area  has  increased,  and  that  the  opaque 


Fig.  463,— Transverse  section  tiirough  embryo  chick  (26  hours),  a,  epiblast;  b,  mesoblast; 
c,  hypoblast ;  d,  central  portion  of  mesoblast,  which  is  here  fused  with  epiblast ;  e,  primitive 
groove;  /,  dorsal  ridge.     (Klein.) 

area  has  also  increased,  no  other  change  can  be  remarked  up  to  the  for- 
mation of  the  two  complete  layers.  There  is,  however,  a  slight  ill- 
defined  opacity  at  the  posterior  part  of  the  area  pellucida,  known  as  the 
embryonic  shield.  This  opacity  is  probably  due  to  the  intermediate  cells 
already  mentioned  as  existing  between  the  epiblast  and  hypoblast. 

In  the  posterior  part  of  the  area  pellucida  now  appears  an  opaque 
streak  which  extends  about  a  third  of  the  diameter  of  the  area  toward 
the  middle  line.  This  is  the  Primitive  streak.  It  is  found  on  trans- 
verse section  of  the  blastoderm  in  this  neighborhood  to  be  due  to  a  pro- 
liferation downward  of  cells  two  or  more  deep  from  the  epiblast.  The 
area  pellucida  now  becomes  oval.     As  the  primitive  streak  becomes  more 


Fig,  464.— Diagram  of  transverse  section  through  an  embryo  before  the  closing-in  of  the 
medullary  groove,  m,  cells  of  epiblast  lining  the  medullary  groove  which  will  form  the  spinal 
cord;  h.  epiblast;  d,  hypoblast;  c/i,  notochord;  «,  protovertebra ;  sp,  mesoblast;  iv,  edge  of 
lamina  dorsalis,  folding  over  medullary  groove.     (KoUiker.) 

defined  the  area  pellucida  changes  its  oval  for  a  pear  shape,  but  the 
streak  increases  in  size  faster  than  the  area,  and  so  after  a  time  is  about 
two-thirds  of  its  length.  In  the  primitive  streak  a  groove,  the  primi- 
tive groove,  runs  along  its  axis.  From  the  primitive  streak  the  cells 
from  the  under  surface  of  the  epiblast  now  extend  as  lateral  wings  to  the 
edge  of  the  pellucid  area;  they  are  not  joined  with  the  hypoblast.     The 


DEVELOPMENT. 


773 


intermediate  layer  of  cells  in  this  position  producing  the  primitive 
streak  is  a  portion  of  the  intermediate  layer  or  mesoblast.  It  is 
formed  chiefly  from  the  epiblast,  but  laterally,  especially  in  the  front 
part  of  the  primitive  streak,  it  appears  to  be  derived  at  any  rate  in  part 
from  the  cells  of  the  primitive  lower  layer.  At  the  most  anterior  part 
of  the  primitive  streak,  at  the  point  which  corresponds  to  the  future 
posterior  end  of  the  embryo,  the  three  layers  are  all  Joined  together. 
The  next  important  change  which  occurs  is  found  in  the  hypoblast  in 
front  of  the  primitive  streak.  The  irregular  layer  of  primitive  cells  of 
which  it  is  composed,  split  into  two  layers,  the  lower  consisting  of  flat- 


Fig.  465.— Portion  of  the  germinal  membrane,  with  rudiments  of  the  embryo;  from  the  ovimi 
of  a  bitch.  The  primitive  groove,  a,  is  not  yet  closed,  and  at  its  upper  or  cephalic  end  presents 
three  dilatations,  b,  which  correspond  to  the  three  divisions  or  vesicles  of  the  brain.  At  its 
lower  extremity  the  groove  presents  a  lancet-shaped  dilatation  (sinus  rhomboidalis)  c.  The 
margins  of  the  groove  consist  of  clear  pellucid  nerve-substance.  Along  the  bottom  of  the  groove 
is  observed  a  faint  streak,  which  is  probably  the  chorda  dorsalis.  d.  Vertebral  plates. 
(Bischoff.) 

tened  cells  which  forms  the  hypoblast  proper  and  an  upper  consisting  of 
several  layers  of  stellate  cells,  the  mesoblast. 

In  the  preceding  account  of  the  formation  of  the  blastodermic  layers,  Bal- 
four's description  has  been  chiefly  followed.  It  differs  somewhat  from  tliat 
which  was  formerly  given.  The  mesoblast  was  described  as  arising  from  the 
hypoblast,  together  with  some  of  the  large  formative  cells,  which  migrate  by 
amoeboid  movement  round  the  edge  of  the  hypoblast  (fig.  466,  il/),  and  no  differ- 
ence was  made  in  the  formation  of  the  mesoblast  in  the  primitive  streak  and 
elsewhere. 

There  now  appears  in  the  middle  line  extending  forward  from  the 
primitive  streak  an  opaque  line,  which  proceeds  almost  to  the  anterior 


774 


HANDBOOK    OF    PHYSIOLOGY. 


edge  of  the  area  pellucida,  stopping  short  at  a  transverse  crescent-shaped 
line,  the  future  headfold.  This  line  is  the  commencing  notochord. 
It  is  a  collection  of  mesoblastic  cells  from  the  hypoblast  in  the  middle 
line,  and  remains  connected  with  the  latter  after  the  lateral  portions  of 
the  mesoblast  have  become  quite  detached  from  it.  The  notochord  and 
the  hypoblast  from  which  it  arises  are  continued  posteriorly  into  the 
primitive  streak.  Thus  the  mesoblast  of  the  area  on  either  side  of  the 
middle  line  in  which  the  embryo  is  formed  arises  from  the  hypoblast,  as 
does  also  the  notochord.  In  the  formation  of  the  medullary  plate 
which  now  appears,  the  epiblast  is  concerned.  In  the  middle  line  above 
the  collection  of  cells  that  will  become  the  notochord  that  layer  becomes 
thickened.  The  sides  of  the  central  thickened  portion  are  elevated 
somewhat  to  form  the  medullary  folds  inclosing  between  them  the 
medullary  groove.  From  this  medullary  plate  is  formed  the  central 
nervous  system.  Although  behind  the  groove  is  a  shallow  one,  if  it 
be  traced  forward  it  becomes  deeper  and  narrower,  and  at  the  headfold 
the  folds  curve  round  and  meet  in  the  middle  line.  Anterior  to  the 
headfold  is  a.  second  fold  parallel  to  it,  which  is  the  commencing  amnion. 


^^^SH^2iiSSMKSS^ 


Fig.  466. — Vertical  section  of  blastoderm  of  chick  (1st  day  of  incubation).  S,  epiblast  con- 
sisting of  short  columnar  cells;  D,  hypoblast,  consisting  of  a  single  layer  of  flattened  cells;  M, 
"formative  cells."  They  are  seen  on  the  I'ight  of  the  figure,  passing  in  between  the  epiblast  and 
hypoblast  to  form  the  mesoblast;  A,  white  yolk  granules.  Many  of  the  large  "formative  cells" 
are  seen  containing  these  granules.     (Strieker.) 


The  medullary  canal  is  bounded  by  its  two  folds  or  longitudinal  ele- 
vations, laminse  dorsales,  which  are  folds  consisting  entirely  of  cells  of 
the  epiblast:  these  grow  up  and  arch  over  the  medullary  groove  (fig. 
464)  till  after  some  time  they  coalesce  in  the  middle  line,  converting  it 
from  an  open  furrow  into  a  closed  tube — the  neural  canal  or  the  prim- 
itive cerebro-spinal  axis.  Over  this  closed  tube,  the  walls  of  which  con- 
sist of  more  or  less  cylindrical  cells,  the  supei'ficial  layer  of  the  epiblast 
is  now  continued  as  a  distinct  membrane. 

The  union  of  the  medullary  folds  or  lamina?  dorsalis  takes  place  first 
about  the  neck  of  the  future  embryo;  they  soon  after  unite  over  the 
region  of  the  head,  while  the  closing  in  of  the  groove  progresses  much 
more  slowly  toward  the  hinder  extremity  of  the  embryo.  The  medullary 
groove  is  by  no  means  of  uniform  diameter  throughout,  but  even  before 
the  dorsal  laminae  have  united  over  it,  is  seen  to  be  dilated  at  the  ante- 


DEVELOPMENT, 


75 


rior  extremity  and  obscurely  divided  by  constrictions  into  the   three 
primary  cerebral  vesicles. 

The  part  from  which  the  spinal  cord  is  formed  is  of  nearly  uniform 
calibre,  while  toward  the  posterior  extremity 
is  a  lozenge-shaped  dilatation,  sinus  rhom- 
boidalis,  which  is  the  last  part  to  close  in 
(tig.  4G5). 

While  the  changes  which  have  been  de- 
scribed are  taking  place  in  the  area  pellu- 
cida,  which  has  enlarged  to  a  certain  extent, 
the  area  opaca  has  also  considerably  extended. 
The  liypoblast  and  mesoblast  have  also  been 
prolonged  laterally,  not  by  mere  extension, 
but  also  from  the  germinal  wall,  which  is 
made  up  of  the  thickened  edge  of  the  blasto- 
derm, together  with  formative  cells  of  the 
yolk ;  on  each  side  of  the  notochord  and 
medullary  canal,  the  mesoblast  remains  as  a 
longitudinal  thickening. 

It  now  however  splits  horizontally  into 
two  layers  or  lamina?  (parietal  and  visceral) : 
of  these  the  former,  when  traced  out  from 
the  central  axis,  is  seen  to  be  in  close  appo- 
sition with  the  epiblast,  and  gives  origin  to 
the  parietes  of  the  trunk,  Avhile  the  latter 
adheres  more  or  less  closely  to  the  hypoblast, 
and  gives  rise  to  the  serous  and  muscular 
walls  of  the  alimentary  canal  and  several 
other  parts. 

The  iimted  parietal  layer  of  the  mesoblast 
with  the  epiblast  is  termed  somatopleure, 
the  united  visceral  layer  and  hypoblast, 
splanchnopleure.  The  space  between  them 
is  the  pleuro-peritoneal  cavity,  which 
becomes  subdivided  by  subsequent  partitions 
into  pericardium,  pleura,  and  peritoneum. 

The  splitting  of  the  mesoblast  extends 
almost  to  the  medullary  canal,  but  a  portion 
on  either  side  (  P.  r.  fig.  408)  remains  undi- 
vided, the  vertebral  plate.  The  divided  portion  is  known  as  the  late- 
ral plate.  The  longitudinal  thickening  of  the  vertebral  plate  is  seen 
after  a  while  to  be  divided  at  right  angles  to  the  medullary  canal  by 
bright  transverse  lines  into  a  number  of  square  segments.     These  seg- 


Fig.  467.— Embryo  chick  f36 
hours),  viewed  from  beneath  as  a 
transparent  object  (magnified). 
pi,  outline  of  peUucid  area,  FB, 
tore-brain,  or  first  cerebral  vesi- 
cle :  from  its  sides  project  op,  the 
optic  vesicle;  SO,  backward  limit 
of  somatopleure  fold,  "tucked  in" 
under  head;  a,  head-fold  of  true 
amnion;  a',  reflected  layer  of  am- 
nion, sometimes  termed  "false 
amnion;"  sp,  backward  limit  of 
splanchnopleure  folds,  along 
which  run  the  omphalomesaraic 
veins  uniting  to  form  7i,the  heart, 
which  is  continued  forward  into 
ba,  the  bulbus  arteriosus;  rf,  the 
fore-gut,  lying  behind  the  heart, 
and  naving  a  wide  crescentic 
opening  between  the  splanchno- 
pleure   folds;     "        


MB. 
bra> 


HB,    hind-brain ; 
mid-brain ;   pi:   protoverte- 


lying  behind  the  fore-gut. 
nic.  line  of  junction  of  medullary 
folds  and  of  notochord  ;  vpl,  ver- 
tebral plates;  pr,  the  primitive 
groove  at  its  caudal  end.  (Foster 
and  Balfour.) 


776 


HANDBOOK    OF   PHYSIOLOGY. 


ments,  which  are  the  surface  appearance  of  cubes  of  mesoblast,  are  the 
mesoblastic  somites  or  proto vertebrae.  The  first  three  or  four  of 
the  protovertebras  make  their  appearance  in  the  cervical  region,  while 
one  or  two  more  are  formed  in  front  of  this  point:  and  the  series  is 
continued  backward  till  the  whole  medullary  canal  is  flanked  by  them 


Fig.  468. — Transverse  section  through  dorsal  region  of  embryo  chick  (45  hrs.).  One  half  of  the 
section  is  represented ;  if  completed  it  would  extend  as  far  to  the  left  as  to  the  right  of  the  line 
of  the  medullary  canal  (ilic).  A,  epiblast;  C,  hypoblast,  consisting  of  a  single  layer  of  flattened 
cells;  Mc,  medullary  canal ;  Pi%  protovertebra ;  Wd,  Wolffian  duct;  So,  somatopleure ;  Sp, 
splanchnopleure ;  pp,  pleuro-peritoneal  cavity;  ch,  notochord;  ao,  dorsal  aorta,  containing 
blood  cells ;  v,  blood-vessels  of  the  yolk-sac.     (Foster  and  Balfour. ) 

(fig.  467).  That  which  is  first  formed  corresponds  to  the  second  cervi- 
cal vertebra.  From  these  somites  the  vertebrae  and  the  trunk  muscles 
are  deriveld. 

Head  and  Tail  Folds.  Body  Cavity. — Every  vertebrate  animal  con- 
sists essentially  of  a  longitudinal  axis  (vertebral  column)  with  a  neural 
canal  above  it,  and  a  body-cavity  (containing  the  alimentary  canal) 
beneath. 

We  have  seen  how  the  earliest  rudiments  of  the  central  axis  and  the 
neural  canal  are  formed ;  we  must  now  consider  how  the  general  body- 


Fig.  469.— Diagrammatic  longitudinal  section  through  the  axis  of  an  embryo.  The  head-fold 
has  commenced,  but  the  tail-fold  has  not  yet  appeared.  FSo,  fold  of  the  somatopleure ;  Fsp, 
fold  of  the  splanchnopleure;  the  line  of  reference,  Fso,  lies  outside  the  embryo  in  the  "moat," 
■which  marks  ofiE  the  overhanging  head  from  the  amnion ;  D,  inside  the  embryo,  is  that  part 
which  is  to  become  the  fore-gut;  Fso  aud-Fsp,  are  both  parts  of  the  head-fdld,  .'and  travel  to  the 
left  of  the  figure  as  development  proceeds ;  pp,  space  between  somatopleure  and  splanchnopleure, 
pleuro-peritoneal  cavity;  Am.  commencing  head-fold  of  amnion;  NC.  neural  canal;  Ch,  noto- 
chord; Ht,  heart;  A,  B,  C,  epiblast,  mesoblast,  hypoblast.     (Foster  and  Balfour.) 

cavity  is  developed.  In  the  earliest  stages  the  embryo  lies  flat  on  the 
surface  of  the  yolk,  and  is  not  clearly  marked  off  from  the  rest  of  the 
blastoderm :  but  gradually  the  head-fold  or  crescentic  depression  (with 


DEVELOPMENT. 


777 


its  concavity  backward)  is  formed  in  the  blastoderm,  limiting  the  head 
of  the  embryo ;  the  blastoderm  is,  as  it  were,  tucked  in  under  the  head, 
which  thus  comes  to  project  above  the  general  surface  of  the  membrane: 
a  similar  tucking  in  of  blastoderm  takes  place  at  the  caudal  extremity, 
and  thus  the  head  and  tail  folds  are  formed. 

Similar  depressions  mark  off  the  embryo  laterally,  until  it  is  com- 
pletely surrounded  by  a  sort  of  moat  which  it  overhangs  on  all  sides,  and 
which  clearly  defines  it  from  the  yolk. 

This  moat  runs  in  further  and  further  all  round  beneath  the  over- 
hanging embryo,  till  the  latter  comes  to  resemble  a  canoe  turned  upside- 


(ATVi' 


Fig.  470.— Diagrammatic  section  showing  the  relation  in  a  mammal  between  the  primitive 
alimentary  canal  and  the  membranes  of  the  ovum.  The  stage  represented  in  this  diagram  cor- 
responds to  that  of  the  fifteenth  or  sevent<?enth  day  in  the  liinnan  embryo,  previous  to  the  ex- 
pansion of  the  allantois;  c,  the  villous  chorion;  ft,  the  amnion;  a',  the  place  of  convergence  of 
the  amnion  and  reflection  of  the  false  amnion  a"  a",  or  outer  or  corneous  layer;  e,  the  head  and 
trunk  of  the  embryo,  comprising  the  primative  vertebra^  and  cerebro-spinal  axis;  i,  /,  the  simple 
alimentary  canal  in  its  upper  and  lower  portions.  Immediately  beneath  the  right  band  i  is 
seen  the  foetal  heart,  lying  in  the  anterior  part  of  the  pleuro-peritoneal  cavity;  r,  the  yolk-sac 
or  umbilical  vesicle;  i'  /,  the  vitello-intestinal  opening;  u,  the  allantois  connected  by  a  pedicle 
"^ith  the  anal  portion  of  the  alimentary  canal.     (Quain.) 


down,  the  ends  and  middle  being,  as  it  were,  decked  in  by  the  folding 
or  tucking  in  of  the  blastoderm,  Avhile  on  the  ventral  surface  there  is 
still  a  large  communication  with  tlie  yolk,  corresponding  to  the  weU  or 
undecked  portion  of  the  canoe. 

This  communication  between  the  embryo  and  the  yolk  is  gradually 
contracted  by  the  further  tucking  in  of  the  blastoderm  from  all  sides, 
till  it  becomes  narrowed  down,  as  by  an  invisible  constricting  band,  to 


778 


HANDBOOK    OF    PHYSIOLOGY. 


a  mere  pedicle  which  passes  out  of  the  body  of  the  embryo  at  the  point 
of  the  future  umbilicus. 

The  downwardly  folded  portions  of  blastoderm  are  termed  the  vis- 
ceral plates. 

Thus  we  see  that  the  body-cavity  is  formed  by  the  downward  folding 
of  the  visceral  plates,  Just  as  the  neural  cavity  is  produced  by  the  up- 
ward growth  of  the  dorsal  laminae,  the  difference  being  that,  in  the  vis- 
ceral or  ventral  laminse,  all  three  layers  of  the  blastoderm  are  concerned. 

The  folding  in  of  the  splanchnopleure,  lined  by  hypoblast,  pinches 
off,  as  it  were,  a  portion  of  the  yelk-sac,  inclosing  it  in  the  body-cavity. 
This  forms  the  rudiment  of  the  alimentary  canal,  which  at  this  period 
ends  blindly  toward  the  head  and  tail,  while  in  the  centre  it  communi- 
cates freely  with  the  cavity  of  the  yolk-sac  through  the  canal  termed 
vitelline  or  omphalo-mesenteric  duct. 

The  yolk-sac  thus  becomes  divided  into  two  portions  which  communi- 
cate through  the  vitelline  duct,  that  portion  within  the  body  giving 


Figs.  471,  472  and  473.— Diagrams  showing  three  successive  stages  of  development.  Trans- 
verse vertical  sections.  The  yolk-sac,  ys,  is  seen  progressively  diminishing  in  size.  In  the 
em.bryo  itself  the  medullary  canal  and  notochord  are  seen  in  section.  a\  in  middle  figure,  the 
alimentary  canal,  becoming  pinched  off,  as  it  were,  from  the  yolk-sac ;  a'  in  right-hand  figure, 
alimentary  canal  completely  closed ;  a,  in  last  two  figures,  amnion ;  ac,  cavity  of  amnion  filled 
with  amniotic  fluid;  pp,  space  between  amnion  and  chorion  continuous  with  the  pleuro-perito- 
neal  cavity  inside  the  body;  vt.  vitelline  membrane;  ys,  yolk-sac,  or  umbilical  vesicle.  (Foster 
and  Balfour.) 


rise,  as  above  stated,  to  the  digestive  canal,  and  that  outside  the  body 
remaining  for  some  time  as  the  umbilical  vesicle  (fig.  473,  ys.).  The 
hypoblast  forming  the  epithelium  of  the  intestine  is  of  course  continuous 
with  the  lining  membrane  of  the  umbilical  vesicle,  while  the  visceral 
plate  of  the  mesoblast  is  continuous  with  the  outer  layer  of  the  umbilical 
vesicle. 

All  the  above  details  will  be  clear  on  reference  to  the  accompanying 
diagrams. 

At  the  posterior  end  of  the  embryo  chick,  when  the  amuiotic  fold  is 
commencing  to  be  formed,  and  the  hind  fold  of  the  splanchnopleure  has 
commenced,  there  remains  for  a  time  a  communication  between  the 
neural  canal  and  the  hind  gut,  which  is  called  the  neurenteric  canal. 


DEVELOPMEXT.  <^'^<j 

It  passes  in  at  the  point  where  the  notochord  falls  into  the  primitive 
streak.  The  anterior  part  of  the  primitive  streak  becomes  the  tail 
swelling,  the  posterior  part  atrophies,  and  the  corresponding  lateral 
part  of  the  Ijlastoderm  forms  part  of  the  body-wall  of  the  embryo. 

The  anterior  part  of  the  medullary  canal  having  been  completely 
roofed  in,  the  foremost  portion  undergoes  dilatation,  and  a  bulb,  the 
first  or  anterior  cerebral  vesicle,  results.  From  either  side  of  this 
dilatation  a  process,  the  cavity  of  which  is  in  communication  with  it, 
is  separated  oft',  which  is  called  the  optic  vesicle. 

Behind  the  first  cerebral  vesicle  two  other  vesicles  now  arise,  the 
second  or  middle,  and  the  third  or  posterior  cerebral  vesicle,  and 
at  tlie  posterior  part  of  the  head  two  small  pits,  the  auditory  vesicles 
or  pits,  are  to  be  seen.  The  folding  of  the  head,  it  should  be  recol- 
lected, is  the  cause  of  the  inclosure  below  the  neural  canal  (fig.  469)  of 
a  canal  ending  blindly,  which  has  in  front  the  sjalanchnopleure,  and 
which  is  just  as  long  as  tlie  involution  of  that  membrane.  This  canal 
is  the  fore-gut.  In  tlie  interior  of  the  splanchnopleure  fold  below  it 
(as  seen  in  fig.  4G9)  in  the  pleuro-peritoneal  cavity  the  heart  is  formed, 
at  the  i^oint  where  the  splanchnopleure  makes  its  turn  forward.  It 
arises  as  a  thickening  of  tlie  mesoblast  on  either  side  as  the  two  splanchno- 
pleure folds  diverge,  and  of  a  thickening  of  the  mesoblast  at  the  point 
of  divergence.  So  that  at  first  the  rudiment  of  the  heart  is  like  an 
inverted  V,  which  by  the  gradual  coming  together  of  the  diverging 
cords  is  converted  into  an  inverted  Y. 

The  cylinders  become  hollowed  out,  and  are  thus  converted  into 
tubes,  which  then  coalesce.  Layers  are  separated  off  toward  the  interior, 
w'hich  become  the  epithelial  lining,  and  the  mass  of  the  mesoblast  sur- 
rounding this,  afterward  form  the  muscle  and  serous  covering,  while  at 
first  the  rudimentary  organ  is  attached  to  the  gut  by  a  mesoblastic  mes- 
entery, the  memcaydiinn. 

FcETAL  Membranes. 

Umbilical  Vesicle  (Volk-sac). — The  splanchnopleure,  lined  by  hy- 
poblast, forms  the  yolk-sac  in  reptiles,  birds,  and  mammals;  but  in 
amphibia  and  fishes,  since  there  is  neither  amnion  nor  aUanfois,  the  wall 
of  the  yolk-sac  consists  of  all  three  layers  of  the  blastoderm,  inclosed,  of 
course,  by  the  original  vitelline  membrane. 

The  body  of  the  embryo  becomes  in  great  measure  detached  from 
the  yolk-sac  or  uml)ilical  vesicle,  which  contains,  however,  the  greater 
part  of  the  substance  of  the  yolk,  and  furnishes  a  source  whence  nutri- 
ment is  derived  for  the  embryo.  This  nutriment  is  absorbed  by  the 
numerous  vessels  (om])halo-mesenteric)  which  ramify  in  the  walls  of  the 
yolk-sac,  forming  what  in  birds  is  termed  the  area  vasculosa.     In 


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birds,  the  contents  of  the  yolk-sac  afford  nourishment  until  the  end  of 
incubation,  and  the  omphalo-mesenteric  vessels  are  developed  to  a  corre- 
sponding degree;  but  in  mammalia  the  office  of  the  umbilical  vesicle 
ceases  at  a  very  early  period,  as  the  quantity  of  the  yolk  is  small,  and 
the  embryo  soon  becomes  independent  of  it  by  the' connections  it  forms 
with  the  parent.  Moreover,  in  birds  as  the  sac  is  emptied,  it  is  gradu- 
ally drawn  into  the  abdomen  through  the  umbilical  opening,  which  then 


Fig.  474. 


Fig,  474. —Diagram  sliowing  vascular  area  in  the  chick 
c,  area  vitellina. 

Fig.  475. — Human  embryo  of  fif  til  week  with  umbilical  vesicle;  about  natural  size 
The  human  umbilical  vesicle  never  exceeds  the  size  of  a  small  pea. 


Fig.  475. 
a,  area  pellucida ;  b,  area  vasculosa ; 
CDalton.) 


closes  over  it :  but  in  mammalia  it  always  remains  on  the  outside ;  and 
as  it  is  emptied  it  contracts  (fig.  473),  shrivels  up,  and  together  with 
the  part  of  its  duct  external  to  the  abdomen,  is  detached  and  disappears, 
either  before  or  at  the  termination  of  intra-uterine  life,  the  period  of 
its  disappearance  varying  in  different  orders  of  mammalia. 

When  blood-vessels  begin  to  be  developed,  they  ramify  largely  over 
the  walls  of  the  umbilical  vesicle,  and  are  actively  concerned  in  absorb- 
ing its  contents  and  conveying  them  away  for  the  nutrition  of  the 
embryo. 

At  an  early  stage  of  development  of  the  foetus,  and  some  time  before 
the  completion  of  the  changes  which  have  been  just  described,  two  im- 
portant structures,  called  respectively  the  amnion  and  the  (dlantois,  begin 
to  be  formed. 

Amnion. — The  amnion  is  produced  as  follows: — Beyond  the  head- 
and  tail-folds  before  described  (p.  776),  the  somatopleure  coated  by  epi- 
blast,  is  raised  into  folds,  which  grow  up,  arching  over  the  embryo,  not 
only  anteriorly  and  posteriorly  but  also  laterally,  and  all  converging 
toward  one  point  over  its  dorsal  surface  (fig.  476).  The  growing  up  of 
these  folds  from  all  sides  and  their  convergence  toward  one  point  very 
closely  resembles  the  folding  inward  of  the  visceral  plates  already  de- 
scribed, and  hence,  by  some,  the  point  at  which  the  amniotic  folds 
meet  over  the  back  has  been  termed  the  amniotic  umbilicus. 

The  folds  not  only  come  into  contact  but  coalesce.     The  inner  of 


DEVELOPMENT.  781 

the  two  layers  forms  tlie  I  rue  aiiDiion,  while  the  outer  or  reflected  layer, 
sometimes  termed  the  tahc  amnion,  coalesces  with  the  inner  surface  of 
the  original  vitelline  membnine  to  form  the  subzonal  membrane  or 
false  cliorion.  Tliis  growth  of  the  amniotic  folds  mast  of  course  be 
clearly  distinguished  from  the  very  similar  process,  already  described,  by 
which  at  a  much  earlier  stage  the  walls  of  the  neural  caual  are  formed. 

The  cavity  between  the  true  amnion  and  the  external  surface  of  the 
embryo  becomes  a  closed  space,  termed  the  amniotic  cavity  (ac,  fig.  473). 

At  first,  the  amnion  closely  invests  the  embryo,  but  it  becomes  grad- 
ually distended  witli  fluid  {Jiquor  amnii),  which,  as  pregnancy  advances, 
reaches  a  considerable  quantity. 

This  fluid  consists  of  water  containing  small  quantities  of  albumen 
and  urea.  Its  chief  function  during  gestation  appears  to  be  the  me- 
chanical one  of  affording  equal  support  to  the  embryo  on  all  sides,  and 
of  protecting  it  as  far  as  possible  from  the  effects  of  blows  and  other 
injuries  to  the  abdomen  of  the  mother. 

The  embryo  up  to  the  end  of  pregnancy  is  thus  immersed  in  fluid, 
which  during  joarturition  serves  the  important  purpose  of  gradually  and 
evenly  dilating  the  neck  of  tlie  uterus  to  allow  of  the  passage  of  the  f  wtus : 
when  this  is  accomplished  the  amniotic  sac  bursts,  and  the  waters  escape. 

On  referring  to  flgs.  4TI,  472  and  473,  it  will  be  obvious  that  the 
cavity  outside  the  amnion,  between  it  and  the  false  amnion,  is  continu- 
ous Avith  the  pleiiro-peritoneal  cavity  at  the  umbilicus.  This  cavity  is 
not  entirely  obliterated  even  at  birth,  and  contains  a  small  quantity  of 
fluid,  which  is  discharged  during  parturition  either  before,  or  afc  the 
same  time  as  the  amniotic  fluid. 

Allantois. — Into  the  pleuro-peritoneal  space  the  allautois  sprouts 
out,  its  formation  commencing  during  the  development  of  the  amnion. 

Growing  out  from  or  near  the  hinder  portion  of  the  intestinal  caual 
(c,  fig.  476),  with  which  it  communicates,  the  allantois  is  at  first  a  solid 
pear-shaped  mass  of  splanchnopleure ;  but  becoming  vesicular  by  the 
projection  into  it  of  a  hollow  outgrowth  of  hypoblast,  and  very  soon 
simply  membraneous  and  vascular,  it  insinuates  itself  between  the  amni- 
otic folds,  just  described,  and  comes  into  close  contact  and  union  with 
the  outer  of  the  two  folds,  which  has  itself,  as  before  said,  become  one 
with  the  external  investing  ^membrane  of  the  egg.  As  it  grows,  the 
allantois  develops  muscular  tissue  in  its  external  wall  and  becomes  ex- 
ceedingly vascular;  in  birds  (fig.  477)  it  envelops  the  whole  embryo — 
taking  up  vessels,  so  to  speak,  to  the  outer  investing  membrane  of  the 
egg,  and  lining  the  inner  surface  of  the  shell  with  a  vascular  membrane, 
by  these  means  affording  an  extensive  surface  in  which  the  blood  may 
be  aerated.  In  the  human  subject  and  in  otlier  mammalia,  the  vessels 
carried  out  by  the  allantois  are  distributed  only  to  a  special  part  of  the 


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HANDBOOK    OF    PHYSIOLOGY. 


outer  membrano  or  false  chorion,  where,  by  interlacement  with  the  vas- 
cular system  of  the  mother,  a  structure  called  the  placenta  is  developed. 
In  mammalia,  as  the  visceral  laminae  close  in  the  abdominal  cavity, 
the  allantois  is  thereby  divided  at  the  umbilicus  into  two  portions ;  the 
outer  part,  extending  from  the  umbilicus  to  the  chorion,  soon  shrivelling ; 
while  the  inner  part  remaining  in  the  abdomen,  is  in  jDart  converted  into 
the  urinary  bladder;  the  portion  of  the  inner  part  not  so  converted, 
extending  from  the  bladder  to  the  umbilicus,  under  the  name  of  the 
urachus.  After  birth  the  umbilical  cord,  and  with  it  the  external  and 
shrivelled  portion  of  the  allantois,  are  cast  off  at  the  umbilicus,  while 
the  urachus  remains  as  an  impervious  cord  stretched  from  the  top  of 
the  urinary  bladder  to  the  umbilicus,  in  the  middle  line  of  the  body, 


Fig.  476. 


Fig.  477. 


Fig.  476. —Diagram  of  fecundated  egg.    a,  umbilical  vesicle;  6,  amniotic  cavity ;  c,  allantois. 

'  Fig.  477.— Fecundated  egg  with  allantois  nearly  complete,  a,  inner  layer  of  amniotic  fold; 
i.  outer  layer  of  ditto ;  c,  point  where  the  amniotic  folds  come  in  contact.  The  allantois  is 
seen  penetrating  between  the  outer  and  inner  layers  of  the  amniotic  folds.  This  figure,  which 
represents  only  the  amniotic  folds  and  the  parts  within  them,  should  be  compared  with  figs. 
478,  479,  in  which  will  be  found  the  structures  external  to  these  folds.     (Dalton.) 

immediately  beneath  the  parietal  layer  of  the  peritoneum.  It  is  some- 
times enumerated  among  the  ligaments  of  the  bladder. 

It  must  not  be  supposed  that  the  phenomena  which  have  been  suc- 
cessively described,  occur  in  any  regular  order  one  after  another.  On 
the  contrary,  the  development  of  one  part  is  going  on  side  by  side  with 
that  of  another. 

The  Chorion. — It  has  been  already  remarked  that  the  allantois  is 
a  structure  which  extends  from  the  body  of  the  foetus  to  the  outer  in- 
vesting membrane  of  the  ovum,  that  it  insinuates  itself  between  the  two 
layers  of  the  amniotic  fold,  and  becomes  fused  with  the  outer  layer, 
Avhich  has  itself  become  previously  joined  with  the  vitelline  membrane. 
By  these  means  the  external  investing  membrane  of  the  ovum,  or  the 
true  chorion,  as  it  is  now  called,  represents  three  layers,  namely,  the 
original  vitelline  membrane,  the  outer  layer  of  the  amniotic  fold,  and 
the  allantois. 

Very  soon  after  the  entrance  of  the  ovum  into  the  uterus,  in  the 
human  subject,  the  outer  surface  of  the  chorion  is  found  beset  with  fine 


DEVELOPMEXT. 


783 


processes,  the  so-called  chorion  villi  {a,  tigs.  478,  479),  whicli  give  it 
a  rough  and  shaggy  appearance.  At  first  only  cellular  in  structure,  these 
little  outgrowths  subsequently  become  vascular  by  the  development  in 


Fig.  478. 


Fig.  479. 
The  viUi  are  shown  to  be  liest  developed   in  the 


Figs.  478  and  479.— o.  chorion  with  villi, 
part  of  the  chorion  to  which  the  allantois  is  extending:  this  portion  ultimately  becomes  the 
placenta;  b,  space  between  the  two  layers  of  the  amnion;  c,  amniotic  cavity ;  cl.  sit\iationof  the 
intestine,  showing  its  connection  with  the  umbilical  vesicle;  e,  umbilical  vesicle;/,  situation  of 
heart  and  vessels;  g,  allantois. 

them  of  loops  of  capillaries  (fig.  480) ;  and  the  latter  at  length  form  the 
minute  extremities  of  the  blood-vessels  which  are,  so  to  speak,  conducted 
from  the  fwtus  to  the  chorion  by  the  allantois.  The  function  of  the 
villi  of  the  chorion  is  evidently  the  absorption  of  nutrient  matter  for 
the  fa3tus;  and  this  is  probably  supplied  to  them  at  first  from  the  fiuid 
matter,  secreted  by  the  follicular  glands  of  the  uterus,  in  which  they 
are  soaked.  Soon,  however,  the  foetal  vessels  of  the  villi  come  into- 
more  intimate  relation  with  the  vessels  of  the 
uterus.  The  part  at  which  this  relation  between 
the  vessels  of  the  foetus  and  those  of  the  parent 
ensues,  is  not,  however,  over  the  whole  surface  of 
the  chorion;  for,  although  all  the  villi  become 
vascular,  yet  they  become  indistinct  or  disappear 
except  at  one  part  where  they  are  greatly  devel- 
oped, and  by  their  branching  give  rise,  with  the 
vessels  of  the  uterus,  to  the  formation  of  the 
placenta. 

To  understand  the  manner  in  which  the  fcefal 
and  maternal  blood-vessels  come  into  relation 
with  each  other  in  the   placenta,  it  is  necessary 

briefly  to  notice  the  changes  which  the  uterus  undergoes  after  impreg- 
nation. These  changes  consist  especially  of  alterations  in  structure  of 
the  superficial  part  of  the  mucous  membrane  which  lines  the  interior  of 
the  uterus,  and  which  forms,  after  a  kind  of  development  to  be  imme- 


Fig.  480. 


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HANDBOOK    OF    PHYSIOLOGY. 


diately  described,  the  memhrana  decidua,  so  called  on  account  of  its 
being  discharged  from  the  uterus  at  birth. 

Formation  of  the  Placenta. 

The  mucous  membrane  of  the  human  uterus,  which  consists  of  a 
matrix  of  connective  tissue  containing  numerous  corpuscles,  and  is  lined 
internally  by  columnar  ciliated  epithelium,  is  abundantly  beset  with 
tubular  glands,  arranged  perpendicularly  to  the  surface  (fig.  481).    These 


Fig.  481. — Section  of  the  lining  membrane  of  a  human  uterus  at  the  period  of  commencing 
pregnancy  showing  the  arrangement  and  other  peculiarities  of  the  glands,  d,  d,  d,  with  their 
orifices,  a,  a,  o,  on  the  internal  surface  of  the  organ.     Twice  the  natural  size. 

follicles  are  very  small  in  the  unimpregnated  uterus;  but  when  examined 
shortly  after  impregnation,  they  are  found  elongated,  enlarged,  and 
much  waved  and  contorted  toward  their  deep  and  closed  extremity, 
which  is  planted  at  some  depth  in  the  tissue  of  the  uterus,  and  may 
dilate  into  two  or  three  closed  sacculi. 

The  glands  are  lined  by  columnar  (  (?)  ciliated)  eiDithelium  and  they 
open  on  the  inner  surface  of  the  mucous  membrane  by  small  round  ori- 
fices set  closely  together  (a,  a,  fig.  481). 

On  the  internal  surface  of  the  mucous  membrane  may  be  seen  the 
circular  orifices  of  the  glands,  many  of  which  are,  in  the  early  period  of 
pregnancy,  surrounded  by  a  whitish  ring,  formed  of  the  epithelium 
which  lines  the  follicles. 

Coincidently  with  the  occurrence  of  pregnancy,  important  changes 
occur  in  the  structure  of  the  mucous  membrane  of  the  uterus.  The 
epithelium  and  sub-epithelial  connective  tissue,  together  with  the  tubu- 
lar glands,  increase  rapidly,  and  there  is  a  greatly  increased  vascularity 
of  the  whole  mucous  membrane,  the  vessels  of  the  mucous  membrane 
becoming  larger  and  more  numerous;  while  a  substance  composed  chiefly 
of  nucleated  cells  fills  up  the  interfollicular  spaces  in  which  the  blood- 
vessels are  contained.  The  effect  of  these  changes  is  an  increased  thick- 
nes,  softness,  and  vascularity  of  the  mucous  membrane,  the  superficial 
part  of  which  itself  forms  the  membrana  decidua. 

The  object  of  this  increased  development  seems  to  be  the  production 


DEVELOPMENT. 


785 


of  nutritive  materials  for  the  ovum;  for  the  cavity  of  the  uterus  shortly 
becomes  filled  with  secreted  fluid,  consisting  almost  entirely  of  nucleated 
cells  in  which  the  chorion  villi  are  imbedded. 

When  the  ovum  first  enters  the  uterus  it  becomes  imbedded  in  the 
structure  of  the  decidua,  which  is  yet  quite  soft,  and  in  which  soon 
afterward  three  portions  are  distinguishable.  These  have  been  named 
the  decidua  vera,  the  decidua  reflexa,  and  the  decidua  serotina. 

The  first  of  these,  the  decidua  vera,  lines  the  cavity  of  the  uterus ; 
the  second,  or  decidua  reflexa,  is  a  part  of  the  decidua  vera  which  grows 
up  around  the  ovum,  and  wrapping  it  closely,  forms  its  immediate 
investment. 

The  third,  or  decidua  serotina,  is  the  part  of  the  decidua  vera  which 
becomes  especially  developed  in  connection  with  those  villi  of  the  cho- 
rion, which,  instead  of  disappearing,  remain  to  form  the  foetal  part  of 
the  placenta. 

In  connection  with  these  villous  processes  of  the  chorion,  there  are 
developed  depressions  or  crypts  in  the  decidual  mucous  membrane,  which 
correspond  in  shape  with  the  villi  they  are  to  lodge;  and  thus  the  chori- 
onic villi  become  more  or  less  imbedded  in  the  maternal  structures. 


Fig.  48:i. —Diagram  of  au  early  stage  of  the  formation  of  the  human  placenta,  o,  embryo; 
6,  amnion;  c,  placental  vessels;  d,  decidua  reflexa;  e,  allantois;  /,  placental  villi;  g,  mucous 
membrane.     (Cadiat.) 

These  uterine  crypts,  it  is  important  to  note,  are  not,  as  was  once  sup- 
posed, merely  the  open  mouths  of  the  uterine  follicles. 

As  the  ovum  increases  in  size,  the  decidua  vera  and  the  decidua 
reflexa  gradually  come  into  contact,  and  in  the  third  month  of  preg- 
nancy the  cavity  between  them  has  almost  disappeared.  Though  the 
two  layers  come  into  contact  at  the  third  month,  they  are  not  closely 
amalgamated  until  the  end  of  the  sixth  month. 

The  Placenta. — During  these  changes  the  deeper  part  of  thr  nni- 
5° 


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HANDBOOK    OF    PHYSIOLOGY. 


ecus  membrane  of  the  uterus,  at  and  near  the  region  where  the  placenta 
is  placed,  becomes  hollowed  out  by  sinuses,  or  cavernous  spaces,  which 
communicate  on  the  one  hand  with  arteries  and  on  the  other  with  veins 
of  the  uterus.  Into  these  sinuses  the  villi  of  the  chorion  protrude, 
pushing  the  thin  wall  of  the  sinus  before  them,  and  so  come  into  inti- 
mate relation  with  the  blood  contained  in  them.  There  is  no  direct 
communication  ietiveen  the  blood-vessels  of  the  mother  and  those  of  the 
foetus;  but  the  layer  or  layers  of  membrane  intervening  between  the 


Fig.  483. — Diagrammatic  view  of  a  vertical  transverse  section  of  tlie  uterus  at  the  seventh 
or  eighth  week  of  pregnancy,  c,  c,  c',  cavity  of  uterus,  which  becomes  the  cavity  of  the  decidua, 
opening  at  c,  c,  the  cornua,  into  the  Fallopian  tubes,  and  at  c'  into  the  cavity  of  the  cervix, 
which  is  closed  by  a  plug  of  mucus ;  d  v,  decidua  vera ;  d  r,  decidua  reflexa,  with  the  sparser 
villi  imbedded  in  its  substance ;  d  s,  decidua  serotina,  involving  the  more  developed  chorionic 
villi  of  the  commencing  placenta.  The  foetus  is  seen  lying  in  the  amniotic  sac ;  passing  up  from 
the  umbilicus  is  seen  the  umbilical  cord  and  its  vessels,  passing  to  their  distribution  in  the  villi 
of  the  chorion ;  also  the  pedicle  of  the  yolk-sac,  which  lies  in  the  cavity  between  the  amnion 
and  chorion.     (Allen  Thomson.) 


blood  of  the  one  and  of  the  other  offer  no  obstacle  to  a  free  interchange 
of  matters  between  them  by  diffusion  and  osmosis.  Thus  the  villi  of  the 
chorion  containing  foetal  blood,  are  bathed  or  soaked  in  maternal  blood 
contained  in  the  uterine  sinuses.  The  arrangement  may  be  roughly 
compared  to  filling  a  glove  with  foetal  blood,  and  dipping  its  fingers 
into  a  vessel  containing  maternal  blood.  But  in  the  foetal  villi  there  is  a 
constant  stream  of  blood  into  and  out  of  the  loop  of  capillary  blood-vessels 
contained  in  it,  as  there  is  also  into  and  out  of  the  maternal  sinuses. 


DEVELOPMENT.  78? 

It  would  seem  that,  at  the  villi  of  the  placental  tufts,  where  the 
foetal  and  maternal  portions  of  the  placenta  are  brought  into  close  rela- 
tion with  each  other,  the  blood  in  the  vessels  of  the  mother  is 
separated  from  that  in  the  vessels  of  the  foetus  by  the  intervention  of 
two  distinct  sets  of  nucleated  cells  (lig.  484).  One  of  these  {b)  belongs 
to  the  maternal  portion  of  the  placenta,  is  placed  between  the  membrane 
of  the  villus  and  that  of  the  vascular  system  of  the  mother,  and  is  prob- 
ably designed  to  separate  from  the  blood  of  the  parent  the  materials 
destined  for  the  blood  of  the  foetus;  the  other  (/)  belongs  to  the  foetal 
portion  of  the  placenta,  is  situated  between  the  membrane  of  the  villus 
and  the  loop  of  vessels  contained  within,  and  probably  serves  for  the 
absorption  of  the  material  secreted  by  the  other  sets  of  cells,  and  for  its 
conveyance  into  the  blood-vessels  of  the  foetus.  Between  the  two  sets  of 
cells  with  their  investing  membrane  there  exists  a  space  (d),  into  which 
it  is  possible  that  the  materials  secreted  by  the  one  set  of  cells  of  the 
villus  are  jDOured  in  order  that  they  may  be  absorbed  by  the  other  set, 
and  thus  conveyed  into  a  foetal  vessel. 

Not  only,  however,  is  there  a  passage  of  materials  from  the  blood  of 
the  mother  into  that  of  the  foetus,  but  there  is  a  mutual  interchange  of 


Fig.  484.— Extremity  of  a  placental  villus,  a,  lining  membrane  of  the  vascular  system  of 
the  mother;  b,  cells  immediately  lining  a;  d,  space  between  the  maternal  and  foetal  portions  of 
the  villus;  e,  internal  membrane  of  the  villus,  or  external  membrane  of  the  chorion;  /,  internal 
cells  of  the  villus,  or  cells  of  the  chorion;  g,  loop  of  umbilical  vessels.     (Goodsir.) 

materials  between  the  blood  both  of  foetus  and  of  parent ;  the  latter  sup- 
plying the  former  with  nutriment,  and  in  turn  abstracting  from  it 
materials  which  require  to  be  removed. 

The  placenta,  therefore,  of  the  human  subject  is  composed  of  a 
fo'fal  part  and  a  maternal  part, — the  term  placenta  properly  including 
all  that  entanglement  of  foetal  villi  and  maternal  sinuses,  by  means  of 
whicli  the  blood  of  the  fa>tus  is  enriched  and  purified  after  the  fashion 
necessary  for  the  proper  growth  and  development  of  those  parts  which 
it  is  designed  to  nourish. 

The  whole  of  this  structure  is  not,  as  might  be  imagined,  thrown 
off  immediately  after  birth.  The  greater  part,  indeed,  comes  away  at 
that  time,  as  the  after-hirth;  and  the  separation  of  this  portion  takes 
place  by  a  rending  or  crushing  through  of  that  part  at  which  its  cohe- 
sion is  least  strong,  namely,  where  it  is  most  burrowed  and  undermined 


788  HAIs^DBOOK    OF    PHYSIOLOGY. 

by  the  cavernous  spaces  before  referred  to.  In  this  way  it  is  cast  off 
with  the  fcetal  membrane  and  the  decidua  vera  and  reflexa,  together 
with  a  part  of  the  decidua  serotina.  The  remaining  portion  withers, 
and  disappears  by  being  gradually  either  absorbed,  or  thrown  off  in  the 
uterine  discharges  or  the  loclda,  which  occur  at  this  period. 

A  new  mucous  membrane  is  of  course  gradually  developed,  as  the 
old  one,  by  its  transformation  into  the  decidua,  ceases  to  perform  its 
original  functions. 

The  umhilical  cord,  which  in  the  latter  part  of  foetal  life  is  almost 
solely  composed  of  the  two  arteries  and  the  single  vein  which  respectively 
convey  foetal  blood  to  and  from  the  placenta,  contains  the  remnants  of 
other  structures  which  in  the  early  stages  of  the  development  of  the 
embryo  were,  as  already  related,  of  great  comparative  importance.  Thus, 
in  early  foetal  life,  it  is  composed  of  the  following  parts : — (1. )  Externally, 
a  layer  of  the  amnion,  reflected  over  it  from  the  umbilicus.  (2)  The  um- 
bilical vesicle  with  its  duct  and  appertaining  omphalo-mesenteric  blood 
vessels,  (3.)  The  remains  of  the  allantois,  and  continuous  with  it  the 
urachus.  (4.)  The  umbilical  vessels,  which,  as  just  remarked,  ultimately 
form  the  greater  part  of  the  cord. 

The  Development  of  the  Oegans. 

Before  considering  very  briefly*  the  main  points  in  the  development 
of  the  chief  organs  and  tissues  of  the  body,  it  will  be  useful  to  have 
before  us  the  following  table,  compiled  by  Schafer,f  showing  the  differ- 
ent parts  derived  from  the  three  blastodermic  layers: — 

From  the  Epihlast. — The  whole  of  the  nervous  system,  including 
not  only  the  central  organs  (brain  and  spinal  cord),  but  also  the  peri- 
pheral nerves  and  sympathetic. 

The  epithelial  structures  of  the  organs  of  special  sense. 

The  epidermis  and  its  appendages,  including  the  hair  and  nails. 

The  epithelium  of  all  the  glands  opening  upon  the  surface  of  the 
skin,  including  the  mammary  glands,  the  sweat  glands  and  the  sebaceous 
glands.     The  muscular  fibres  of  the  sweat  glands. 

The  epithelium  of  the  mouth  (except  that  covering  the  tongue,  and 
the  adjacent  posterior  part  of  the  floor  of  the  mouth,  which  is  derived 
from  the  hypoblast),  and  that  of  the  glands  opening  into  it. 

The  enamel  of  the  teeth. 

The  epithelium  of  the  nasal  passages,  of  the  adjacent  upper  part  of  the 
pharynx  and  of  all  the  cavities  and  glands  opening  into  the  nasal  pas- 


*  For  a  more  detailed  account  the  reader  is  referred  to  special  text-books  of 
embryology. 

t  Qnain's  Anatomy,  Xth  Ed.,  Vol.  I.,  Part  T.,  p.  25. 


ItEVELOPMEXT. 


789 


From  the  MesuOlcDit. — The  urinary  and  generative  organs  (except  the 
epithelium  of  the  urinary  bladder  and  urethra). 

All  the  voluntary  and  involuntary  muscles  of  the  body  (except  the 
muscular  fibres  of  the  sweat  glands). 

The  whole  of  the  vascular  and  lynipliatic  system,  iiichiding  the 
serous  membranes  and  spleen. 

The  skeleton  and  all  the  connective  tissues  and  structures  of  the  body. 

From  the  Hypoblast. — The  epithelium  of  the  alimentary  canal  from 
the  back  of  the  mouth  to  the  anus,  and  that  of  all  the  glands  which 
open  into  this  part  of  the  alimentary  tube. 

The  epithelium  of  the  Eustachian  tube  and  tympanum. 

The  epithelium  of  the  bronchial  tubes  and  air  sacs  of  the  lungs. 

The  epithelium  lining  the  vesicles  of  the  thyroid  body. 

The  epithelial  nests  of  the  thymus. 

The  epithelium  of  the  urinary  bladder  and  urethra. 

It  remains  now  to  consider  in  succession  the  development  of  the 
several  organs  and  systems  of  organs  in  the  further  progress  of  the 


^  \  W    /    /    /  y 


Fig.  485.— Embryo  chick  C-lth  da>0.  viewed  as  a  transparent  object,  lying  ou  its  left  side 
(magnified).  C  if,  cerebral  hemispHeres;  F  B.  fore-brain  or  vesicle  of  third  ventricle,  with  Pn, 
pineal  gland  projecting  from  its  summit;  MB.  mid-brain;  Cb.  cerebellum;  IV.  V.  fourth  ven- 
tricle; L.  lens;  c  h  .s,  choroidal  slit;  Cen  V.  auditory  vesicle;  s  m.  superior  maxillary  process; 
IJiT,  2F,  etc.,  first,  second,  third,  and  fourth  visceral  folds:  V.  fifth  nerve,  sending  one  branch 
(ophthalmic)  to  the  eye,  and  another  to  the  first  visceral  arch  :  VII.  seventh  nerve,  jjassing  to  the 
second  visceral  arch:  G  Ph.  glosso-pharyngeal  nerve,  passing  to  the  third  visceral  arch;  P g. 
pneumogastrie  nerve,  passing  toward  the  fourth  visceral  arch:  i  v,  investing  mass;  ch.  noto- 
chord;  its  front  end  cannot  be  seen  in  the  living  embryo,  and  it  does  not  end  as  shown  in  the  fig- 
ure, but  takes  a  sudden  Isend  downward,  and  then  terminates  in  a  point;  Bt.  heart  seen  through 
the  walls  of  the  chest:  M  P.  muscle  plates:  ^V.  wing,  showing  commencing  differentiation  of 
segments,  corresponding  to  arm,  forearm,  and  hand;  H  L.  hind-limb,  as  yet  a  shapeless  hud, 
showing  no  differentiation.     Beneath  it  is  seen  the  curved  tail.     (Foster  and  Balfour.) 

embryo.     The  accompanying  figure  (fig.  485)  shows  the  chief  organs  of 
the  body  in  a  moderately  early  stage  of  development. 

The  Vertebral  Column  and  Cranium. — The  primitive  part  of 
the  vertebral  column  in  all  the  vortebrata  is  the  chorda  dorsalis  or  noto- 


-j-gQ  HANDBOOK    OF    PHYSIOLOGY. 

chord,  which  consists  entirely  of  soft  cellular  cartilage.  This  cord 
tapers  to  a  point  at  the  cranial  and  caudal  extremities  of  the  animal. 
In  the  progress  of  its  development,  it  is  found  to  become  inclosed  in  a 
membranous  sheath,  which  at  length  acquires  a  fibrous  structure,  com- 
posed of  transverse  annular  fibres.  The  chorda  dorsalis  is  to  be  regarded 
as  the  azygos  axis  of  the  spinal  column,  and,  in  particular,  of  the  future 
bodies  of  the  vertebrae,  although  it  never  itself  passes  into  the  state  of 
hyaline  cartilage  or  bone,  but  remains  inclosed  as  in  a  case  within  the 
persistent  parts  of  the  vertebral  column  which  are  developed  around 
it.  It  is  permanent,  however,  only  in  a  few  animals :  in  the  majority 
only  traces  of  it  persist  in  the  adult  animal. 

In  many  fish  no  true  vertebra  are  developed,  and  there  is  every 
graduation  from  the  ampliioxus,  in  which  the  notochord  persists 
through  life  and  there  are  no  vertebrae,  through  the  lampreys  in  which 
there  are  a  few  scattered  cartilaginous  vertebrae,  and  the  sharks,  in 
which  many  of  the  vertebra  are  partly  ossified,  to  the  bony  fishes,  such 
as  the  cod  and  herring,  in  which  the  vertebral  column  consists  of  a 
number  of  distinct  ossified  vertebrae,  with  remnants  of  the  notochord 
between  them.  In  amphibia,  reptiles,  birds,  and  mammals,  there  are 
distinct  vertebrge,  which  are  formed  as  follows: — 

The  mesoblastic  somites,  which  have  been  already  mentioned  (p. 
776),  send  processes  downward  and  inward  to  surround  the  notochord, 
and  also  upward  between  the  medullary  canal  and  the  epiblast  covering 
it.  In  the  former  situation,  the  cartilaginous  bodies  of  the  vertebrae 
make  their  appearance,  in  the  latter  their  arches,  which  inclose  the 
neural  canal. 

The  vertebrae  do  not  exactly  correspond  in  their  position  with  the 
protovertebrge :  but  each  permanent  vertebra  is  developed  from  the  con- 
tiguous halves  of  two  protovertebrae.  The  original  segmentation  of  the 
protovertebrae  disappears  and  a  fresh  subdivision  occurs  in  such  a  way 
that  a  permanent  invertebral  disc  is  developed  opposite  the  centre  of 
each  protovertebra.  Meanwhile  the  protovertebrae  split  into  a  dorsal 
and  ventral  portion.  The  former  is  termed  the  musculo-CAitaneous  plate, 
and  from  it  are  developed  all  the  muscles  of  the  back  together  with  the 
cutis  of  the  dorsal  region  (the  epidermis  being  derived  from  the  epiblast). 
The  ventral  portions  of  the  protovertebrae,  as  we  have  already  seen, 
give  rise  to  the  vertebrge  and  heads  of  the  ribs. 

The  chorda  is  now  inclosed  in  a  case,  formed  by  the  bodies  of  the 
vertebrae,  but  it  gradually  wastes  and  disappears.  Before  the  disappear- 
ance of  the  chorda,  the  ossification  of  the  bodies  and  arches  of  the  verte- 
brae begins  at  distinct  points. 

The  ossification  of  the  body  of  a  vertebra  is  first  observed  at  the 
point  where  the    two  primitive  elements  of  the  vertebras   have   united 


DEVELOPMENT.  791 

inferiorly.  Those  vertebrse  which  do  not  bear  ribs,  such  as  the  cer- 
vical vertebrae,  have  general!}'  an  additional  centre  of  ossification  in 
the  transverse  process,  which  is  to  be  regarded  as  an  abortive  rudi- 
ment of  a  rib.  In  the  fa:}tal  bird,  these  additional  ossified  portions 
exist  in  all  the  cervical  vertebra,  and  gradually  become  so  much  developed 
in  the  lower  part  of  the  cervical  region  as  to  form  the  ujiper  false  ribs 
of  this  class  of  animals.  The  same  parts  exist  in  mammalia  and  man; 
those  of  the  last  cervical  vertebras  are  the  most  developed,  and  in  chil- 
dren may,  for  a  considerable  period,  be  distinguished  as  a  separate 
part  on  each  side  like  the  root  or  head  of  a  rib. 

The  true  cranium  is  a  prolongation  of  the  vertebral  column,  and  is 
developed  at  a  much  earlier  period  than  the  facial  bones.  Originally, 
it  is  formed  of  but  one  mass,  a  cerebral  capsule,  the  chorda  dorsalis 
being  continued  into  its  base,  and  ending  there  with  a  tapering  point.. 
At  an  early  period  the  head  is  bent  downward  and  forward  round  the 
end  of  the  chorda  dorsalis  in  such  a  way  that  the  middle  cerebral  vesicle, 
and  not  the  anterior,  comes  to  occupy  the  highest  position  in  the  head. 

Pituitary  Body. — In  connection  with  this  must  be  mentioned  the 
development  of  the  pituitary  body.  It  is  formed  by  the  meeting  of  two 
outgrowths,  one  from  the  foetal  brain,  which  grows  downward,  and  the 
other  from  the  epiblast  of  the  buccal  cavity,  which  grows  up  toward  it. 
The  surrounding  mesoblast  also  takes  part  in  its  formation.  The  con- 
nection of  the  first  process  with  the  brain  becomes  narrowed,  and  per- 
sists as  the  infundibulum,  while  that  of  the  other  process  with  the  buccal 
cavity  disapjoears  completely  at  a  spot  corresponding  with  the  future 
position  of  the   body  of  the  sphenoid. 

Cranium. — The  first  appearance  of  a  solid  support  at  the  base  of  the 
cranium  observed  by  Muller  in  fish,  consists  of  two  elongated  bands  of  car- 
tilage (trabeculae  cranii),  one  on  the  right  and  the  other  on  the  left  side, 
which  are  connected  with  the  cartilaginous  capsule  of  the  auditory  ap- 
paratus, and  which  diverge  to  inclose  the  pituitary  body  uniting  in 
front  to  form  the  septum  nasi  beneath  the  anterior  end  of  the  cerebral 
capsule.  Hence,  in  the  cranium,  as  in  the  spinal  column,  there  are  at 
first  developed  at  the  sides  of  the  chorda  dorsalis  two  symmetrical  ele- 
ments, which  subsequently  coalesce,  and  may  wholly  inclose  the  chorda. 

The  brain-case  consists  of  three  segments:  occipital,  parietal,  and 
frontal,  corresponding  in  their  relative  position  to  the  three  primitive 
cerebral  vesicles;  it  may  also  be  noted  that  in  front  of  each  segment  is 
developed  a  sense-organ  (auditory,  ocular,  and  olfactory,  from  behind 
forward).  The  basis  cranii  consists  at  an  early  period  of  an  unsegmented 
cartilaginous  rod,  developed  round  the  notochord,  and  continued  for- 
ward beyond  its  termination  into  the  trabeculcB  cranii^  which  bound  the 
pituitary  fossa  on  either  side. 


792 


HANDBOOK    OF    PHYSIOLOGY. 


In  this  cartilaginous  rod  three  centres  of  ossification  appear :  basi- 
occipital,  basi-sphenoid,  and  pre-sphenoid,  one  corresponding  to  each 
segment. 

The  bones  forming  the  vault  of  the  skull,  viz.,  the  frontal,  parietal, 
squamous  portion  of  temporal  and  the  squamo-occipital,  are  ossified  in 
membrane. 

The  Visceral  Clefts  and  Arches. 

As  the  embryo  enlarges,  the  heart,  which  at  first  occupied  a  position 
close  to  the  cranial  flexure,  is  carried  further  and  further  backward  until  a 
considerable  part,  in  which  the  mesoblast  is  undivided,  intervenes  between 


Fig.  486.— A.  Magnified  view  from  before  of  the  head  and  neck  of  a  human  embryo  of  about 
three  weeks  (from  Ecker.)— 1,  anterior  cerebral  vesicle  or  cerebrum;  2,  middle  ditto;  3,  middle 
or  fronto-nasal  process;  4,  superior  maxillary  process;  5,  eye;  6,  inferior  maxillary  process,  or 
first  visceral  arch,  and  below  it  the  first  cleft ;  7,  8,  9,  second,  third,  and  fourth  arches  and  clefts. 
B.  Anterior  view  of  the  head  of  a  human  foetus  of  about  the  fifth  week  (from  Ecker,  as  before, 
fig.  IV.).  1,  3,  3,  5,  the  same  parts  as  in  a;  4,  the  external  nasal  or  lateral  frontal  process:  6, 
the  superior  maxillary  process;  7,  the  lower  jaw;  X,  the  tongue;  8,  first  branchial  cleft  becom- 
ing the  meatus  auditorius  externus. 

it  and  the  head.  This  becomes  the  neck.  On  section  it  is  seen  that  in 
it  the  whole  three  layers  are  represented  in  order,  and  that  there  is  no 
interval  between  them.  In  the  neck  thus  formed  soon  appear  the  vis- 
ceral or  branchial  clefts  on  either  side,  in  series,  across  the  axis  of 
the  gut  not  quite  at  right  angles.  They  are  four  in  number,  the  most 
anterior  being  first  found.  At  their  edges  the  hypoblast  and  their 
epiblast  are  continuous.  The  anterior  border  of  each  cleft  forms  a  fold 
or  lip,  the  branchial  or  visceral  fold.  The  posterior  border  of  the  last 
cleft  is  also  formed  into  a  fold,  so  that  there  are  four  clefts  and  five  folds, 
but  the  three  most  anterior  are  far  more  prominent  than  the  others,  and 
of  these  the  second  is  the  most  conspicuous.  The  first  fold  nearly  meets  its 
fellow  in  the  middle  line,  the  second  less  nearly,  and  the  others  in  order 
still  less  so.  Thus  in  the  neck  there  is  a  triangular  interval,  into  which 
by  the  splitting  of  the  mesoblast  at  that  part  the  pleuroperitoneal  cavity 
extends.  The  branchial  clefts  and  arches  are  not  all  permanent.  The 
first  arch  gives  off  a  branch  from  its  front  edge,  which  passes  forward  to 
meet  its  fellow,  but  these  offshoots  do  not  quite  meet,  being  separated 


DEVELOPMENT.  793 

by  a  process  which  grows  downward  from  the  head.  Between  the 
branches  and  the  main  first  fold  is  the  cavity  of  the  mouth.  The  branches 
represent  the  superior  maxilla,  and  the  main  folds  the  mandible  or  lower 
jaw.  The  central  process,  which  grows  down,  is  the  fronto-nasal  pro- 
cess. 

Ill  this  way  the  so-called  visceral  arches  and  <-lefts  are  formed,  four 
on  each  side  (fig.  4-8G,  a). 

From  or  in  connection  with  these  arches  the  following  parts  are  devel- 
oped : — 

The  first  arch  (mandibular)  contains  a  cartilaginous  rod  (Meckel's 
cartilage),  around  the  distal  end  of  which  the  lower  jaw  is  developed, 
while  the  malleus  is  ossified  from  the  proximal  end. 

When  the  maxillary  processes  on  the  two  sides  fail  partially  or  com- 
pletely to  unite  in  the  middle  line,  the  well-known  condition  termed 
deft  2i(^lO't^  results.  When  the  integument  of  the  face  presents  a  similar 
deficiency,  we  have  the  deformity  known  as  hare-lip.     Though  these  two 


Fig.  487.— Embryo  chick  (4th  day),  viewed  a.s  a  transparent  object,  lying  on  its  left  side 
(magnified).  C  H,  cerebral  hemispheres;  F B,  fore-brain  or  vesicle  of  third  ventricle,  with  Pn, 
pineal  gland  pi'ojectine:  from  its  summit;  MB,  mid-brain;  C  b.  cerebellum;  IV.  V,  fourth  ven- 
tricle; L,  lens;  c  h  .s,  choroidal  slit;  CV,i.  I',  auditory  vesicle;  s  hi.  superior  maxillary  process; 
IF,  ZF,  etc.,  lirst,  second,  third,  and  fourth  visceral  folds;  F,  fifth  nerve,  sending  one  branch 
Cophthalmic)  to  the  eye,  and  another  to  the  first  visceral  arch ;  TV/,  seventti  nerve,  passing  to 
the  second  visceral  arch;  O.  Fh,  ^losso-pharynseal  nerve,  passing  to  the  third  visceral  arch; 
F  g,  pneumogastric  nerve,  passing;  toward  the  fourth  visceral  arch;  /  c,  investing  mass;  c  h, 
notochord;  its  front  end  cannot  be  seen  in  the  livinp  embryo,  and  it  does  not  end  as  sliown  in 
the  flgu:e,  but  takes  a  suilden  bend  downward,  and  then  terminates  in  a  point;  Ht.  limirt  seen 
through  the  walls  of  the  cliest ;  M  F.  nuiscle-plates ;  11',  wing,  showing  commencing  dilTcrentia- 
tion  of  segments,  corresponding  to  arm.  forearm,  and  hand;  S  S,  somatic  stalk;  Al,  allantois; 
Ff  L,  hind-limb,  as  yet  a  shapeless  bud.  showing  no  differentiation.  Beneath  it  is  seen  the 
curved  tail.     (Foster  and  Balfour. ) 

deformities  frequently  co-exist,  they  are  by  no  means  always  necessarily 
associated. 

The  upper  part  of  the  face  in  the  middle  line  is  developed  from  the 
so-called  frontal-nasal  process  (a,  3,  fig.  486.)     From   the  second  arch 


794 


HAJs^DBOOK    OF    PHYSIOLOGY. 


are  developed  the  incus^  stapes,  and  stapedius  muscle,  the  styloid  process 
of  the  temporal  bone,  the  stylo-hyoid  ligament,  and  the  smaller  cornu  of 
the  hyoid  hone.  From  the  third  visceral  arch,  the  greater  cornu  and  body 
of  the  hyoid  bone.  In  man  and  other  mammalia  the /owr^/i  visceral  arch 
is  indistinct.  It  occupies  the  position  where  the  neck  is  afterward 
developed. 

A  distinct  connection  is  traceable  between  these  visceral  arches  and 
certain  cranial  nerves :  the  trigeminal,  the  facial,  the  glosso-pharyngeal, 
and  the  vagus.  The  ophthalmic  division  of  the  trigeminal  supplies  the 
fronto-nasal  process;  the  superior  and  inferior  maxillary  divisions  supply 
the  maxillary  and  mandibular  arches  respectively. 

The  facial  nerve  distributes  one  branch  (chorda  tympani)  to  the 
first  visceral  arch,  and  others  to  the  second  visceral  arch.  Thus  it 
divides,  inclosing  the  first  visceral  cleft. 

Similarly,  the  glosso-pharyngeal  divides  to  inclose  the  second  visceral 
cleft,  its  lingual  branch  being  distributed  to  the  second,  and  its 
pharyngeal  branch  to  the  third  arch. 

The  vagus,  too,  sends  a  branch  (pharyngeal)  along  the  third  arch, 
and  in  fishes  it  gives  off  paired  branches,  which  divide  to  inclose  several 
successive  branchial  clefts. 

The  Extremities. 

The  extremities  are  developed  in  a  uniform  manner  in  all  verte- 
brate animals.     They  appear  in  the  form  of  leaf -like  elevations  from  the 


Fig.  488.— A  human  embryo  of  the  fourth  week,  3i^  lines  in  length.— 1,  the  chorion;  3,  part 
of  the  amnion;  4,  umbilical  vesicle  with  its  long  pedicle  passing  into  the  abdomen;  7,  thi; 
heart ;  8,  the  liver ;  9,  the  visceral  arch  destined  to  form  the  lower  jaw,  beneath  which  are  two 
other  visceral  arches  separated  by  the  branchial  clefts;  10,  rudiment  of  the  upper  extremity;  11, 
that  of  the  lower  extremity;  12,  the  umbilical  cord;  15,  the  eye;  16,  the  ear;  17,  cerebral  hemi- 
spheres; 18,  optic  lobes,  corpora  quadrigemina.     (Miiller.) 

parieties  of  the  trunk  (see  fig.  488) ,  at  points  where  more  or  less  of  an 
arch  will  be  produced  for  them  within.  The  primitive  form  of  iha 
extremity  is  nearly  the  same  in  all  vertebrata,  whether  it  be  destined  for 


DEVELOPMENT.  795 

swimming,  crawling,  walking,  or  flying.  In  the  human  foetus  the  lin- 
gers are  at  first  united,  as  if  webbed  for  swimming;  but  this  is  to  be 
regarded  not  so  much  as  an  approximation  to  the  form  of  aquatic 
animals,  as  the  primitive  form  of  the  hand,  the  individual  parts  of  which 
subsequently  become  more  completely  isolated. 

The  fore-limb  always  appears  before  the  hind-limb,  and  for  some 
time  continues  in  a  more  advanced  state  of  development.  In  both 
limbs  alike,  the  distal  segment  (hand  or  foot)  is  separated  by  a  slight 
notch  from  the  proximal  part  of  the  limb,  and  this  part  is  subsequently 
divided  again  by  a  second  notch  (knee  or  elbow-joint). 

The  Vascular  System. — At  an  early  stage  in  the  development  of 
the  embryo-chick,  the  so-called  area  vasculosa  begins  to  make  its  appear- 
ance. A  number  of  branched  cells  in  the  mesoblast  send  out  processes 
which  unite  so  as  to  form  a  network  of  protoplasm  with  nuclei  at  the 
nodal  points.  A  large  number  of  nuclei  acquire  red  color;  these  form  the 
red  blood-corpuscles.  The  protoplasmic  processes  become  hollowed 
out  in  the  centre  so  as  to  form  u  closed  system  of  branching  canals,  in 
the  walls  of  which  the  rest  of  the  nuclei  remain  imbedded.  In  the 
blood-vessels  thus  formed,  the  circulation  of  the  embryonic  blood  com- 
mences. 

According  to  Klein,  the  first  blood-vessels  in  the  chick  are  developed 
from  embryonic  cells  of  the  mesoblast,  which  swell  up  and  become  vacuo- 
lated,while  their  nuclei  undergo  segmentation.  These  cells  send  out  proto- 
plasmic processes,  which  unite  with  corresponding  ones  from  other  cells, 
and  become  hollowed, give  rise  to  the  capillary  wall  composed  of  endothelial 
cells ;  the  blood  corpuscles  being  budded  off  from  the  endothelial  wall  by  a 
process  of  gemmation. 

Heart. — About  the  same  early  period  the  heart  makes  its  appearance 
as  a  solid  mass  of  cells  of  the  splanchnopleure  in  the  manner  before  indi- 
cated. 

At  this  period  the  anterior  part  of  the  alimentary  tube  ends  blindly 
beneath  the  notochord.  It  is  beneath  the  posterior  end  of  i\i\Q  fore-gut 
that  the  heart  begins  to  be  developed.  The  heart  when  first  formed  is 
made  up  of  two  not  quite  complete  tubes  which  coalesce  to  form  one,  and 
so  when  the  cavity  is  hollowed  out  in  the  mass  of  cells,  the  central  cells 
float  freely  in  the  fluid,  which  soon  begins  to  circulate  by  means  of  the 
rhythmic  pulsations  of    the  embryonic   heart. 

These  pulsations  take  place  even  before  the  appearance  of  a  cavity, 
and  immediately  after  the  first  laying"  down  of  the  cells  from  which 
the  heart  is  formed,  and  long  before  muscular  fibres  or  ganglia  have  been 
formed  in  the  cardiac  walls.  At  first  they  seldom  exceed  from  fifteen 
to  eighteen  in  the  minute.  The  fluid  within  the  cavity  of  the  heart 
shortly  assumes  the  characters  of  blood.     At  the  same  time,   tlie  cavity 


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HANDBOOK    OF    PHYSIOLOGY, 


itself  forms  a  commuuication  with  the  great  vessels  in  contact  with  it, 
and  the  cells  of  which  its  walls  are  comprised  are  transformed  into  fibrous 
and  muscular  tissues,  and  into    epithelium.     In    the  developing  chick 


Fig.  480. 


Fig.  491. 


Fig.  489. —Capillary  blood-vessels  of  the  tail  of  a  young  larval  frog,  a,  capillaries  perme- 
able to  blood ;  6,  fat  granules  attached  to  the  walls  of  the  vessels,  and  concealing  the  nuclei ;  c, 
hollow  prolongation  of  a  capillary,  ending  in  a  point;  d,  a  branching  cell  with  nucleus  and  fat- 
granules ;  it  communicates  by  three  branches  with  prolongation  of  capillaries  already  formed ; 
e,  e,  blood  corpuscles  still  containing  granules  of  fat.     X  350  times.     (Kolliker.) 

Fig.  490. — Development  of  capillaries  in  the  regenerating  tail  of  a  tadpole,  abed,  sprouts 
and  cords  of  protoplasm.     (Arnold.) 

Fig.  491. — The  same  region  after  the  lapse  of  24  hours.  The  "sprouts  and  cords  of  proto- 
plasm "  have  become  channelled  out  into  capillaries.     (Arnold.) 

it  can  be  observed    with  the  naked  eye  as  a  minute  red  pulsating  little 
mass  before  the  end  of  the  second  day  of  incubation. 

Blood-vessels. — Blood-vessels  appear  to  be  developed  in  two  ways,  ac- 
cording to  their  size.  In  the  formation  of  large  blood-vessels,  masses  of 
embryonic  cells  similar  to  those  from  which  the  heart  and  other  struct- 
ures of  the  embryo  are  developed,  arrange  themselves  in  the  position, 
form,  and  thickness  of  the  developing  vessel.  Shortly  afterward  the  cells 
in  the  interior  of  a  column  of  this  kind  seem  to  be  developed  into  blood- 


DEVELOPMENT.  ;y7 

corpuscles,  while  the  external  layer  of  cells  is  converted  into  the  walls 
of  the  vessel. 

In  the  development  of  capillaries  another  plan  is  pursued.  This  has 
been  well  illustrated  by  Kolliker,  as  observed  in  the  tails  of  tadpoles. 
The  first  lateral  vessels  of  the  tail  have  the  form  of  simple  arches,  ]>ass- 
ing  between  the  main  artery  and  vein,  and  are  produced  by  the  junction 
of  prolongations,  sent  from  both  the  artery  and  vein,  with  certain  elon- 
gated or  star-shaped  cells,  in  the  substance  of  the  tail.  When  these  arches 
are  formed  and  are  permeable  to  blood,  new  jDrolongations  pass  from  them, 
join  other  radiated  cells,  and  thus  form  secondary  arches.  In  this  manner, 
the  capillary  network  extends  in  proportion  as  the  tail  increases  in  length 
and  breadth,  and  it,  at  the  same  time,  becomes  more  dense  by  the  forma- 
tion, according  to  the  same  plan,  of  fresh  vessels  within  its  meshes.  The 
prolongations  by  which  the  vessels  communicate  with  the  star-shaped  cells, 
consist  at  first  of  narrow  pointed  projections  from  the  side  of  the  vessels, 
which  gradually  elongate  until  they  come  in  contact  with  the  radiated 
processes  of  the  cells.  The  thickness  of  such  a  prolongation  often  does 
not  exceed  that  of  a  fibril  of  fibrous  tissue,  and  at  first  it  is  perfectly 
solid;  but,  by  degrees,  especially  after  its  junction  with  a  cell,  or  with 
another  prolongation,  or  with  a  vessel  already  permeable  to  blood,  it 
enlarges,  and  a  cavity  then  forms  in  its  interior  (see  figs.  491,  492). 
This  tissue  is  well  calculated  to  illustrate  the  various  steps  in  the  devel- 
opment of  blood-vessels  from  elongating  and  branching  cells. 

In  many  cases  a  whole  network  of  capillaries  is  developed  from  a  net- 
work of  branched,  embryonic  connective-tissue  corpuscles  by  the  join- 


Fig.  492.— Capillaries  frorn  the  vitreous  humor  of  a  fcetal  calf.  Two  vessels  are  seen  con- 
nected by  a  "cord"  of  protoplasm,  and  clothed  with  an  adventitia,  containing  numerous  nuclei, 
n,  insertion  of  this  "cord  "  into  the  primary  walls  of  the  vessels.     (Frey.) 

ing  of  their  processes,  the  multiplication  of  their  nuclei,  and  the  vacuo- 
lation  of  the  cell-substance.  The  vacuoles  gradually  coalesce  till  all  the 
partitions  are  broken  down,  and  the  originally  solid  protoplasmic  celU 
substance  is,  so  to  speak,  tunnelled  out  into  a  number  of  tubes. 

Capillaries  may  also  be  developed  from  cells  which  are  originally 
spheroidal,  vacuoles  form  in  the  interior  of  the  cells  gradually  becoming 


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HANDBOOK    OF    PHYSIOLOGY. 


united  by  fine  protoplasmic  processes:  by  the  extension  of  the  vacuoles 
into  them,  capillary  tubes  are  gradually  formed. 

Morphology.  Heart. — When  it  first  appears,  the  heart  is  approxi- 
mately tubular  in  form,  being  at  first  a  douile  tuie  then  a,  single  one.  It 
receives  at  its  two  posterior  angles  the  two  omphalo-mesenteric  or  vitel- 
line veins,  and  gives  off  anteriorly  the  primitive  aorta  (fig.  493).  The 
junction  of  the  two  veins  which  pass  into  the  auricle  becomes  removed 
farther  and  farther  away  from  the  heart,  and  the  vessel  thus  formed  is 
called  sinus  venosus  near  to  the  auricle,  and  ductus  venosus  farther 
away, or  if  it  be  called  by  one  name  that  of  meatus  venosus  may  be  used. 

It  soon,  however,  becomes  curved  somewhat  in  the  shape  of  a  horse- 
shoe, with  the  convexity  toward  the  right,  the  venous  end  being  at  the 
same  time  drawn  up  toward  the  head,  so  that  it  finally  lies  behind  and 
somewhat  to  the  right,  of  the  arterial.  It  also  becomes  partly  divided  by 
constrictions  into  three  cavities. 

Of  these  three  cavities  which  are  developed  in  all  vertebrata,  that  at 
the  venous  end  is  the  simple  auricle,  with  the  sinus  venosus,  that  at  the 
arterial  end  the  bulbus  arteriosus,  and  the  middle  one  is  the  simple  ven- 
tricle. 

These  three  parts  of  the  heart  contract  in  succession.  The  auricle 
and  the  bulbus  arteriosus  at  this  period  lie  at  the  extremities  of  the 


Fig.  493. — Foetal  heart  in  successive  stages  of  development.    1,  venous  extremity ;  3,  arterial  ex- 
tremity ;  3,  3,  pulmonary  branches ;  4,  ductus  arteriosus.     CDalton. ) 


horse-shoe.  The  bulging  out  of  the  middle  portion  inferiorly  gives  the 
first  indication  of  the  future  form  of  the  ventricle  (fig.  493).  The  great 
curvature  of  the  horse-shoe  by  the  same  means  becomes  much  more 
developed  than  the  smaller  curvature  between  the  auricle  and  bulbus; 
and  the  two  extremities,  the  auricle  and  bulb,  approach  each  other 
superiorly,  so  as  to  produce  a  greater  resemblance  to  the  later  form  of 
the  heart,  while  the  ventricle  becomes  more    and  more  developed  in- 


DEVELOPMEXT.  T99 

feriorly.  The  heart  of  fishes  retains  these  cavities,  no  further  division 
by  internal  septa  into  right  and  left  chambers  taking  place.  In 
amphibia,  also,  the  heart  throughout  life  consists  of  the  three  muscular 
divisions  which  are  so  early  formed  in  the  embryo  and  the  sinus  venosus; 
but  the  auricle  is  divided  internally  by  a  septum  into  a  pulmonary  and 
systemic  auricle.  In  reptiles,  not  merely  the  auricle  is  thus  divided  into 
two  cavities,  but  a  similar  septum  but  incomplete  is  more  or  less  developed 


Fig.  494.— Heart   of  the  chick  at  the  45th,  65th,   and   85th   hours  of   incubation.    1,  the  venous 
trunks;  2,  the  aiu-icle;  3,  the  ventricle;  4,  the  bulbus  arteriosus.     (AHen  Thomson.) 

in  the  ventricle.  In  birds  and  mammals,  both  auricle  and  A'entricle 
undergo  complete  division  by  septa;  Avhile  in  these  animals  as  well  as  in 
reptiles,  the  bulbus  aorta?  is  not  permanent,  but  becomes  lost  in  the  ven- 
tricles. The  septum  dividing  the  ventricle  commences  at  the  apex  and 
extends  upward.  The  subdivision  of  the  auricles  is  very  early  fore- 
shadowed by  the  outgrowth  of  the  two  auricular  appendages,  which 
occurs  before  any  septum  is  formed  externally.  The  septum  of  the 
auricles  is  developed  from  a  semilunar  fold,  which  extends  from  above 
downward.  In  man,  the  septum  between  the  ventricles,  according  to 
Meckel,  begins  to  be  formed  about  the  fourth  week,  and  at  the  end  of 
eight  weeks  is  complete.  The  septum  of  the  auricles,  in  man  and  all 
animals  which  possess  it,  remains  imperfect  throughout  foetal  life.  When 
the  partition  of  the  auricles  is  first  commencing,  the  two  vena3  cavae  have 
different  relations  to  the  two  cavities.  The  superior  cava  enters,  as  in 
the  adult,  into  the  right  auricle;  but  the  inferior  cava  is  so  placed  that 
it  appears  to  enter  the  left  auricle,  and  the  posterior  part  of  the  septum 
of  the  auricles  is  formed  by  the  Eustachian  valve,  which  extends  from 
the  point  of  entrance  of  the  inferior  cava.  Subsequently,  however,  the 
septum,  growing  from  the  anterior  wall  close  to  the  upper  end  of  the  ven- 
tricular septum,  becomes  directed  more  and  more  to  the  left  of  the  vena 
cava  inferior.  During  the  entire  period  of  foetal  life,  there  remains 
an  opening  in  the  septum,  which  the  valve  of  the  foramen  ovale,  devel- 
oped in  the  third  month,  imperfectly  closes. 

The  hulhns  arteriosus,  which  is  originally  a  single  tube,  becomes 
gradually  divided  into  two  by  the  growth  of  an  internal  septum,  which 
springs  from  the  posterior  wall,  and  extends  forward  toward  the  front 
wall  and  downward  toward  the  ventricles.  This  partition  takes  a  some- 
what spinal  direction,  so  that  the  two  tubes  (aorta  and  pulmonary  artery) 


8()0  HANDBOOK    OF    PHYSIOLOGY. 

which  result  from  its  completion,  do  not  run  side  by  side,  but  are 
twisted  round  each  other. 

As  the  septum  grows  down  toward  the  ventricles,  it  meets  and  coa- 
lesces with  the  upwardly  growing  ventricular  septum,  and  thus  from 
the  right  and  left  ventricles,  which  are  now  completely  separate,  arise 
respectively  the  pulmonary  artery  and  aorta,  which  are  also  quite  dis- 
tinct. The  auriculo-ventricular  and  semi-lunar  valves  are  formed  by  the 
folds  of  the  endocardium. 

At  its  first  appearance,  as  we  have  seen,  the  heart  is  placed  just 
beneath  the  head  of  the  foetus,  and  is  very  large  relatively  to  the  whole 
body;  but  with  the  growth  of  the  neck  it  becomes  further  and  further 
removed  from  the  head,  and  is  lodged  in  the  cavity  of  the  thorax. 

Up  to  a  certain  period  the  auricular  is  larger  than  the  ventricular  divi- 
sion of  the  heart ;  but  this  relation  is  gradually  reversed  as  development 
proceeds.  Moreover,  all  through  foetal  life,  the  walls  of  the  right  ven- 
tricle are  of  very  much  the  same  thickness  as  those  of  the  left,  which 
may  probably  be  explained  by  the  fact  that  in  the  foetus  the  right  ven- 
tricle has  to  propel  the  blood  from  the  pulmonary  artery  into  the  aorta, 
and  thence  into  the  placenta,  while  in  the  adult  it  only  drives  the  blood 
through  the  lungs. 

Arteries. — The  primitive  aorta  arises  from  the  bulbus  arteriosus  and 
divides  into  two  branches  which  arch  backward,  one  on  each  side  of  the 
foregut  and  unite  again  behind  it,  and  in  front  of  the  notochord  into  a 
single  vessel. 

This  gives  off  the  two  omphalo-mesenteric  arteries,  which  distribute 
branches  all  over  the  yolk-sac;  this  a7'ea  vasculosa  in  the  chick  attaining 
a  large  development,  and  being  limited  all  round  by  a  vessel  known  as 
the  sinus  terminalis. 

The  blood  is  collected  by  the  venous  channels,  and  returned  through 
the  omphalo-mesenteric  veins  to  the  heart. 

Behind  this  pair  of  primitive  aortic  arches,  four  more  pairs  make 
their  appearance  sucessively,  so  that  there  are  five  pairs  in  all,  each  one 
running  along  one  of  the  visceral  arches. 

These  five  are  never  all  to  be  seen  at  once  in  the  embryo  of  higher 
animals,  for  the  two  anterior  pairs  gradually  disappear,  while  the  pos- 
terior ones  are  making  their  appearance,  so  that  at  length  only  three 
remain. 

In  fishes,  however,  they  all  persist  throughout  life  as  the  branchial 
arteries  supplying  the  gills,  while  in  amphibia  three  pairs  persist  through- 
out life. 

In  reptiles,  birds,  and  mammals,  further  transformations  occur. 

In  reptiles  the  fourth  pair  remains  throughout  life  as  the  permanent 
right  and  left  aorta;  in  birds  the  right  one  remains  as  the  permanent 


DEVELOPMENT. 


HOl 


aorta,    curving   over    the   right    bronchus   instead    of    the   left    us    in 
mammals. 

In  mammals  the  left  fourth  aortic  arch  develops  into  the  permanent 
aorta,  the  right  one  remaining  as  the  subclavian  artery  of  that  side. 
Thus  the  subclavian  arterj'  on  the  right  side  corresponds  to  the  aortic 
arch  on  the  left,  and  this  homology  is  further  confirmed  by  the  fact  that 


Fig.  495.— Diagram  of  the  aortic  aix'hes  iu  a  nuuuinal.  sliowing  transformations  which  give  rise 
to  the  permanent  arterial  vessels.  A,  primitive  aiterial  stem  or  aortic  bulb,  now  divided  into 
A,  the  ascending  part  of  the  aortic  arch,  and  j).  the  imlnionary ;  a  a',  right  and  left  aortic  roots; 
A',  descending  aorta;  1,  3,  3,  4,  5,  the  five  primirive  aortic  or  branchial  arches;  /,  //,  /i/,  IV. 
the  four  branchial  clefts  which,  for  the  sake  of  clearness,  have  been  omitted  on  the  right  side. 
The  permanent  .systenii(;  vessels  are  deeply,  the  pulmonary  arteries  lightly,  shaded;  the  parts 
of  the  primitive  arches  which  are  transitory  are  simply  outlined;  e,  placed  between  the  per- 
manent common  carotid  arteries;  ce,  external  carotid  arteries;  c  /,  internal  carotid  arteries;  s, 
right  subclavian,  rising  from  the  right  aortic  root  bej'ond  the  fifth  arch;  v.  right  vertebral  from 
the  same,  opposite  the  fourth  arch;  v'  .s',  left  vertebral  and  subclavian  arteries  rising  together 
from  the  left  or  permanent  aortic  root,  opposite  the  fourth  arch;  ji.  pulmonary  arteries  rising 
together  from  the  left  fifth  arch;  d,  oviter  or  back  part  of  the  left  fifth  arch,  "forming  ductus 
arteriosis;  p  n,  p  n\  right  and  left  pneumogastric  nerves  descending  in  front  of  aortic  arch, 
with  their  recurrent  branches  represented  diagramnu'tically  as  passing  behind,  to  illustrate  the 
relations  of  these  nerves  respectively  to  the  riglit  sululavian  artery  (4)  and  the  arch  of  the  aorta 
and  ductus  arteriosus  (rf).      (Alh^n  Thomson,  aftci-  llatlike.) 

the  recurrent  laryngeal  nerve  hooks  under  the  subclavian  on  the  right 
side,  and  the  aortic  arch  on  the  left. 

The  third  aortic  arch  remains  as  the  internal  carotid  artery,  while 
the  fifth  disappears  on  the  right  side,  but  on  the  left  forms  the  pulmo- 
nary artery.  The  distal  end  of  this  arch  originally  opens  into  the  descend- 
ing aorta,  and  this  communication  (which  is  permanent  throughout 
life  in  many  reptiles  on  both  sides  of  the  body)  remains  through- 
out foetal  life  under  the  name  of  duohis  arteriosus:  the  branches  of  the 
pulmonary  artery,  to  the  right  and  left  lung,  are  very  small,  and  most 
of  the  blood  which  is  forced  into  the  pulmonary  artery  passes  through 
the  wide  ductus  arteriosus  into  the  descending  aorta.  All  these  points 
will  become  clear  on  refereni^p  to  thp  accompanying  diagram  (fig.  495). 
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HANDBOOK    OF    PHYSIOLOGY. 


As  the  umbilical  vesicle  dwindles  in  size,  the  portion  of  the  omphalo- 
mesenteric arteries  outside  the  body  gradually  disappears,  the  part  inside 
the  body  remaining  as  the  mesenteric  arteries. 

Meanwhile  with  the  growth  of  the  allantois  two  new  arteries  {umbil- 
ical) appear,  and  rapidly  increase  in  size  till  they  are  the  largest  branches 
of  the  aorta:  they  are  given  off  from  the  internal  iliac  arteries,  and  for 
a  long  time  are  considerably  larger  than  the  external  iliacs  which  supply 
the  comparatively  small  hind-limbs. 

Veins. — The  chief  veins  in  the  early  embryo  may  be  divided  into 
two  groups,   visceral  and  parietal:    the  former  includes  the  omphalo- 


Fig.  496. 


Fig.  497. 


Fig.  496.  —Diagram  of  young  embryo  and  its  vessels,  showing  course  of  circulation  in  the 
umbilical  vesicle;  and  also  that  of  the  allantois  (near  the  caudal  extremity),  which  is  just  com- 
mencing.    (Dal  ton.) 

Fig,  497.  —Diagram  of  embryo  and  its  vessels  at  a  later  stage,  showing  the  second  circuls/- 
tion.  The  pharynx,  cesophagus,  and  intestinal  canal  have  become  further  developed,  and  the  mes- 
enteric arteries  have  enlarged,  while  the  umbilical  vesicle  and  its  vascular  branches  are  very- 
much  reduced  in  size.  The  large  umbilical  arteries  are  seen  passing  out  in  the  placenta.  (Dalton. ) 

mesenteric  and  umbilical,   the  latter  the  jugular  and  cardinal  veins. 
The  former  may  be  first  considered. 

The  earliest  veins  to  appear  in  the  foetus  are  the  omphalo-mesenteric 
or  vitelline,  which  return  the  blood  from  the  yolk-sac  to  the  developing 
auricle.  As  soon  as  the  placenta  with  its  umbilical  veins  is  developed, 
these  unite  with  the  omphalo-mesenteric,  and  thus  the  blood  which 
reaches  the  auricle  comes  partly  from  the  yolk-sac  and  partly  from  the 
placenta.  The  right  omphalo-mesenteric  and  the  right  umbilical  veins 
soon  disappear,  and  the  united  left  omphalo-mesenteric  and  umbilical 
veins  pass  through  the  developing  liver  on  the  way  to  the  auricle.  Two 
sets  of  vessels  make  their  appearance  in  connection  with  the  liver  (venae 
hepaticse  advehentes,  and  revehentes),  both  opening  into  the  united 
omphalo-mesenteric  and  umbilical  veins,  in  such  a  way  that  a  portion 
pf  the  venous  blood  traversing  the  latter  is  diverted  into  the  developing 


DEVELOPMENT.  S(»8 

liver,  and,  having  passed  through  its  capillaries,  returns  to  the  umbili- 
cal vein  through  the  venae  hepaticae  revehentes  at  a  point  nearer  the 
heart  (see  fig.  498) .  The  portion  of  vein  between  the  afferent  and  effe- 
rent veins  of  the  liver  becomes  the  ductus  venosus.     The  \ense  hepaticae 


Fig.  498. — Diagrams  illustrating  the  development  of  veins  about  the  liver.  B.  d  c,  ducts  of 
Cuvier,  right  and  left;  c  a,  right  and  left  cardinal  veins;  o.  left  omphalo-mesenteric  vein;  o'. 
right  omphalo-mesenteric  vein,  almost  shrivelled  up ;  it  ti\  umbilical  veins,  of  which  u',  the  right 
one,  has  almost  disappeared.  Between  the  vense  cardinales  is  seen  the  outline  of  the  rudiment- 
ary liver  with  its  vense  hepaticae  advehentes,  anil  revehentes.  D,  ductus  venosus;  I\  hepatic 
veins;  c  i,  vena  cava  inferior;  P,  portal  vein;  P'P\  venae  advehentes;  m,  mesenteric  veins. 
(Kolliker.) 

advehentes  become  the  right  and  left  branches  of  the  portal  vein,  the 
vense  hepaticte  revehentes  become  the  hepatic  veins,  which  open  just  at. 
the  junction  of  the  ductus  venosus  Avith  another  large  vein  (vena  cava 
inferior),  which  is  now  being  developed.  The  mesenteric  portion  of 
the  omphalo-mesenteric  vein  returning  blood  from  the  developing  intes- 
tines remains  as  the  mesenteric  vein,  which,  by  its  union  with  the  splenic 
vein,  forms  the  portal. 

Thus  the  foetal  liver  is  supplied  with  venous  blood  from  two  sources, 
through  the  umbilical  and  portal  vein  respectively.  At  birth  the  circu- 
lation through  the  umbilical  vein  of  course  completely  ceases  and  the 
vessel  begins  at  once  to  dwindle,  so  that  now  the  only  venous  supply  of 
the  liver  is  through  the  portal  vein.  The  earliest  appearance  of  the 
parietal  system  of  veins  is  the  formation  of  two  short  transverse  veins 
(ducts  of  Cuvier)  opening  into  the  auricle  on  either  side,  which  result 
from  the  union  of  an  anterior  cardinal,  afterward  forming  a  jugular, vein, 
collecting  blood  from  the  head  and  neck,  and  a  posterior  cardinal  vein 
which  returns  the  blood  from  the  WolfiBau  bodies,  the  vertebral  column, 
and  the  parieties  of  the  trunk.  This  arrangement  persists  throughout 
life  in  fishes,  but  in  mammals  the  following  transformations  occur. 

As  the  kidneys  are  developing  a  new  vein  appears  (vena  cava  infe- 
rior), formed  by  the  junction  of  their  efferent  veins.  It  receives  branches 
from  the  legs  (iliac)  and  increases  rapidly  in  size  as  they  grow;  further 
up  it  receives  the  hepatic  veins,  which  by  now  have  lost  their  original 
opening  into  the  ductus  venosus.     The  heart  gradually  descends  into 


804 


HANDBOOK    OF   PHYSIOLOGY. 


the  thorax,  causing  the  ducts  of  Ouvier  to  become  oblique  instead  of 
transverse.  As  the  fore-limbs  develop,  the  subclavian  veins  are  formed. 
A  transverse  communicating  trunk  now  unites  the  two  ducts  of 
Cuvier,  and  gradually  increases,  while  the  left  duct  of  Cuvier  becomes 
almost  entirely  obliterated  (all  its  blood  passing  by  the  communicating 
trunk  to  the  right  side)  (i5g.  499,  c.d.).  The  right  duct  of  Cuvier 
remains  as  the  right  innominate  vein,  while  the  communicating  branch 
forms  the  left  innominate.  The  remnant  of  the  left  duct  of  Cuvier 
generally  remains  as  a  fibrous  band,  running  obliquely  down  to  the  coro- 
nary vein,  which  is  really  the  proximal  part  of  the  left  duct  of  Cuvier. 
In  front  of  the  root  of  the  left  lung,  another  relic  may  be  found  in  the 


Fig.  499. — Diagrams  iUustrating  the  development  of  the  great  veins,  d  c,  ducts  of  Cuvier ;  j, 
jugular  veins;  /i,  hepatic  veins;  c,  cardinal  veins;  .s,  subclavian  vein;  j  i,  internal  jugular  vein; 
/  e,  external  jugular  vein ;  a  z,  azygos  vein ;  c  i,  inferior  vena  cava ;  r,  renal  veins ;  i  I,  iliac  veins ; 
hij,  hypogastric  veins.     (Gegenbaur. ) 

form  of  the  so-called  vestigial  fold  of  Marshall,  which  is  a  fold  of  peri- 
cardium running  in  the  same  direction. 

In  many  of  the  lower  mammals,  such  as  the  rat,  the  left  ductus 
Cuvieri  remains  as  a  left  superior  cava. 

Meanwhile,  a  transverse  branch  carries  across  most  of  the  blood  of 
the  left  posterior  cardinal  vein  into  the  right;  and  by  this  union  the 
great  azygos  vein  is  formed. 

The  upper  portions  of  the  left  posterior  cardinal  vein  remains  as  the 
left  superior  intercostal  and  vena  azygos  minor. 


Circulation  of  Blood  ik  the  Foetus. 

The  circulation  of  blood  in  the  foetus  differs  considerably  from  that 
of  the  adult.     It  will  be  well,  perhaps,  to  begin  its  description  by  trac- 


DEVELUl'MKNT, 


805 


ing  the  coarse  of  the  blood,  which,  after  beiug  carried  out  to  the  pla- 
centa by  the  two  umbilical  arteries,  has  returned,  cleansed  and  replen- 
ished, to  the  foetus  by  the  umbilical  vein. 

It  is  at  first  conveyed  to  the  under  surface  of  the  liver,  and  there  the 
stream  is  divided, — a  part  of  the  blood  passing  straight  on  to  the  in- 


Z.  ^ulclaf. 


SafUJ-tor-  Vena.  Cax 


S..Auricle--U.^-!i:i-  ., 


HicfhtLobt 


/  /^"^-C^  Wmr-  —  - -InftriorVena  Cou. 


w 


FiK-  500.  — Diaprara  of  the  Foetal  Circulation. 


ferior  vena  cava,  tlirougli  a  venous  canal  called  the  dmtus  veiiosu^,  while 
the  remainder  passes  into  the  portal  vein,  and  reaches  the  inferior  vena 
cava  only  after  circulating  through  the  liver.  Whether,  however,  by 
the  direct  route  through  the  ductus  venosus  or  by  the  roundabout  way 
through  the  liver, — all  the  blood  which  is  returned  from  the  placenta  by 
the  umbilical  vein  reaches  the  inferior  vena  cava  at  last,  and  is  carried 
by  it  to  the  right  auricle  of  the  heart,  into  which  cavity  is  also  pouring 


g06  HAXBBOOK    OF    PHYSIOLOGY. 

the  blood  that  has  circulated  in  the  head  and  neck  and  arms,  and  has 
been  brought  to  the  auricle  by  the  superior  vena  cava.  It  might  be 
naturally  expected  that  the  two  streams  of  blood  would  be  mingled  in 
the  right  auricle,  but  such  is  not  the  case,  or  only  to  a  slight  extent. 
The  blood  from  the  superior  vena  cava — the  less  pure  fluid  of  the  two — 
passes  almost  exclusively  into  the  right  ventricle,  through  the  auriculo- 
ventricular  opening,  just  as  it  does  in  the  adult;  while  the  blood  of  the 
inferior  vena  cava  is  directed  by  a  fold  of  the  lining  membrane  of  the 
heart,  called  the  Eustacliian  valve.,  through  the  foramen  ovale  into  the 
left  auricle,  whence  it  passes  into  the  left  ventricle,  and  out  of  this  into 
the  aorta,  and  thence  to  all  the  body,  but  chiefly  to  the  head  and  neck. 
The  blood  of  the  superior  vena  cava,  which,  as  before  said,  passes  into 
the  right  ventricle,  is  sent  out  thence  in  smaU  amount  though  the  pul- 
monary artery  to  the  lungs,  and  thence  to  the  left  auricle,  as  in  the 
adult.  The  greater  part,  however,  by  far,  does  not  go  to  the  lungs,  but 
instead,  passes  through  a  canal,  the  ductus  arteriosus,  leading  from  the 
pulmonary  artery  into  the  aorta  just  below  the  origin  of  the  three  great 
vessels  which  supply  the  upper  parts  of  the  body ;  and  there  meeting 
that  part  of  the  blood  of  the  inferior  vena  cava  which  has  not  gone  into 
these  large  vessels,  it  is  distributed  with  it  to  the  trunk  and  lower  parts, 
— a  portion  passing  out  by  way  of  the  two  umbilical  arteries  to  the 
placenta.  From  the  placenta  it  is  returned  by  the  umbilical  vein  to  the 
under  surface  of  the  liver,  from  which  the  description  started. 

Changes  after  Birth. — After  birth  the  foramen  ovale  closes,  and  so 
do  the  ductus  arteriosus  and  ductus  venosus,  as  well  as  the  umbilical 
vessels;  so  that  the  two  streams  of  blood  which  arrive  at  the  right  auri- 
cle by  the  superior  and  inferior  vena  cava  respectively,  thenceforth 
mingle  in  this  cavity  of  the  heart,  and  passing  into  the  right  ventricle, 
go  by  way  of  the  pulmonary  artery  to  the  lungs,  and  through  these  after 
purification,  to  the  left  auricle  and  ventricle,  to  be  distributed  over  the 
body. 

The  Nervous  System. 

The  Cranial  and  Sinnal  Nerves. — The  cranial  nerves  are  derived  from 
a  continuous  band,  called  the  neural  band.  They  are  formed  before  the 
neural  canal  is  complete.  The  neural  band  is  made  up  of  two  laminte 
going  from  the  dorsal  edges  of  the  neural  groove  to  the  external  epiblast. 
It  becomes  separated  from  the  epiblast,  and  then  forms  a  crest  attached 
to  the  upper  surface  of  the  brain.  The  posterior  roots  of  the  spinal 
nerves  arise  as  outgrowths  of  median  processes  of  cells  from  the  dorsal 
side  of  the  spinal  cord,  which  become  attached  laterally  to  the  spinal 
cord  as  their  original  point  of  attachment  disappears.  The  anterior 
roots  probably  arise  from  the  ventral  part  of  the  cord  as  a  number  of 


DEVELOPMEXT.  g07 

strauds  for  each  uerve.  They  appear  later  than  the  posterior  roots. 
The  rudiment  of  the  posterior  root  is  differentiated  into  a  proximal 
round  uerve  connected  to  the  cord,  a  ganglionic  portion  and  a  distal 
portion.     To  the  last  the  anterior  nerve-root  becomes  attached. 

The  Spinal  Cord. — The  spinal  cord  consists  at  first  of  the  undiffer- 
entiated epiblast  of  the  walls  of  the  neural  canal,  the  cavity  of  which  is 
large,  with  almost  parallel  sides.  The  walls  are  at  first  composed  of 
elongated  irregular  nucleated  columnar  cells,  arranged  in  a  radiate 
manner.  The  cavity  then  becomes  narrow  in  the  middle  and  of  an 
hour-glass  shape  (fig.  501).     When  the  spinal  nerves  make  their  first 


Fig.  501. — Diagram  of  development  of  spinal  cord,     c  c,  central   canal;  o/,  anterior  fissure;  ;>/, 
posterior  fissure ;  g,  gT&j  matter;  w,  white  matter.     For  further  explanation,  see  text. 

appearance,  about  the  fourth  day  in  the  chick,  the  epiblastic  walls  be- 
come differentiated  into  three  i)arts :  {a)  the  epithelium  lining  the  central 
canal;  {b)  the  gray  matter;  (c)  the  external  white  matter.  The  last  is 
derived  from  the  outermost  part  of  the  epiblastic  Avails  by  the  conversion 
of  the  cells  into  longitudinal  nerve-fibres.  The  fibres  being  without  any 
myelin  sheath,  are  for  a  time  gray  in  appearance.  The  white  matter 
corresponds  in  position  to  the  anterior  and  posterior  nerve-roots,  and 
are  the  anterior  and  posterior  white  columns.  It  is  at  first  a  very  thin 
layer,  but  increases  in  thickness  until  it  covers  the  whole  cord.  The 
gray  matter  too  arises  from  the  cells  by  their  being  prolonged  into  fibres. 
The  change  in  the  central  cells  is  sufficiently  obvious.  The  anterior  and 
posterior  cornua  of  gray  matter  and  the  anterior  gray  commissure  then 
appear.  The  anterior' fissure  is  formed  on  the  fifth  day  by  the  growth 
downward  of  the  anterior  cornua  of  gray  matter  toward  the  middle 
line.  The  posterior  fissure  is  fornied  later.  The  whole  cord  now  be- 
comes circular.     The  posterior  gray  commissure  is  then  formed. 

When  it  first  appears,  the  spinal  cord  occupies  the  whole  length  of 
the  medullary  canal,  but  as  development  proceeds,  the  spinal  column 
grows  more  rapidly  than  the  contained  cord,  so  that  the  latter  appears 
as  if  drawn  up  till,  at  birth,  it  is  opposite  the  third  lumbar  vertebra, 
and  in  the  adult  opposite  the  first  lumbar.  In  the  same  way  the  in- 
creasing obliquity  of  the  spinal  nerves  in  the  neural  canal,  as  we  approach 
the  lumbar  region,  and  the  cauda  eqiiina  at  the  lower  end  of  the  cord, 
are  accounted  for. 

Brain. — We  have  seen  that  the  front  portion  of  the  medullary  canal 


SU8 


HANDBOOK    OF    PHYSIOLOGY. 


is  almost  from  the  first  widened  out  and  divided  into  tliree  vesicles. 
From  the  anterior  vesicle  (thalamencephalon)  the  two  primary  optic 
vesicles  are  budded  off  laterally :  their  further  history  will  be  traced  in 
the  next  section.  Somewhat  later,  from  the  same  vesicle  the  rudiments 
of  the  hemispheres  appear  in  the  form  of  two  outgrowths  at  a  higher 
level,  which  grow  upward  and  backward.  These  form  the  prosen- 
cephalon. 

In  the  walls  of  the  posterior  (third)  cerebral  vesicle,  a  thickening 
appears  (rudimentary  cerebellum)  which  becomes  separated  from  the 
rest  of  the  vesicle  by  a  deep  inflection. 

At  this  time  there  are  two  chief  curvatures  of  the  brain  (fig,  502). 
(1.)  A  sharp  bend  of  the  whole  cerebral  mass  downward  round  the  end 


Fiff.  502.— Early  stages  in  development  of  human  brain  (magnified).  ],  2,  3.  are  from  an 
embryo  about  seven  weeks  old;  4,  about  three  months  old.  /»,  middle  cerebral  vesicle  (.mesen- 
cephalon); c,  cerebellum ;  mo,  medulla  oblongata:  ;.  thalamencephalon;  h.  hemisphieres ;  i',  in- 
fundibulum;  Fig.  3  shows  the  several  curves  which  occur  in  the  course  of  development;  Fig. 
4  is  a  lateral  view,  showing  the  great  enlargement  of  the  cerebral  hemispheres  which  have 
covered  in  the  thalami,  leavmg  the  optic  lobes,  m,  uncovered.     (Kolliker.) 

N.  B.— In  Fig.  2  the  line  /  terminates  in  the  right  hemisphere;  it  ought  to  be  continued  into 
the  thalamencephalon. 


of  the  notochord,  by  which  the  anterior  vesicle,  which  was  the  highest 
of  the  three,  is  bent  downward,  and  the  middle  one  comes  to  occupy 
the  highest  position.  (2.)  A  sharp  bend,  with  the  convexity  forward, 
which  runs  in  from  behind  beneath  the  rudimentary  cerebellum  sepa- 
rating it  from  the  medulla. 

Thus,  five  fundamental  parts  of  the  foetal  brain  may  be  distinguished, 
whicli,  together  with  the  parts  developed  from  them,  may  be  presented 
in  the  following  tabular  view : — 


UEVELOPMEN  r. 


809 


Table  of  Parts  developed  from  Fundamental  Parts  of  Brain. 


II. 


III. 


Anterior 
Primary 
Vesicle, 
or  Fore- 
brain. 


Middle 
Primary 
Vesicle, 
or  Mid- 
brain. 
Posterior 
Primarj' 
Vesicle, 
or  Hind- 
brain. 


First    Secondary    Vesicle 
of  Prosencephalon. 


Second  Secondary  Vesicle 
or  Thalamencephalon 
(Diencephaloni . 


f  Anterior  end  of  third  ventricle, 
j  foramen  of  Monro,  lateral  ven- 
J  tricles,  cerebral  hemispheres, 
I  corpora  striata,  corpus  callosum, 
fornix,  lateral  ventricles,  olfac- 
I       tor}-  bulb. 

I  Tlialami  optici,  pineal  gland,  part 
I  of  pituitary  body,  third  ventri- 
I  cle,  optic  nerve  and  retina,  iu- 
I       fundibulum. 


Third    Secondary  Vesicle  \  Corpora  quadrigemina,  crura  cere- 
or   Mesencephalon.         '/      bri,  aqueduct  of  Sylvius. 


Fourth  Secondary  Vesicle 


I       (jr  Epencephalon.  !  Fom-th  ven- 

)   Fifth    Secondarv   Vesicle   ( 


tricle. 


)r  Metencephalon. 


J 


Cerebellum,  pons, 
medulla  oblon- 
gata. 

(Quain. ) 


The  cerebral  hemispheres  grow  rapidly  upward  and  backward,  wliile 
from  their  inferior  surface  the  olfactory  bull>s  are  budded  off,  and  tlie 
prosencephalon,  from  which  they  spring,  remains  to  form  the  third  ven- 
tricle and  optic  thalami.  The  middle  cerebral  vesicle  (mesencephalon) 
for  some  time  is  the  most  prominent  part  of  the  foetal  brain,  and  in 
fishes,  amphibia,  and  reptiles,  it  remains  uncovered  through  life  as  the 
optic  lobes.  But  in  birds  the  growth  of  the  cerebral  hemispheres  thrusts 
the  optic  lobes  down  laterally,  and  in  mammalia  completely  overlaps 
them. 

In  tlie  lower  mammalia  the  backward  growth  of  the  hemispheres 
ceases  as  it  were,  but  in  the  higher  groups,  such  as  the  monkeys  and 
man,  they  grow  still  further  back,  until  they  completely  cover  in   the 


FiK-  503.— Side  view  of  fu-ial  liraiii  at  six  uioiiths,  showing  commencement  of  formation  of 
the  principal  fissures  and  convolutions.  F,  frontal  lobe;  P.  parietal:  O.  occipital;  T,  temporal; 
a  a  a,  commencing  frontal  convolutions;  s,  Sylvian  fissure;  s',  its  anterior  division;  c.  within 
it  the  central  lobe  or  island  of  Reil;  r,  fissure  of  Rolando:  ;>,  perpendicular  fis-sure.  (R. 
Wagner.) 

cerebellum,  so  that  on  looking  down  on  the  brain  from  above,  the  cere- 
bellum is  quite  concealed  from  view.  The  surface  of  the  hemispheres 
is  at  first  quite  smooth,  but  as  early  as  the  tliird  month  the  great  Sylvian 
fissure  begins  to  be  formed  (fig.  503). 


SIO  HANDBOOK    OF    PHYSIOLOGY. 

The  next  to  appear  is  the  parieto-occipital  or  perpendicular  fissure; 
these  two  great  fissures,  unlike  the  rest  of  the  sulci,  are  formed  by  a  curv- 
ing round  of  the  whole  cerebral  mass. 

In  the  sixth  month  the  fissure  of  Kolando  appears :  from  this  time 
till  the  end  of  foetal  life  the  brain  grows  rapidly  in  size,  and  the  convo- 
lutions appear  in  quick  succession;  first  the  great  primary  ones  are 
sketched  out,  then  the  secondary,  and  lastly  the  tertiary  ones  in  the 
sides  of  the  fissures.  The  commissures  of  the  brain  (anterior,  middle, 
and  posterior),  and  the  corpus  callosum,  are  developed  by  the  growth  of 
fibres  across  the  middle  line. 

The  Hippocampus  major  is  formed  by  the  folding  in  of  the  gray 
matter  from  the  exterior  into  the  lateral  ventricles.  The  essential  points 
in  the  structure  and  arrangement  of  the  various  parts  of  the  brain,  are 
diagrammatically  shown  in  the  two  accompanying  figures  (figs.  502,  503). 

The  Special  Sense  Oegans. 

The  Eye. — Soon  after  the  first  three  cerebral  vesicles  have  become 
distinct  from  each  other,  the  anterior  one  sends  out  a  lateral  vesicle  from 
each  side  (primary  optic  vesicle),  which  grows  out  toward  the  free  sur- 
face, its  cavity  of  course  communicating  with  that  of  the  cerebral  vesicle 
through  the  canal  in  its  pedicle.     It  is  soon  met  and  invaginated  by  an 

A 


Fig.  504. —Longitudinal  section  of  the  primary  optic  vesicle  in  the  chick  magnified  (from 
Remak). — A,  from  an  embryo  of  sixty-five  hours;  B,  a  few  hours  later;  C,  of  the  fourth  day;  c, 
tiie  corneous  layer  or  epidermis,  presenting  in  A  the  open  depression  for  the  lens,  which  is 
closed  in  B  and  C ;  I,  the  lens  follicle  and  lens ;  pr,  the  primary  optic  vesicle ;  in  A  and  B,  the 
pedicle  is  shown;  in  C,  the  section  being  to  the  side  of  the  pedicle,  the  latter  is  not  shown;  v, 
the  secondary  ocular  vesicle  and  vitreous  humor. 

ingrowing  process  from  the  epiblast  (fig.  504),  very  much  as  the  grow- 
ing tooth  is  met  by  the  process  of  epithelium  which  produces  the  enamel 
organ.  This  process  of  the  epiblast  is  at  first  a  depression,  which  ulti- 
mately becomes  closed  in  at  the  edges  so  as  to  produce  a  hollow  ball, 
which  is  thus  completely  severed  from  the  epithelium  with  which  it  was 
originally  continuous.  From  this  hollow  ball  the  crystalline  lens  is 
developed.  The  way  in  which  this  occurs  has  been  indicated  in  a  pre- 
vious chapter  under  the  head  of  structure  of  the  lens.  By  the  ingrowth 
of  the  lens  the  anterior  wall  of  the  primary  optic  vesicle  is  forced  back 
nearly  into  contact  with  the  posterior,  and  thus  the  primary  optic  vesi- 


DEVELOPMENT. 


HU 


cle  is  almost  obliterated.  The  cells  in  the  anterior  wall  are  much  longer 
than  those  of  the  posterior  wall ;  from  the  former  the  retina  proper  is 
developed,  from  the  latter  the  retinal  pigment. 

The  cup-shaped  hollow  in  which  the  lens  is  now  lodged  is  termed 
the  secondary  optic  vesicle:  its  walls  grow  up  all  round,  leaving,  how- 
ever, a  slit  at  the  lower  part. 

Choroidal  Fissure. — Through  this  slit  (fig.  506),  often  termed  the 
choroidal  fissure,    a  process  of  mesoblast  containing  numerous  blood- 


FiR.  505. 


Fig.  506. 


Fig.  505.— Diagrammatic  sketch  of  a  vertical  longitudinal  section  through  the  eyeball  of  a 
human  foetus  of  four  weeks.  The  section  is  a  little  to  the  side,  so  as  to  avoid  passing  through 
the  ocular  cleft;  c,  the  cuticle  where  it  becomes  later  the  corneal  epithelium:  J.  the  lens:  op. 
optic  nerve  formed  by  the  pedicle  of  the  primary  optic  vesicle;  vp.  primary  medullary  cavity  or 
optic  vesicle;  p,  the  pigment  layer  of  the  retina:  r,  the  inner  wall  forming  the  retina  proper; 
vs,  secondary  optic  vesicle  cont;iining  the  rudiment  of  tlie  vitreous  humor.     X  100.     OKolliker.) 

Fig.  506. —Transverse  vertical  section  of  the  eyeball  of  a  human  embryo  of  four  weeks.  The 
anterior  half  of  the  section  is  represented:  pi\  the  remains  of  the  cavity  of  the  primary  optic 
vesicle;  p.  the  inner  part  of  the  outt^-  layer  forming  the  retinal  pigment';  i\  the  thickened  inner 
f)ai-t  givmg  rise  to  the  columnar  and  other  structures  of  the  retina;  r.  the  commencing  vitreous 
iuimor  within  the  secondary  optic  vesicle;  v'.  the  ocular  cleft  through  which  the  loop  of  tlie 
central  blood-vessel,  a,  projects  from  below;  /,  the  lens  with  a  central  cavity.  X  100. 
CKiilliker.) 


vessels  projects,  and  occupies  the  cavity  of  the  secondary  ojitic  vesicle 
behind  the  lens,  filling  it  with  vitreous  humor  and  furnishing  the  lens 
capsule  and  the  capsulo-pupillary  membrane.  This  process  in  mammals 
projects,  not  only  into  the  secondary  optic  vesicle,  but  also  into  the 
])edicle  of  the  primary  optic  vesicle  invaginatiug  it  for  some  distance 
from  beneath,  and  thus  carrying  up  the  arteria  centralis  retina'  into  its 
permanent  })ositiou  in  the  centre  of  the  optic  nerve. 

This  invagination  of  the  optic  nerve  does  not  occur  in  birds,  and 
consequently  no  arteria  centralis  retina?  exists  in  them.  But  they  pos- 
sess an  important  permanent  relic  of  the  original  protrusion  of  the  meso- 
blast through  the  choroidal  fissure,  in  the  pecte/i,  while  a  remnant  of 
the  same  fissure  sometimes  occurs  in  man  under  the  name  coloboma  iri- 
dis.  The  cavity  of  the  primary  optic  vesicle  becomes  completely  obliter- 
ated, and  the  rods  and  cones  growing  u]i  from  the  external  limiting 
membrane,  get  into  apposition  with   the  pigment  layer  of  the   retina. 


812 


HAS^DBOOK    OF    PHYSIOLOGY. 


The  inner  segments  of  the  rods  become  the  first  formed,  then  the  outer. 
The  cavity  of  its  pedicle  disappears  and  the  solid  optic  nerve  is  formed. 
Meanwhile  the  cavity  which  existed  in  the  centre  of  the  primitive  lens 
becomes  filled  up  by  the  growth  of  fibres  from  its  posterior  wall.  The 
epithelium  of  the  cornea  is  developed  from  the  epiblast,  while"  the  cor- 
neal tissue  proper  is  derived  from  the  mesoblast  which  intervenes  between 
the  epiblast  and  the  primitive  lens  which  was  originally  continuous 
with  it.  The  sclerotic  coat  is  developed  round  the  eyeball  from  the 
general  mesoblast  in  which  it  is  embedded.  The  choroid  is  developed 
from  the  mesoblast  on  the  outside  of  the  optic  cup  and  the  iris  by  the 
growing  forward  of  the  anterior  edge  of  the  optic  cup,  both  layers  of 
which  becoming  pigmented  remain  as  the  uvea.  Externally  the  cho- 
roidal mesoblast  grows  inward  to  form  the  main  structure.  The  ciliary 
processes  arise  from  the  hypertrophy  of  the  edge  of  the  optic  cup  which 
forms  folds  into  which  the  choroidal  mesoblast  grows,  and  in  which 
blood-vessels  and  pigmeut-cells  develop. 

The  iris  is  formed  rather  late,  as  a  circular  septum  projecting  in- 
ward, from  the  fore  part  of  the  choroid,  between  the  lens  and  the 
cornea.  In  the  eye  of  the  foetus  of  mammalia,  the  pupil  is  closed  by  a 
delicate  membrane,  the  memhrcma pupillm'is,  which  forms  the  front  por- 
tion of  a  highly  vascular  membrane  that,  in  the  foetus,  surrounds  the 


Fig.  507. — Blood-vessels  of  the  eapsulo-pupillary  membrane  of  a  new-born  kitten,  magnified. 
The  drawing  is  taken  from  a  preparation  injected  by  Tiersch,  and  shows  in  the  central  part  the 
convergence  of  the  net- work  of  vessels  in  the  pupillary  membrane.     (Kolliker.) 

lens,  and  is  named  the  membrana  capsulo-pupillaris  (fig.  507).  It  is 
supplied  with  blood  by  a  branch  of  the  arteria  centralis  retince,  which, 
passing  forward  to  the  back  of  the  lens,  there  subdivides.  The  mem- 
brana capsulo-pupillaris  withers  and  disappears  in  the  human  subject  a 
short  time  before  birth. 

The  eyelids  of  the  human  subject  and  mammiferous  animals,  like 


DEVELOPMENT.  813 

those  of  birds,  are  first  developed  in  the  form  of  a  ring.  They  t!ien  ex- 
tend over  the  globe  of  the  eye  until  they  meet  and  become  firmly 
agglntinated  to  each  other.  But  before  birth,  or  in  the  carnivora  after 
birth,  they  again  separate. 

The  Ear. — Very  early  in  the  development  of  the  embryo  a  depres- 
sion or  ingrowth  of  the  epiblast  occurs  on  each  side  of  the  head  which 
deepens  and  soon  becomes  a  closed  follicle.  This  2irimary  oiotic  vesicle, 
which  closely  corresj)onds  in  its  formation  to  the  lens  follicle  in  the  eye, 
sinks  down  to  some  distance  from  the  free  surface;  from  it  are  developed 
the  epitlielial  lining  of  the  memhranous  labyrinth  of  the  internal  ear, 
consisting  of  the  vestibule  and  its  semicircular  canals  and  the  scala  media 
of  the  cochlea.  The  surrounding  mesoblast  gives  rise  to  the  various 
fibrous  bony  and  cartilaginous  parts  which  complete  and  inclose  this 
membranous  labyrinth,  the  bony  semicircular  canals,  the  walls  of  the 
cochlea  with  its  scala  vestibuli  and  scala  tympani.  In  the  mesoblast 
between  the  primary  optic  vesicle  and  the  brain,  the  auditory  nerve  is 
gradually  differentiated  and  forms  its  central  and  peripheral  attachments 
to  the  brain  and  internal  ear  respectively.  According  to  some  authori- 
ties, however,  it  is  said  to  take  its  origin  from  and  grow  out  of  the  hind 
brain. 

The  Eustachian  tube,  the  cavity  of  the  tympanum,  and  the  external 
auditory  passage,  are  remains  of  the  first  branchial  cleft.  The  meni- 
brana  tympani  divides  the  cavity  of  this  cleft  into  an  internal  space, 
the  tympanum,  and  the  external  meatus.  The  mucous  membrane  of 
the  mouth,  which  is  prolonged  in  the  form  of  a  diverticulum  through 
the  Eustachian  tube  into  the  tympanum,  and  the  external  cutaneous 
system  come  into  relation  with  each  other  at  this  point;  the  two  mem- 
branes being  separated  only  by  the  proper  membrane  of  the  tympanum. 

The  pinna  or  external  ear  is  developed  from  a  process  of  integument 
in  the  neighborhood  of  the  first  and  second  visceral  arches,  and  prolxibly 
corresponds  to  the  gill-cover  (operculum)  in  fishes. 

The  Nose. — The  nose  originates  like  the  eye  and  ear  in  a  depression 
of  the  superficial  epiblast  at  each  side  of  the  fronto-iuisal  process  (pri- 
mary olfactory  groove),  which  is  at  first  completely  separated  from  the 
cavity  of  the  mouth,  and  gradually  extends  backward  and  downward  till 
it  opens  into  the  mouth. 

The  outer  angles  of  the  fronto-nasal  process,  uniting  with  the  max- 
illary process  on  each  side,  convert  what  was  at  first  a  groove  into  a 
closed  canal. 

The  Alimentary  Canal. 

The  alimentary  canal  in  the  earliest  stages  cf  its  development  con- 
sists of  tbrep  rlistipet  parts — the  fore  and  hind  gut  ending  blindly  at 


814 


HANDBOOK    OF    PHYSIOLOGY. 


each  end  of  the  body,  and  a  middle  segment  which  communicates  freely 
on  its  ventral  surface  with  the  cavity  of  the  yolk-sac  through  the  vitel- 
line or  omphalo-mesenteric  duct. 

From  the  fore-gut  are  formed  the  pharynx,  oesophagus,  and  stomach ; 
from  the  hind -gut,  the  lower  end  of  the  colon  and  the  rectum.  The 
mouth  is  developed  by  an  involution  of  the  epiblast  between  the  maxil- 
lary and  mandibular  processes,  which  becomes  deeper  and  deeper  till  it 
reaches  the  blind  end  of  the  fore-gut,  and  at  length  communicates  freely 
with  the  pharynx  by  the  absorption  of  the  partition  between  the  two. 

At  the  other  end  of  the  alimentary  canal  the  anus  is  formed  in  a  pre- 
cisely similar  way  by  an  involution  from  the  free  surface,  which  at  length 

D 


Fig.  508.— Outlines  of  the  form  and  position  of  the  alimentary  canal  in  successive  stages  of 
its  development.  A,  alimentary  canal,  etc.,  in  an  embryo  of  four  weeks;  B,  at  six  weeks;  C,  at 
eight  weeks ;  D,  at  ten  weeks ;  I,  the  primitive  lungs  connected  with  the  pharynx ;  s,  the  stomach ; 
d,  duodenum;  i,  the  small  intestine;  t',  the  large;  c,  the  caecum  and  vermiform  appendage;  r,  the 
rectum ;  cl,  in  A,  the  cloaca ;  a,  in  B,  the  anus  distinct  from  s  i,  the  sinus  uro-genitalis ;  v,  the 
yolk-sac ;  v  i,  the  vitello-intestinal  duct ;  w,  the  urinary  bladder  and  urachus  leading  to  the  al- 
lantois ;  gf,  genital  ducts.     (Allen  Thomson.) 

opens  into  the  hind-gut.  When  the  depression  from  the  free  surface 
does  not  reach  the  intestine,  the  condition  known  as  imperforate  anus 
results.  A  similar  condition  may  exist  at  the  other  end  of  the  alimen- 
tary canal  from  the  failure  of  the  involution  which  forms  the  mouth,  to 
meet  the  fore-gut.  The  middle  portion  of  the  digestive  canal  becomes 
more  more  and  closed  in  till  its  originally  wide  communication  with  the 
yolk-sac  becomes  narrowed  down  to  a  small  duct  (vitelline).  This  duct 
usually  completely  disappears  in  the  adult,  but  occasionally  the  proximal 
portion  remains  as  a  diverticulum  from  the  intestine.  Sometimes  a 
fibrous  cord  attaching  some  part  of  the  intestine  to  the  umbilicus,  re- 
mains to  represent  the  vitelline  duct.  Such  a  cord  has  been  known  to 
cause  in  after-life  strangulation  of  the  bowel  and  death. 


DEVELOPMENT. 


815 


The  alimentary  canal  lies  in  the  form  of  a  straight  tube  close  beneath 
the  vertebral  column,  but  it  gradually  becomes  divided  into  its  special 
parts,  stomach,  small  intestine,  and  large  intestine  (fig.  508),  and  at 
the  same  time  comes  to  be  suspended  in  the  abdominal  cavity  by  means 
of  a  lengthening  mesentery  formed  from  the  splanchnopleure  which  at- 
taches it  to  the  vertebral  column.  The  stomach  originally  has  the  same 
direction  as  the  rest  of  the  canal;  its  cardiac  extremity  being  superior, 
its  pylorus  inferior.  The  changes  of  position  which  the  alimentary  canal 
undergoes  may  be  readily  gathered  from  the  accompanying  figures  (fig. 
508). 

Pancreas  and  Salivary  Glands. — The  principal  glands  iu  connec- 
tion with  the  intestinal  canal  are  the  salivary,  jjancreas,  and  the  liver. 
In  mammalia,  each  salivary  gland  first  appears  as  a  simple  canal  with  bud- 


Fig.  509.— Lobules  of  the  parotid,  with  the  salivary  ducts,  in  the  embryo  of  the  sheep,  at  a  more 

advanced  stage. 

like  processes  (fig.  509),  lying  in  a  gelatinous  nidus  or  blastema,  and 
communicating  with  the  cavity  of  the  mouth.  As  the  development  of 
the  gland  advances,  the  canal  becomes  more  and  more  ramified,  increas- 
ing at  the  expense  of  the  blastema  in  which  it  is  still  inclosed.  The 
branches  or  salivary  ducts  constitute  an  independent  system  of  closed 
tubes  (fig.  509).  The  pancreas  is  developed  exactly  as  the  salivary 
glands,  but  is  developed  from  the  hypoblast  lining  the  intestine,  while 
the  salivary  glands  are  formed  from  the  epiblast  lining  the  mouth. 

The  Liver. — The  liver  is  developed  by  the  protrusion,  as  it  were, 
of  a  part  of  the  walls  of  the  fore-gut,  in  the  form  of  two  conical  hollow 
branches,  which  embrace  the  common  venous  stem  (figs.  510,  511).     The 


816 


HANDBOOK    OF    PHYSIOLOGY. 


outer  part  of  these  cones  involves  the  omphalo-mesenteric  vein,  which 
breaks  up  in  its  interior  into  a  plexus  of  capillaries,  ending  in  venous 
trunks  for  the  conveyance  of  the  blood  to  the  heart.  The  inner  portion 
of  the  cones  consists  of  a  number  of  solid  cylindrical  masses  of  cells, 


Fiff.  510.— Diagram  of  part  of  digestive  tract  of  a  chick  (4th  day).  The  black  line  represents 
hypoblast,  the  outer  shading  mesoblast ;  I  g,  lung  diverticulum  with  expanded  end  forming  pri- 
mary lung-vesicle ;  St,  stomach ;  I,  two  hepatic  diverticula,  with  their  terminations  imited  by 
solid  rows  of  hypoblast  cells;  p,  diverticulum  of  the  pancreas  with  the  vesicular  diverticula 
coming  from  it.     (Gotte.) 

derived  probably  from  the  hypoblast,  which  become  gradually  hollowed 
by  the  formation  of  the  hepatic  ducts,  and  among  which  blood-vessels 
are  rapidly  developed.  The  gland  cells  of  the  organ  are  derived  from 
the  hypoblast,  the  connective  tissue  and  vessels  without  doubt  from  the 


Fig.  511.— Rudiments  of  the  liver  on  the  intestine  of  a  chick  at  the  fifth  day  of  incubation 
1,  heart;  2,  intestine;  3,  diverticulum  of  the  intestine  in  which  the  liver  (4)  is  developed;  5,  part 
of  the  mucous  layer  of  the  germinal  membrane.     (Miiller.) 


mesoblast.  The  gall-bladder  is  developed  as  a  diverticulum  from  the 
hepatic  duct.  The  spleen,  lymphatic,  and  thymus  glands  are  developed 
from  the  mesoblast:  the  thyroid  partly  also  from  the  hypoblast,  which 
grows  into  it  as  a  diverticulum  from  the  fore-gut. 


development.  317 

The  Respiratory  Apparatus. 

The  Lungs,  at  their  first  development,  appear  as  small  tubercles  or 
diverticula  from  the  abdominal  surface  of  the  oesophagus. 

The  two  diverticula  at  first  open  directly  into  the  oesophagus,  but  as 
they  grow,  a  separate  tube  (the  future  trachea)  is  formed  at  their  point 
of  fusion,  opening  into  the  oesophagus  on  its  anterior  surface.  These 
primary  diverticula  of  the  hypoblast  of  the  alimentary  canal  send  off 
secondary  branches  into  the  surrounding  mesoblast,  and  these  again 
give  off  tertiary  branches,  forming  the  air-cells.  Thus  we  have  the 
lungs  formed:  the  epithelium  lining  their  air-cells,  bronchi,  and  trachea 
being  derived  from  the  hypoblast,  and  all  the  rest  of  the  lung-tissue, 


'1 


Fig.  512  illustrates  the  development  of  the  respiratory  organs,  a,  is  the  ( esophagus  of  achick 
on  the  fourth  day  of  ineuhatiou,  with  the  rudiments  of  the  trachea  on  the  lung  of  the  left  side, 
viewed  laterally;  1.  the  inferior  waU  of  the  oesophagus;  2,  the  upper  portion  of  the  same  tube; 
3,  the  rudimentary  lung ;  4,  the  stomach ;  b,  is  the  same  object  seen  from  below,  so  that  both 
lungs  are  visible,  c,  ^ows  the  tongue  and  respiratory  organs  of  the  embryo  of  a  horse;  1,  the 
tongue ;  2,  the  larynx ;  3,  the  trachea ;  4,  the  lungs  viewed  from  the  upper  side.     (After  Rathke. ) 

nerves,  lymphatics,  and  blood-vessels,  cartilaginous  rings,  and  muscular 
fibres  of  the  bronchi  from  the  mesoblast.  The  diaphragm  is  early  de- 
veloped. 

The  Genito-Urinary  Apparatus. 

The  Wolffian  bodies  are  organs  peculiar  to  the  embryonic  state, 
and  may  be  regarded  as  temporary,  rather  than  rudimental,  kidneys; 
for  although  they  seem  to  discharge  the  functions  of  these  latter  organs, 
they  arc  not  developed  into  them. 

The  Wolffian  duct  makes  its  appearance  at  an  early  stage  in  the  his- 
tory of  the  embryo,  as  a  cord  running  longitudinally  on  each  side  in 
the  mass  of  mesoblast,  which  lies  just  externally  to  the  intermediate  cell- 
mass  {ung,  fig.  513).  This  cord,  at  first  solid,  becomes  gradually  hol- 
lowed out  to  form  a  tube  (AVolffian)  which  sinks  down  till  it  projects 
beneath  the  lining  membrane  into  the  pleuro-peritoueal  cavity. 

The  primitive  tube  thus  formed  sends  off  secondary  diverticula  at 

frequent  intervals  which  grow  into  the  surrounding  mesoblast:  tufts  of 

vessels  grow  into  the  blind  ends  of  these  tubes,  iuvaginating  them  and 

producing  Afalpighian  bodies  very  similar  in  appearance  to  those  of  the 

52 


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HANDBOOK    OF    PHYSIOLOGY. 


permanent  kidney,  which  constitute  the  substance  of  the  Wolffian  body. 
Meanwhile  another  portion  of  mesoblast  between  the  Wolffian  body  and 
the  mesentery  projects  in  the  form  of  a  ridge,  covered  on  its  free  surface 


Fig.  513.— Transverse  section  of  embryo  chick  (third  day),  mr,  rudimentary  spinal  cord;  the 
primitive  central  canal  has  become  constricted  in  the  middle ;  c h,  notochord ;  utvh,  primordial 
vertebral  mass;  m,  muscle-plate;  dr,  df,  hypoblast  and  visceral  layer  of  mesoblast  lining 
groove,  which  is  not  yet  closed  in  to  form  the  intestines;  a  o,  one  of  the  primitive  aortse;  u  n. 
Wolffian  body;  itragr,  Wolffian  duct;  v  c,  vena  cardinalis;  h,  epiblast;  hp,  somatopleure  and  its 
reflection  to  form  af,  amniotic  fold;  p,  pi  euro-peritoneal  cavity.     (Koluker.) 

with  epithelium  termed  germ  epithelium.  From  this  projection  is  de- 
veloped the  reproductive  gland  (ovary  or  testis  as  the  case  may  be). 

Simultaneously,  on  the  outer  wall  of  the  Wolffian  body,  between  it 
and  the  body- wall  on  each  side,  an  involution  is  formed  from  the  pleuro- 
peritoneal  cavity  in  the  form  of  a  longitudinal  furrow,  whose  edges  soon 
close  over  to  form  a  duct  (Miiller's  duct). 

All  the  above  points  are  shown  in  the  accompanying  figures,  513,  514. 

The  Wolffian  bodies,  or  temporary  kidneys,  as  they  may  be  termed, 
give  place  at  an  early  period  in  the  human  foetus  to  their  successors,  the 
permanent  kidneys,  which  are  developed  behind  them.  They  diminish 
rapidly  in  size,  and  by  the  end  of  the  third  month  have  almost  entirely 
disappeared.  In  connection,  however,  with  their  upper  part,  in  the 
male,  there  are  developed  from  a  new  mass  of  blastema,  the  vasa  effe- 
re7itia,  coni  vasculosis  und  globus  major  ot  the  epididymis;  and  thus  is 
brought  about  a  direct  connection  between  the  secreting  part  of  the 
testicle  and  its  duct.  The  Wolffian  ducts  persist  in  the  male,  and  are 
developed  to  form  the  body  and  globus  minor  of  the  epididymis,  the  vas 
deferens,  and  ejaculatory  duct  on  each  side,  the  vesiculas  seminales  form- 
ing diverticula  from  their  lower  part.  In  the  female  a  small  relic  of 
the  Wolffian  body  persists  as  the  jxirovarinm;  in  the  male  a  similar  relic 
is  termed  the  organ  of  Giraldes.  The  lower  end  of  the  Wolffian  duct 
remains  in  the  female  as  the  duct  of  Gaertner  which  descends  toward, 
and  is  lost  upon,  the  anterior  wall  of  the  vagina. 


DEVELOPMENT. 


819 


From  the  lower  end  of  the  Wolffian  duct  a  diverticulum  grows  back 
along  the  body  of  the  embryo  toward  its  anterior  extremity,  and  ulti- 
mately forms  the  ureter.  Secondary  diverticula  are  given  ofE  from  it 
and  grow  into  the  surrounding  blastema  of  blood-vessels  and  cells. 

Malpighian  bodies  are  formed  just  as  in  the  Wolffian  body,  by  the 
invagination  of  the  blind  knobbed  end  of  these  diverticula  by  a  tuft  of 
vessels.  This  process  is  precisely  similar  to  the  invagination  of  the  pri- 
mary optic  vesicle  by  the  rudimentary  lens.  Thus  the  kidney  is  devel- 
oped, consisting  at  first  of  a  number  of  separate  lobules ;  this  condition 
remaining  throughout  life  in  many  of  the  lower  animals,  e.g.,  seals  and 
whales,  and  traces  of  this  lobulation  being  visible  in  the  human  foetus  at 
birth.     In  the  adult  all  the  lobules  are  fused  into  a  compact  solid  organ. 


Fig.  514.— Section  of  intermediate  cell-mass  on  the  fourth  day.  m,  mesentery;  L,  somato- 
pfeure;  o,  germinal  epithelium,  from  which  z.  the  duct  of  Muller,  becomes  involuted;  o,  thick- 
ened part  (if  germinal  epithelium  iu  which  the  primitive  ova  O  and  o,  are  lying:  £,  modified 
mesohlast,  which  will  form  the  stroma  of  the  ovary;  TT'JT,  Wolflfian  body;  ?/,  Wolffian  duct;  X 
160.     tWaldeyer.) 


The  supra-renal  capsules  originate  in  a  mass  of  mesoblast  just  above 
the  kidneys;  soon  after  their  first  appearance  they  are  very  much  larger 
than  the  kidneys  (see  fig.  516) ,  but  by  the  more  rapid  growth  of  the 
latter  this  relation  is  soon  reversed. 

The  first  appearance  of  the  generative  gland  has  been  already  de- 
scribed: for  some  time  it  is  impossible  to  determine  whether  an  ovarv 
or  testis  will  be  developed  from  it;  gradually  however  the  special  cha:- 
acters  belonging  to  one  of  them  appear,  and  in  either  case  the  organ 


820 


HANDBOOK    OF   PHYSIOLOGY. 


soon  begins  to  assume  a  relatively  lower  position  in  the  body;  the  ovaries 
being  ultimately  placed  in  the  pelvis;  while  toward  the  end  of  foetal 
existence  the  testicles  descend  into  the  scrotum,  the  testicle  entering 
the  internal  inguinal  ring  in  the  seventh  month  of  fcetal  life,  and  com- 
pleting its  descent  through  the  inguinal  canal  and  external  ring  into 
the  scrotum  by  the  end  of  the  eighth  month.  A  pouch  of  peritoneum, 
the  processus  vagmalis,  precedes  it  in  its  descent,  and  ultimately  forms 


VKrf 


ym 


Fie.  515.  —Diagram  showing  the  relations  of  the  female  (the  left-hand  figure  ?  )  and  of  the 
male  (the  right-hand  figure  i  )  reproductive  organs  to  the  general  plan  (the  middle  figure  of 
these  organs  in  the  higher  vertebrata  (including  man).  CI,  cloaca:  R,  rectum:  B  I,  urinary 
bladder;  f7,  ureter;  Z^,  kidney;  [/■  A,  urethra;  (x,  genital  gland,  ovary,  or  testis;  TF,  WolfiSan 
body;  W  d.  Wolffian  duct;  M,  Miillerian  duct;  P s  t,  prostate  gland ;  C p,  Cowper's  gland ;  Gap, 
corpus  spongiosum ;  C  c,  corpus  cavernosum. 

In  the  female.— V,  vagina;  U  t,  uterus;  Fp,  Fallopian  tube;  G  /,  Gaertner's  duct;  Pv,  par- 
ovarium ;  A,  anus ;  C  c,  u  s  p,  clitoris. 

In  the  male. — C  s  p,  C  c,  penis;  U  t,  uterus  masculinis;  V s,  vesicula  seminalis;  Vd,  vas 
deferens.     (Huxley. ) 


the  tunica  vaginalis  or  serous  covering  of  the  organ ;  the  communica- 
tion between  the  tunica  vaginalis  and  the  cavity  of  the  peritoneum  being 
closed  only  a  short  time  before  birth.  In  its  descent,  the  testicle  or 
ovary  of  course  retains  the  blood-vessels,  nerves,  and  lymphatics,  which 
were  supplied  to  it  while  in  the  lumbar  region,  and  which  are  compelled 
to  accompany  it,  so  to  speak,  as  it  assumes  a  lower  position  in  the  body. 
Hence  the  explanation  of  the  otherwise  strange  fact  of  the  origin  of  these 
parts  at  so  considerable  a  distance  from  the  organ  to  which  they  are  dis- 
tributed. 

Descent  0/  the  Testicles  into  the  Scrotum. — The  means  by  which  the 


UKVIiLuPMKNT.  S-^1 

descent  of  the  testicles  iutu  the  scrotum  is  effected  are  not  fully  and 
exactly  known.  It  was  formerly  believed  that  a  membraneous  and  partly 
muscular  cord,  called  the  guheTnaailum  testis,  which  extends  while  the 
testicle  is  yet  high  in  the  abdomen,  from  its  lower  part,  through  the 
abdominal  wall  (in  the  situation  of  the  inguinal  canal)  to  the  front  of 
the  pubes  and  lower  part  of  the  scrotum,  was  the  agent  by  the  contraction 
of  which  the  descent  was  effected.  It  is  now  generally  thought,  how- 
ever, that  such  is  not  the  case,  and  that  the  descent  of  the  testicle  and 
ovary  is  rather  the  result  of  a  general  process  of  development  in  these 
and  neighboring  parts,  the  tendency  of  which  is  to  produce  this  change 
in  the  relative  position  of  these  organs.  In  other  words,  the  descent  is 
not  the  result  of  a  mere  mechanical  action,  by  which  the  organ  is  dragged 
down  to  a  lower  position,  but  rather  one  change  out  of  many  which 
attend  the  gradual  development  and  re-arrangement  of  these  organs. 
It  may  be  repeated,  however,  that  the  details  of  the  process  by  which 
the  descent  of  the  testicle  into  the  scrotum  is  affected  are  not  accurately 
known. 

The  homologue,  in  the  female,  of  the  gubernaculum  testis  is  a 
structure  called  the  roicnd  ligament  of  the  uterus,  which  extends  through 
the  inguinal  canal,  from  the  outer  and  upper  part  of  the  uterus  to  the 
subcutaneous  tissue  in  front  of  the  symphysis  pubis. 

At  a  very  early  stage  of  foetal  life,  the  Wolffian  ducts,  ureters,  and 
Miillerian  ducts,  open  into  a  receptacle  formed  by  the  lower  end  of  the 
allantois,  or  rudimentary  bladder;  and  as  this  communicates  with  the 
lower  extremity  of  the  intestine,  there  is  for  the  time,  a  common  recep- 
tacle or  cloaca  for  all  these  parts,  which  opens  to  the  exterior  of  the 
body  through  a  part  corresponding  with  the  future  anus,  an  arrange- 
ment which  is  permanent  in  reptiles,  birds,  and  some  of  the  lower  mam- 
malia. In  the  human  foetus,  however,  the  intestinal  portion  of  the 
cloaca  is  cut  off  from  that  which  belongs  to  the  urinary  and  generative 
organs;  a  separate  passage  or  canal  to  the  exterior  of  the  body,  belong- 
ing to  these  parts,  being  called  the  sinus  iiro-genitalis.  Subsequently, 
this  canal  is  divided,  by  a  process  of  division  extending  from  before 
backward  or  from  above  downward,  into  a  'pars  urinaria'  and  a  'pars 
genitalis. '  The  former,  continuous  with  the  nrachus,  is  converted  into 
the  urinary  bladder. 

The  Fallopian  tubes,  the  uterus,  and  the  vagina  are  developed  from 
the  Miillerian  ducts  (fig.  516,  m),  whose  first  appearance  has  been  al- 
ready described.  The  two  Miillerian  ducts  are  united  below  into  a  sin- 
gle cord,  called  the  genital  cord,  and  from  this  are  developed  the  vagina, 
as  well  as  the  cervix  and  the  lower  portion  of  the  body  of  the  uterus; 
while  the  ununited  portion  of  the  duct  on  each  side  forms  the  upper 
part  of  the  uterus,  and  the  Fallopian  tube.     In  certain  cases  of  arrested 


g.^2  HANDBOOK    OF    PHYSIOLOGY. 

or  abnormal  development,  these  portions  of  the  Mlilleriau  ducts  may  not 
become  fused  together  at  their  lower  extremities,  and  there  is  left  a 
cleft  or  horned  condition  of  the  upper  part  of  the  uterus  resembling  a 
condition  which  is  permanent  iu  certain  of  the  lower  animals. 

In  the  male,  the  Miillerian  ducts  have  no  special  function,  and  are 
but  slightly  developed.  The  hydatid  of  Morgagni  is  the  remnant  of  the 
upper  part  of  the  Mullerian  duct.  The  small  prostatic  pouch,  uterus 
masculinus,  or  sinus  pocularis^  forms  the  atrophied  remnant  of  the  dis- 


Fig.  516.  —Diagram  of  the  Wolffian  bodies,  MiiUerian  ducts  and  adjacent  parts  previous  to 
sexual  distinction,  as  seen  from  before.  si\  the  supra-renal  bodies ;  r,  the  kidneys ;  ot,  common 
blastema  of  ovaries  or  testicles ;  W,  Wolffian  bodies ;  iv.  Wolffian  ducts ;  m  m,  Mullerian  ducts ; 
g  c,  genital  cord;  «gr,  sinus  urogeni talis ;  i,  intestine;  rf,  cloaca.     (Allen  Thomson.) 

tal  end  of  the  genital  cord,  and  is,  of  course,  therefore,  the  homologue, 
in  the  male,  of  the  vagina  and  uterus  in  the  female. 

The  external  parts  of  generation  are  at  first  the  same  in  both  sexes. 

The  opening  of  the  genito-urinary  ajjparatus  is,  in  both  sexes,  bounded 
by  two  folds  of  skin,  while  in  front  of  it  there  is  formed  a  penis-like 
body  surmounted  by  a  glans,  and  cleft  or  furrowed  along  its  under  sur- 
face. The  borders  of  the  furrows  diverge  posteriorly,  running  at  the 
sides  of  the  genito-urinary  orifice  internally  to  the  cutaneous  folds  just 
mentioned.  In  the  female,  this  body  becoming  retracted,  forms  the 
clitoris,  and  the  margins  of  the  furrow  on  its  under  surface  are  converted 
into  the  nymphae  or  labia  minora,  the  labia  majora  pudendse  being  con- 
stituted by  the  great  cutaneous  folds.     In  the  male  foetus,  the  margins 


DEVELOPMENT,  H'lo 

of  the  furrow  at  the  under  surface  of  the  penis  unite  at  about  the  four- 
teenth week,  and  form  that  part  of  the  urethra  which  is  included  in  the 
penis.  The  large  cutaneous  folds  form  the  scrotum,  and  later  (in  the 
eighth  mouth  of  development),  receive  the  testicles,  which  descend  into 
them  from  the  abdominal  cavity.  Sometimes  the  urethra  is  not  closed, 
and  the  deformity  called  hypospadias  then  results.  The  appearance  of 
hermaphroditism  may,  in  these  cases,  be  increased  by  the  retention  of 
the  testes  within  the  abdomen. 


APPENDIX. 


CLASSIFICATION  OF   THE  ANIMAL  KINGDOM 


A.— VERTEBRATA. 


Mammalia 

2  \ll>  ica  I  exaiiqjkti . 

Monodelphia 

Primates 

Man,  ape. 

Cheiroptera 

Bat. 

Insectivora 

Hedgehog. 

Carnivora 

Cat,  dog,  bear. 

Proboscidea 

Elephant. 

Hyracoidea 

Hyrax. 

Ungulata 

Horse,  sheep,  pig 

Sirenia 

Dugong. 

Cetacea 

Whale. 

Rodentia     . 

Rabbit,  rat. 

Edentata 

Armadillo. 

Didelphia  . 

Kangaroo. 

Ornithodelphia 

Duck-billed  platypus 

Aates    • 

Carinatae 

Fowl,  duck. 

Ratitae  . 

Ostrich. 

Reptilia 

Crocodilia 

Crocodile. 

Ophidia 

Snake. 

Chelonia    . 

Tortoise. 

Lacertilia 

Lizard. 

Amphibia 

Anura 

Frog. 

Urodela 

Newt. 

Pisces      .... 

Lamprey,  shark,  cod. 

B.  — INVERTEBRATA. 

MOLLUSCA 

Odontophora 

Whelk,  snail. 

Lamellibranchiata 

Mussel,  oj'ster. 

Brachiopoda 

Terebratula. 

Polyzoa 

Sea  mat. 

Arthropoda 
Crustacea 

Lobster. 

Arachnida 

Scorpion,   spidei-. 

Insecta 

Bee,  fly. 

Myriapoda 

Centipede. 

EcriINODERM.\TA   . 

Sea  stars. 

Vermes 

Annelida    . 

Earthworm. 

Platyhelminthes    . 

Tapeworm,  fluke. 

Nemathelminthes 

Round-worm,  threadworm 

CCELENTERATA 

Actinozoa 

Sea  anemone. 

Hydrozoa 

Hydra. 

Protozoa 

Amoeba,  Vorticella. 

825 


826  APPENDIX. 


Organic  Chemical  Substances. 

Nearly  all  of  the  most  important  substaaces  found  in  the  animal  body- 
have  been  mentioned  and  described  in  the  preceding  pages.  It  will  be 
only  necessary  here  to  add  some  brief  notes. 

Certain  terms  have  been  used  without  explanation. 

Hydrocarbons. — Compounds  of  carbon  and  hydrogen.  Carbon 
being  a  tetrad  element,  the  simplest  hydrocarbon  is  C'^H'^,  methane  or 
marsh  gas.  It  is  found  in  the  gases  of  the  alimentary  canal  (intestines) 
(p.  406).  It  is  the  tirst  of  the  series  known  as  paraffins.  The  different 
members  of  the  series  increase  by  CH„,  so  that  the  next  paraffin  is 
C.^Hg,  ethane;  C.,H^,  propane,  and  so   on.     The  general  formula  being 

Alcohols. — From  a  hydrocarbon,  by  substituting  OH  (hydroxyl)  for 
H,  we  obtain  the  corresponding  alcohol;  thus  from  CH^H  we  obtain 
CH^  OH,  methyl  alcohol;  from  C.^H^H,  C^H^  OH,  ethyl  alcohol;  from 
C^H^H,  C^  H^  OH,  propyl  alcohol,  and  the  like.  They  are  hydrates  of 
the  hydrocarbons. 

Ethers. — The  ethers  are  obtained  from  their  corresponding  alcohols 
by  dehydration  ;  e.g.,  2(C^HJ  OH  -  H^O  =  (C^HJ.p,  ethylic  ether. 

Aldehydes. — The  aldehydes  are  obtained  by  oxidation  of  alcohols 
thus :— C„_H^  OH  +  0  =  CH3  COH  +  H^,  ethyl  aldehyde. 

Acids. — The  acids  are  obtained  by  further  oxidation,  one  atom  of  0 
being  substituted  for  H^,  e.g.,  CH^  CO  OH,  acetic  acid. 

The  series  of  acids  obtained  from  the  first  series  of  paraffins  is  known 
as  fatty  acids  ;  those  which  are  most  familiar  as  fatty  acids  being 
C^H^O„,  butyric  acid ;  C^,Hj„0„,  caproic  acid;  Cj^H^^O^,  palmitic,  and 
Cj^HjiP^,  stearic,  derived  from  0^^^  (butane),  C^H^^  (Jiexane),  Cj^H^^ 
{hecdecane),  and  Cj^H^^,  respectively. 

Soaps  and  Fats. — The  fatty  acids  in  combination  with  soda  or 
potash,  or  similar  bases,  form  soaps,  and  when  combined  with  glycerine 
form  fats. 

Other  series  of  hydrocarbons. — The  first  series  of  paraffins  consists  of 
saturated  hydrocarbons ;  many  other  series  exist,  however,  in  which  the 
C  is  unsaturated."  Their  general  formulae  are  as  follows:  CH  ; 
C  H„  _  :  C  H       :  C  H„  _„,  and  so  on. 

From  each  series  of  hydrocarbons,  the  corresponding  alcohols,  acids, 
aldehydes,  and  ethers  are  obtainable.  The  alcohols  derived  from  series 
of  ethene,  C.,H,,  are  called  glycols.  But  in  glycols  there  are  two  OH 
united  to  the  radicle  instead  of  one — these  are  therefore  called  diatomic 
alcohols;  and  similarly  acids,  of  two  kinds,  may  be  obtained,  by  the  sub- 


APPENDIX.  ,S*^7 

stitutiou  of  one  or  of  two  atoms  of  U  for  tlie  coirfspomliiii;  il^  or  H^. 
An  example  or  two  may  be  cited : — 

Cj  H^,  ethene  ;  C„  H^  OH,  ethene  glycol;  C^  H^  0  ,  glycolic  o.cid  : 
C^  Hj  0^,  oxalic  acid;  and  C3  K^,  pr opens  ;  C,  H^  OH^,  propene  r/lycnl ; 
C^  H^  0.,,  lactic  acid ;  C3  H^  O^,  malonic  acid 

The  next  series  of  hydrocarbons,  C\,  H^^^  j,  is  represented  by  C.,  H.,, 
(icetiilciie  :  the  next  C  H,  ,,  by  terebinthene,  (',„  H,,;  the  next  (J  H,  . 
by  benzene,  C„  H,,. 

I'''roiu  these  we  obtain  ti'iatomic  alcohols,  ('.</.,  (jli/ri'i-inc,  C^  H^  OH^,, 
tetratomic  alcohols,  e.g.,  eyi/flirite,  C^  H,  OH,,  and  hexatomic  alcohols, 
e.g.,  mannite,  C,.  H^  OHj  from  the  last,  the  carbohydrates  are  derived. 

Of  the  liydrocarbons,  only  one  is,  as  we  have  said,  found  in  the  l)ody, 
viz.,  methane;  of  the  alcohols,  cholesterine,  0.,„  H^.^  OH,  a  monatomic, 
and  glycerine,  C^  H^  OH^,  a  triatomic  alcohol. 

Of  the  aldehydes  and  ketones  (analogous  products  to  aldehyde,  ob- 
tained from  isomeric  alcohols),  acetove,  or  propyl  ketone,  is  found  in  blood 
and  in  urine,  particularly  in  diabetes.  The  glucoses  are  aldehydes  of 
mannite,  and  the  other  carbohydrates  are  derived  from  that  class. 

Fdttji  Acids. — Formic,  acetic,  propionic,  butyric,  caproic  and  caprylic, 
are  all  more  or  less  represented  in  the  secretions  and  tissues  of  the  body. 
Palmitic  and  stearic  in  fats. 

Glycol  Acids. — Lactic  acid,  of  which  there  are  three  isomeric  bodies, 
and  leucic  acid  and  two  other  acids,  oxalic  and  succinic. 

Aromatic  Scries. — The  foundation  is  the  benzol  ring,  C^H_,,  and  all 
bodies  containing  this  radicle  are  closely  related.  They  differ  in  regard 
to  the  position  in  the  ring  of  the  H  atoms  which  are  replaced,  as  well  as 
in  regard  to  the  substances  which  replace  them;  the  derivatives  often 
occur  in  the  decomposition  of  proteids.  Plieiiol  or  oxybenzol  (C^H^O) 
is  found  in  combination  in  the  urine  and  faeces.  Oxybenzoic  acid 
(C,.H^,  OH,  COOH)  is  a  common  decomposition  product  of  proteids;  one 
atom  of  H  is  replaced  by  hydroxyl  and  another  by  carboxjd.  The  action 
of  Millon's  reao-ent  is  due  to  the  benzol  rinar. 


Nitrogenous  Prndi(cf.s  of  Profeid  Decomposition. 

Amines. — These  are  bodies  of  the  ammonia  type  (NH^)  in  whicli  one 
or  more  of  the  H  atoms  of  the  ammonia  are  replaced  by  hydrocarbon 
radicles;  e.g.,  jN"H„,  CK^  =  methylamine  or  mono-methylamine.  Tin- 
■methylamine,  N(CHj)^,  often  occurs  in  putrefaction. 

Protamines. — These  are  basic  proteid  bodies  which  give  the  Biuret 
reaction;  on  decomposition  they  yield  the  nitrogenous  bases  but  no  leucin 
or  tyrosin.      They  occur  in   th(>  de('()in]iositi()n  of  all  ])roteids  and  also  as 


8-?8  APPENDIX. 

primarj  constitueots  of  cells,  especially  in  spermatozoa.      In   Ihis  grouji 
are  argenim.,  h/sin,  aiid  hystidin. 

Amides. — These  are  bodies  of  the  ammonia  type  (NHJ  in  which  one 
or  more  of  the  H  atoms  are  replaced  by  organic  acid  residues  (an  acid 
residue  =  the  acid  minus  hydroxyl;  e.g.,  CH.CO  is  the  residue  of 
CH3  COOH).  Monacetamide  =  NH,,  CH^CO  There  are  also  more 
complicated  amides  which  are  built  up  from  two  molecules  of  ammonia ; 
f.tj.,  urea  or  carbamide,  which  is  formed  from  carbonic  acid  and  is  usu- 
ally written  CO,  NH,^,  NH.,. 

Amido-aeids. — These  are  bodies  of  the  ammonia  type  (NHJ  in  which 
one  or  more  of  the  H  atoms  of  the  ammonia  are  replaced  by  organic  acid 
radicles;  they  may  also  be  regarded  as  acids  in  which  one  or  more  of  the 
H  atoms  of  the  acid  radicle  are  replaced  by  amidogen,  NH^.  As  the 
term  implies  that  they  are  acids,  it  is  necessary  that  they  contain  the 
carboxyl  group  (COOH)  intact.  For  example,  glycin  (amido-acetic  acid) 
i-  either  NH^,  CH,  COOH  or  CH^  (NH^),  COOH. 

Nitrogenous  or  Nnclem  Bases. — The  members  of  this  group  are  very 
closely  related  and  consist  of  hypoxanthin  (C^H^N^O),  xanthin 
(C^H^N^J,  adenin  (C^H^iSTJ,  and  guanin  (C^H.iST^).  Besides  occur- 
ring in  ordinary  proteid  decomposition,  they  are  also  always  present  in 
all  downward  chemical  changes  in  the  cells.  Uric  acid  (CH^N^OJ, 
though  not  a  member  of  the  group,  is  shown  to  be  closely  related  by 
studying  their  chemical  composition.  By  oxidation  uric  acid  yields  urea 
and  alloxan  (C^H^N^O J ;  it  has  been  found  that  in  alloxan  there  is  pres- 
ent a  radicle  CJ^^  known  as  the  purin  or  alloxan-uric  nucleus ;  purin  is 
formed  from  this  radicle  by  the  substitution  of  H  atoms.  Both  uric  acid 
and  the  nuelein  bases  can  be  derived  from  this  base ;  hypoxanthin  is  oxy- 
purin,  uric  acid  is  tri-oxypurin,  adenin  is  amino-oxypu^rin,  etc. 

Protargons. — These  are  very  complex  phosphorus-containing  bodies 
which  are  chiefly  obtained  from  nervous  tissues.  Protargon  was  at  one 
time  considered  an  entity,  but,  according  to  the  most  recent  views,  it  is 
merely  a  mixture  of  cerebrin  and  lecithin. 

Of  the  bodies  which  constitute  the  above-mentionod  gr()U])s,  only  the 
following  need  be  described : 

Glycin,  Glycocol,  Glycocin,  or  i  ^    tt   >^q    _  /  ^itt  ^NH„        \ 
Amido-acetic  acid.  f     ^      '■>         2  —  \    -"     2     Q,Q  OH./ 

This  substance  occurs  in  the  body  in  combination  as  in  the  biliary 
acids,  but  is  never  free.  Glycocholic  acid,  when  treated  with  weak  acids, 
with  alkalies,  or  with  baryta  water,  splits  up  into  cholic  acid  and  glycin, 
or  amido-acetic  acid.  Thus :  C,,H„NO,  +  H,0  =  C,„  H„  O,  +  C,  H,  NO,. 
Glycocholic  acid  -f  water  =  cholic  acid  -f  glycin,  and  under  similar 
circumstances  Taurocholic  acid   splits  up  into  cholic  acid  and  taurin  : 


API'ENDIX.  S->9 

C^,  H,,  O,  NSO,  +  H,0  =  C.,„  H,„  U,  +  C,  H,  N80^,  or  amido-isethionic 
acid.  Taurocholic  acid  -|-  water  =  cholic  acid  and  tauriii.  Glycin  occurs 
also  in  hippuric  acid.  It  can  be  prepared  from  gelatin  by  the  action  ol 
acids  or  alkalies,  and  can  also  lie  obtained  from  hippuric  acid. 

Sarcosi/i  or  Methyl   \    .,    „    x-,-x    /        nxs    ^^H  CH  \      .^  . 
amido-actitie  acid.     )       ■■  ■  \  -     CO  OH.    / 

stituent  of  kreatin,  and  als(^  of  catt'eine,  but  has  never  been  found  free  in 
the  human  body.  It  may  be  obtained  from  these  bodies  by  boiling  with 
baryta  water. 

Leucm  or  Armdo-  I  ^  j^^q    (=zCH..CH„CH„CH  .CH(XH  )C0  OH 
caproic  acid,         j      e      13         2  v  :         222         v         •.■-' 

occurs  normally  in  many  of  the  organs  of  the  body,  and  is  a  product  of 
the  pancreatic  digestion  of  proteids.  It  is  present  in  the  urine  in  certain 
diseases  of  the  liver  in  which  there  is  loss  of  substance,  especially  in 
acute  yellow  atrophy.  It  occurs  in  circular  oily  discs  or  crystallizes  in 
plates,  and  can  be  prepared  either  by  boiling  horn  shavings,  or  any  of 
the  gelatins  with  sulphuric  acid,  or  out  of  the  products  of  pancreatic 
digestion. 

Guanidin,  CN.^H.  f    =  CNH  <attt' )  is  a  derivative  of  urea,  the  atom 

of  0  being  replaced  by  NH. 

Kreatin,  or  Methyl         '  f'  u  v  o    /  _  (^^\i  ^^^-H.,  \ 

gnanidhi  acetic  arid,  \  ^  .^■.'-^..  '-■  y  -  ^'-^^  ^XCH,,  (JH.,,  OOOH^ 

is  one  of  the  primary  products  of  muscular  disintegration.      It  is  always 

found  in  the  juice  of  muscle.     It  is  formed  by  the  action  of  guanidin  on 

methyl  amido-acetic  acid.      It  is  generally  decomposed  in   the  blood  into 

urea  and  sarcosin,  and  only  appears  in  the  urine  as  kreatinin.     Treated 

with  either  sulphuric  or  hydrochloric  acid,  it  is  converted  into  kreatinin; 

thus — 

C,  H„  N3  0.^  =  C,  H^  X^,  0+  H,  (). 

It  luis  l)e(Mi    made  synthetically  V)y  l)riiigiiig  togctlici-  cyaiiiuiidi'   and 

sarcosine. 

.,     xr  ^         ,x.,,      ^'H— CO     V 

hrrafnn/i,  (      H.  ^.  O  |  —  (_  JS  H  <  I         )   is   present  ni  human 

V  N(CH,)CH.,/ 

urine,  derivetl  from  dehydration  of  kreatin.      Ft  does  not  appear  to  he 

present  in  muscle.      It  is  basic,  having  lost  the  COOH  group,  aiul  reacts 

as  an  alkaline  body,  combining  with  salts  to  form  double  salts,  etc.     On 

decomposition  it  yields  urea,  sarcosin,  and  methyl  guanidin. 

Taurin  or  Amido-  \  ^   t^^   >tci<-\    /     /i     n    ^»^0    II \  •  .-.        , 

.    '  .     .        .,      -  C,  H.  r^SO,  (=C'.,  H.<rxT-iLi       I  i«  a  constituent 
isethionic  acid,     \      •      ■  M        ■       '     JNH,    / 

of  the  bile   acid,   taurocholic  acid,  and   is  found  also  in  traces  in  the 

muscles  and  lungs.     It  has  been  pre])ared  syuthetioally  from   isethioni(^ 

acid.      It  is  a  crvstalline  substance,  vew  stable. 


830  APPENDIX. 

Hippuric  Aaklov         j    ^    ^    ^^-^   ^  .^   ^   COiS^  CH„  CO  OH), 
Benzol  amido-aeetie  acid  j      'j       '•*         3       ^    «      s  2 

a  normal  constituent  of  human  urine,  the  quantity  excreted  being  in- 
creased by  a  vegetable  diet,  and  therefore  it  is  present  in  greater  amount 
in  the  urine  of  herbivora.  It  may  be  decomposed  by  acids  into  glycin 
and  benzoic  acid.  It  crystallizes  in  semi-transparent  rhombic  prisms, 
almost  insoluble  in  cold  water,  soluble  in  boiling  water. 

Tyrosinov Para-oxyjjhen- \  .,    tt     ivrn /  — P    R  ^^^  \ 

yl-amido-proprlonic  acid,        f  ^'^  "^^  ^^ ^\-^.  ^     C,,H3,  NH^,  COOH  /. 

This  is  found  generally  together  Avith  leucin,  in  certain  glands,  e.g.,  pan- 
creas and  spleen ;  and  chiefly  in  the  products  of  pancreatic  digestion  or 
of  the  putrefaction  of  proteids.  It  is  found  in  the  urine  in  some  diseases 
of  the  liver,  especially  acute  yellow  atrophy.  It  crystallizes  in  hne  nee- 
dles, which  collect  into  feathery  masses.  It  gives  the  proteid  test  with 
Millon's  reagent,  and  heated  with  strong  sulphuric  acid,  on  the  addition 
of  ferric  chloride  gives  a  violet  color. 

-CH,,,O.C„H33CO 

Leekhln,  C,,  H^^  PN  0^  (       *^^'  ^'^^  ^-/^^ 

CH^,  O.PO<Q^^jj^^^jj^^^^,jj.^^^g 

It  is  a  combination  of  cholin  with  glycero-phosphoric  acid  in  which  the 
two  H  atoms  of  the  glycerine  are  replaced  by  fatty  acid  radicles.  The 
chemical  formula  varies  in  accordance  Avith  the  kind  of  fatty  acid ;  in  the 
above  formula  one  radicle  is  that  of  oleic  acid  and  the  other  that  of  pal- 
mitic. In  character  it  is  a  complex  nitrogenous  fatty  body,  containing 
phosphorus,  which  has  been  found  mixed  with  cerebrin  and  oleo-phospho- 
ric  acid  in  the  brain.  It  is  also  found  in  blood,  bile,  and  serous  fluids, 
and  in  larger  quantities  in  nerves,  pus,  yolk  of  egg,  semen,  and  white 
blood-corpuscles.  On  boiling  with  acids  it  yields  cholin,  glycero-phos- 
phoric  acid,  and  fatty  acids. 

Cerebrin,  C,^  H.,^  ^0.^,  is  a  light  amorphous  powder,  tasteless  and 
odorless,  which  is  found  in  nerves,  pus  corpuscles,  and  in  the  brain.  It 
is  a  nitrogenous  body  whose  chemical  constitution  is  not  known,  though 
the  large  amount  of  C  which  it  contains  indicates  the  presence  of  a  fatty 
acid.  It  swells  up  like  starch  when  boiled  with  water.  When  decom- 
posed it  yields,  besides  other  substances,  a  sugar  (gelactose). 

Uric  Acid  or  Tri-oxypuriit,  G^  H^  N^  0.,,  occurs  in  the  urine,  sparingly 
in  human  urine,  abundantly  in  that  of  birds  and  reptiles,  where  it  repre- 
sents the  chief  nitrogenous  decomposition  product.  It  occurs  also  in  the 
blood,  spleen,  liver,  and  sometimes  is  the  only  constituent  of  urinary 
calculi.  It  is  probably  converted  in  the  blood  into  urea  and  carbonic 
acid.      It  generally  occurs  in  urine  in  combination  with  bases,  forming 


APPENDIX.  «31 

urates,  aud  never  free  unless  under  abnormal  conditions.  A  deposit  of 
urates  may  occur  when  the  urine  is  concentrated  or  extremely  acid,  and 
in  febrile  disorders. 

Xanthin  or  Di-oxyjmrin,  C^  H^  N,  0^,  has  been  obtained  from  the 
liver,  spleen,  thymus,  muscle,  and  the  blood.  It  is  found  in  normal 
urine,  and  is  a  constituent  of  certain  rare  urinary  calculi. 

Hypoxauthln  or  O.ryjmrlii,  C.  H^  N^  O,  is  found  in  juice  of  tiesh,  in 
the  spleen,  thymus,  and  thyroid. 

Guanin  ov  Aviino-oxijjiurin,  C^.  H,^  N,  0,  has  been  found  in  the  human 
liver,  spleen,  and  faeces,  but  does  not  occur  as  a  constant  product. 

Adeniii  or  Amino-purln,  C,^  H.  K^,  is  the  simplest  member  of  the 
purin  group.  It  exists  abundantly  in  the  liver  and  urine  of  leucocy- 
themic  patients. 

Allantoin,  C^  H^.  N^  0.,,  found  in  the  allantoic  fluid  of  the  foetus,  and 
in  the  urine  of  animals  for  a  short  period  after  their  birth.  It  is  one  of 
the  oxidation  products  of  uric  acid,  which  on  oxidation  gives  urea. 

In  addition  to  the  above  compounds  and  probably  related  to  them,  are 
certain  coloring  and  excrementitious  matters,  which  are  also  most  likely 
distinct  decomposition  compounds. 


Pigments,  Etc. 

Bilirubin,  C,,,  H^^  N.,  0.,,  is  the  best  known  of  the  bile  jiigments.  It 
is  best  made  by  extracting  inspissated  bile  or  gall  stones  with  water 
(which  dissolves  the  salts,  etc.),  then  with  alcohol,  which  takes  out  cho- 
lesterin,  fatty  and  biliary  acids.  Hydrochloric  acid  is  then  added,  which 
decomposes  the  lime  salt  of  bilirubin  and  removes  the  lime  After  ex- 
tracting with  alcohol  and  ether,  the  residue  is  dried  and  finally  extracted 
with  chloroform.  It  crystallizes  of  a  bluish-red  color.  It  is  allied  in 
composition  to  haematin,  as  has  been  described. 

Bilirei'diii,  C,^,  H,^  X„  0^,  is  made  by  i)assing  a  current  of  air  through 
an  alkaline  solution  of  bilirubin,  and  bv  precipitation  with  hydro- 
chloric acid.  It  is  a  green  pigment  which  is  an  oxidation  ])roduct  of 
bilirubin. 

BUifuscin,  Cj  H,,  NOj,  is  made  b}'  treating  gall  stones  with  ether, 
then  with  dilute  acid,  and  extracting  witli  absolute  alcohol.  It  is  a 
non-crystallizable  brown  pigment. 

BiliiJrasiii  is  a  pigment  of  a  green  color,  which  can  be  obtained  from 
gall  stones,  and  from  bile  which  has  been  allowed  to  decompose 

BiHJnim'ui  (Staedeler)  is  a  dark  lirnwn  oaithy-looking  substance,  of 
which  the  formula  is  unknown. 

Urochrome  and  UrobUin  occur  in  bile  and  in  urine;  the  latter  is  prob- 


832  APPENDIX. 

ably  identical  Avith  stercobiUn,  which  is  found  in  the  faeces.  Uroerythrm 
is  one  of  the  coloring  matters  of  the  urine.  It  is  orange  red  and  con- 
tains iron,  as  is  also  CJioletelin 

Melanin  is  a  dark  brown  or  black  pigment  which  occurs  especially  in 
epidermal  tissues,  where  it  is  associated  with  keratin.  It  is  found  in  the 
lungs,  bronchial  glands,  hair,  choroid,  skin  of  negroes,  etc. ;  also  in  the 
urine  and  in  melanotic  diseases,  e.fj.,  sarcoma.  It  is  a  transformation 
product  of  proteids,  to  which  it  is  closely  related,  and  can  be  made  arti- 
ficially by  boiling  proteid  with  sulphuric  acid.  It  contains  C,  H,  0,  N,  S, 
and  (rarely)  Fe. 

Lipochromes  are  pigments,  usually  yellow  or  yellowish-red,  which  are 
associated  with  fat,  being  almost  always  present  in  adij)ose  tissue.  Lit- 
tle is  known  about  them,  but  they  are  thought  to  consist  only  of  C,  H, 
and  0. 

Hcematiii  has  been  fully  treated  of,  p.  162  et  seq. 
■  Indican  or  Potussiuin  Indoxyl  sidphatt,  C^  H^^  NKSO,,  is  found  in  the 
urine  and  is  derived  from  proteid  putrefaction  in  the  intestines.     It  is 
colorless. 

Ind'ujo  or  Jiuliyo-blue,  0^^.  H^^^  N.,  (J„,  is  formed  from  indican.  It  is 
usually  found  free  in  small  amounts  in  decomposing  urine,  Avhere  it  may 
give  a  bluish  color  to  the  sediment;  in  very  rare  instances  it  makes  the 
whole  urine  blue. 

Indol,  C^  H.  ]N,  Itelougs  to  the  aromatic  series  and  is  a  product  of 
proteid  putrefaction  in  tlie  intestine.  It  is  found  in  the  faeces  and  helps 
cause  their  odor.  When  absorbed,  it  is  excreted  in  the  urine  as  potas- 
sium indoxyl  sulphate  (indican). 

Skatol,  C,j  H,j  N,  is  also  one  of  the  aromatic  series,  a  product  of  pro- 
teid putrefaction  in  the  intestines.  It  is  found  in  the  faeces  and  contrib- 
utes to  their  odor.  When  absorbed,  it  is  excreted  in  the  urine  as  sodiun) 
or  potassium  skatoxyl  sulphate.  Both  indol  and  skatol  are  crystalline; 
and  volatile. 

■    NitrorfenoHH  Bodies  of  fjnr.frtain  NatMre. 

Fenitents  are  bodies  vvhieli  possess  the  property  of  exciting  chemical 
changes  in  matter  with  which  they  come  in  contact.  They  are  at  j^resent 
divided  into  two  classes,  called  (1)  organized,  and  (2)  unorganized  or 
soluble. 

(1.)  Of  the  oir/anized,  yeast  may  be  taken  as  an  example.  Its  activ- 
ity depends  upon  the  vitality  of  the  yeast  cell,  and  disappears  as  soon  as 
the  cell  dies,  neither  can  any  substance  be  obtained  from  the  yeast  by 
means  of  precipitation  with  alcohol  or  in   any  other  way  wliich   has  the 


APPENDIX.  833 

power  of  exciting  the  ordinary  change  i)roduced  by  the  plant  itself. 
The  action  of  micro-organisms  in  the  alimentary  canal  and  elsewhere  is 
also  an  example  of  the  same  nature. 

(2.)  Unorganized  or  soluble  ferments  are  those  which  are  found  in 
secretions  of  glands,  or  are  produced  by  chemical  changes  in  animal  or 
vegetable  cells  in  general;  when  isolated  they  are  colorless,  tasteless, 
amorphous  solids  soluble  in  water  and  glycerin,  and  precipitated  froiH 
the  aqueous  solutions  by  alcohol  and  acetate  of  lead.  Chemically  many 
of  these  are  said  to  contain  nitrogen. 

Mode  of  action. — Without  going  into  the  theories  of  how  these  un- 
organized ferments  act,  it  will  suffice  to  mention  that: 

(1.)  Their  activity  beyond  a  certain  point  does  not  depend  upon  the 
actual  amount  of  the  ferment  jjresent.  (2.)  That  the  activity  is  de- 
stroyed by  high  temperature,  and  various  concentrated  chemical  re- 
agents, but  increased  by  moderate  heat,  about  40°  C,  and  by  weak  solu- 
tions of  either  an  acid  or  alkaline  fluid.  (3.)  The  ferments  themselves 
appear  to  undergo  no  change  in  their  own  composition,  and  waste  very 
slightly  during  the  process. 

The  chief  classes  of  unorganized  ferments  are : — 

(1.)  Amylolytic,  which  possess  the  property  of  converting  starch 
into  glucose.  They  add  a  molecule  of  water,  and  may  be  called  hydro- 
lytic.  The  principal  amylolytic  ferments  are  Ptyalin,  found  in  the 
saliva,  and  a  ferment,  probably  distinct,  in  the  pancreatic  juice,  called 
Atni/lopsin.  These  both  act  in  an  alkaline  medium,  Amylolytic  fer- 
ments have  been  found  in  the  blood  and  elsewhere. 

(2.)  Proteolytic  convert  proteids  into  peptones.  The  nature  of  their 
action  is  probably  hydrolytic.  The  pi-oteolytic  ferments  of  the  body 
are  called  Pepsin,  from  the  gastric  juice  acting  in  an  acid  medium. 
Trypsin,  from  the  pancreatic  juice  acting  in  alkaline,  neutral,  or 
acid  media.  The  Succus  entericus  is  said  to  contain  a  third  such  fer- 
ment. 

(3.)  Inversive,  which  convert  cane  sugar  or  saccharose  into  grape 
sugar  or  glucose.  Such  a  ferment  was  found  by  Claude  Bernard  in  the 
Succus  entericus;  and  probably  exists  also  in  the  stomach  mucus. 

(4.)  Ferments  which  act  upon  fats. — Such  a  body,  called  Steapsin, 
has  been  found  in  pancreatic  juice. 

(5.)  Milh-curdU ng  ferments. — It  has  been  long  known  that  rennet,  a 
decoction  of  the  fourth  stomach  of  a  calf,  in  brine,  possessed  the  power 
of  curdling  milk.  This  power  does  not  depend  upon  the  acidity  of  the 
gastric  juice,  since  the  curdling  Mill  take  place  in  a  neutral  or  alkaline 
medium;  neither  does  it  depend  upon  the  pepsin,  as  pure  pepsin  scarcely 
curdles  milk  at  all,  and  the  rennet  which  rapidly  curdles  milk  has  no 
j)roteolytic  action.  From  this  and  other  evidence  it  is  believed  that  a 
53 


834         '  APPENDIX. 

distinct  milk-ciirdliug  ferment  exists  in  the  stomach.  W.  Eoberts  has 
shown  that  a  similar  but  distinct  ferment  exists  in  pancreatic  extract, 
which  acts  best  in  an  alkaline  medium,  next  best  in  an  acid  medium, 
and  worst  in  a  neutral  medium.  The  ferment  of  rennet  acts  best  in  an 
acid  medium,  and  worst  in  an  alkaline,  the  reaction  ceasing  if  the  alka- 
linity be  more  than  slight.     Also  in  the  Succus  entericus. 

In  addition  to  the  above  ferments,  many  others  most  likely  exist  in 
the  body,  of  which  the  following  are  the  most  important: 

(6.)  Fibrin-forming  ferment  (Schmidt),  (see  p.  136  et  seq.),  found  in 
the  blood,  lymph  and  chyle. 

(7.)  A  ferment  loMch  converts  glycogen  into  glucose  in  the  liverj 
being  therefore  an  amylolytic  ferment. 

(8.)  Myosin  ferment. 

Carbo-hydkates  or  Amyloids. 

The  divisions  of  carbo-hydrates,  and  the  chief  substances  forming 
each  class  with  their  properties,  have  been  already  given  (p.  122  et  seq). 
The  following  additional  information  may  be  useful. 

The  glucoses  may  be  considered  as  the  aldehydes  of  mannite,  thus : 

CHa  OH        )  CHa  OH         ) 

(CH  0H)4     \  Ce  Hu  Og,  (OH  0H)4      V  Ce  H12  0, 

CH2  OH        )  CO  H  ) 

mannite.  glucose. 

The  Saccharoses  or  sucroses  are  made  up  of  two  volumes  of  glucose 
minus  one  molecule  of  water. 

Ce  H12  Oe  +  Ce  H12  Oe  —  H2  0  =  C12  H22  On. 
The   amyloids    are   anhydrides   of   the   glucoses,    Ce  H12  Oe  —  Hj  0  = 
CeHioOs. 

Tests  for  Glucose.— (i.)  Tromfner's. — This  test  depends  upon  the 
power  sugar  possesses  of  reducing  copper  salts  to  their  sub-oxide.  It  is 
done  in  the  following  w^ay: — An  excess  of  caustic  potash  and  then  a 
solution  of  copper  sulphate,  drop  by  drop,  are  added  to  the  solution 
containing  the  sugar  in  a  test-tube,  as  long  as  the  blue  precipitate  which 
forms  redissolves  on  shaking  the  tube.  The  upper  portion  of  the  fluid  is 
then  heated,  and  a  yellowish-brown  precipitate  of  copper  suboxide  ap- 
pears. The  test  may  also  be  done  by  taking  only  a  drop  or  two  of  the 
copper  sulphate  solution. 

(ii.)  Moore's. — If  a  solution  of  sugar  in  a  test-tube  is  boiled  with 
caustic  potash,  a  brown  coloration  appears. 

(iii.)  Fermentation. — If  a  solution  of  sugar  be  kept  in  the  warm  plate 
for  a  time  after  the  addition  of  yeast,  the  sugar  is  converted  into  alcohol 
and  carbon  dioside.     (CgHiaOe  =  2C2H5OH  +  2CO2.) 

(iv.)  Bottcher's  test. — A  little  bismuth  oxide  or  subnitrate  and  an 
excess  of  caustic  potash  are  added  to  the  solution  in  a  test-tube,  and  the 
mixture  is  heated ;  the  solution  becomes  at  first  gray  and  then  black. 


APPENDIX.  835 

(y.)  Picric  acid  test, — To  the  solution  about  a  fourth  of  its  bulk  of 
picric  acid  (saturated  solution)  and  an  equal  quantity  of  caustic  potash 
are  added,  and  the  solution  is  boiled;  the  liquid  becomes  of  a  very  deep 
coffee-brown. 

(vi.)  Indigo-carmine  test. — Add  a  solution  of  indigo  carmine  to  color 
sugar  solution  distinctly  blue,  and  add  solution  of  sodium  carbonate,  and 
heat.  The  blue  color  changes  to  jnirple  and  then  to  brown  and  yellow, 
but  is  restored  on  shaking  the  solution. 

(vii.)  Phenyl  hydrazine  test. — A  solution  of  phenyl  hydrazine  hy- 
drochloride and  sodium  acetate  is  added.  Keep  in  water- bath  at  boiling 
for  some  minutes,  then  cool.     Yellow  crystals  result. 

Quantitative  Estimation  of  Grajje  Sugar. 

1.  Fehling's  Method. — Solution  required  =  copper  sulphate  and  caus- 
tic soda,  with  some  sodic  potassic  tartrate  of  such  a  strength  that  10  c.c. 
of  solution  contain  the  amount  of  cupric  oxide  which  0.5  grm.  of  sugar 
can  reduce  to  cuprous  oxide.  (This  solution  should  be  freshly  pre- 
pared.) It  is  made  as  follows:  Take  of  sul2)liate  of  copper,  40  grms. ; 
neutral  tartrate  of  potash,  160  grms.;  caustic  soda  (sp.  gr.  1.12),  750 
grms.;  add  distilled  water  to  1154.5  c.c.  Each  10  c.c.  contains  .05  grm. 
of  sugar. 

Method. — ^Take  10  c.c.  of  the  saccharine  solution  free  from  albumen, 
and  add  90  c.c.  of  distilled  water.  Place  this  in  a  burette.  Put  into  a 
flask  or  dish  10  c.c.  of  the  standard  solution,  and  dilute  with  four  times 
its  bulk  of  water  and  boil.  Eun  into  it,  from  burette,  some  of  the 
diluted  urine,  say  20  c.c,  and  boil.  Allow  precipitate  to  settle,  and  if 
supernatant  fluid  is  still  blue,  add,  say,  5  c.c.  from  burette,  and  boil 
again,  and  so  on,  till  the  fluid  ceases  to  have  a  blue  tinge,  taking  care, 
toward  the  end  of  the  process,  to  add  only  a  few  drops  each  time.  If, 
after  adding  20  c.c.  of  diluted  urine  and  boiling,  the  fluid  has  been 
decolorized,  too  much  of  the  solution  has  been  added,  and  another  esti- 
mation with  a  second  10  c.c.  of  standard  solution  must  be  made,  but 
less  than  20  c.c.  of  the  saccharine  solution  should  be  added  (say  10  c.c.) 
in  first  instance. 

When  the  number  of  c.c.  of  diluted  urine  required  to  decolorize  the 
solution  has  been  determined,  that  volume  contains  the  amount  of  sugar 
necessary  to  reduce  10  c.c.  of  standard  solution,  i.e.,  .05  grm.  But  one- 
tenth  only  of  this  is  the  saccharine  solution,  .*.  one-tenth  of  number  of 
c.c.  used  contains  .05  grm.  of  sugar.  From  this,  the  percentage  can  be 
easily  calculated. 

2.  Pavy's  Modification  of  Fehling's  Method. — By  Fehling's  method  it 
is  difficult  and  tedious  to  judge  of  the  point  of  complete  reduction  of 
the  cupric  oxide.  Dr.  Pavy,  accordingly,  uses  a  strongly  ammoniacal 
solution  of  the  above.     A  certain  amount  is  introduced  into  a  small 


836  APPENDIX. 

flask,  which  is  then  heated  till  the  vapor  of  ammonia  escapes  by  a  nar- 
row tube.  The  sugar  solution  is  then  allowed  to  flow  from  a  burette 
into  the  flask  until  the  blueness  has  disappeared,  the  solution  being 
kept  boiling  all  the  time.  The  blueness  is  apt  to  disappear  suddenly, 
and  care  should  therefore  be  taken  toward  the  end  of  the  process. 
Calculate  as  in  Fehling's  method. 

3.  Bstimation  of  sugar  liy  fermentation. — In  the  case  of  saccharine 
urine,  it  is  allowable  as  a  single  test  to  use  the  following  method : — Take 
specific  gravity  of  urine  before  and  after  fermentation.  Each  degree 
of  specific  gravity  lost  by  the  urine  represents  one  grain  of  sugar  per 
ounce  of  urine. 

4.  Sugar  may  also  be  estimated  by  adding  yeast  to  urine,  and  col- 
lecting the  carbon  dioxide  evolved.  The  carbon  dioxide  is  a  measure 
■of  the  amount  of  sugar  present. 

5.  The  estimation  may  also  be  done  by  the  saccharimeter,  an  instru- 
ment for  the  estimation  of  the  degree  of  polarization  which  a  ray  of 
light  undergoes  in  passing  through  a  solution  of  sugar,  either  to  the  left 
or  to  the  right. 

Urea,  CO  (NH2)2.  The  properties  and  relations  of  urea  have  been 
treated  of  at  some  length  in  the  chapter  upon  excretion.  There  re- 
mains to  be  described  the  method  of  its  quantitative  estimation  in  the 
urine.     There  are  two  chief  methods,  viz. : — 

(i.)  Hypobromite  Method. — One  of  the  forms  of  apparatus  employed 
in  this  method  (Russell  and  West's)  consists  of  («)  a  water-bath  sup- 
ported by  three  iron  bands,  arranged  as  a  tripod.  The  bath  is  provided 
with  a  cylindrical  depression,  and  with  a  hole,  into  which  fits  a  perfo- 
rated india-rubber  cork;  (Z>)  a  bulb  tube  with  a  constricted  neck;  (c)  a 
glass  rod  provided  with  an  india-rubber  band  at  one  extremity;  {d)  a 
pipette  of  five  cubic  centimetres  capacity ;  (e)  a  graduated  glass  collect- 
ing tube;  (/)  a  spirit  lamp;  {g)  a  wash-bottle  with  distilled  water;  (Ji) 
hypobronious  solution.  The  hypobromous  solution  is  made  in  the  fol- 
lowing way:  three  and  a  half  ounces  (100  grm.)  of  solid  caustic  soda  is 
dissolved  in  nine  ounces  (250  grm.)  of  distilled  water.  When  the  solu- 
tion is  cold,  seven  drachms  (25  c.c.)  of  pure  bromine  are  to  be  added 
carefully  and  gradually.  The  mixture  is  not  to  be  filtered;  it  keeps 
badly,  and  for  this  reason  it  should  be  made  shortly  before  it  is  required ; 
or  the  solution  of  caustic  soda  in  water  may  be  made  in  large  quantities 
as  it  does  not  undergo  any  change,  the  bromine  in  the  proper  propor- 
tion being  added  at  the  time  it  is  required  for  use. 

Method. —  Fill  the  pipette  to  the  mark  on  the  stem  with  the  urine  to 
be  examined;  pour  the  5  c.c.  of  urine  thus  measured  out  into  the  bulb; 
fill  up  the  bulb  tube  as  far  as  the  constricted  neck  with  distilled  water 
from  the  wash-bottle;  insert  the  glass  rod  (c)  in  such  a  way  that  the 
india-rubber  band  at  the  extremity  fills  up  the  constricted  neck;  the 


APPENDIX.  837 

diluted  urine  should  exactly  occupy  the  bulb  and  neck  of  the  tube,  no 
bubble  of  air  being  below  the  elastic  band  on  the  one  hand,  while  on 
the  other  the  fluid  should  not  rise  above  the  band;  in  the  former  case 
a  little  more  water  should  be  added,  in  the  latter  a  fresh  portion  of 
urine  must  be  used,  and  the  experiment  repeated.  iVfter  adjusting  the 
glass  rod,  fill  up  the  rest  of  the  bulb  tube  with  hypobromous  solution; 
it  will  not  mix  with  the  urine  so  long  as  the  rod  is  in  place.  The 
water-bath  having  been  previously  erected,  and  the  india-rubber  cork 
fixed  firmly  into  the  aperture,  the  bulb  tube  is  to  be  thrust  from  below 
through  the  perforation  in  the  cork.  The  greater  part  of  the  tube  is 
then  beneath  the  water-bath,  the  upper  extremity  alone  being  grasped 
by  the  cork.  Fill  the  water-bath  half  full  of  water,  fill  also  the  grad- 
uated glass  tube  (e)  with  water,  and  invert  it  in  the  bath;  in  doing 
this  no  air  must  enter  the  tube,  which  when  inverted  should  be  com- 
pletely filled  with  Avater.  Now  slide  the  graduated  tube  toward  the 
orifice  of  the  bulb  tube,  at  the  same  time  withdrawing  the  glass  rod 
which  projects  into  the  bath  through  the  cork.  At  the  instant  that  the 
rod  is  withdrawn  the  hyj)obromous  solution  mixes  with  the  diluted 
urine,  and  a  decomposition  takes  place  represented  thus :  CO]Sr2H4  + 
3NaBrO  +  2NaH0  =  3  NaBr  +  BHaO  +  NaaCOg  +  N2.  Urea  -f-  sodium 
hypobromite  -j--  caustic  soda  =  sodium  bromide  -|-  water  +  sodium  carbon- 
ate -f  nitrogen.  The  nitrogen  produced  is  given  off  as  gas,  and  dis- 
places the  water  in  the  graduated  tube,  which  is  held  over  it.  The  gas 
is  at  first  evolved  briskly,  but  afterward  more  slowly;  to  facilitate  its 
evolution,  the  bulb  of  the  tube  may  be  slightly  ^varnied  Avith  a  spirit 
lamp;  as  a  rule,  however,  this  is  unnecessary.  After  ten  minutes,  the 
amount  of  water  displaced  by  the  gas  should  be  read  off  on  the  tube, 
which  is  divided  into  tenths.  Each  number  on  the  tube  represents  one 
gram  of  urea  in  100  c.c.  of  urine.  Normal  urine  should  yield  roughly 
1.5-2.5  parts  of  nitrogen  by  this  test.  If  5  c.c.  of  urine  gives  off  more 
nitrogen  than  fills  the  tube  to  iii.,  dilute  the  urine  with  an  equal  volume 
of  water,  and  take  5  c.c;  read  off  and  multiply  by  two.* 

Several  apparatus  may  be  employed  instead  of  the  one  described,  viz., 
those  of  Dupre,  Gerard,  and  Squibb.  The  chemical  reactions  in  each 
case  are  the  same. 

(ii.)  Liebig's  Method. — Tliis  method  is  of  greater  accuracy.  Tlie 
solutions  required  are  (a)  baryta  mixture  =  2  vols,  of  saturated  solution 
of  barium  nitrate  and  1  vol.  of  saturated  solution  of  barium  hydrate; 
(b)  standard  solution  of  mercuric  nitrate,  such  that  1  c.c.  will  precipitate 
.01  grm.  of  urea,  and  (c)  a  solution  of  carbonate  of  soda. 

Meiltod. — Take  40  c.c.  of  urine,  add  20  c.c.  of  {((),  filter  off  the  pre- 
cipitate of  sulphates  and  phosphates;  keep  the  filtrate.     Fill  a  burette 

*  Several  corrections  have  to  be  made  before  tlie  result  can  he  considered  as 
accurate ;  for  these  the  detailed  accounts  in  practical  handbooks  of  Physiology 
should  be  consulted. 


838  APPENDIX. 

with  (b),  and  take  15  c.c.  of  the  filtrate  in  a  dish.  Let  (b)  fall  drop  by- 
drop  into  the  15  c.c.  in  the  dish,  stirring  constantly.  Have  ready  a  glass 
plate  with  several  separate  drops  of  (c),  and  from  time  to  time  add  a 
drop  of  the  urine  mixture  by  means  of  a  glass  rod  to  one  of  the  drops. 
When  a  yellow  color  Jirst  appears  in  a  drop  of  the  NaCOs,  the  mercuric 
nitrate  is  just  in  excess.     Head  the  burette.     Calculate  as  follows: 

1  c.c.  of  mercuric  solution  precipitates  .01  grm  of  urea,.',  the  No.  of 
c.c.  used  X  .01  =  amount  of  urea  in  15  c.c.  of  filtrate,  i.e.,  in  10  c.c.  of 
urine.  But  10  c.c.  of  urine  usually  contains  enough  NaCl  to  act  on  2  c.c. 
of  mercury  solution.*  Hence,  when  reckoning  the  number  of  c.c.  of 
standing  mercury  solution  used,  a  deduction  of  2  c.c.  must  always  be 
made. 

Quantitative  Estimation  of  Chlorides. 

LieMg's  Method. —  The  solutions  required  are  a  baryta  mixture  as 
above;  and  {b)  standard  solution  of  mercuric  nitrate,  such  that  1  c.c. 
would  be  capable  of  decomposing  .01  grm.  of  sodium  chloride. 

Method. — Take  40  c.c.  of  urine  free  from  albumen,  and  add  20  c.c.  of 
(a).  Filter.  Take  15  c.c.  of  filtrate  and  place  in  a  flask  or  dish,  adding 
a  drop  or  two  of  nitric  acid.  Fill  a  burette  with  {b),  and  slowly  run 
some  of  this  solution  into  the  filtrate  in  the  dish,  stirring  constantly. 
As  soon  as  a  distinct  cloud  appears  in  the  diluted  urine,  and  does  not 
disappear  on  stirring,  then  all  the  sodium  chloride  in  urine  has  been 
decomposed.       Eead  burette.     Calculate  as  follows : 

1  c.c.  of  mercury  solution  decomposed  .01  grm.  of  NaCl,  .-.  the 
number  of  c.c.  used  X  .01  grm.  =  number  of  grms.  of  NaCl  in  15  c.c.  of 
filtrate,  i.e.,  10  c.c.  of  urine. 

Quantitative  Estimation  of  Phosphates. 

The  solutions  required  are  {a)  solution  of  sodium  acetate,  containing 
100  grm.  of  sodium  acetate,  100  c.c.  of  acetic  acid,  and  900  c.c.  of  distilled 
water;  {b)  a  solution  of  uranium  acetate  or  nitrate,  such  that  1  c.c.  will 
precipitate  .005  grm.  of  phosphoric  acid;  and  {c)  a  solution  of  ferro- 
cyanide  of  potassium. 

Method. — Take  50  c.c.  of  urine.  Add  some  {a)  solution,  and  heat  on 
water-bath  to  nearly  100°  C.  Fill  burette  with  (Z;),  and  allow  this  to 
fall  into  the  urine  slowly.  Have  ready  a  glass  plate  with  several  distinct 
drops  of  potassium  ferro-cyanide  solution.  From  time  to  time  add  a 
drop  of  urine  mixture  to  one  of  the  drops;  and  when  there  fiest  ap- 
pears a  reddish-brown  color  in  a  drop  of  potassium  ferro-cyanide,  all  the 
phosphates  are  precipitated.     Eead  burette.     Calculate  thus: 

1  c.c.  precipitates  .005  grm.  of  phosphoric  acid,  .-.  the  number  of  c.c. 
used  X  .005  grm.  =  number  of  grms.  of  phosphoric  acid   in  50  c.c.  of 

urine. 

*  This  is  only  a  rough  estimate. 


INDEX. 


AiJDUCENS  nei've,  604 
Absorption,  408 

channels  of,  422 

conditions  for,  411 

in  the  alimentary  canal,  424 

in  tiie  large  intestine,  425 

in  the  small  intestine,  42") 

in  the  stomach,  424 

rapidity  of,  410 

through  the  lungs,  426 
the  skin,  425 

where  it  may  occur,  424 
Accommodation  of  vision,  713 
Achromatic  spindle,  15 
Achromatiu,  12 
Acliroodextiin,  339 
Acid  albumin,  115 
Acids,  826 

Addison's  disease,  317 
Adenin,  831 
Adenoid  tissue,  46 
Adipose  tissue,  48 

development  of,  49 

uses  of,  50 
After-birth,  the,  787 
Air  cells,  259 
Akinesis,  13 
Albuminates,  115 
Albumin    molecule,    action    of    gastric 

juice  on,  361 
Albuminoids,  120 
Albumose,  362 
Alcohols,  826 
Aldehydes,  826 

Alimentary  canal,  development  of,  813 
Alkali  albumin,  116 
Allantoin,  831 
Allantois,  781 
Amides,  828 
Amido-acids,  828 
Amidulin,  339 
Amines,  828 


Amitosis,  13 
Amitotic  division,  13 
Ammonium  carbamate.  432 

carbonate,  431 
Amnion,  780 

Amo'boid  movement,  4,  146 
Amylopsin,  383 
Amyloses,  122 
Anabolism,  7 
Anacrotic  wave,  219 
Anaphases,  17 
Anelectrotonus,  530 
Animal  heat,  449 

Animal  kingdom,  classificatidu  of,  825 
Anode,  531 

Ano-spinal  centre,  579 
Autipeptoue,  382 
Apnaui,  286 

Appendices  epiploicre,  377 
Appendix,  825 
Areolar  tissue,  45 
Aromatic  series,  827 
Arteries,  180 

development  of,  800 

structure  of,  180 

tone  of,  245 
Articulate  sounds,  549 
Asphyxia,  292 

cause  of  death  in,  294 
Astigmatism,  720 
Atmosphere,  composition  of.  271 
Attraction  sphere,  12 
Auditory  centre,  641 

nerve,  606 

vesicles,  779 
Auerbach's  plexus,  371 
Augmentor  nerve,  239 
Auricles,  action  of,  189 
Axis-cylinder,  92 

B.vsopniT-,  146 

Beef,  composition  of.  327 


840 


INDEX. 


Bezold's  ganglion,  234 
Bidder's  ganglion,  234 
Bile  as  an  antiseptic,  393 
as  an  excretion,  394 
as  a  purgative,  394 
discharge  of,  394 
disposal  of,  396 
pigments,  391 

test  for,  392 
properties  of,  390 
Bile  salts,  390 

test  for,  391 
secretion  of,  394 
Bilifulvin,  391 
Bilifuscin,  831 
Bilihumin,  831 
Bilin,  390 
Biliprasin,  391,  831 
Bilirubin,  391,  831 
Biliverdin,  391,  831 
Bioplasm,  2 
Biuret  reaction,  113 
Bladder,  urinary,  469 
Blastema,  2 
Blastoderm,  22,  769 
Blastosphere,  767 
Blind  spot,  723 
Blood,  129 

arterial  flow,  213 
capillary  flow  of,  222 
carbon  dioxide  of,  164 
chemical  composition  of,  150 
circulation  of,  171 
in  foetus,  804 
coagulation  of,  131 
colorless  corpuscles,  145 
corpuscles,  hyaline,  146 
corpuscles,  varieties,  146 
corpuscles,  140 

chemical  composition  of,  154 
development  of,  167 
enumeration  of,  148 
red,  140 

red.  varieties,  142 
spieen  in  formation  of,  322 
differences  between  arterial  and  ve- 
nous, 165 
flovF,  regulation  of,  231 
gases  of,  155 
oxygen  of,  156 
piiysical  characters,  129 


Blood  plasma,  150 

chemical  composition  of,  151 

plates,  147 

pressure,  205 

proofs  of  circulation  of,  249 

quantity  of,  130 

respiratory  changes  in,  276 

serum,  chemical  composition  of,  153 

uses  of,  170 

variations  in  composition,  164 

velocity  of  flow,  235 

venous  flow,  234 
Blood-vessels,  development  of,  796 
Blushing,  247 

Body,  chemical  composition  of,  110 
Bone,  55 

canaliculi  of,  57 

development  of,  60 

functions  of,  69 

growth  of,  68 

Haversian  canals  of,  58 

lacunae  of,  57,  59 

marrow,  56 

ossification  in  cartilage,  63 
in  membrane,  61 

periosteum  of,  57 
Brain,  581 

development  of,  807 

distinctive    characters    of     human, 
635 

fore-,  809 

gray  matter  in,  587,  620 

gyri  of,  618 

hind-,  809 

lobes  of,  617 

mid-,  809 

motor  areas  of,  626 

areas  of  human,  629 
areas  of  monkey's,  627 
tracts  in,  630 

relation  of  different  parts,  581 

sulci  of,  618 

weight  of,  624 
Branchial  clefts,  793 

folds,  793 
Bronchi,  354  . 
Brownian  movement,  3 
Brunner's  glands,  374 
Buflfy  coat,  133 
Bulb,  the,  587 

centres  in,  594 


INDEX. 


841 


Bulb,   connections  with  cerebrum    and 
cerebellum,  593 
functions  of,  593 
Bulbus  arteriosus,  799 

C^CUM,  376 

Calorimeter,  453 

Cane-sugar,  133 

Capillaries,  development  of,  797 

structure  of,  183 
Capillary  tlow,  333 
Carbohydrates,  133,  834 
Carbon  dioxide  in  expired  air.  371 
Cardiac  cycle,  193 
Cardio-accelerator  centres,  595 
Cardiogram,  198 
Cardiograph,  198 
Cardio-iuhibitory  centre,  340,  595 
Carotid  gland,  335 
Cartilage,  51 

development  of,  55 

functions  of,  55 

hyaline,  51 

white  fibro-,  54 

j'ellow  elastic,  53 
Casein,  130,  311 

insoluble  cakiuiu-,  130 

soluble,  130 
Caseinogeu,  119,  311 
Caudate  nucleus,  583,  615 
Cell,  difl'erences  between  plant  and  ani- 
mal, 17 

division  of,  13 

functions  of,  18 

nucleus  of,  11 

reticulum  of,  9 

structure  of,  9 
Cells,  decay  and  death  of.  38 

tixed,  40 

functions  of,  22 

migratory,  41 

modes  of  connection,  37 

plasma,  41 

shapes  of,  36 
Cellulose,  338 
Centres,  sensory,  639 
Centrosome,  13 
Cerebellum,  583,  043 

connection  with  bulb,  593 

functions  of,  647 
Cerebral  ventricles,  583 


Cerebiin,  830 
Cerebrum,  583,  617 

arrangement  of  parts  of,  633 

connection  with  bulb,  598 

effects  of  removal  of,  634 

functions  of,  633 

motor  areas  of  cortex,  636 

unilateral  action  of,  630 
Cheyne-Stokes  breathing,  385,  393 
Chlorides,     quantitative    estimation  of, 

838 
Choletelin,  478 
Chondrin,  131 
Chordte  tendinciE,  179 
Chorda  tympani,  343,  605 
Chorion,  783 

villi,  783 
Choroidal  tissure,  811  « 

Choroid  plexus,  583 
Chromatin,  13 
Chromoplasm,  13 
Chromo-proteids,  118 
Chromosome,  16 
Chyle,  414,  431 

corpuscles,  431 
Chyme,  361 
Cilia,  35 

Ciliary  motion,  36 
Circulation,  coronary.  344 

effect  of  respiration  on.  387 

in  brain,  338 

in  erectile  structures,  330 

local  peculiarities  of,  338 

of  blood,  171 

velocity  of,  319,  335 
Claustrum,  615 
Coagulation,  calcium  salts  in,  136 

conditions  affecting,  138 

schema  of,  133,  137 

theories  of,  136 
Coccygeal  gland,  335 
Cochlea,  679 
Cohuheim's  fields,  85 
Cold,  influence  of  extreme.  459 
Collagen,  55,  130 
Collaterals,  98 
Colloids,  410 
Colon,  376 
Color  blindness,  736 
Color,  Ilering's  theory  of,  734 

sensiitions,  734 


842 


INDEX. 


Color,  Youug's  and  Ilelmholtz's  tlieoiy 

of,  734 
Colorless  corpuscles,  145 

and  thymus  gland,  324 
Colostrum,  310 

corpuscles,  308 
Columnae  carneae,  179 
Column  of  Burdach,  565 

of  Goll,  565 
Common  sensations,  657 
Complemental  air,  268 
Compound  proteids,  118 
Concentric  corpuscles  of  Hassall,  324 
Conjunctiva,  694 
Connective  tissues,  40 

classification  of,  43 

cells  of,  40 

development  of,  47 

white  fibrous,  43 

fibrous,  development  of,  47 

yellow  elastic,  44 
Consonants,  549 
Contractility  of  muscle,  505 
Cornea,  structure  of,  695 
Corona  radiata,  614 
Coronary  circulation,  244 
Corpora  cavernosa,  755 

dentata,  587,  617 

geniculata,  617 

functions  of,  649 

quadrigemina,  616 
functions  of,  649 

striata,  615 

functions  of,  642 
Corpus  albicans,  583 

callosum,  583 

luteum.  760 

striatum,  583 
Corpuscles  of  Krause,  106 
Coughing,  279 
Cowper's  glands,  755 
Cranial  nerves,  596 

development  of,  806 
Cranium,  development  of,  791 
Crassamentum,  132 
Crura  c-erel)ri,  582,  613 
Crusta,  613 

petrosa,  76 

phlogistica,  133 
Crypts  of  Lieberkiihn,  373 
Crvstalloids,  410 


Cutaneous  sensations,  centre  for,  642 
Cutis  vera,  491 
Cystin  in  urine,  481 

Daltonism,  736 
Daniel's  battery,  508 
Decidua  retlexa,  785 

serotina,  785 

vera,  785 
Defecation,  407 

centre,  579 
Deglutition,  352 

nervous  mechanism  of,  353 

time  occupied  in,  353 
Dendrite,  91 
Dental  papilla,  78 
Depressor  nerve,  247 
Descemet.  membrane  of,  696 
Deutero-proteose,  362,  382 
Development,  22,  766 
Dextrin,  123 
DL'Xtrose,  124 
Diabetes  mellitus,  438 
Diabetic  centre,  596 
Diapedesis,  224 
Diastole  of  heart,  189 
Dicrotic  notch,  219 

pulse,  220 

wave,  219 
Dicrotism,  causes  of,  221 
Diencephalon,  809 
Diet,  effect  of  albuminoid,  430 
carbohj^drate,  434 
fatty,  434 
proteid,  429 

requisites  of  a  normal,  441 

tables,  442 

valuations  in,  444 
Digestion,  331 

in  intestines,  379 
Diplopia,  738 
Direct  cell  division,  13 
Direction,  visual  estimation  of,  732 
Dobie's  line,  85 
Dogiel's  cells,  234 
Dreams,  638 
Du  Bois  Reymond's  induction  coil,  509 

key,  509 
Ductless  glands,  312 
Ducts  of  Cuvier,  803 
Ductus  arteriosus,  801 


INDEX. 


843 


Duel  us  venosus,  805 
Dura  mater,  558 
Dyspnoea,  285,  292 

Eau,  cochlea  of,  670 

development  of,  HI" 

external,  667 

internal,  679 

membranous  lahyriiitii  i>f.  680 

middle,  677 

osseous  labyriutli  of,  079 

ossicles  of,  678 

vestibule  of,  679 
Edestrine,  117 
Egg-albumin,  114 
Eggs,  chemical  conipositiou  of,  3'28 
Eighth  nerve,  606 
Elustin,  43,  121 
Electrodes,  508 

non-polarizable,  503 
Elect  rotomis,  529 
Eleventh  nerve,  611 
Emission  centre,  579 
Enamel  cap,  79 

organ,  76 
Enchylema,  9 
Endocardiac  i)ress\ire,  198 
Endofardium,  178 
Endomysium,  83 
Endoneiirium,  97 
Endosmonieter,  499 
Endothelium.  29 
Enzymes,  331 
Eosinophil,  146 
Epencephalon,  809 
Epiblast,  22,  771 

organs  developed  from,  788 
Epicardium,  172 
Epidermis,  28 

structure  of,  489 
Epididymis,  751 
Epiglottis,  253 
Epimysium,  82 
Epinephrin,  317 
Epineurium,  97 
Epithelial  tissues,  28 
Epithelium,  29 

functions  of,  39 

simple,  29 

stratified,  37 

transitional,  37 


Erection  fciUre,  580 
Erythroblasts.  169 
Erythrodextrin.  339 
Ethers,  826 
Excretion,  460 

definition  of.  297 
Expiration,  264 
Expired  air,  271 

how  changes  effected  in,  275 

volume  of.  273 
External  capsule.  615 
Extremities,  development  of,  794 
Eye,  anatomy  of.  793 

and  the  camera.  722 

cliambers  of,  708 

chromatic  aberration  of.  721 

development  of,  810 

movements  of,  717 

muscles  concerned  in  movement.  717 

optical  axis  of.  711 

refractive  surfaces  and  media  of,  710 

sphericjil  aberration  of,  720 
Eyeball.  694 

blood  vessels  of,  708 

iris  of,  698 

lens  of,  699 

retina  of,  701 

structure  of  choroid  coat,  697 
of  cornea,  695 
of  sclerotic  coat.  694 

Faci.m.  nerve,  604 

paralysis  of,  605 
Faces,  composition  of,  405 
Fallopian  tubes,  748 
Fasciculus  cuneatus,  588 

gracilis,  588 

of  Rolando,  588 

solitarius.  607 
Fats,  122 

digestion  of,  384,  393 

emulsitication  of,  383,  393 

saponification  of,  383,  398 
Fatty  acids,  826 
Fermentation  in  intestines,  402 
Ferments.  832 
Fibres  of  liemak,  95 
Fit)nn,  118,  132.  154 

ferment,  136 

formation  of,  133 

.sources  of,  138 


844 


INDEX. 


Fibrinogen,  135 
Fifth  nerve,  599 
Fillet,  593,  616,  632 
Filtration,  410 
Fission,  9 
Fixed  cells,  40 
Fffital  membranes,  779 
Food  and  digestion,  326 

effects  of  deprivation  of,  439 
of  too  much,  438 

mastication  of,  332 

salts  of,  329 
Foods,  326 

effects  of  cooking,  330 

inorganic,  326,  329 

liquid,  330 

nitrogenous,  326 

compcsition  of,  327 

organic,  326 

non-nitrogenous,  329 
Foramen  of  Munro,  583 
Forced  movements,  649  ^ 

Fore -brain,  585,  809 
Fore-gut,  779 
Form,  estimation  of,  732 
Fornix,    583 
Fourth  nerve,  598 
Fovea  centralis,  701 

Galactophorous  ducts,  307 
Galactose,  125 
Gall-bladder,  389 
Galvanic  currents,  508 
Gastric  digestion,   conditions   affecting, 
363 

products  of,  362 

time  of,  364 
juice,  358 

chemical  composition  of,  351 

pepsin  of,  359,  360 
Gelatin,  120 
Gelatinous  tissue,  46 
Gemmation,  9 
Genital  organs  of  female,  744 

of  male,  750 
Genito-spinal  centre,  579 
Germinal  matter,  2 
Glands,  secreting,  302 

varieties  of,  302 
Globulins,  116 
Globus  pallidus,  615 


Glosso-pharyngeal  nerve,  607 
Glucase,  338,  359,  364,  381,  383 
Gluco-nucleo-proteids,  118 
Gluco-proteids,  118 
Glucose,  124 

tests  for,  834 
Glucoses,  122,  834 
Glycin,  828 
Glycogen,  123 

destination  of,  436 

effect  of  different  diets  on,  436 

formation  of,  435 

source  of,  435 
Glycogenesis,  435 
Glycol  acids,  827 
Glycosuria,  437 
Gmelin's  test,  382,  392 
Graafian  follicles,  745 
Gramme-calorie,  452 
Granulose,  338 
Grape  sugar,    quantitative   estimatioD 

835 
Guanidin,  829 
Guanin,  831 
Gullet,  351 
Gustatory  buds,  349 

cells,  349 

H^MACHKOMOGEN,   162 

Haemacytometer,  148 
Hsematin,  162 
Hsematochometer,  221 
Ilsematoidin,  163 
llsematoporphjn'in,  162 
Haimin,  163 
Haimoglobin,  157 

action  of  gases  on,  159 

derivatives  of,  162 

estimation  of,  160 

reduced,  159 
H«moglobinometer,  161 
Hair,  structure  of,  494 
Haversian  canals,  58 
Heart,  172 

action  of,  189 

automaticity  of,  233 

capacity  of,  177 

chambers  of,  174 

development  of,  795 

effect  of  poisons  on,  241 
of  temperature  on,  241 


IXDEX. 


845 


Heart,  force  of  action,  204 
frequency  of  action,  208 
impulse  of,  19G 

intiuence  of  central  nervous  system 
on,  237 
of  sympathetic  on,  289 
of  vagus  on,  237 
metabolism  of,  243 
morphology  of,  798 
muscle,  88 

properties  of,  282 
ncirves  of,  234 
origin  of  nerve-fibres,  289 
regulaticm  of  force  and  frcijuency  of 

contraction,  282 
size  of,  177 
sounds  of,  194 
structure  of,  177 
valves  of,  178 

action  of,  190 
weight  of,  177 
work  of,  205 
Heart-beat,  electrical  phenomena  of,  243 

method  of  investigating,  241 
Heat,  animal,  449 

influence  of  extreme.  4r)9 

of  nervous  system  on,  457 
loss  from  surface  of  body,  454 

througli  lungs,  455 
-producing  tissues,  452 
production  of  body-.  451 
regulation  of  body-.  458 
variations  in  loss  of.  458 
in  production  of.  45(3 
Hearing,  670 

physiology  of,  684 
Hemianopsia,  640 
Henle's  membrane,  45 
Henson's  disc,  85 
Hetero-proteose,  362,  382 
Hiccougli,  279 
Hind-brain,  585,  809 
IIilipocami)us  minor,  619 
llippuric  acid,  477,  828 

formation  of,  484 
Homoiothermal  animals,  450 
Hj'uloplasm.  9 
Hydrol)ilirul)in,  892,  478 
Hj'droearbons,  826 

Hydrochloric  acid,  combined,  841.  860 
test  for  free,  360 


Hypcrmetropia.  720 
Hyperpnoca,  292 
Hypoblast,  22,  771 

organs  developed  from,  789 
Hypoglos.sal  nerve,  612 
Hypoxanthin,  831 

li.EO-CvKCAL  valve,  876,  378 
Income  of  energy,  444 
Indican,  478,  832 
Indigo,  832 

in  urine,  478 
Indirect  cell  division,  14 
Indol,  403,  832 
Indoxyl,  408 

Induced  electric  currents,  508 
Induction  coil,  508 
Inorganic  foods,  329 
Inosite,  125 
Insalivation,  333 
Inspiration,  261 
forced,  263 
muscles  of,  262 
quiet,  263 
Intercellular  substance,  27,  41 
Interlobular  veins,  387 
Internal  capsule.  614,  680 

secretions,  312 
Intestinal  digestion,  influence  of  nervous 
system  on,  404 
duration  of,  404 
secretion,  398 
Intestine,  large,  376 

glands  of,  377 
structure  of,  377 
small,  villi  of,  375 
Intestines,  370 

action  of  bacteria  in,  401 
digestion  in,  379 
fermentation  in,  402 
gases  in,  405 
movements  of.  408 
putrefaction  in,  408 
Invertebi-atiB,  825 
Invertin.  898 
lodothyrin.  814 
Iris,  698 
Island  of  Roil,  618 

.I('D(iMKNTS.  659 

Kakvokfnksis.  14 


S4<G 


ESDEX. 


EiaiyopbsniL,  I'S 

KialiidiolisiiL,  7 

Eatacradc  waves,  219 

Kaielectrot)»iiBs,  ^SQ 

KM.'&iode,  -331 

KeiaitiiB,  122 

KMbst'S,  blGnod-Tiessels  of,  4S5 

loop  of  H(Qile  of,  4^ 

3iaipi^uan  bodies  of,  461 

nerresot,  488 

stmcltMJne  and  fmscstkms  of,  ^i>9 

tobiiM  nirlniferi  of,  461 

Tasa.  effieremtia  of,  4S7 

vasa.  vecta  of,  4I!7 
K^HofTraiwwiiiP-r-aloritP-  462 
Ki;anse''s  nuanibiane,  S6 
Kjneaflim,  S29 
KrealtmaH,  f$2S 

l&nssaiwm.  of,  -^B4 

in.  fflrinte,  4il^ 
KjmogKsipIi,  20§ 


Lachktjiai- 
LaciralbuiiiiD,  311 
Lacteal,  375,  422 

Liactifeioias  dects,  307 
Lacto-globiiiliia,  311 
Lactose,  124,  311 
La;vii3©9e,  124 
Jjaminsp  dorsalss,  774 
Lax^  iolestiaie',  376 

suummaiy  of  djgistion  in,  400 
Laryngoscope,  541 
Laiymx,  253,  536 

anatcaiB J  of,  -^7 
Laii^MiHg,  281 
LecitMm,  ^^^ 
Le^raminoms  fruits,  329 
LeaiticnlaT  nucieias,  615 
Lemcin,  S39 
Le«iC)QC|lbe&,  145 
LJebetkUm's  jcly,  116 
life,  pbenomieina  of,  1 
Linin,  12 
Lipoduomies,  '^2 
Liquid  foods^  ^Q 
Liqu<n-  sanguinis^  129 
LiT^,  385 

deTelopment  of,  S15 

fandioDS  of,  389 

intamal  secstetaon  of,  31S 


LixeT.  stnietnTe  of.  3S5 
Locus  carulfcTit,  ."67 

ni^tT,  614 
Ltuigs  and  pleurae,  25^5 

blood  supply  of.  260 

dcTelopmeDt  of.  817 

1  vmpliatacs  of,  "261 

nerves  of,  261 

stTQetare  of,  256 
Luxus  consumplioD,  4-50 
LjinpL,  421 

capiHiiries,  412 
origin  of,  414 

chemical  CTomposdou  of.  422 

flow,  416 

heart,  417 

qoantity  of,  422 
LympMtic  glaads,  417 

syst^n,  412 

tissue,  M 
Lymphatics,  423 

eoninnmications  of,  415 
Lymphocyte,  146 
Lymjjhoid  lissue,  46 

Maxpiohias  bodie^^,  461 
Maltose.  124 
Mammary  gl^ids.  806 
areo^  of,  308 
Mknometer.  207 
Mastication.  832 

muscles  of,  833 

nerrous  mechanism  of,  333 
Mast-oid  cells,  677 
Meconium,  394 
Medulla  oblongata,  -582,  587 

functions  of,  5^3 
Medullarr  folds,  774 

groove,  774 

plate.  774 

slieatli,  92 
Meissner's  plexus,  371 
Melanin,  8-32 
Membrana  decidua.  784 

propria,  27 

tympani,  677 
Menstrual  discbarge,  759 
Menstruation,  757 
Jliesencepbalon,  80& 
MesoUast,  22,  771,  773 

organs  develoj.<ed  from,  799 


INDEX. 


847 


Mesoblastic  somites,  T7fi 
Metabolism,  7 

nutrition  and  diet,  -127 
Metapliases,  16 
Meteijcephalon,  809 
Methtemoglohin,  IGO 
Micturition,  488 
centre,  579 
Mid-brain,  585,  809 
Milk,  809 

as  a  food,  328 

chemical  composition  of,  310,  328 
coagulation  of,  310 
digestion  of,  363 
globules,  309 
,  salts  of,  311 
Millon's  reaction,  113 
Mineral  foods,  329 
Mitosis,  14 

Motor  oculi  nerve,  597 
Mouth,  description  of,  332 
Movement,  visual  estimation  of,  733 
Mucin,  118 

Mucous  membranes,  300 
Mucus,  301 

in  urine,  479 
Murexide  test,  477 
Muscle  at  rest,  502 

blood  supply  of,  89 

-caskets  theory,  85 

chemical  composition  of,  500 

-clot,  500 

conditions  affecting  irritability,  505 

contractility  of,  505 

currents,  502,  504 

negative  variation  of,  516 
of  action,  516 
of  rest,  505 
curve,  513 

effect  of  blood  supply  on,  505 
of  disuse  on,  506 
of  separation  from  the  nervous 

system  on,  506 
of    single   induction  shock  on, 

513   ' 
of  temperature  on,  507 
of  use  on,  506 
fatigue  of,  506,  519 
heart,  88 
in  activity,  505 
natural  currents,  505 


Muscle-nerve  physiology,  500 
plain,  81 
plasma,  500 
reticulum  theory,  86 
serum,  500 
sound,  514 
stimuli  of,  507 
striated,  82 
Muscles,  action  of  involuntary,  527 
of  voluntary,  522 
as  heat  producers,  452 
centre  for  tone  of,  570 
Muscular   contraction,    accompauinients 
of,  514 
conditions    affecting    character 

of,  516 
differences    between    voluntary 

and  involuntary,  519 
latent  period  of,  513 
phenomena  of,  507 
record  of,  510 
single,  513 

stage  of  contraction,  513 
stage  of  elastic  after-vibration, 

514 
stage  of  elongation,  513 
coordination  centres  for,  63(i 
metabolism,  533 
sensations,  centre  foi-,  642 
sense,  665 
tissue,  81 
work,  518 
Musculi  papillares,  179 
Mutton,  composition  of,  327 
Myelin  sheath,  92 
Myelocyte,  146 
Myeloplaxe,  56 
Myograph,  pendulum,  512 
Myoha^natin,  501 
Myopia,  719 
Myosin,  116 

ferment,  501 
Myxanlema,  314 

Nails,  structure  of,  495 
Native  albumins,  114 
Neural  canal,  774 
Neuraxon,  91 
Neurenteric  canal,  778 
Neurilemma,  93 
Neuroglia,  107 


848 


INDEX. 


Neuron,  91 

Neutrophil,  146 

Nerve-cells,  99 

Nerve-centres,  automatism  of,  558 

functions  of,  555 

inhibition  and  augmentation  of,  558 
Nerve  collaterals,  98 

-corpuscles,  93 

effect  of  constant  current  on,  538 

electrotonus  in,  529 

-fibres,  91 

functions  of,  552 
medullated,  91 

impulse,  velocity  of,  554 

plexuses,  99 

stimuli,  528 

terminations,  102 

trunks,  97 
Nerves,   effect  of    battery   currents  on 
human,  531 

electrical  currents  in,  527 

vaso-motor,  246 
Nervous  metabolism,  534 

system,  552 

cerebro-spinal.  554 
development  of,  806 
Neuro-keratin,  122 
Ninth  nerve,  607 
Nitrogenous  bases,  828 
Nitrogenous  equilibrium,  429 
Nodes  of  Ranvier,  95 
Noeud  vital,  282 
Normal  saline  solution,  35,  134 
Nose,  development  of,  813 
Notochord,  774 
Nuclear  matrix,  13 
Nucleic  acid,  119 
Nuclein  bases,  119,  828 
Nucleins,  119 
Nucleoli,  12 
Nucleoproteids,  119 
Nucleus,  11 

ambiguus,  607 

of  Pander,  771 

structure  of,  12 

Odontoblasts,  72 
OEsophagus,  351 
Oils,  122 

Olfactory  bulb,  671 
centre,  641 


Olfactory  tract,  641 
Olivary  bodies,  587 
Omphalo-mesenteric  duct,  778 
Oncograph,  483 
Oncometer,  483 
Ophthalmoscope,  725 
Optic  centre,  639 

lobes,  649 

thalami,  583,  616 

functions  of,  642 
Optical  apparatus,  709 

anatomy  of,  693 

defects  of,  718 
Organ  of  Corti,  683 
Organic  chemical  substances,  826 

substances.  111  , 

Organized  ferments,  401 
Organs,  development  of,  788 
Osmosis,  408 
Osseous  labyrinth,  679 
Osteoclasts,  65 
Osteogenetic  fibres,  61 
Output  of  energy,  444 
Ovaries,  744 
Oviducts,  748 
Ovum,  746 

changes  in,  766 

following  impregnation,  767 
prior  to  impregnation,  766 
Oxygen  in  expired  air,  273 
Oxyhgemoglobin,  158 
Oxyntic  cells,  356 
Oxyphil,  146 

Pacinian  corpuscles,  104 
Pain.  664 
Pancreas,  379 

development  of,  815 
internal  secretion  of,  318 
structure  of,  379 
Pancreatic  diabetes,  318 
juice,  381 

conditions   favoring   action  of,- 

384 
functions,  382 

nervous  mechanism  of  secretion, 
384 
Paraglobulin,  117,  135 
Parathyroids,  313 
Parotid  gland,  secretion  of,  342 
Parturition  centre,  580 


^ 


INDEX. 


849 


Penis,  754 
Pepsiu,  3 

actiou  of,  361 

functions  of,  361 

how  obtained,  361 
Pepsinogen,  357 
Peptone,  117,  361 

characteristics  of,  362 
Perceptions,  659 

Perforating  fibres  of  Sharpey,  60 
Perfusion  canula,  241 
Pericardium,  172 
Perimysium,  82 
Perineurium,  97 
Periosteum,  57 

Periplieral  resistance,  206,  245 
Perspiration,  496 
Pettenkofer's  test,  391 
Peyer's  patclies,  374 
Pfliigcr's  law  of  contractions,  530 
Phagocyte,  146 
Pharynx,  349 

Plienol  formed  in  intestine,  403 
Phosphates,   quantitative  estimation  of, 
■  838 

Pliosphoric  acid  in  urine,  480 
Phrenograph,  266 
Pia  mater,  559 
Pineal  gland,  325 
Pigments,  831 
Pituitary  bod}^  317 

development  of,  791 
Placenta,  785 

formation  of,  784 
Plasma,  129,  150 

cells,  41 

salted,  134 
Plasmine,  134 
Pleura,  257 

Pneumogastric  nerve,  608 
Pneumograph,  265 
Poikilothermal  animals,  450 
Polar  cell,  766 
Pons  Varolii,  582.  612 
Pork,  composition  of,  327 
Post-dicrotic  wave,  219 
Potassium  iudoxyl  sulphate,  832 
Poultry,  composition  of,  327 
Predicrotic  wave,  219 
Presbyopia,  722 
I'ressor  nerves,  246 
54 


I'riniary  areola-,  64 
Primitive  groove,  772 

streak,  772 
Pro  nucleus,  female,  754 
Propliases,  15 
Prosencephalon,  808 
Prostate  gland,  756 
Protamines,  827 
Protargons,  828 
Proteids,  111 

chemical  reactions  of,  112,  113 

circulating,  430 

coagulated,  117 

digestion  of,  362 

floating,  430 

morphotic,  430 

tissue.  430 

varieties,  114 
Proteoids,  120 
Pioteoses,  117,  362,  382 

primary,  362,  382 

reactions  of,  363 

secondary,  362.  382 
Protoplasm,  2 

chemistry  of,  3 

definition  of,  3 

growth  of,  7 

irritability  of,  6 

movement  of,  4 

properties  of,  3 

reproduction  of,  8 

stimuli  of,  6 

vital  characteristics  of,  4 
Proto-proteosc,  362,  382 
Protovertebnv,  776 
Pseudoscope,  743 
Pseudo-stomata,  32 
Ptyalin,  338 

action  of,  339 
Pulse,  206,  215 
Pulvinar,  616 
Pupil,  699 

movements  of,  717 
Purin  base,  119 

nucleus,  119,  828 
Purkinjes  cell,  644 

figures,  723 
Putamen,  615 
Putrefaction  in  intestines,  403 

Reaction  of  degeneration,  532 


850 


INDEX. 


Recurrent  sensibility,  572 
Eed  coi'iDuscles,  action  of  reagents  on, 
U2 
destruction  of,  in  spleen,  o23 
formation  in  spleen,  322 
varieties,  142 
Red  nucleus,  587 
Reflex  action,  555 
inhibition  of,  577 
morbid,  578 

relation  of  stimulus  to,  556 
Reflexes,  cutaneous,  576 
Remak's  fibres,  95 
ganglion,  234 
Renniu,  363 

Reproductive  organs,  744 
Reserve  air,  268 
Residual  air,  268 
Respiration,  251 

effect  of  altitude  on,  296 
effect  on  circulation,  287 
effect  of  various  gases  on,  295 
effect  of  vitiated  air  on,  287 
influence  of  general  sensory  nerves 
on,  284 
of  glossopharyngeal  nerves  on, 

284 
of  superior  laryngeal  nerve  on, 

283 
of  vagi  on,  283 
inspiration,  261 
mechanism  of,  261 
movements  of  vocal  cords  in,  544 
nervous  apparatus  of,  281 
rliythm  of,  267 
special  acts,  278 
Respirations,  number  of,  269 
Respiratory  apparatus,  252 
capacity,  268 

conditions  affecting,  269 
centre,  282 

automatic  action  of,  284 
method  of  stimulating,  285 
centres,  595 

changes  in  air  breathed,  271 
in  the  blood,  276 
in  the  tissues,  277 
movements,   methods  of  recording, 
265 
of  nostrils  and  glottis,  267 
murmur,  267 


Respiratory  muscles,  force  of,  269 

quotient,  274 
Restiform  body,  590 
Retiform  tissue,  46 
Retina,  701 

cones  of,  703 

excitation  of,  723 

layers  of,  702 

reciprocal  action  of  parts  of,  736 

rods  of,  703 
Rheoscopic  frog,  527 
Rhythmical  contractility,  232 
Ribs,  movements  of,  in  respiration,  202 
Rigor  mortis  of  muscle,  521 
Rima  giottidis,  253 
Ritter's  tetanus,  531 
Roy's  tonometer,  242 
Running,  527 

Sacchakoses,  122,  834 
Saliva,  337 

action  of,  on  starch,  338 
chemical  composition  of,  337 
conditions  affecting  action  of,  340 
nervous     mechanism    of    secretion, 

341 
properties  of,  337,  338 
ptyalin  of,  338 
quantity  of,  338 
rate  of  secretion,  338 
uses  of,  338 
Salivary  digestion  in  stomach,  341,  360 
glands,  333 

changes  in  cells  during  secre- 
tion, 344 
development  of,  815 
nerves  of,  336 
structure  of,  333 
varieties  of,  385 
Sanson's  images,  715 
Sarcode,  2 
Sarcolemma,  83 
Sarcomeres,  87 
Sarcoplasm,  85 
Sarcosin,  829 

Schiff's  test  for  uric  acid,  477 
Sebaceous  glands,  493 
Secreting  glands,  302 
Secretion,  297 

circumstances  influencing,  305 
discharge  of,  304 


INDEX. 


851 


Secretion,  orsjans  and  tissues  of.  298 

process  of,  804 
Secretions,  internal,  oli 

relations  between,  oOO 
Segmentation  in  ciiick,  TW) 
Semicircular  canals.  ()7!> 
Semilunes  of  Ileidenhain,  335 
Sensations,  common,  657 

of  color,  734 

special,  G58 
Sense,  muscular,  665 

of  pain,  664 

of  sight,  693 

of  .smell,  670 

of  taste,  667 

of  temperature,  663 

of  toucli.  660 

organs,  development  of.  810 
Senses,  657 
Sensory  centies,  630 
Septum  lucidum,  563 
Serous  membranes,  functions  of,  299 

in  secretion,  298 
Serum,  132.  152 

-albumin.  115,  152 

-globulin,  135,  153 
Seventh  nerve,  604 

■Sexual    organs,  female,   jijiysiology  of, 
757 
male,  physiology  of,  763 
Sighing,  279 
Sight,  693 
Singing,  280 
Sixth  nerve,  604 

Size  (of  objects),  estimation  of.  731 
Skatol.  403.  s:}2 
Skatoxyl.  403 
Skein,  15 

Skeletal  muscle.  82 
Skin,  functions  of,  496 

glands  of,  492 

papilla'  of,  491 

structure  and  functions  of,  489 
Sleep,  637 
Small  intestine,  371 

glands  of,  373 

structure  of,  37 1 

summar}-  of  digestion,  398 
Smell.  670 
Sneezing,  280 
Snidlng,  280 


Soaps,  826 

Sol)biug,  281 

Solidity,  judgment  of,  742 

Somatopleure,  775 

Sonmambidi.sm,  638 

Sounds.  691 

Speaking,  280 

Special  i-espiratory  acts,  278 

sensations,  658 
Speech,  549 

action  of  tongue  in,  551 
Spermatoblasts,  753 
Spermatozoa,  763 
Spliygmogram,  219 
Si)liygmograph,  216,  218 
Sphygmometer,  218 
Spinal  accessory  nerve,  611 
bulb,  582 
centres,  578 
cord,  560 

antero-lateral    ascending   tract, 

567 
antero-lateral  descending  tract, 

566 
ascending  degeneration  of.  565 
columns  of,  565 
comma  tract.  566 
conduction  in,  572 
course  of  motor  impressions  in, 

574 
course    of  sensory   impressions 

in,  573 
descending  degeneration  of.  565 
development  of,  807 
direct  cerebellar  tract.  567 
direct  pyramidal  tract.  566 
functions  of,  572 
gray  matter  of,  563 
peculiarities    of    different      re- 
gions, 570 
posteromedian  column.  566 
posterior  marginal  zone.  567 
retlex  action  in,  575 
A\  hite  matter  of,  560 
nerve-roots,  functions  of.  571 
nerves.  567 

anterior  roots,  568 
course  of  fibres  of,  568 
development  of,  806 
posterior  roots,  569 
Spirem,  l""* 


852 


INDEX. 


Spirometer,  268 
Splanclinopleura,  775 
Spleeu,  318 

functious  of,  321 
influence  of  drugs  on,  323 

of  nervous  system  on.  323 
lobules  of,  320 

Malpigliiau  corpuscles  of,  321 
pulp,  320 
structure  of,  319 
Spongioplasm,  9 
Stammering,  551 
Stannius'  experiment,  236 
Starch,  123 

action  of  saliva  on,  339 
formation  of,  19 
granules,  structure  of,  338 
Starvation,  439 
Steapsin,  384 
Stercobilin,  393 
Stercorin,  397 
Stereoscope,  732 
Stethograph,  265 
Stethometer,  265 
Stokes'  fluid,  159 
Stomach,  354 

blood-vessels  of,  357 
changes  in  gland  cells  during  secre- 
tion, 357 
digestion  of,  after  death.  368 
gases  in,  406 
glands  of,  356 
lymphatics  of,  357 
movements  of,  364 
nerves  of,  358 

nervous  control  of  secretion,  367 
influence  on  movements,  366 
structure  of,  354 
Stratum  intermedium  of  Hamiover.  79 
Striated  muscle,  82 
Stromuhr,  Ludwig's,  226 
Sublobular  veins,  387 
Submaxillary  gland,   action  of  atropine 
on,  343 
paralytic  secretioti,  343 
secretion  of,  342 
Succus  entericus,  398 
Sucking,  281 
Sudoriferous  glands,  492 
Sugar,  test  for,  340 
Suprarenal  capsules,  314 


Suprarenal  capsules  and  Addison's  dis- 
ease, 317 
functions  of,  316 
nerves  of,  315 
structure  of,  314 
Swallowing,  352 
Sweat,  496 

chemical  composition  of,  497 
glands,  492 

influence  of  nervous  system  on  se- 
cretion, 498 
Sympathetic     ganglia,     functions     and 
structure,  655 
nervous  system,  650 
functions  of,  653 
Synovial  fluid,  300 

membranes,  298 
Systole  of  heart,  189 

Tactile  corpuscles,  105 

menisques,  107 
Taste,  667 

after-,  669 

centre,  641 

-goblets,  349 

varieties  of,  668 
Taurin,  829 
Teeth,  69 

dentine  of,  73 

development  of,  76 

enamel  of,  75 

permanent,  70 

structure  of,  72 

temporary,  70 

wisdom,  71 
Tegmentum,  613 
Telophases,  17 
Temperature,  regulation  of  body,  453 

sense  of,  663 

variations  in  body,  449 
Tenth  nerve,  608 
Testes,  751 

Testicles,  descent  into  scrotum,  820 
Tetanus,  518 

Ritter's,  531 
Thalamencephalon,  809 
Third  eye,  325 

nerve,  597 
Thoracic  duct,  413 

Thorax,  respiratory  changes  in  diameter. 
262 


INDEX. 


853 


Tlirombin,  186 
Thymus  gland,  824 
Thyroid  glaud,  312 

function  of,  314 
Thyroids,  accessory,  313 
Tidal  air,  268 

Tissue  elements,  derived,  27 
Tissues,  connective,  40 

elementary,  26 

respiratory  changes  in,  277 
Tongue,  epithelium  of,  348 

papilht  of,  347 

structure  of,  346 
Tonometer,  242 
Tonsils,  350 
Touch  corpuscles,  105 

sense  of,  660 
Trachea,  254 
Tract  of  Gowers  and  Tooth,  567 

of  Lissaucr,  567 
Traube-Hering  curves,  292 
Trigeminus,  599 
Trochlearis,  598 
Trypsin,  382,  833 

action  of,  382,  383 
Tubuli  seminiferi,  752 

uriniferi,  461 
Twelfth  nerve,  612 
Tympanum,  677 
Ty rosin,  830 

Umbilical  vesicle,  779 
Unstriped  muscle,  81 
Urea,  biiu'et  reaction,  474 
chemical  nature,  474 
formation  of,  433 
in  the  urine,  472 
properties  of,  473 
quantitative  estimation  of,  475 
variations     in     (luantity    excreted, 
474 
Ureters,  468 

Ureters,  structure  of,  468 
Urethra,  755 
Uric  acid,  475.  830 

condition  of,  in  urine,  476 
formation  of,  433 
properties  of,  475 
tests  for,  476 

variations  in  quantity  of,  476 
Urina  cibi,  472 


Urina  potus,  473 

sanguinis,  472 
Urinary  bladder.  469 
Urine,  469 

abnormal  constituents  of.  472 

average  daily  quantity  of  constitu- 
ents, 471 

chemical  composition.  469 

chlorine  in,  481 

colored  by  medicines.  478 

cystine  in,  481 

extractives  of,  479 

tiltration  theory  of  secretion,  483 

gases  in,  482 

hippuric  acid  in,  477 

iudican  in,  478,  832 

indigo  in,  478,  832 

kreatinin  in,  479 

method  of  secretion,  482 

mucus  in,  479 

passage  of,  into  bladder,  488 

pigments  of,  477 

phosphoric  acid  in,  480 

phj^sical  properties  of,  469 

quantity  of,  472 

reaction  of,  470 

relation  of  secretion  to  arterial  press- 
ure, 485 

saline  matter  in,  479 

secretion  theory,  486 

solids  of,  472 

sulphuric  acid  in,  479 

urea  in,  472 

uric  acid  of,  475 

variations  in  specific  gravity,  471 

xanthin  in.  479 
Urobilin,  393,  477,  831 
Urochrome,  477,  831 
Uroerythrin,  478,  883 
Uromelanin.  478 
Uterus,  749 

Vagixa.  750 
Vagus  nerve,  608 

effects  of  section,  610 

functions  of,  609 
Valvulse  conuiveutes,  372 
Vascular  system,  development  of,  795 
Vas  deferens,  751 
Vasoconstrictor  nerves,  246 
Vasodilator  nerves,  346 


854 


INDEX. 


Vasomotor  centres,  246,  595 

nerves,  246 

course  of,  248 

reflexes,  246 
Veins,  186 

development  of,  802 

valves  of,  187 
Velum  interpositum,  583 
Venous  flow,  224 
Ventilation,  287 

Ventricles  of  heart,  action  of,  189 
Ventriloquism,  551 
Vernix  caseosa,  497 
Vertebral  columns,  development  of,  789 

plate,  775 
Vertebratae,  825 
Vesico-spinal  centre,  579 
Vesiculse  seminales,  753 
Vesicular  breathing,  267 
Villi,  372 
Visceral  arches,  792 

clefts,  792 

folds,  792 
Vision,  accommodation  of,  713 

binocular,  738 

field  of,  730 

mechanism  of  accommodation,  715 

range  of  distinct,  716 

reversion  of  image,  728 
Visual  axis,  712 


Visual  centre,  639 

judgments,  728 

perceptions,  728 

purple,  727 

sensations,  723 

duration  of,  724 
intensity  of,  724 
Vital  capacity,  268 
Vitellin,  120 
Vitelline  duct,  778 
Vocal  cords,  movements  of,  544 
Voice,  536 

difference  between  male  and  female, 
536 

in  singing  and  speaking,  545 
Voiniting,  369 
Vowels,  549 

Walking,  524 
Wallerian  degeneration,  565 
Wharton's  jelly,  46 
Wolffian  bodies,  817 

Xanthin,  831 

base,  119 

in  ui-ice,  479 
Xantho-proteic  reaction,  113 

Yawning,  281 
Yolk-sac,  789 


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This  book  is  due  on  the  date  indicated  below,  or  at  the 
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^f^*  1902 

Kirkes 


